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  • Analytical Chemistry and Spectroscopy  (2,959)
  • LUNAR AND PLANETARY EXPLORATION  (2,004)
  • Chemical Engineering  (1,326)
  • Humans  (1,039)
  • 1990-1994  (7,328)
  • 1980-1984
  • 1925-1929
  • 1993  (3,620)
  • 1992  (3,708)
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  • 1990-1994  (7,328)
  • 1980-1984
  • 1925-1929
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 35 (1992), S. 7-16 
    ISSN: 1432-1432
    Keywords: Alu source genes ; Humans ; Gorillas ; Retrotransposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A member of the young PV Alu sub-family is detected in chimpanzee DNA showing that the PV subfamily is not specific to human DNA. This particular Alu is absent from the orthologous loci in both human and gorilla DNAs, indicating that PV subfamily members transposed within the chimpanzee lineage following the divergence of chimpanzee from both gorilla and human. These findings and previous reports describing the transpositional activity of other Alu sequences within the human, gorilla, and chimpanzee lineages provide phylogenetic evidence for the existence of multiple Alu source genes. Sequences surrounding this particular Alu resemble known transcriptional control elements associated with RNA polymerase III, suggesting a mechanism by which cis-acting elements might be acquired upon retrotransposition.
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  • 2
    Electronic Resource
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    Springer
    Journal of molecular evolution 34 (1992), S. 336-344 
    ISSN: 1432-1432
    Keywords: Humans ; Mitochondrial DNA ; Nuclear polymorphisms ; Heteroplasmy ; Genetic differentiation ; Sickle cell ; Rain forest refuges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The identification of genetically coherent populations is essential for understanding human evolution. Among the culturally uniform ethnic groups of west Africa, there are two geographically distinct populations with high frequencies of sickle-cell hemoglobin (HbS). Although the HbS mutation in each group is found on distinguishable chromosomes 11, these populations have been assumed to be parts of a single population. Analysis of mitochondrial DNA (mtDNA) in these populations demonstrated that the two populations identified by alternative chromosomes 11 bearing HbS have distinct distributions of mitochondrial genotypes, i.e., they are maternally separate. These studies also showed that, contrary to expectation, the mtDNA of some individuals is heteroplasmic. For nuclear loci, a comparison of the frequency of alternative alleles established that these populations are genetically distinct. Both the mitochondrial and nuclear data indicate that these populations have been separate for approximately 50,000 years. Although HbS in the two populations is usually attributed to recent, independent mutations, the duration of the separation and the observed geographic distribution of the population allow for the possibility of an ancient origin of HbS. Assuming an ancient mutation and considering the known biogeography, we suggest that HbS protected selected populations from malaria in rain forest refuges during the most recent ice age.
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  • 3
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    Springer
    Mycopathologia 124 (1993), S. 73-77 
    ISSN: 1573-0832
    Keywords: Assessment ; Cancer ; Humans ; Hydrazines ; Mushroom
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This assessment focuses on the concentrations of some chemicals present in theAgaricus bisporus mushroom, the cancer-inducing doses of these chemicals or mushroom used in the animal experiments, the total amounts of these chemicals or mushroom needed to induce cancer in these mice, and the estimated total amounts of these chemicals or mushroom needed to induce cancer in humans. By adding the estimated amounts of chemicals needed to induce cancer and by comparing it with the amount of raw mushroom needed to induce the same effect, it becomes obvious that we have accounted for less than 2% of the carcinogenic components of theAgaricus bisporus mushroom. Since some unavailable data handicapped this assessment, it should be regarded as tentative and subject to further adjustment.
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  • 4
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study of simultaneous acoustic and rheometric (dynamic mechanical) measurements of the epoxy curing process is undertaken to assess the validity of using acoustic cure-monitoring sensors for process control. Our results demonstrate that the acoustic technique provides a sensitive means for monitoring the cure of neat epoxy over the entire cure cycle. The acoustic modulus calculated from the shear velocity qualitatively tracks the mechanically measured dynamic modulus and correctly ranks the stiffness of two epoxy compositions. When the frequency difference is accounted for, using time-temperature superposition of the dynamic mechanical measurements, quantitative agreement between the acoustic and mechanical moduli for fully cured epoxy resins is also quite good.
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  • 5
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 467-474 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The grafting of maleic anhydride (MAH) on high density polyethylene in a counter-rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non-linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.
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  • 6
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 488-493 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Gear pump assisted extrusion is becoming popular in the plastics processing industries. The growth has been tremendous since 1980. In this study, the benefits of gear pump assisted extrusion, especially in single screw applications, is critically reviewed, and a method of predicting the operational conditions of the gear pump assisted extrusion system is discussed. Further, shortening the length to diameter ratio of the extruder in gear pump assisted extrusion was analyzed and found to produce a reduction in energy consumption, provided melting is completed.
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  • 7
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 8
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 506-515 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Internal stresses in injection-molded parts are the result of thermal, flow, and pressure histories. Internal stresses can be roughly divided into thermal and flow-induced stresses. In this paper, a modified layer-removal method is presented to determine thermal stress distributions in injection-molded flat plates. With this method, the curvature of a rectangular specimen is determined after the removal of a layer from one surface. This curvature is converted into a stress via a mathematical relation, originally derived by Treuting and Read. By determining the local curvatures after successive layer removals, stress distributions along the flow path were obtained within a single specimen. Validation of this modified layer-removal method is described. A good reproductibility was obtained. The method can be regarded as semi-quantitative. Flat plates were injection-molded from three amorphous polymers: polystyrene, polycarbonate, and a polyphenylene ether/high-impact polystyrene blend. In general, the flat-plate cross-section shows a three-region stress distribution with a tensile stress region both at the surface and in the core of the flat plate and an intermediate region with compressive stresses. The modified layer-removal method was used to determine influences of mold temperature, annealing treatment, and pressure history on the thermal stress distributions. Increasing mold temperature results in a decreasing overall stress level, while the compressive stress region shifts to the surface. An annealing treatment significantly reduces the overall stress level, without affecting the stress pattern. Stress distributions along the flow path were influenced by the varying pressure histories from the entrance to the end of the mold cavity. The various features of the stress profiles are explained by the influence of the pressure decay rate in the injection-molding process.
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  • 9
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    Polymer Engineering and Science 32 (1992), S. 529-534 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The network formation processes for imidazole-cured epoxy resins were examined by relating the reaction chemistry and the physical properties during cure. Network formation models were developed based on kinetic studies and the laws of conditional probability. These models were used to predict the weight-average molecular weight, the gel point, and the sol fraction as a function of the resin composition and the processing conditions. Rheological and extraction experiments were conducted to confirm the model results and to develop criteria for identifying the gel point.
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  • 10
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 535-541 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of cyclotrimerization and the thermal stability of bisphenol Abased cyanate ester resin systems were determined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. The bisphenol A dicyanate was cured with 4 phr nonylphenol and with the octoates of zinc and manganese, and cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. An empirical rate law was used to predict the cyanate concentration profiles. The observed reaction rate showed a first-order dependenće on the initial metal concentration and a second-order dependence on the cyanate concentration in the kinetically controlled regime. For the uncatalyzed systems, the kinetics was described by a second-order autocatalytic model. The thermal stability of the network was found to be dependent on the catalyst concentration for the zinc catalysts. For the samples cured with manganese, no effect of concentration on the thermal stability was observed.
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  • 11
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 558-566 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ar+ irradiation and annealing at an elevated temperature are used to improve the adhesion of deposited Cr thin films by vacuum evaporation onto polyimide (PI) substrates. The Ar+ ions of 50 and 200 keV and various Ar+ doses ranging from 1 × 1013 to 2 × 1016 ions/cm2 are chosen for the experiments, after many preliminary trials. The surface analyses are conducted employing Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM). Ar+ irradiation produces an interfacial layer of about 100 Å (10 nm) thick in which Cr particles and PI molecules are physically mixed and chemically bonded. The chemical bonds of Cr—O and a trace of Cr≡C are observed by XPS and FTIR. Impact-wear tests are also conducted in order to determine the effects of the Ar+ irradiation on the wear property of a Cr/PI system. A significant increase in the property is observed and the increase appears to be a function of the degree of adhesion of the Cr film to the PI substrate.
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  • 12
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 581-581 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 13
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 582-585 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Deep penetration welding of polymers can be carried out at high speed with relatively low laser power. This results from an efficient coupling CO2 laser radiation to polymers that leads to volume heating. A brief review of energy coupling and heat transfer effects in polymers under CO2 laser welding conditions is given. Some examples of low power (10 to 100 watt) CO2 welding of polypropylene and polyethylene at depths of up to 1.5 cm are discussed.
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  • 14
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 15
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 206-212 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Coat-hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat-hanger die, a two-dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat-hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical treatments.
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  • 16
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    Polymer Engineering and Science 32 (1992), S. 213-220 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A general computation of multilayer coextrusion flow in a flat die geometry is presented. For any given number of layers of different polymers, characterized by their thermal and rheological behaviors, the model permits computation of velocity and temperature fields along the flow in constant or slightly varying geometries. The influence of different operating parameters (wall regulation temperature, flow rate, initial temperatures) on the interface positions and temperature evolutions is evaluated. Theoretical predictions of interface positions are in agreement with experiments carried out on an industrial multimanifold flat die.
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  • 17
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    Polymer Engineering and Science 32 (1992), S. 221-230 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A critical part of any master model used to simulate or control a composite material manufacturing process is the description of resin flow through the fiber bed. We present here a review of both theoretical and experimental studies of fluid flow through porous media, including fiber beds. For the practical porosity range of interest in continuous fiber composites processing (0.3〈 ∊ 〈 0.6), the permeability cannot be accurately described using the Blake-Kozeny-Carman equation, even though the flow is Newtonian at very low Reynold's number. For aligned fiber situations, the Kozeny constant, k, deviates radically from theory, depends on bed nonuniformities, and is only constant over very narrow porosity ranges. Thus, one cannot experimentally determine k at high porosities and use this value to describe low porosity situations. Theoretical attempts, based on perfectly spaced and aligned arrays of cylinders, adequately describe the transverse permeability of ideal fiber beds in the high porosity range, but do not succeed at porosities below 0.6. For axial flow through aligned fiber beds, the theory yields permeabilities much lower than are experimentally observed throughout the entire porosity range. For randomly arranged fibers, random cylinder theory also predicts permeabilities that are significantly lower than are measured.
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  • 18
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    Polymer Engineering and Science 33 (1993), S. 393-399 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The univariant element, Q1 P0, and the multivariant elements, Q1+P0 and R2+ P0, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q1 P0 element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q1+ P0 and R2+ P0, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.
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  • 19
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    Polymer Engineering and Science 33 (1993), S. 377-382 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.
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  • 20
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    Polymer Engineering and Science 33 (1993), S. 400-409 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model for the filling stage of injection molding of viscoelastic thermoplastics in cavities of complex shape is presented. The model considers two-dimensional melt flow, with converging and diverging flow patterns induced by complex boundary shape and by the presence of an obstacle. The model is non-isothermal (with the melt loosing heat to the mold walls as it travels into the cavity) and handles a viscoelastic (following the White-Metzner model) material with properties that vary with temperature, shear rate, and pressure. The numerical method is based on finite differences, with boundary fitted curvilinear coordinates used in the mapping of the flow field (which has an arbitrary shape that evolves with time) into a time invariant rectangle. The numerical results reveal geometry-induced asymmetries in the flow and thermal fields as well as the effect of various process parameters on the pressure and temperature profiles in the cavity. The model admits variable cavity thickness, thus allowing for a treatment of the cavity thickness as a process parameter in the simulations.
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  • 21
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    Polymer Engineering and Science 32 (1992), S. 240-253 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A method is presented for measuring three-dimensional fiber orientation in fiber-reinforced polymers and placing confidence limits on the results. The orientations of individual fibers are determined from the elliptical intersections between the cylindrical fibers and a polished section. This can be done using either manual digitization or automated image analysis. Volume averages for the sample are computed using an orientation-dependent weighting function that corrects for the bias of an area-based sample. Equations are developed for nonuniform fiber lengths, using both number-average and weight-average measures of orientation. Sources of systematic, measurement, and sampling error are discussed and equations for sampling error and the propagation of measurement error are derived. The results use a second-rank tensor to characterize fiber orientation, but the error analysis can be applied to any type of orientation parameter. We implement the technique using manual digitization of optical micrographs. Our implementation accurately measures samples with known orientation, and produces identical results from two perpendicular sections of a glass fiber/nylon injection-molded sample.
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  • 22
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    Polymer Engineering and Science 32 (1992), S. 273-279 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have studied the impact strength, by Charpy and Izod tests, of blends of polyamide 6 with different rubbers, 10 wt% of each, or rubbers and glass fibers (8.5 wt% and 15 wt% respectively). The rubbers are from three different families: (i) a nonreactive cross-linked terpolymer, methyl methacrylate/butadiene/styrene (17/64.5/18.5); (ii) two block copolymers compatible with the matrix, poly(tetramethylene glycol)/polamide 12 (70/30 or 34/66); and (iii) two polymers containing reactive functionality, a terpolymer ethylene/ethyl acrylate/maleic anhydride (68/30.5/1.5) and a copolymer ethylene/acrylic acid (90/10). The classification of additives in regard to improved impact depends on the procedure used for the impact strength measurement, particularly on whether the samples are notched or unnotched. The results are discussed in relation to the dimensions and the adhesion of the rubber particles. The level of adhesion has been estimated from observations in scanning electron microscopy of cavities due to pullout nodules and of nonextracted rubber after treatment in boiling xylene. Strong variations in the morphologies are found, depending on the chemical nature of the rubber. The crystalline state of the polyamide in the blends has also been evaluated from differential scanning calorimetry.
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  • 23
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    Polymer Engineering and Science 32 (1992), S. 287-297 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sheet composites of polypropylene and poly(ethylene terephthalate) were produced by melt consolidation of alternating layers of polymer films and random glass fiber mats. The composites had a nominal glass content of 50 wt% (∼30 vol%). The sheets were stamped into a complex part from which test specimens were machined, and mechanical properties determined. Flexural strengths as high as 159 MPa were recorded for polypropylene composites and 313 MPa for poly(ethylene terephthalate) composites. The flexural modulus of the polypropylene composites reached 9.1 MPa, whereas the modulus of the stiffest poly(ethylene terephthalate) composite was 15 GPa. The impact properties of the composites were equally high. Polypropylene composites absorbed up to 257 J/cm during an instrumented falling dart impact test. Poly(ethylene terephthalate) composites absorbed as much as 116 J/cm in the same test.
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  • 24
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    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 25
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    Polymer Engineering and Science 32 (1992), S. 298-304 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The fiber straightening pre-tension applied during the sample preparation of single fiber composites is suggested here to significantly affect the number of fragments as well as the value of the Kelly-Tyson interface shear strength obtained from single filament composite tests. This implies that fragmentation tests performed under seemingly identical conditions, but in which the fiber pre-tension is not accurately controlled during sample preparation, might yield widely differing experimental results. We present and discuss a new set of experimental results dealing with fiber pre-tension effects in carbon/epoxy single fiber composites.
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Surface-induced transcrystallization in fibers has been reported in some advanced polymer composites. It is believed that transcrystalline interphase may affect stress transfer efficiency between the reinforcing fiber and the matrix. In this study, attempts were made to examine the effects of transcrystallinity on composite performance, particularly on fiber-matrix interfacial bond strength, and to investigate possible attributes of transcrystallization. Three polymer resins, poly(etherketoneketone) (PEKK), poly(etheretherketone) (PEEK), and poly(phenylenesulfide) (PPS), and four types of fiber, polyacrylonitrile (PAN)-based AU-4 (untreated AS-4) carbon, pitch-based carbon, poly (p-phenylene terephthalamide) (PPDT) aramid, and E-glass were used. It was found that PPDT aramid and pitch-based carbon fibers induce a transcrystalline interphase in all three polymers because of an epitaxial effect. Under certain conditions, transcrystallization was also observed in PAN-based carbon and E-glass fibers, which may be partially attributed to the thermal conductivity mismatch between the fiber and the matrix. Plasma treatment on fiber surface showed a negligible effect on inducing transcrystallization, whereas solution-coating of PPDT on the fiber surface showed a positive effect. The Microdebonding test, which measures the interfacial bond strength between the fiber and the matrix, consistently showed more than 40% increments for various single filament systems with transcrystalline interphase versus without. However, the effects of transcrystallinity on the interfacial bond strength appeared to decrease as the fiber content increased in composites.
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  • 27
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    Polymer Engineering and Science 33 (1993), S. 497-500 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.
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  • 28
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    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 29
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    Polymer Engineering and Science 33 (1993), S. 513-521 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP)-dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Half-time was determined via differential scanning calorimetry as a function of the experimentally controlled variables dilution, crystallization temperature, and the addition of nucleating agent. The influence of these variables on crystallization mechanism and spherulitic structure, as implied by the Avrami analysis, was determined. The influence of these variables on fold surface energy was examined by the Lauritzen and Hoffman analysis.
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  • 30
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall non-isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Crystallization peak temperature was determined via differential scanning calorimetry as a function of the experimentally controlled variables iPP concentration, cooling rate, and nucleating agent concentration. The influence of these variables on crystallization mechanism and spherulitic structure as implied by the Ozawa and Ziabicki analyses was determined. The non-isothermal crystallization kinetics presented here are the first for iPP-diluent systems with and without nucleating agent.
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  • 31
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    Polymer Engineering and Science 33 (1993), S. 543-548 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The static shear strength and static friction of three thermoplastics have been investigated for the case of contact between a bulk plastic sample and a very smooth metallic plate. The minimum tangential force required to shear the interfacial adhesion bonds between the two surfaces was measured and defined as the adhesion component of friction Fa. Experimental results showed that Fa is large when the surface energy is high or the interfacial energy is small and that a correlation may exist between this force and the work of adhesion evaluated from Dupré equation. The real area of contact Ar was also measured using an optical device designed to handle samples and experimental conditions similar to the static friction tests. It was found that Ar is proportional to Pa0.9 where Pa is the apparent pressure of contact and an increase of Fa with Pr was observed. The static shear strength τ has been evaluated as the ratio Fa/Ar, and its relationships with the real contact pressure P approximated by linear functions. It was concluded that τ increases at high P, although it has not been verified for ultra-high-molecular-weight polyethylene. An attempt has been made to explain the observed break in the data. The results indicated that (τ/τb) = κ′(τa/Pa) where b refers to bulk, a to apparent values, and κ′ is a proportionality constant that depends on the plastic material.
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  • 32
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    Polymer Engineering and Science 33 (1993), S. 549-558 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A variety of different styrene monomers [styrene (S), p-fluorostyrene (p-FS), pentafluorostyrene (PFS), p-chlorostyrene (p-ClS), p-bromostyrene (p-BrS), p-methylstyrene (p-MS), p-tert-butylstyrene (p-tBS), p-methoxystyrene (p-MOS), p-ethoxystyrene (p-EOS), and p-propoxystyrene (p-POS)] have been polymerized by radical and cationic mechanisms. Copolymers of S/PFS, S/p-ClS, S/2-vinyl-naphthalene (2-VN), and S/p-phenylstyrene (p-PhS) were prepared by radical polymerization. All polymers were fully amorphous and transparent and exhibited only one glass transition temperature in the temperature range 77 to 141°C. Thin films of the polymers were subjected to external electrical partial discharges (PD). Typically, 20 PD experiments were conducted for each polymer and the data for the time to breakdown were adapted to the two-parameter Weibull distribution function. The resistance towards PD of the various polymers was found to depend strongly on the monomeric structure. Complementary PD experiments on a series of narrow molecular mass polystyrenes confirmed that the minor variation in molecular mass between the different styrene polymers is of no importance for the PD resistance. The PD resistance of the homopolymers decreased in the following order: PS ≍ P(p-MS) 〉 P(p-tBS) ≍ P(p-BrS) 〉 P(p-POS) 〉 P(p-ClS) ≍ P(p-MOS) 〉 P(p-EOS) ≍ P(p-FS) 〉 P(PFS). The time to breakdown for copolymers of S and PFS decreased monotonously with increasing PFS content. Styrene copolymers with low molar contents of 2- VN and p-PhS exhibited a higher resistance towards PD than PS. The results are discussed with reference to various properties of the studied polymers, such as segmental mobility, ionization potential, resonance stabilization, and reactivity of the radicals formed.
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  • 33
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    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 34
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    Polymer Engineering and Science 33 (1993), S. 614-621 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The glass transition temperatures in bismaleimide-based resins were investigated using different stoichiometric ratios of 1, 1′-(methylenedi-4, 1-phenylene)bismaleimide (BMI) and 4, 4′-methylenedianiline (MDA). The resin cure involves a low temperature primary amine addition to the maleimide double bonds and a high temperature homopolymerization of the maleimide double bonds. The network topology and the glass transition temperature changes with resin composition and curing conditions were determined using differential scanning calorimetry (DSC). An empirical model was used to relate the glass transition temperature to the extents of the amine addition and the homopolymerization reactions in 1:1 and 2:1 BMI:MDA resins. The changes in thermal properties with resin post-cure were also examined.
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  • 35
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    Polymer Engineering and Science 33 (1993), S. 640-644 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.
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  • 36
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    Polymer Engineering and Science 33 (1993), S. 665-674 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse-quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two-dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses.
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  • 37
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    Polymer Engineering and Science 33 (1993), S. 675-685 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The objective this work was to determine the effects of selected polyester catalysts on the reaction of a polyester with epoxy functional polymers. Polyesters containing various catalyst metals were melt blended with either an ethylene-co-glycidyl methacrylate or a styrene-co-glycidyl methacrylate copolymer. The viscosities of the blends were monitored as a function of mixing time using torque rheometry. In addition, the molecular weight distributions of selected samples were analyzed using gel permeation chromatography. Both the torque rheometry and the gel permeation chromatography results indicate that the polyester reacts with epoxy functional polymers. This reaction occurs under conditions and at processing times which are readily obtainable in conventional melt processing equipment. Furthermore, the reaction kinetics of polyesters with glycidyl methacrylate copolymers are dramatically affected by the nature of the catalyst system used to prepare the polyester. Under the conditions used, antimony catalysts are particularly effective at promoting the reaction between polyesters and the epoxy functionality and the activity of the catalysts studied appears to decrease in the following order: antimony 〉 gallium 〉 tin ≃ titanium 〉 germanium. Manipulation of the polyester catalyst system may offer a method to control the extent of reaction obtained in reactive processing of polyesters with epoxy functional compounds.
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  • 38
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    Polymer Engineering and Science 33 (1993), S. 709-715 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flow kinematics of power-law fluids in fishtail dies is studied. A general isothermal three-dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super-elliptical curves, which allows a smooth transition from a circle to a slit. The three-dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power-law index does not affect the residence time distribution significantly.
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  • 39
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    Polymer Engineering and Science 33 (1993), S. 736-741 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The polymers of the aromatic nitrogen compounds N-methyl-pyrrole (P-N-Me-PPY), carbazole (PCarb), and aniline (PANI) have been investigated with electro-optical and surface analytical methods. The in-situ reflection spectra indicate the formation of polarons or bipolarons during electrochemical oxidation, depending on polymer type. The absorption bands can be attributed to changes in the electronic structure with regard to the applied potential. Photocurrent spectra of P-N-Me-PPY and PCarb show a p-type semiconducting behaviour for the polymers in the reduced state. The transition to the oxidized state with quasi-metallic properties is indicated by a significant shift in the Fermi level energy and can be followed with XPS and UPS measurements.
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  • 40
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    Polymer Engineering and Science 32 (1992), S. 475-480 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An approach to formulation is presented that is based on a statistical experimental design package for use on a personal computer. The total level of phosphite + hindered phenol, and the ratio of phosphite to hindered phenol are used as experimental variables. The approach was tested on extrusions of polypropylene using melt flow retention and yellowness index as observed variables. A quadratic model gave a satisfactory fit to the data for both variables. Contour plots are presented of the performance of the systems for two commercially available hindered phenols and two polypropylene samples. The largest difference between the resins is in the degree of color generation on extrusion. For both hindered phenols, a resin made using “3rd generation” or “high activity” catalyst gave lowest color development on extrusion. There were also small differences in the response of the melt flow of the resins to phosphite level.
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  • 41
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    Polymer Engineering and Science 32 (1992), S. 481-487 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The consumption of hot-fillable poly(ethylene terephthalate) bottles is extremely large and is still increasing in Japan. This type of bottle is generally manufactured by the heat-set method using hot molds after stretch-blow molding. In this study, the method is simulated using a setting application in which sheets can be stretched constraining their sizes on a hot aluminum block. The crystallinities of the sheets are found to depend on the thermal history, i.e., the duration and temperature of the heat-set cycle. Heat-setting mitigates thermal-shrinkage of the sheets which is due to the increase in crystallinity or in the tense segments in the amorphous region. The structure of the heat-set sheet varies depending on the original stretched sheet. For a sample of low draw ratio, the crystallinity does not increase because of the heat-set. For a sample of medium draw ratio, the crystallinity increases greatly and the tense segments in the amorphous region also increase because of heat-set. For a sample of high draw ratio, the crystallinity increases a little but the numbers of the crystallite and tense segments in the amorphous region do not change with the heat-set.
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  • 42
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert-butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.
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  • 43
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    Polymer Engineering and Science 33 (1993), S. 838-844 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Extruded films of liquid crystalline polymer (LCP)/fluoropolymer blends were melt drawn to develop uniaxial orientation of a microfibrillar dispersed LCP phase. The anisotropy of the films increased with increasing draw and LCP content in the blend. Laminated composite plates were prepared using the extruded sheets as prepreg. The mechanical properties and coefficient of thermal expansion (CTE) of the prepreg and laminates agreed well with predictions from composite lamination theories. The potential for replacing glass fiber reinforced fluoropolymers with LCP/fluoropolymer blends in applications such as microwave circuit boards is discussed.
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    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 45
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    Polymer Engineering and Science 33 (1993), S. 865-876 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This review presents a general picture of suspension, dispersion, and interfacial polycondensation processes employed for the preparation of beaded resins, dry powders, and high solid dispersions. The polymer systems covered include polyamides, polyesters, polycarbonates, polyurethanes, and phenol-formaldehyde and urea-formaldehyde resins. Basic features of heterogeneous polycondensation processes are outlined, and different mechanisms of particle formation in suspension, dispersion, and interfacial polycondensation are discussed. Effects of manufacturing parameters such as feed ratio, droplet/particle stabilizer, and stirrer speed on product characteristics are also briefly covered.
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  • 46
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    Polymer Engineering and Science 33 (1993), S. 781-788 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi-empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.
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  • 47
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    Polymer Engineering and Science 33 (1993), S. 819-826 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Much work in recent years had focused on the improvements of the impact properties of engineering thermoplastics by the addition of a low modulus modifier that contains polar moieties as a result of polymerization or that has been modified to contain polar moieties as a result of various grafting techniques. Styrenic block copolymers (styrene-ethylene/butylene-styrene) functionalized with maleic anhydride have proved useful as impact modifiers and compatibilizers in blends with engineering thermoplastics. This paper focuses on the use of these functionalized elastomers to modify nylon 6. In such compositions, a nylon material with unique mechanical performance may be achieved using the functionalized elastomer either alone or in combination with an unfunctionalized styrenic block copolymer. The optimization of performance in these rubber toughened polyamide blends using various types of styrenic block copolymers is discussed. The morphology as it pertains to performance is also reviewed. The information contained herein may prove useful in obtaining a better understanding of the mechanisms of compatibilization and modification of nylon 6 systems.
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  • 48
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    Polymer Engineering and Science 33 (1993), S. 827-837 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Oriented blends of poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) with and without compatibilizing agent have been studied with regard to orientation temperature, stretch rate, extension ratio, mode of orientation, and blend composition. These oriented blends have been characterized using infrared spectroscopy and differential scanning calorimetry. The tensile and tensile impact properties were also investigated. The results show that blends with compatibilizer show strain hardening upon orientation, whereas the blend without compatibilizer does not strain harden upon orientation. The blends with less PET content have been difficult to orient. The morphology of these blends show fibril structure, highly oriented in the direction of stretch. Infrared measurements show that PET within the blend has undergone strain induced crystallization upon orientation. It has also been observed that the mechanical properties, such as the modulus and ultimate stress, show improvement upon orientation. Simultaneously stretched blends show better physical properties than sequentially oriented blends.
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  • 49
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    Polymer Engineering and Science 32 (1992), S. 586-592 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thin microtomed samples from hot-tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long-term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress-strain response of the weld material to be determined.
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    Polymer Engineering and Science 32 (1992), S. 600-611 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ultrasonic welding of oriented polypropylene (OPP) using tie-layer materials has been examined. The thermal cycle at the joint interface was evaluated using a high speed data acquisition system, and concurrent changes in horn displacement (penetration) and the output power were monitored. The model explaining process operation involves four phases, i.e., I-where heating occurs because of the stresses generated in asperities on the contacting surfaces; II-where the whole tie-layer reaches the melting point; III-where the polymer melt is subjected to intense heating from viscous dissipation and is squeezed out; and IV-where the joint cools after welding. In the early stages of ultrasonic welding the heat generated at asperities on the contacting surfaces leads to melting of the tie-layer/oriented polypropylene interface within 50 ms. The tie-layer heats up because of a combination of viscoelastic dissipation and heat conduction from the oriented polypropylene/tie-layer interface, and the rate of temperature rise at the midline of the tie-layer is in the range 200°/s to 400°/s. The reduction in thickness of the test specimens (penetration) is negligible up to the time when the tie-layer melts completely, and then changes rapidly when the melted polymer at the joint interface is squeezed out. The influence of machine parameters (amplitude and contact pressure) and of tie-layer Melt Flow Index is also examined. The total time required for completion of the welding process decreases when the amplitude and applied pressure are increased. The use of low Melt Flow Index tie-layers produces peak temperature as high as 600° at the bondline, and little material is ejected during the ultrasonic welding operation.
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    Polymer Engineering and Science 33 (1993), S. 895-900 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper illustrates the factors that control brittle failure under fatigue loading for test specimens cut from medium-density polyethylene pipes for gas distribution. A square bar specimen cut from a pipe with a notch was made and a fatigue test was conducted to cause a brittle failure. To obtain the correlation among stress range, frequency, temperature, and cycles to failure in this fatigue test, Coffin-Manson's frequency-modified fatigue life equation was adopted and the material constants were determined. By gradually lowering the frequency, the resistance to creep can be estimated because cycles to failure - indicating the fatigue damage - decreased, and the actual loading time - indicating the creep damage - increased.
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    Polymer Engineering and Science 33 (1993), S. 923-930 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide-6, polystyrene/polyamide-6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.
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    Polymer Engineering and Science 33 (1993), S. 937-943 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unidirectional sheets were extruded of an in-situ composite of thermotropic liquid crystalline Vectra B950 in a matrix of polyphenylene-ether and polystyrene. Three important processing parameters were systematically varied: draw-ratio, slit opening and extruder throughput. Morphology and mechanical properties of these films were determined, and qualitatively related to the processing conditions.
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    Polymer Engineering and Science 33 (1993), S. 959-970 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is of great importance to accurately measure or predict the Residence Time Distribution (RTD) in designing extruders and/or in setting up a proper operating condition, because chemical reactions depend significantly on the RTD and temperature when chemical reactions take place during the extrusion process. A previous method to predict the RTD can analytically determine RTD, Residence Time Distribution Function f(t) and Cumulative Residence Time Distribution Function F(t), based on a simplified two-dimensional velocity field in an extruder. However, this previous method cannot accurately take into account the three-dimensional circulatory flow inside the extruder. The present paper suggests a new method to accurately determine the RTD taking into account the three-dimensional circulatory flow and presents a new formula derived to calculate f(t). In order to demonstrate the applicability of the new method including the circulatory flow effect, RTD, f(t) and F(t) were calculated based on a three-dimensional velocity field obtained via a quasi-three-dimensional finite element analysis. It was found that the previous method has a tendency to underestimate the RTD, owing to the neglect of the three-dimensional circulatory flow in comparison with the new method.
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    Polymer Engineering and Science 33 (1993), S. 980-988 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm h} = {\rm c\beta }_{\rm 0} {\rm k}^{{\rm \beta }_{\rm 1} } {\rm \omega }^{{\rm \beta }_{\rm 2} } {\rm t}^{{\rm \beta }_{\rm 3} } \quad\quad\quad\quad{\rm (1)} $$\end{document} in which \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {c = {\rm polymer\, solution\, solid\, weight\, fraction;}} \\ {\beta _i = {\rm fitted\, coefficient\, (Greek\, letter\, beta)};} \\ \quad{h = {\rm film\, thickness\, after\, cure\, or\, solvent\, removal};} \\ \quad{k = {\rm polymer\, solution\, kinematic\, viscosity, centistokes};} \\ {t = {\rm time},{\rm and;}} \\ \quad{\omega = {\rm wafer\, spin\, speed, rpm (Greek\, letter\, omega)}.} \\ \end{array} $$\end{document}.
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  • 56
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ternary systems consisting of polypropylene (PP), ethylene-propylene-dieneterpolymer (EPDM) and different types of inorganic fillers (kaolin, BaSO4) have been investigated with respect to their mechanical behavior. On the basis of an Interphase model, it was possible using the modified van der Poel equation to describe the temperature dependence of the storage modulus G′(T) and the loss modulus G″(T). The interphase properties G′(T) and G″(T) could be calculated.
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    Polymer Engineering and Science 33 (1993), S. 1251-1260 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Signal deterioration of optical discs depends strongly on the substrate surface roughness. Characteristics of surface roughness of the molded substrate have been studied in order to clarify the transcription mechanism of smooth surfaces in injection molding of polycarbonate resin. When the melt temperature, mold temperature, and injecting rate are low, microscopic flow marks more than 5 nm deep are observed on the surface. These flow marks are formed when the melted resin near the mold wall is cooled to the no-flow temperature of resin before it comes into contact with the mold wall. Molding transcription improves by optimizing the molding conditions for preventing these flow marks. As a result, the surface roughness of the molded substrate obtained is 3.2 nm in maximum height Rmax, which is nearly equal to that of the mold stamper at 2.7 nm in Rmax.
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    Polymer Engineering and Science 33 (1993), S. 1279-1287 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A finite element numerical analysis of preform inflation associated with the injection blow molding process has been developed using a neo-Hookean constitutive model. The analysis is capable of predicting final wall thickness distributions for axisymmetric mold geometries. Experimental studies were conducted on a Uniloy injection blow molding machine (Model 189-3 and Model 122). A twelve ounce (355 mL) cylindrical bottle mold was instrumented with contact sensors, thermocouples, and pressure transducers. Visualization studies of the inflation process were performed using specialized tooling and high-speed video cameras. The experimental studies provide justification for analyzing the deformation by means of a static elastic approach. The predicted wall thickness distribution is in reasonable agreement with the experimental data. Nonuniformities in the temperature distribution in the preform were found to have the most significant impact on the inflation behavior and the resulting wall thickness.
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    Polymer Engineering and Science 33 (1993), S. 1301-1307 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dielectric α-relaxation of a bisphenol-A type epoxide oligomer has been investigated in the vicinity of the glass transition temperature (Tg) by the direct current (DC) transient method. The logarithm of the DC transient current for the oligomer was well approximated by the third order function of the logarithm of time. The complex dielectric constant was calculated through the Fourier transformation of that approximation function according to Simpson's integration rule in a frequency range of 10-5 - 1 Hz. At the temperature around the Tg (45°C), the dielectric α-relaxation process of the oligomer was found to be governed by the Havriliak-Negami equation. The relationship between the DC conductivity (σ) and the dielectric relaxation time (τ), σ·τm = const, is valid near and above the Tg of the oligomer. The DC transient current method combined with the DC conduction and the dielectric bridge measurements is considered to be a practical tool for analyzing the dielectric α-relaxation process of the epoxide oligomer over a wide frequency and temperature range.
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    Polymer Engineering and Science 33 (1993), S. 1329-1335 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this study, styrene-(ethylene-co-butylene)-styrene (SEBS) triblock copolymer (Kraton G-1652) was modified with maleic anhydride (MA). The maleated SEBS was used as compatibilizer for the blends of Nylon 6 (PA6) and SEBS. The morphology and impact strength of the blends were measured as functions of concentration and MA graft ratio of maleated SEBS. The compatibility and fracture mechanism of the blends were evaluated from the SEM micrographs of the xylene-etched surfaces and of fractured surfaces. Some of the blends exhibited an impact strength up to about 30 fold greater than neat PA6. The fracture involved both both cavitation and shear yielding. The mechanism of compatibilization of maleated SEBS in the ternary components blends was proposed.
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    Polymer Engineering and Science 33 (1993), S. 1341-1351 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible-chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e., orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.
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    Polymer Engineering and Science 33 (1993), S. 1370-1371 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 33 (1993), S. 1381-1389 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Because of the inability of existing automotive bumpers to absorb energy during impacts over the supports, energy absorbers have to be used to make bumpers effective in barrier impacts. A parametric analysis of a novel double-beam bumper concept has shown that its performance, in terms of energy absorption and impact forces, is insensitive to the location of the point of impact. Physical realizations of this concept, which may not require more material than existing designs, and which are particularly suited to thermoplastic materials, have been developed.
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    Polymer Engineering and Science 32 (1992), S. 810-822 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This work presents an analytical technique to describe the orientation behavior of short fibers in arbitrary two-dimensional homogeneous flows. It is shown that the fiber orientation, specified by a unit vector, can be analytically calculated at any instant using any initial orientation and flow kinematics. The rotation of a fiber with the bulk fluid deformation is expressed in terms of orientation vector components by utilizing an equivalent strain tensor calculated from the fluid kinematics. This technique is then used to evaluate the orientation behavior of a large number of fibers starting from different initial orientations, representing an orientation state. The orientation distribution function is generated statistically by considering the frequency distribution curve of the orientation of the large number of fibers. It is shown that using a combination of analytical solutions and statistical methods provides a convenient description of fiber orientation behavior. The accuracy of the generated orientation distribution function is found to be dependent on the number of fibers used in the analytical solution. The statistical orientation distribution function is compared with the exact solutions for certain homogeneous flows and found to be in close agreement.
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    Polymer Engineering and Science 32 (1992), S. 836-840 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A commercial epoxy resin, consisting of a mixture of diepoxides based on diglycidyl ether of bisphenol-A (DGEBA) and containing an epoxidized polypropylene glycol as reactive diluent, was characterized by 1HNMR, FTIR, SEC, and chemical analysis. The kinetics of the cure with ethylenediamine (EDA) was catalyzed by the (OH) groups present in a large amount in the commercial formulation. A second order kinetic behavior gave an accurate fitting of results obtained by different experimental techniques (DSC in dynamic and isothermal modes and SEC in the pregel stage). The activation energy was E = 59.1 kJ/mol (14.1 kcal/mol), in very close agreement with values reported for the catalytic mechanism of the DGEBA-EDA polymerization. From the gel conversion and the critical stoichiometric ratio for samples containing an epoxy excess it was found that the average functionality of epoxidized species was f = 1.58.
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    Polymer Engineering and Science 32 (1992), S. 841-844 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Elastic moduli of injection molded blends of polycarbonate with poly(styrene-co-acrylonitrile) (SAN) have been obtained at temperatures between the glass transition temperatures of the two components. When compared with compression molded blends as a function of composition, the moduli were found to differ by as much as a factor of three at intermediate compositions. The variations are ascribed to differences in connectivity between minor component particles. The morphologies of these materials have been modeled using percolation concepts to quantify continuity of the individual phases. The effects of phase continuity resulting from composition as well as dispersed phase shape differences were evaluated. It was found that shape per se has only a minor effect on percolation. However, shape as reflected in the size of dispersed particles relative to the extent of the domain in which they reside is primary for developing a model for continuity of the phases. An empirical relation for percolation in finite domains was devised from Monte Carlo simulations. Modulus values calculated from these continuity considerations agree well with the observed data.
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    Polymer Engineering and Science 32 (1992), S. 854-860 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The morphology, rheology, and mechanical properties of blends of polysulfone (PSF) with up to 65% of a wholly aromatic liquid crystalline polymer (LCP) were investigated. In injection molded specimens a skin-core morphology was observed with the LCP minor phase oriented in the skin and globular in the core. Scanning electron microscopy of fractured surfaces showed sharp phase boundaries, suggesting low interfacial adhesion. The neat PSF and blends with low amounts of LCP exhibited a low shear Newtonian plateau not observed in the blends with high LCP levels. The addition of LCP to PSF resulted in an increase in stiffness, a small increase in tensile strength, and a significant improvement in processability.
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    Polymer Engineering and Science 32 (1992), S. 861-867 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Commercial polysulfone/polycarbonate (PSU/PC) polymer blends were reprocessed up to five times to determine the influence that reprocessing has on their structure and physical properties. All the high strain properties, mainly ductility, significantly decreased under harsh processing conditions, such as five cycles at 320°C. The results of reprocessing the blends at 320°C have been compared with results at a lower temperature and also with those of the separate components with the aim of clarifying the origin of the degradation. These results plus Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis, and melt flow index measurements (MFI) indicate that the presence of the two polymers together clearly decreases the resistance to degradation of each component. Moreover, degradation under the stated conditions is mainly thermal and does not change the chemical nature of the blends. However, a clear decrease in molecular weight was observed both by viscosimetry and MFI measurements as was a shift to higher temperatures of the low temperature secondary transition of both PC and PSU. Both molecular weight and secondary transition changes usually deteriorate mechanical properties but not in the degree observed here. This probably means that the fine and difficult-to-observe structure of the blend has also changed.
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    Polymer Engineering and Science 32 (1992), S. 886-893 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) concurrently show that polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends have a two-phase structure. The differences between the Tgs of parent polymers and the Tgs of conjugate phases, determined by both DMTA and DSC, indicate a limited miscibility of components and allow the approximate composition of conjugate phases to be calculated. The Flory-Huggins interaction parameter calculated by using these data assumes values about 0.035 ± 0.010. Phase inversion occurs in an interval close to the 50/50 composition, though the molar masses and melt viscosities of the polymers were rather different. Partial miscibility of components ensures interfacial adhesion capable of sustaining the stress transfer between phases up to fracture. Yield stress of the blends is very close to values foreseen by the rule of mixtures. A specific feature of the blends studied is that the addition of 10 to 20 vol% of PMMA to PC increases the strain at break and work to fracture, which are rather low for the PC used. The enhanced capability of the blends to absorb mechanical energy is probably linked to plastic deformation of the dispersed PMMA.
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    Polymer Engineering and Science 32 (1992), S. 894-902 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this work, blends of polycarbonate and a high density polyethylene were investigated through their morphology, mechanical properties, and the effect of compatibilizers: a copolymer styrene-butadiene-styrene and an ionomer. Blending was performed in the melt state at 220°C, and the concentration of the compatibilizers was varied from 1% to 5% by weight. In the case of the copolymer modified blend, the results showed no change in the mechanical properties compared to the neat blend, whereas the morphology showed that the copolymer might interact with only one phase. For the ionomer, the addition of 1% increased the Young's modulus and the tensile strength of the blend. For the morphology, a large change in the size of the dispersed phase (polyethylene) is observed. This was attributed to the compatibility of the ethylene group of the ionomer with the minor phase, and the reaction between the carbonate group of polycarbonate (PC) and the acid group of the ionomer. An investigation on the binary blends of PC and the ionomer showed the occurrence of a chemical reaction that might be of a transesterification type. Differential scanning calorimetry and Fourier transform infrared techniques were used to characterize these blends.
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    Polymer Engineering and Science 33 (1993), S. 1270-1278 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Flow in a three-dimensional channel with a sinusoidally-wavy, vertical wall is examined for the case of applied down- and cross-channel velocity components. An important parameter for the analysis of the nature of laminar mixing in the flow field occurs when the changes in the downstream direction can be decoupled from the changes in the cross-channel direction, thereby allowing for a two-dimensional solution of the system of equations. This paper shows the effect on the nature of laminar mixing when the decoupling of the momentum equations from a fully three-dimensional case to one where a two-dimensional solution can be performed. Experiments are performed on a channel with sinusoidally varying vertical walls that cover the range of decoupling criteria. Silicone pigmented either white or black was run in the apparatus, cured, and cross-sectioned. The cross sections embody a local, detailed history of the state of mixing as it proceeds down the mixer. The amount of mixing is presented as a function of position at each cross section for the different channel configurations. The nature of mixing changes from a linear growth rate in the amount of interfacial area to an exponential rate as the amplitude of the wave is increased. Results demonstrate the existence of chaos, islands, and the factors affecting the mixing behavior.
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    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 32 (1992), S. 921-923 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The melt flow index and oxidation induction period of low-density polyethylene crosslinked with dicumyl peroxide (DCP) in the presence of tetrakis (methylene β-3, 5-di-butyl-4-hydroxypheny1)-propionate methane (Antioxidant 1010) were determined. The results suggest that there is a negative synergism between this crosslinking agent and antioxindant. Part of the antioxidant terminated the chain propagation by trapping radicals, and thus reduced the efficiency of crosslinking. The antioxidant efficiency was also reduced owing to meaningless consumption.
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    Polymer Engineering and Science 32 (1992), S. 909-919 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fractography has been used in the post-failure analysis of single edge notched specimens of injection molded blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene terpolymer (ABS). The mode of ductile tensile fracture of single edge notched specimens depended on comosition. Plane stress shear tearing was observed in the composition range PC/ABS 90/10 to 70/30 by weight where PC was the continuous phase. Intermediate compositions, PC/ABS 60/40 to 40/60, had a co-continuous or almot co-continuous phase morphology; these blends fractured by mixed mode pop-in, where a tunneling center crack relieved the triaxiality and permitted plane stress shear lips to form near the edges. Herringbone fracture, a plane strain mode characterized by discontinuous crack growth, was observed when ABS was the continuous phase, PC/ABS 30/70 to 10/90. An S-shaped relationship was observed between the ductile-to-brittle transition temperature and the composition. Addition of ABS to PC increased ductility up to PC/ABS 70/30 and 60/40, which were the most ductile compositions. Further addition of ABS decreased the ductility, and the least ductile compositions were PC/ABS 30/70 and 10/90.
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    Polymer Engineering and Science 32 (1992), S. 1086-1096 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A finite element algorithm developed previously has been successfully extended to the study of nonlinear time-dependent problems. Nonlinear viscoelastic and viscoplastic models have been used to study the time-dependent deformation and failure of high density polyethylene (HDPE). Two classes of nonlinear models have been identified; those that allow stress redistribution with time under specified traction boundary conditions, and those that do not. The implications of using viscoelastic vs. viscoplastic models, as well as the specific mathematical form of the constitutive equations selected for use, have been studied. Strains predicted using the FE algorithm have been compared with experimental measurements for (i) a HDPE plate with a hole and (ii) a double edge notch HDPE specimen, both under remote tension. Excellent agreement was obtained between numerical predictions and the experimental values.
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    Polymer Engineering and Science 32 (1992), S. 1105-1113 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The influence of sample thickness on fatigue crack propagation rates in injection molded nylon 66 was determined by preparing 12.7 mm thick plaques along with more conventional 3.0 mm thick samples. Initial results suggested a large effect of thickness as the crack propagation rates were accelerated in the thicker samples and the stress dependence was also increased. Since the calculated thickness for a plane stress to plane strain transition in nylon 66 is 9.0 mm, it was thought that these results were related to the stress state at the crack tip. However, a more thorough study of the thicker plaques has now demonstrated that neither the magnitude nor the stress dependence of the fatigue crack growth rates is necessarily changed under plane strain conditions as similar results can be obtained for thick and thin plaques. It is suggested that the earlier results were confounded by a previously unrecognized processing history effect which does accelerate fatigue fracture. The latter effect is shown by thermal analysis and optical microscopy to be related to a rearrangement of the polymer network during melt processing.
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    Polymer Engineering and Science 32 (1992), S. 1114-1125 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fatigue crack propagation rates in injection molded nylon 66 were previously shown to be strongly affected by prior processing history. To provide a physical basis for the observed acceleration in crack growth rates, microtomed sections were cut through the tips of stable fatigue cracks and examined by optical microscopy. A reduction in spherulite size occurs with reprocessing along with an accompanying decrease in the amount of deformation at the crack tip. For the initially processed nylon 66 this deformation consists of a vast array of independently initiated craze-like zones. Patchy type regions observed on the fatigue fracture surface are similar in size to the initially formed crazed zones. Crack advance occurs by the breakdown and coalescence of the crazed regions via matrix shearing. The extensive damage zone is believed to result in a reduction in stress intensity at the crack tip thereby reducing the crack propagation rates. For the reprocessed nylon 66, one observes fewer crazes and a sharper fatigue crack tip with a consequent acceleration in crack propagation rates and a smoother fracture surface.
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  • 78
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    Polymer Engineering and Science 32 (1992), S. 1126-1137 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Brittle failure, a significant design issue for plastic components subject to impact loads, is especially catastrophic when the material is normally ductile. Such behavior is not adequately understood relative to the micromechanisms, controlling parameters, and design consequences in plastics. Previous work has identified the process of crazing as being relevant to these failures in thermoplastics. The relationship between crazes generated through mechanical loading and subsequent brittle failure of amorphous thermoplastics is discussed and the hypothesis that the craze event is a necessary but insufficient condition for brittle failure is employed. Emphasis is focused upon the engineering prediction of craze formation and its use as a conservative brittle failure criteria for defining geometric details to prevent brittle failure. First, a series of experiments using one geometry is applied to study the concept of crazing as a precursor to brittle fracture in the two amorphous polymers polycarbonate and polyetherimide. Second, three-dimensional finite element analyses are used to assess the effects of changes in geometric detail upon the continuum stress state and eventual failure of the specimen for these two materials.
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    Polymer Engineering and Science 32 (1992), S. 1138-1146 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The compressive-stress strain response of polyurethane foam under uniaxial compressive impact loading has been studied. The development of a uniaxial constitutive model from strain rate controlled compression tests is detailed. Density and temperature functions have been added to the integral power model proposed by Schwaber, Meincke, and Nagy. The model assumes that the effects of density, temperature, strain and strain rate on stress are separable functions. The model correlated well with actual static compression tests and was used successfully to predict the impact response of energy absorbing polyurethane foam under uniaxial compressive loading.
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    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 81
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 32 (1992), S. 1163-1173 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper exmines the influence of process variables on final thickness distributions for vacuum-formed thermoplastic parts. The process variables investigated include evacuation rate, sheet surface temperature, mold temperature, and material slip over the mold surface. The experimental data presented include, in addition to thicknesses, sheet surface temperature obtained via infrared thermography. A finite element program to model the vacuum-forming process is discussed, and the wall thickness distribution predicted by this program for a vacuum-formed part is compared with the results of the experiments.
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    Polymer Engineering and Science 32 (1992), S. 1350-1357 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dynamic creep behavior of a filled poly(dimethylsiloxane) elastomer was studied under cyclic stress. The stress level was chosen such that the increase in the internal temperature was small and that microcracks were not observed. This work has demonstrated that cyclic stress in combination with high temperature accelerates the degradation of the elastomer. The results suggest that because of the applied force, breaks in the load-bearing chains of the network occur. These breaks, while relieving the mechanical stress, create highly reactive ionic fragments. It is believed that because of the subsequent reactions of the ionic fragments, changes in the specific gravity, storage modulus, effective crosslink density, and length of the sample (creep) are observed. The observed decrease in the storage modulus is thought to occur because of the reaction of the ionic fragments with moisture, which results in the formation of silanol chain ends that reduce the effective crosslink density. The results also show that contrary to the prediction of the Boltzmann's Superposition Principle, the rate of creep is greatly enhanced when the sample is subjected to a sinusoidally varying dynamic load as compared to a comparable static load. The polymer weight loss was found to be linear with time and strongly dependent on the level of applied dynamic and static force. In addition, the weight loss and rate of creep were also found to be strongly dependent upon temperature.
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    Polymer Engineering and Science 32 (1992), S. 1358-1365 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Interest in the development of polymeric materials for high temperature, electronic and microelectronic applications has led to an increasing number of new polymers. Many of these polymers have complex organic ring structures and semirigid backbones, characteristics that have posed some difficulties for structural analysis. The purpose of this paper is to test and compare two practical nondestructive optical techniques, polarized optical microscopy and polarized refractometry, for the determination of three-dimensional surface and bulk anisotropy in these advanced materials. The optical techniques are first tested on a series of optically homogeneous uniaxially oriented isotactic polypropylene films and then applied to the analysis of high refractive index Kapton (PMDA-ODA) polyimide films. The study includes a test of the validity of the compensator method, including the effect of fringe jumping, the use of polymer retarders, and the tilting technique of Stein.
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    Polymer Engineering and Science 32 (1992), S. 1372-1378 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polymer coatings are widely used to protect glass from indentation damage. A model for the strength degradation that occurs when a sharp indenter penetrates through the coating is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile-up of coating material underneath the indenter. The model predicts the strength degradation as a function of indentation load, coating and substrate hardnesses, and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda-lime glass substrates shows good agreement.
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    Polymer Engineering and Science 32 (1992), S. 1500-1508 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Novolak resins provide the best overall performance for “g” and “i”-line photoresists. There is a continuing need for advanced novolak designs that will provide improved lithographic, thermal, and etch characteristics that may be reproducibly synthesized. A novolak synthesis process was developed using the solution condensation technique. Cresol mixtures with m-cresol and 3,5-xylenol at specific ratios provide reproducible novolaks with controlled molecular weights. In order to achieve high thermal and etch performance, while retaining photospeed and resolution characteristics, three basic approaches were investigated: (1) increase in molecular weight, which produces novolaks with Tg ranging from 120 to 130°C with relatively slow dissolution rates; (2) incorporation of multi-hydroxyphenols such as resorcinol to tailor the dissolution rate, resolution, thermal, etch, and adhesion characteristics; (3) partial esterification of multi-hydroxy novolaks giving a Tg range of 140 to 150°C. Lithographic evaluation of the novolak resins was performed by formulating with a 2,1,4-diazonaphthoquinone (DNQ) sensitizer. Results on resin synthesis, molecular weights, lithographic, thermal, and etch characteristics are discussed.
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    Polymer Engineering and Science 32 (1992), S. 1511-1515 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The quantum yield for acid generation from alkyl and arylsulfonic acid esters of pyrogallol was measured in resist films composed of a sulfonate, tBOC-BA, and novolak resin. It was found that the quantum yield increases with decreasing molecular size of the sulfonyl group, which can explain the differences in sensitivity of the resist systems. Methanesulfonic acid esters of various phenol derivatives were synthesized to see the effect of backbone structure on the efficiency of acid generation. The sensitivity measurement of resists containing these sulfonates indicates that the number of sulfonyloxy groups bonded to a benzene ring is important. The higher number of the sulfonyloxy groups gives a higher efficiency of acid generation.
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    Polymer Engineering and Science 32 (1992), S. 1516-1522 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: t-Butyloxycarbonyl (t-BOC) blocked compounds based on the protection of phenolic groups, e.g. poly-4-hydroxystyrene derivatives, Bisphenol A type dissolution inhibitors, or onium salt photoacid generators, have found widespread research interest for photoresist systems with excellent photosensitivity and high resolution power. We have made an extension of this approach using new phenol type polymers. This contribution presents first details on the chemistry of these systems and results of their lithographic evaluation as positive tone photoresists for deep UV applications.
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    Polymer Engineering and Science 32 (1992) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 32 (1992), S. 1557-1557 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Polymer Engineering and Science 32 (1992), S. 1545-1549 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The multiple interference effect is one of the major causes of the fluctuation in critical dimension control (CD) and in mark detection for alignment. Suppressing this effect is critical for future photolithography. We propose a new photolithography technique called anti reflective coating on resist (ARCOR), which improves linewidth accuracy and overlay accuracy by suppressing multiple interference. ARCOR consists of relatively simple processes: A clear antireflective film is spun onto the resist prior to the mark detecting for alignment and exposure. The film is subsequently removed and the resist developed in the conventional way. ARCOR differs from ARC, which suppresses the reflection at the resist/substrate interface. ARCOR suppresses the reflection at the air/resist interface. ARCOR allows mark detection and exposure without light intensity-loss and multiple interference. The experiments mainly examine polysiloxane and perfluoroalkylpolyether as ARCOR materials. It is shown that linewidth accuracy can be improved from 0.3 to 0.03 μm. The signal-to-noise ratio of the alignment signal is drastically improved, and the overlay error is about half that of the conventional method. ARCOR is also effective for directly measuring the reflectivity at the resist/substrate interface, which is a key parameter of the multiple interference effect and the halation. Using ARCOR and a thin resist film, the measured ratio of reflected light to incident light indicates the reflectivity at the resist/substrate interface. Because, the probe light does not reflect off the resist surface and the intensity-loss at the resist surface is suppressed. With perfluoroalkylpolyether film, the measurement error is ∼ 1.5%.
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  • 92
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    Journal of Chemometrics 6 (1992) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 6 (1992), S. i 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 6 (1992), S. 63-64 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 95
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    Journal of Chemometrics 6 (1992), S. 65-83 
    ISSN: 0886-9383
    Keywords: Trilinear decomposition ; Receptor modeling ; Source identification ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In many cases, monitoring data for ambient airborne particles can be organized in the form of a three-way data table with one way for chemical species, one for sampling periods and one for sites. A direct trilinear decomposition followed by a matrix reconstruction (DTDMR) is developed to analyze such a data table as a whole. The three-way data set is composed into three two-way matrices by a direct trilinear decomposition (DTD). The column vectors of each of the matrices are called ‘source profiles’, ‘emission patterns’ and ‘site coefficients’ respectively. Particulate sources are identified by examining both their source profiles and emission patterns. After the sources have been identified, emission patterns and site coefficients are used to produce a three-way matrix that gives estimates of mass contributions of sources to the samples collected at every site in every period. By simulation study, not only has the method been verified, but a good indicator has been found that shows the number of factors (i.e. sources) in the system. Unlike other receptor models, DTDMR does not require source profile data and does not involve trial-and-error procedures. Since DTDMR identifies sources based on variations in two dimensions, it has a higher potential to distinguish two sources that have similar chemical compositions. The DTDMR model has provided excellent results with simulated data and has been applied in a real world three-way data set.
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    Journal of Chemometrics 6 (1992), S. 113-116 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 6 (1992), S. 117-118 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 6 (1992), S. 151-161 
    ISSN: 0886-9383
    Keywords: NIR spectroscopy ; Wavelength selection ; Interaction effects ; Multicomponent mixtures ; Partial least squares ; Generalized least squares ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modern scanning (near-)infrared reflectance/absorption (NIR) spectroscopes measure the absorptions or reflectances at a sequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed sample mixtures for which the true composition of the mixture is either known by formulation or accurately determined by wet chemistry. In future one wishes to predict the true composition from the spectrum. In this paper we compare a simple wavelength selection approach with methods which retain all the wavelengths. It offers a powerful yet simple technique for choosing those wavelengths that are specific to each pure component as against the other components (including the medium) for the varying compositions. In the presence of a defined range of ingredients in thus chooses wavelengths which are highly selective for each particular component. It has the added advantage of selecting wavelengths which are little effected by interaction effects and consequent non-linearities.The calibration data used consist of 125 observations of three sugars, each varying at five levels in a full 53 design. The validation set consists of 21 further samples specially selected to have compositions outside the range of the training sample. The selection methods perform much better on this prediction set than methods which retain all the wavelengths, 700 in this case. The leave-one-out cross-validation internal to the calibration data would point to the opposite finding and suggests that such crossvalidations may be overly flattering to techniques such as partial least squares and may encourage overfitting. After selection, simple straightforward least squares methods may be used, eschewing the need for ‘shrinkage’ methods such as partial least squares or ridge regression.
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    Journal of Chemometrics 7 (1993), S. 75-76 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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