ALBERT

Notes: This investigation considers a hypothetical three-phase ordered composite to permit the design of a new material both stiffer and tougher than the matrix phase alone. The required elastic solution is greatly simplified and was based on a single layered inclusion in an otherwise infinite matrix under uniaxial tension. The solution presented is exact and generalized to accommodate any number of concentric layers of different thickness and composition.

Notes: Attempts to use low-cycle fatigue techniques derived from the work of Coffin and Manson to predict the fatigue performance of six diverse structural plastics are discussed. Through an analysis of dynamic property and thermal behavior studies of polymer samples in reversed-tension fatigue, an improved model for the polymer fatigue process has been proposed. Laboratory test data are presented illustrating the relationship between the various models.

Notes: It is postulated that property gradients exist at the interface forming an “interphase” between the insert and the matrix. Such gradients might be caused by partial solubility and diffusivity of the two phases comprising a composite. For simplicity, the “interphase” is replaced by a shell exhibiting averaged properties (Eshell = 1/2 Einsert + 1/2 Ematrix, etc.). An exact linear elastic solution was employed to evaluate stress fields throughout all regions. The possible effect of the “interphase” and its thickness on several physical properties of the composite are evaluated in terms of the particular stress fields.

Notes: An investigation of the dynamic mechanical properties of several molten polymers was performed using the Maxwell Orthogonal Rheometer. Relaxation spectra derived from experimental data for the terminal region of viscoelastic response indicate that as molecular weight distribution broadens, terminal relaxation phenomena associated with molecular disentanglement and translation extend over a corresponding wider frequency range. The same data indicate that a true maximum relaxation time beyond which no elastic response is observed exists for the materials studied. Moreover, the maximum relaxation time corresponds to the reciprocal of the frequency where the dynamic viscosity deviates from its zero-shear value. Thus an estimate of the time necessary for complete elastic recovery in polymer melts is readily obtained experimentally.

Notes: Tensile creep measurements were carried out on a commercial ABS polymer over a temperature range from 40 to 100°C at stress levels from 0.6 to 1.8 × 108 dynes/cm2. Experiments were conducted in a prototype of an apparatus designed to be compatible with digital acquisition systems. Analysis of the data indicated that application of the time-temperature super-position principle was of limited value due to the use of test temperatures near and below the effective glass transition temperature of the acrylonitrile-styrene component of the polymer. A strong stress dependence of the compliance was observed, even at relatively short times after loading. This was analyzed in terms of a model in which the height of the potential energy barrier to motion of the molecular flow unit is lowered by the application of stress. Analysis of the temperature dependence of the compliance at low stress levels indicated that the effective Tg of the acrylonitrile-styrene phase is about 85°C. The temperature dependence of the magnitude of the activation energy is considered as is the stress dependence of the glass transition temperature. Implications of short-time response in creep with regard to response under impact loading are pointed out. Practical application of results to the prediction of dimensional stability of molded parts is discussed as well as the limitations involved in extrapolation of experimental data to long times and high stress levels.

Notes: Fine structures of several plastic/rubber two -phase polymer systems were studied by means of direct observations of ultrathin sections under the electron microscope using osmium tetroxide staining and a hardening procedure developed recently by Kato. Samples used are several types of both ABS polymers and high -impact polystyrenes, and several PVC/rubber blends and the results were discussed in relation to their dynamic viscoelastic properties. It is suggested that these studies may fruitfully be extended to clarify the structure -to property relationships by use of this method.

Notes: The purpose of this paper is to describe a new deformation calorimeter, which is based on differential thermometry and uses a flowing gas stream as a heat transfer medium which allows it to operate under near-isothermal conditions. Also presented are some preliminary test measurements with a crosslinked polyurethane elastomer and crystalline polybutene-1.

Notes: Antiplasticizers are considered to be diluents which when added to polymers result in mechanical property behavior opposite to that of plasticization. The addition of antiplasticizers to certain polymers such as Bisphenol A polycarbonate, polysulfone, and polyvinyl chloride results in the elimination of the secondary loss transitions of these polymers. As a drop in modulus accompanies these transitions, their elimination results in higher tensile strength and tensile modulus. As secondary transitions are commonly associated with ductility and impact strength, their elimination also results in the observed embrittlement characteristics. The addition of anti-plasticizers to polymers also restricts the diffusion of penetrants resulting from the decrease of molecular flexibility in the polymer matrix.

Notes: A useful concept in polymer science is the degree of crystallinity - the fraction of the polymer that exists in a relatively ordered state. Methods of determination of the degree of crystallinity using density, infrared, thermal, N.M.R. and X-ray measurements are examined in light of modern notions of the structure of semi-crystalline polymers.

Notes: The changes occurring when polythene melts are subjected to shear, have been investigated using a rotating bob fitted into a ram extruder. In addition to chain scission, low density polythene exhibits reversible changes in mechanical and viscoelastic properties. The magnitude of the changes is controlled by total shear strain, and is related to molecular weight and long chain branching. The mechanism appears to be one of reversible disentanglement operating mainly on the large highly branched molecules. The work is relevant to various extrusion processes and to other long-branched polymers.

Notes: This investigation deals with the fatigue behavior of a group of thermoplastics fortified with discontinuous glass fibers dispersed by an injection molding process. The thermoplastics included nylon, polystyrene and polyethylene reinforced with short (1/8 in.) and long (1/2 in.) glass fibers.Several aspects of the fatigue behavior are included in the study. First, classical S-N curves were generated under fluctuating tension with R = 0.05 to show the loss of strength due to cyclic load application. Next, the extent of progressive fatigue damage was established by measuring the residual strength after cyclic loading. Finally, hypotheses pertaining to the fatigue mechanisms operative in all four materials were made based on microscopic examinations of sections removed from fatiguedamaged specimens.

Notes: Twelve polymers and copolymers reinforced with random short glass fibers are used for the study of the strength -composition relationship. Six of these reinforced systems are new and have not been reported elsewhere. The effect of fiber volume fraction on tensile and flexural strengths is related to the Kelly and Tyson equation. For each composition the strengthening factor, F, is calculated and discussed with respect to the structure of the polymer. One factor pertaining to the actual performance of fiber glass, fiber efficiency, K, has been extrapolated for the fiber glass used for this study. The effects of fibers on toughness and the Izod notched impact strength are discussed. It is the impact strength ratio and not the toughness which is used to describe the net result of reinforcement.The deviations between the wet and the dry strengths are used to illustrate the effect of the fiber -matrix interfacial bond. A new parameter, Δθ, is introduced to describe the effect of structure on the fiber -matrix interface. The effect of water at the fiber -matrix interface is further demonstrated through the determination of dielectric constant and dissipation factor of the composite before and after water immersion. The rule of mixtures was found to apply to dry electrical properties of composites.

Notes: The effects of shear stress on the crystallization kinetics and morphology of linear polyethylene and polybutene-1 were studied with the aid of a specially designed apparatus. With this equipment, it was possible to heat a thin polymer sample between glass slides to a melt temperature, quench the sample to a crystallization temperature, and then deform the sample in shear by applying a constant load to one of the glass slides. During the deformation, the crystallization process was observed and photographed under a polarizing microscope. Also, the displacement of the glass slide was simultaneously recorded which made possible a determination of the shear strain as a function of time.The results demonstrate that two phenomena may occur in the initially supercooled polymer samples in response to the applied shear stress. In one case, the sample deformed until it fractured, generally exhibiting no evidene of crystallization; in the other, the sample deformed until an inflection point was reached after which the sample became rigid. This latter phenomenon was attributed to crystallization.At low shear stresses, the inflection point was associated with the growth of spherulites which simply became large enough to bridge the glass slides and prevent further deformation of the sample. This generally occurred prior to the completion of the radial growth of the lamellae.At high shear stresses, however, no evidence of crystallization was seen in the microscope until the inflection point was reached. At this point, birefringence was observed in the sample. The resulting structure generally could not be resolved in the microscope, thereby indicating very profuse nucleation.The results obtained clearly demonstrate that the application of a sufficiently high shear stress to an initially supercooled melt has a substantial effect on the rates of crystallization of both polyethylene and polybutene-1. This was shown most dramatically at temperatures close to the melting point, e.g., both polyethylene at 130°C and polybutene-1 at 113°C, which require over 104 sec to crystallize under quiescent conditions, crystallized at approximately 0.05 seconds.The application of a shear stress to a polymer melt is envisaged as resulting in molecular orientation. In accord with the theories of Flory, and Krigbaum and Roe, the associated decrease in entropy of the melt may be considered to increase the supercooling. Under high stresses at which large increases in supercooling result, crystallization occurs more rapidy at the high temperatures and with polymers of lower molecular weight. At low shear stresses, the influence of temperature and molecular weight on the crystallization kinetics is essentially the same as that obseved under quiescent conditions.Observations through the microscope have shown that the application of a shear stress to a polymer melt leads to large increases in the number of crystalline structures formed and to the formation of oriented morphologies. This latter phenomenon arises due to nucleation lines formed by impurities and spherulites in the deforming melt. The impurities and spherulites apparently cause a disturbance which is thought to result in a local increase in stress of the melt and, hence, a local increase in supercooling. Lamellae then nucleate on these lines and grow out radially.

Notes: Equilibrium sorption isotherms were obtained for the sulfur dioxide-epoxy resin of aliphatic diglycidyl ether system over a temperature range of 1° to 45°C. The sorption isotherms indicated the presence of Langmuir sorption due to specific interaction. This is uncommon for rubbery polymers, though similar behavior was also observed previously. Zimm-Lundberg's clustering analysis indicated a slight tendency for clustering of the penetrant molecules at low temperatures and higher activities. The number of Langmuir sites for sorption was found to be independent of temperature. The mobilities of the molecules sorbed in Henry's law mode and the Langmuir mode were found to be approximately equal. Predictions of the permeability values for this system are presented and compared with other data from the literature. The temperature dependence of different sorption parameters is presented and discussed in detail.

Notes: Uniaxial tension tests to the yield point were performed on a crystalline polymer, poly(4-methyl pentene-1) (PMP) as a function of temperature from 21° to 200°C at a strain rate of 2 min-1. After testing, the specimens showed considerable stress whitening as a result of microvoid formation. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (240°C). Thus, the behavior of this crystalline polymer is similar to that of glassy polymers, but with the melting temperature, rather than the glass transition temperature, as the reference point. The ratio of thermal to mechanical energy input to produce yielding is an order of magnitude smaller for PMP than it is for glassy polymers. The ratio of yield stress to Young's modulus is about 0.02, which is typical for polymers. Yield stress is a linear function of log strain rate, which implies that yielding can be described as a segmental flow rate process in which the applied stress biases the activation energy. The activation volume is on the order of 20 monomer unit volumes and increases as the temperature increases. The activation energy is 19 kcal/mol.

Notes: Samples of poly(methyl methacrylate) with a central circular hole are compressed, and crazes form on or after unloading, provided that the strain attains or exceeds a threshold value ∊t. Crazes induced in air are transformed rapidly to cracks, but environmental crazes are more stable. These residual stress crazes form at the diameter of the hole on a plane perpendicular to the applied stress direction. In contrast, during loading, crazes form on the vertical plane containing the hole axis. Unloading crazes are relatively insensitive to changes in strain rate, whereas loading erazes have a pronounced rate dependence. Environmental residual stress crazing exhibits an apparent rate sensitivity at constant time, but the critical applied strain ∊t is essentially constant, irrespective of rate, if the sample is in contact with the environment for a sufficiently long time to ensure that the minimum ∊t is obtained. Residual stress crazes appear to initiate at the equator of the hole, and the maximum tensile residual strain, indicated by a strain gauge, occurs in this position.

Notes: Head-to-head polyisobutylene degrades at a maximum rate at 320°C, a temperature about 65°C lower than head-to-tail polyisobutylene. Under our conditions, head-to-tail (the regular polyisobutylene) degrades (as do many other disubstituted vinyl monomers) to a high yield of the monomer isobutylene. Surprisingly, head-to-head polyisobutylene also degraded, primarily to isobutylene. Liquid, low-molecular compounds, probably dimers, were also obtained from head-to-tail and head-to-head polyisobutylene. A mechanism of this degradation is proposed.

Notes: This paper presents a new low-energy method to separate solvents from polymers. The method is based upon the lower critical solution temperature (LCST), a phenomenon exhibited by all nonpolar polymer-solvent systems. Three key issues concerning this new separation method are discussed for the specific system of high cis polybutadiene in a commercial grade n-hexane. The first issue, energy cost, is greatly reduced from present commercial separation processes by avoiding the liquid-vapor phase transition for more than half of the solvent. The predicted energy cost for the new method (not including inefficiencies) is about 15 percent of the present energy cost (including inefficiencies). The second issue, recycling of the dilute phase with terminator, is shown not to be a serious problem, and a solution is suggested based upon available methods. The third issue discussed, and perhaps the most difficult, is the physical separation of the two phases. This is solved by inducing spinodal decomposition, which leads to rapid gravity separation. Several alternative separation scenarios based upon this idea are presented at the end of the article.

Notes: A basis for design of two-stage extractor screws is developed with special focus on determining optimum design of the final pumping section in order to maximize pressure-generating capability. Departure from the conventional square-pitch helix angle of 17.7° appears justified in this section of the screw where pressure-development capability is critical to successful performance. Optimization can produce gains of 5 to 30 percent in pressure (or in corresponding length reductions), the exact benefits depending on the non-Newtonian behavior of the melt and on the optimization strategy selected.

Notes: The properties of a series of polyisobutylene (PIB) based polyurethanes were studied and compared to those reported in the literature for polyether, polyester, and polybutadiene-based polyurethanes. Good phase separation was reflected in the invariance of the soft segment Tn with increasing hard segment content. Increasing hard segment content resulted in larger domains, higher modulus and lower ultimate elongation. The modulus above the soft segment Tn was higher than that previously reported for polyurethanes of similar hard segment contant; improved phase separation and short contour lengths of the PIB chains were cited as possible causes of this behavior. Stress-strain data indicated a change from isolated to interconnected domain morphology with incerasing hard segment contant. Generally similar trends were seen for all types of urethanes. The overall properties of polybutadiene polyurethanes were closest to those of the polyisobutylene polyurethanes studied. The properties of both of these systems were suggested to suffer from significant synthesis problems in urethane formation due to the incompatibility of the nonpolar hydrocarbon soft segment and the polar diol chain extender. Preliminary environmental tests indicated that polyisobutylene based materials exhibit improved hydrolytic stability and reduced moisture permeability compared to polyether and polyester polyurethanes and greater oxidative stability compared to polybutadiene based materials.

Notes: This paper discusses the shrinkage characteristics of armored (reinforced) rubber articles for two types of boundary conditions: (a) cases where the armoring material is neither flexible nor thermoexpansive, and (b) cases where the armoring material has a finite thermal expansion between room and vulcanization temperature. A quantiative analysis of shrinkage strains and stresses is developed for the two boundary conditions.

Notes: This note draws together the Han-Villamizar experimental observations on the critical pressure at which gas bubbles became visible in flowing thermoplastic melts and a simple method of predicting the equilibrium pressure based on gas solubility. It is shown that the observed pressure is 40 to 75 percent of the calculated pressure.

Notes: The effects of thermal aging on the dynamic mechanical properties of rigid poly(vinyl chloride) (PVC) and chlorinated poly(vinyl chloride) (CPVC) are examined in the glass transition (Tg) and β transition (Tβ) regions. PVC, when quenched through Tg and then annealed at 40°C, exhibits a sub-Tg peak in the loss modulus function. The position of the peak moves to higher temperatures with increasing annealing time. The effect is analogous to sub-Tg endothermic peaks previously observed by differential scanning calorimetry (DSC). A sub-Tβ peak in the tan δ or the loss modulus functions can be produced by quenching through Tβ. The effect of heating rate on the sub-Tβ peak is explored.

Notes: The strength and elongation to break of an acetal copolymer were measured at four elongation rates, from 0.2 to 20 in./min, at temperatures from 239 K to 339 K. Both strength and elongation results could be reduced to master curves by means of time-temperature superposition. The temperature dependence of the shift factors was given by an equation of the WLF form, with parameters close to those found for most amorphous polymers, at a reference temperature equal to the γ-transition temperature of the polymer. Extrapolation to much higher testing rates and to much slower creep rates was satisfactory. Similar but less extensive tests were run on two other samples with different molecular weights. The yield stress was independent of molecular weight, but elongation increased with increasing molecular weight at all conditions.

Notes: A critical review of the specification of orientation and its development in polymer-processing operations is presented. Orientation may in general be specified by orientation distribution functions, but is most conveniently expressed in terms of orientation factors which are second moments of the distribution. The Hermans orientation factor represents polymer-chain orientation for systems with fiber symmetry (uniaxial orientation) and the Hermans-Stein orientation factors express uniaxial orientation for each of the crystallographic axes of crystalline polymers. Biaxial orientation is, however, developed in tubular film extrusion, blowmolding and, indeed, all processing operations other than fiber formation. Orientation factors developed previously by the authors express biaxial orientation in terms of the angles between the machine and transverse directions and the polymer chain axis or crystallographic axes. In flowing polymer melts, the Rheo-Optical Law, which relates birefringence and stress, represents a relationship between polymer-chain orientation and stress. In vitrified polymeric glasses (e.g. polystyrene), the orientation factors are related linearly to the stress field at vitrification. This has been shown experimentally for melt spinning and tubular film extrusion. The results of studies of blowmolding and injection molding are consistent with this. The crystalline orientation factors have also been found to be determined by the stress field at solidification in melt spinning and tubular film extrusion.

Notes: A novel approach for producing multiaxially oriented polymers with ultrahigh mechanical properties in more than one direction is discussed. According to the approach, which is adaptable to conventional commercial processes, the polymer is processed in a contained geometry at a temperature near to but below the isotropic crystalline melting point under curvilinear flow conditions generated by the combined effects of a compressive force and a rotational force perpendicular to the compressive force. The process is demonstrated with thermoplastic and thermotropic polymers using simple torsional flow. The general features of the process and the properties of the multiaxially oriented polymers are discussed in view of the different flow conditions.

Notes: A simple equation enabling the prediction of the thermal conductivity of plastic foams, without the aid of adjustable parameters, is proposed. The equation is based on a recurrent method, previously developed, that showed reasonable agreement with experimental results. Ways of decreasing the thermal radiation contribution are shown. In particular, the influence of cell size, radiation transmission through solid membranes, and low-emissivity boundary surfaces are analyzed. Errors involved in steady techniques of measuring the thermal conductivity associated with radiation are discussed.

Notes: In this paper we introduce the concept of the length of a transfer unit (LTU) for polymer devolatilization and show that the LTU is an appropriate measure of the effectiveness of the process unit in which the devolatilization operation is conducted. The utility of the concept is demonstrated for the case when the process unit is a twin screw extruder for which values of the LTU were determined from experimentally measured values of devolatilization rates. Values of the LTU were found to depend solely on the fluid mechanics in the extruder as expected and were in good agreement with the predictions of a theoretical expression developed for the system that was studied. Finally, we discuss the implications of the LTU concept in relation to the engineering design and analysis of polymer devolatilization processes.

Notes: Whitening phenomena, characterized by optically opaque regions when a highly oriented glassy polymer is immersed in some liquids, were investigated as a function of temperature, extent of molecular orientation, different solvent and molecular weight, using oriented polymethyl methacrylate (PMMA) obtained by hot-stretching and cold drawn polycarbonate (PC). Whitened PMMA is highly porous resembling foamed plastics and shows the same Tg as in unwhitened PMMA, while whitened PC is denser with much smaller pores and exhibits melting behavior characteristic of solvent-induced crystallinity. Whitening progresses with a sharp boundary between whitened and unwhitened layers, which advanced at a constant velocity. This feature is similar to Case II transport. However, whitening differs from Case II sorption in that it only occurs in highly oriented polymers in contact with liquids of negligible sorption. Activation enthalpy of 44.1 and 39.7 kcal/mol has been found in a certain temperature range for PMMA/N-methyl formamide (N-MF) and PC/di-isopropyl amine (DIPA) respectively. At a given temperature, a higher extent of orientation leads to faster whitening process. Entropy correlation theory, in which the decrease in the configurational entropy (ΔSc) due to orientation is assumed to approximate an inerease in the activation entropy, was employed to correlate the dependency of the whitening rate on orientation. For hotstretched PMMA, where ΔSc is proportionl to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document} since affine deformation applies, a good correlation is observed. For cold drawn PC, correlation was poor, probably because ΔSc cannot be expressed to be proportational to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document}. In PMMA, when the molecular weight is in the same order as the average molecular weight between entanglements, the orientation and the whitening rate are both lower than higher molecular weight speciments. This may be due to a smaller number of chain entanglements and consequent chain slippage. In PMMA, whitening induced liquids seem to have a solubility parameter somewhat greater (2.5 ∼ 5.0) than that of PMMA. For PC, no consistent tendency is found.

Notes: The mechanical behavior of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks (PUR/PAc IPN's) was investigated. Stress-strain and impact resistance measurements were made on IPN's with a variable PUR content. The effect of the degree of crosslinking of each network on the mechanical properties was also studied. It appears that only the ultimate elongation varies largely upon changing the crosslink degree. The results are interpreted in terms of the contribution of each network to the mechanical behavior, but also by the interpenetration of both components and by the phase continuity of the PAc network.

Notes: The plane strain fracture toughness of medium density polyethylene pipe materials has been investigated over a range of test temperatures and rates. Conditions are defined under which valid fracture toughness values can be obtained; at higher temperatures the material is notch-insensitive. Fracture surface morphology is described, and features are compared with predictions from the Dugdale model. The toughness derives from a band of fibrillar, drawn morphology associated with crack initiation or slow growth. The plane strain fracture toughness correlates with percent crystallinity according to the same relationship whether the crystallinity is varied by thermal treatment, comonomer content, or molecular weight.

Notes: Fibers made of phenol formaldehyde are relatively new to the market place and are currently manufactured in Japan. They have certain characteristics which make them attractive as a reinforcement for rubber, thermoplastics, and thermosets. This paper will discuss the properties of molded polypropylene thermoplastics as a function of fiber weight percent and surface treatment. It is shown that the elevated temperature properties are improved without sacrifice of low-temperature brittleness.

Notes: Phase diagrams of two types of rigid rod polymer/flexible coil polymer/methanesulfonic acid (MSA) ternary systems were determined by polarized optical microscopy at ambient conditions. The rigid rod polymer is a wholly aromatic high temperature resistant (no measurable Tg) poly (p-phenylenebenzobisthiazole) (PPBT). One of the flexible coil polymers is a wholly aromatic high temperature resistant poly (2,5′(6′) benzimidazole) (ABPBI), the other is a thermoplastic poly[2,2′ -(1-4-phenylene)-6,6′ -bis (3-phenyl-quinoxaline)] (PPQ) with Tg of 359°C. The solvent is methane-sulfonic acid (MSA). The experimentally determined critical concentration points, Ccr, are in excellent agreement with Flory's recent theory. Total phase segregation between the polymer pair in ternary solution was predicted and observed at C 〉 Ccr. Different decomposition mechanisms of phase separation were observed as a function of concentration.

Notes: Thermotropic liquid crystal polymers consist of rod-like molecules and are often called “self reinforcing thermoplastics.” Their rheological behaviors as well as orientation development during processing are often very similar to those of short fiber-filled composites. Without reinforcement, the polymer shows superior mechanical properties to conventional glass fiber-reinforced engineering resins. The orientation distribution in the crosssection as well as flow patterns in the molded thermotropic polymers are clearly visible to the naked eye due to color differences. This makes it particularly convenient to study the orientation distribution as well as the flow patterns of packing, back flow, jetting, flow instabilities, and weld line formation in injection molding. This paper discusses physical properties of a typical ther motropic polymer and their relationship to mold filling process in the injection molding.

Notes: Structural and mechanical data have been compared for reaction injection molding (RIM) polyurethanes prepared from uretonimine-modified diphenylmethane 4,4′-diisocyanate (MDI), ethylene glycol (EG), and a polyol (a polyether; Mn ≃ 5000), in order to investigate the effect of addition of a small amount of a polyetherdiamine (PEDA; Mn ≃ 400) to the reaction mixture, A series of specimens containing 18 parts and 30 parts EG, with and without the diamine additive, were examined both as-prepared and after thermal annealing. The specimens were compared in terms of their x-ray crystallinity, elongation, flexural modulus, impact strength, and heat-sag behavior. All of the specimens showed evidence for crystalline hard segments, which are more abundant in the series containing 30 parts EG. The crystallinity is lowest in the as-prepared specimens without the PEDA additive, and is increased by annealing for 1 hour at 120°C. The as-prepared specimen with additive has a hard segment crystallinity similar to that of the annealed specimen without additive. These results correlate with the mechanical property data, which improve as a result of annealing and/or the use of a PEDA additive. It is argued that the use of the polyetherdiamine enhances the phase separation and facilitates hard segment crystallization, leading to better heat-sag behavior. It is significant that the unannealed/with PEDA and annealed/without PEDA specimens have similar properties. Use of PEDA additive improves the green strength and impact strength of molded parts.

Notes: We have analyzed the deformation behavior of compatible and incompatible polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends by a combination of mechanical and vibrational spectroscopy. Macroscopic properties and segmental orientation were found to be sensitive to molecular weight, strain rate, and temperature of measurement above the glass-transition temperature. Considerably different orientation functions were found for the PS and PVME components. For the experiments carried out above the Tg of the blends, the deformation behavior measured was consistent with expectations of a rubbery network.

Notes: Physical Blends of ultrahigh-molecular-weight linear polyethylene (UHMW LPE) and normal-molecular-weight linear polyethylene (NMW LPE) have been evaluated in terms of melt flow rate, tensile stress-strain behavior, heat of fusion, melting temperature, and crystallinity. The behavior of the blends is intermediate between that of the parent polymers; no synergistic effects are observed. The addition of small quantities of NMW LPE does not improve the flow behavior of UHMW LPE sufficiently to render it amenable to conventional melt processing.

Notes: In order to analyze the failure phenomenon of plastic liners in freezers and refrigerators the mechanical properties of the freon blown polyurethane (PU) foam insulator material and the acrylonitrile-butadiene-styrene (ABS) plastic liner are determined. The properties considered essential for this problem are the elastic modulus, the tensile strength and the fracture toughness over the temperature range -40 to 20°C. By laminating a layer of the polyurethane foam to the ABS liner and depending on the test temperature brittle to semi-brittle fractures are promoted and the maximum load fracture toughness of the liner material is reduced. The reduction is more severe for notched bend than for single-edge notched tension specimens. Based on these mechanical properties plausible reasons for liner fractures are discussed.

Notes: A recent development suggests an approach to measure the equilibrium modulus through an impulse method. This paper is to report an attempt to apply such methods in measuring the changes of the equilibrium modulus of a thermosetting system during isothermal cures. Dynamic modulus changes were also measured and the results were correlated with that from the impulse method. At two different temperatures of cure, the equilibrium modulus values measured were very similar when the dynamic measurements showed tan δ = 1. At this point, it is not certain if the measured modulus is the real time independent portion of the elastic modulus, or contains the long relaxation time constant portion of the relaxation spectrum which appears to be pseudo-time independent at the time scale and the instrumental sensitivity of the present experimental set-up. This paper demonstrates the ease with which the impulse technique can be applied and suggests possible limitations or refinements.

Notes: The production of polymer blends increases at a rate of about 13 percent/y. Most of the commercial blends are multiphase systems of complex morphology, determined by the thermodynamic properties of the components and the rheology. Since the diffusion rates are relatively low, the blends are seldom at equilibrium. In most cases, the blend products have properties imposed by the morphology, created by a particular combination of the thermal and deformational history. There are three main reasons for studying the melt flow of blends: optimization of the processing conditions, search for the appropriate means to generate the desired morphology, and the interest in the basic study of the rheology of these complex systems.In this paper the results published during the last five years are reviewed. The data for polymer blends are compared with those obtained for simpler model systems: liquid mixtures, emulsions, and polymer blends. From the rheological point of view, the blends are divided into three groups: those where viscosity shows positive deviation from the log-additivity rule, PDB, those where the opposite effect is observed, NDB, and the remaining mixed-behavior systems, PNDB. To PDB belong the miscible blends and those with strong inter-domain interactions. To NDB belong those where the interactions are weak. To PNDB belong the blends in which there is a concentration-dependent transition of structure. The shear dependent properties of blends are also discussed.

Notes: Polymer blends with varying amounts of poly(vinyl chloride) (PVC), acrylonitrile-butadiene-styrene (ABS) and polyester have been developed to produce parts with highly flexible, good impact strength, and flame retardant hinge properties. In the present work, the rheological and dynamic mechanical properties are balanced by changing the blend formulations. It is shown that blends morphology and rheology have greater impact on the dimensional stability and delamination at the surface of the molded hinge parts.

Notes: Miscible blends of the polyhydroxy ether of bisphenol-A, Phenoxy, with a series of aliphatic polyesters were studied using melting point depression analysis and sorption to obtain the Flory-Huggins polymer-polymer interaction parameter, B. The B values obtained from these measurements were found to agree well in sign, magnitude, and variation with ester repeat structure and to also agree well with B values measured calorimetrically for mixtures of low molecular weight compounds with structures which are analogous to those of the polymers. These comparisons suggest that the same mechanisms are responsible for the exothermic heats of mixing measured directly for the analog compounds and indirectly for the miscible polymer blends. For this general system, evidence is provided which suggests that hydrogen bond formation between the hydroxyl group on Phenoxy and the ester moiety is probably responsible for the exothermic interactions and polymer blend miscibility observed.

Notes: A sequential interpenetrating polymer network, IPN, may be defined as a combination of two polymers in network form, at least one of which was polymerized or crosslinked in the presence of the other. Two major problems of interest to sequential IPN's relate to phase continuity and extent of mixing within each phase. A first attempt to define the molar volume of a network is made in terms of the molar volume of the polymer between crosslinks. This permits a thermodynamic calculation of the changes in molecular mixing expected as a function of crosslink density. The experimental system was poly(n-butyl acrylate)/polystyrene IPN's, where the PnBA was crosslinked with acrylic acid anhydride. This last may be selectively hydrolyzed, forming a semi-IPN, and then the PnBA can be extracted. Scanning electron microscopy and dynamic mechanical spectroscopy were carried out at each stage.

Notes: The rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10-1 to 103 rad/s at 23°C. The storage modulus G′ (ω) and loss modulus G″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non-Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero-shear rate viscosity ηo and steady-state compliance Je0, where also determined from the dynamic data and compared to previous steady shear flow results.

Notes: The rheological and thermal properties of composites of polystyrene (PS) and two liquid crystalline low-molecular-weight additives have been studied. Both additives act as plasticizers as evidenced by decreases in the glass transition and the melt viscosity. In addition both are miscible with PS over a broad range of concentrations. Partial phase diagrams of the two systems are presented and discussed.

Notes: Experimental studies of fiber wet-spinning and solution processing of films of molecular composites are presented. The rigid rod polymer was poly (p-phenylenebenzobisthiazole) (PPBT) and the flexible polymers were poly (2,5(6′)-benzimidazole) (ABPBI) and poly (2,5(6′)-benzothiazole) (ABPBT). Effects of the flexible polymer molecular entanglements in solution on the processing are discussed. These fibers and films have very high modulus and strength, which improve upon heat treatment. The uniaxial modulus of highly oriented molecular composites follows the linear rule of mixtures.

Notes: Increasing the nominal injection pressure up to 500 MP a improves the mechanical properties (modulus and strength) of injection-molded high-molecular-weight high-density polyethylene substantially. By a proper combination of barrel and mold temperature, the modulus of the molded parts (test bars) may be increased at least eight times compared to parts molded at 100 MPa. This improvement is partly due to the formation of high-strength crystalline modifications of the polyethylene induced by flow and pressure. The extent to which these structure modifications occur in the samples molded at various conditions has been determined by thermal analysis (DTA). When increasing the thickness of the samples, a sharp reduction of the modulus and strength was observed, even though the concentration of the crystalline high-strength phase was higher. An explanation of this effect in terms of the relaxation of the tie-molecules connecting the crystallites is suggested.

Notes: In this work it is shown that rebound experiments, carried out at low blow impact and by means of instrumented pendula, can be described in terms of the equation for a freely oscillating linear viscoelastic body with added mass. The experimental and calculated load-time curves are in very good agreement when the behavior of the material is linear viscoelastic; the assumptions made (transitory time shorter than rebound time, and negligible mechanical friction) are thus proved to be reasonable. The rebound test, which can be carried out on unnotched or notched specimens, allows one to obtain quickly and easily relevant material properties such as Young modulus or compliance, stored and dissipated energies, and the upper linear elastic limit at a testing speed not too far from that of impact testing.

Notes: A method is described to modify profiles of resist patterns in novolac and diazo-oxide containing systems. After patterning of the resist, two successive uniform flood exposures are given, one with deep UV (254 nm) at water-free conditions and the next with near UV (λ 〉 300 nm) at normal atmospheric conditions. The profile which results after development is vertical, concave or overhanging depending on flood exposure conditions and development processing. As the method includes a flood near UV exposure at atmospheric conditions the imagewise exposure energy can be reduced to approximately 35 percent of the normal value. Furthermore it gives also the possibility of using the resist as a deep UV resist. Another important implication is that standing wave effects are completely eliminated.

Notes: This paper describes new techniques for evaluating orientation in polymer moldings. Injection moldings of isotactic polypropylene, a semicrystalline polymer, have been used to demonstrate the analytical procedures.

Notes: It is of interest to produce plastic corrugated tubing as strong as possible with a minimum amount of material. Simultaneously, the tubing has to resist stretching, and maintain flexibility for transport purposes. To find the optimum profile geometry, two mathematical models were employed. One model was used to calculate the strength of the tubing per unit length and a second model was used to predict the elongation of corrugated tubing for a given load. Data was then generated for different profile configurations, and plotted for an optimum design procedure. The results showed that, while the wall thickness can be varied during production, the most critical parameter is the corrugation depth. The corrugation depth is fixed by the moldblock design, and the data presented can be used to obtain an optimum geometry.

Notes: The physical properties of high-pressure ethylene vinylacetate (EVA) copolymers having an average melt index of 8.5 g/10 min and a mol% of VA less than 20 are studied. A comparison is made with the properties of their saponified derivatives, the ethylene vinylalcohol (EVAl) co- and ethylene vinylalcohol vinylacetate (EVAlVA) terpolymers. A melt-index effect is noted. Density, thermal, and mechanical properties of EVA copolymers are determined by the degree of crystallinity, which depends on the mol% VA and on the degree of alkyl shortchain branches. EVAlVA terpolymer properties depend on the residual mol% VA. EVAl copolymers proved to have some properties similar to low-density polyethylene. The hydrogen-bonding effect via hydroxyl groups was negligible for this level of vinylalcohol incorporation.

Notes: This work concerns itself with laminar mixing of viscous liquids. The primary focus is on mechanical mixing of immiscible fluids but mixing of diffusing and reacting fluids is also briefly considered. Operations such as thermal homogenization and reactive mixing usually not treated in the context of laminar mixing are also included here. The emphasis is on mixing of polymeric liquids and on basic experimentation and theory. Dispersion of solids, mechanisms of demixing (such as gradient coagulation), properties of mixtures, and the description of mixing equipment are not considered. There are no substantial reviews covering developments of theory and applications in laminar mixing in terms of a fundamental unifying theory and analyses relating operating variables to mixing quality. This review, although an attempt in this direction, is not self sufficient and cannot stand alone without recourse to the indicated references. The reader is assumed to have some familiarity with the literature on mixing. Thus, basic concepts are not explained but merely reviewed. Emphasis is given to recent theoretical developments; application examples are provided. The objective here is to condense results from several diverse sources, to present and extend recent developments, to point out the relation of the subject to seemingly unrelated work, and to suggest areas for further research.

Notes: The importance of hydrogen bonding interactions in promoting polymer miscibility has been the subject of much recent investigation. In this study, we address the question of the effect of molecular size and geometry on the intensity of the hydrogen bonding interaction. To this end, the interaction of the functional group in various molecules with a variety of acid and base polymer matrices has been monitored using infrared spectroscopy. The “probes” used in this study each contained only one functional group per molecule to prevent intra-molecular association. The probes were acetone, di-n-hexyl ketone, 10-nonadecanone, cyclohexanone, cyclododecanone, isopropanol, 4-decanol, 10-nonadecanol, cyclohexanol, and cyclododecanol. The interactions of the base probes with poly-(vinyl chloride), poly(vinylidine fluoride), phenoxy, poly(styrene-co-allyl alcohol), and a variety of cellulosic polymers were studied. Acid probe interactions were measured in poly(pivalolactone), poly(butanediol-1,4-terephthalate), poly-(acetal), poly(∊-caprolactone), poly(vinyl methyl ether), poly(4-methoxy styrene) and poly(ethylene oxide). The effect of the presumably inert poly(styrene) and ethylene-propylene rubber matrices on the probe's functional group was studied for comparison.

Notes: A common framework for the analysis of styrene-acrylic ester systems has been developed by analyzing the pertinent kinetic information. This is shown to lead to a well defined strategy for the design of copolymerization reactors especially in the industrially relevant high conversion region. The existence of stable steady states and its influence on the system parameters has been illustrated for the case of a continuous stirred tank reactor (CSTR). A novel strategy of a CSTR operated with a recycle is proposed. This is shown to lead to an operation in the unique steady state with the added advantage of a high conversion and uniform copolymer composition. This would seem to be the first such analysis in the high conversion region.

Notes: The length reduction of reinforcing fibers in short-fiber reinforced plastics during processing has been studied experimentally. It has been shown that fiber volume fraction, initial length, and initial state of dispersion have little effect on the final fiber length. In dilute suspension theory based on shearing flow conditions and fiber properties the flow stresses are found to be compatible with the experimental results and results which are found in the literature.

Notes: Thin polymer films were irradiated in a high vacuum environment with energetic (∼2 MeV) ions. The emitted molecular species were studied with a quadrupole mass spectrometer during bombardment. The emitted species are predominantly small molecules. The efficiency of emission depends strongly upon the electronic energy loss of the incident ions in the film and, hence, upon the velocity and atomic number of the incident ion. The emission efficiency of all species decreases with increasing damage in the film. By pulsing the ion beam, the time dependence of irradiation induced emission of molecular species from the films has been studied. Emission delays of hundreds of milliseconds are observed in some cases. These delays are found to depend upon the emitted species as well as the host film and seem to be associated with diffusion of the species in the films.

Notes: Submicron lines in negative working, substituted polystyrene resists by focused-ion-beam lithography were demonstrated. These features were transferred into an underlying molybdenum layer by plasma etching using the resist as an etch mask, with the minimum continuous line having a width of 0.20 μm.

Notes: Poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) has been evaluated as a high-sensitivity, high-resolution, high temperature-resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E-beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight-average-molecular-weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster-scan-type or vector-scan-type electron-beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma-etch resistance was about twice that of PMMA.

Notes: Detailed crazing behavior in several plastic/rubber twophase polymer systems was studied by means of direct observation of ultrathin sections under the electron microscope by employing osmium tetroxide staining and hardening procedure. Samples used are ABS polymer, high -impact polystyrene and several PVC/rubber blends. All of the systems investigated showed evidence of stress -crazing when under flexural stress. Relationships between the dispersed rubber particles and the crazing behaviors were studied, and the role of rubber particles in the toughening mechanism of plastics was discussed based on these observations.

Notes: The effects of temperature and penetrant activity on the sorption kinetics and equilibria of a series of alkanes in glassy, biaxially oriented polystyrene were studied. Normal isomers of pentane, hexane, and heptane cause crazing of polystyrene film samples at high penetrant activities (〉 0.85). Crazing kinetics are identical to the kinetics of Case II transport. Transport of these normal hydrocarbons in glassy polystyrene in the temperature range 25 to 50°C is markedly non-Fickian; limiting Case II transport is observed at activities in exces of 0.6. Sorption appears to be controlled by highly activated relaxation processes including primary bond breakage at these high penetrant activities. Fickian diffusion behavior is approached, however, as penetrant activity is reduced. Sorption of the branched isomers of these compounds does not result in polymer microfailure. The sorption kinetics of the branched isomers, although time dependent, appear to be controlled primarily by thermally activated diffusion rather than large scale polymer relaxations which control Case II transport.

Notes: Some of the thermodynamic and physical properties of crystals of linear polyethylene, formed from dilute solution are discussed. These properties include density, enthalpy of fusion, infrared absorption spectrum, selective oxidation and dynamic mechanical measurements. Despite the fact that electron microscopic examination reveals an apparent geometric regularity to these crystals, all these physical measurements yield a consistent interpretation in that they require about 15-20% of the chain units to be in a non-random conformation, and to form a disordered amorphous overlayer.Detailed studies of the experimentally observed relations between the crystallite thickness, crystallization temperature, and dissolution temperature (melting temperature in a dilute solution) are also presented. A thermodynamic analysis of the dissolution temperature-size relations, based on independently determined equilibrium solubility temperatures, indicates that the interfacial free-energy characteristic of the mature crystallites is significantly different from that involved in nucleation. The interfacial structures of the nucleus and the crystallites must, therefore, also be different. Size control by a nucleation process can be demonstrated from very general theoretical considerations. However, the detailed molecular structure characteristic of the nucleus cannot be specified solely from the fact that this process is size controlling.

Notes: Work at Stanford Research Institute on the deterioration of polymers is based on the assumption that aging in the light is the most serious problem and that it has at least three components that must be separated if we are to understand the overall process. We have started by measuring the production of free radicals on the polymer when pairs of t-butoxy radicals are generated from thermal decomposition of di-t-butylperoxy oxalate (DBPO) in bulk atactic polypropylene at temperatures approximating service conditions, 35-50°C. Our preliminary experiments have brought out experimental difficulties and have raised more theoretical questions than they have answered. Nevertheless, they show that the efficiency of production of polymer radicals is low and sensitive to the mobilities of the polymer chains. They also suggest that two kinetically different oxidation processes, with different dependencies on rates of initiation and with different susceptibilities to inhibitors, are proceeding simultaneously. The implications of these findings for results of some previous work and for design of improved accelerated tests is considered.

Notes: Starting with specific constitutive equations, methods of evaluating material properties from experimental data are outlined and then illustrated for some polymeric materials; these equations have been derived from thermodynamic principles, and are very similar to the Boltzmann superposition integral form of linear theory. The experimental basis for two equations under uniaxial loading and the influence of environmental factors on the properties are first examined. It is then shown that creep and recovery data can be conveiently used to evaluate properties in one equation, while two-step relaxation data serve the same purpose for the second equation. Methods of reducing data to accomplish this characterization and to determine the accuracy of the theory are illustrated using existing data on nitrocellulose film, fiber-reinforced phenolic resin, and polyisobutylene. Finally, a set of three-dimensional constitutive equations is proposed which is consistent with nonlinear behavior of some metals and plastics, and which enables all properties to be evaluated from uniaxial creep and recovery data.

Notes: Equations have been derived to convert Brabender flow curves to Instron flow curves for practical application purposes. The technique involved is simple and has been described and discussed in detail. Nine pairs of Brabender and Instron flow curves of three different high polymers, each at three operating temperatures, have been found to fit each other quite well. The converted Brabender flow curves overlap a part of the Instron curves and extend the shear range toward the Newtonian flow region. An important consequence of this work is that the Brabender Plastograph can now be regarded as a formal viscometer while still functioning as a miniature of the Banbury mixers used in industry. More work is being done to take advantage of this consequence.

Notes: Constant stress creep and recovery experiments were performed in the nonlinear range under combined tension and torsion on a tubular specimen of polycarbonate. Nonlinear viscoelasticity theory was employed to describe the test results. It was found that the first three orders of stress terms and a power function of time adequately described the experimental results. The modified superposition principle satisfactorily predicted the recovery following creep. Recovery was almost complete in several days following two hours of creep.

Notes: The physical optics of iridescent multilayered plastic films are analyzed theoretically relating the layer thickness, layer arrangement, and refractive index difference between layers to the reflection spectra for light at normal incidence. Very vivid iridescent and metallic-appearing films may be made by proper control of layer distribution.

Notes: Salts of polyacrylic acid can be fabricated in heated molds using mixed powders of polyacrylic acid and metal oxides. Because of the strong intermolecular forces in these polyelectrolyte salts, they have elastic moduli several times greater than the moduli of conventional plastics. They also have very low coefficients of expansion and high compression strengths. Composites containing metallic and inorganic fillers have also been made and their mechanical properties measured.

Notes: The dynamic thermal stability of rigid PVC resin compositions as determined from Brabender torque rheometer tests has a linear relationship of stability time and torque from which a practical measure of processability at a fixed torque can be derived. The stability time at 1500 m-g torque, t1500, has been used to characterize differences between PVC homopolymer and copolymer resins in tin, calcium-zinc, lead, and bariumcadmium stabilizer systems. In every case, the vinyl chloride-propylene copolymers are unique in giving substantial process-ability advantages.The logarithm of stability time at a fixed torque, t1500, is a linear function of intrinsic viscosity, [η], for PVC homopolymers, giving a single line function corresponding to the expression log t1500 = A + B [η]. The constants, A and B, vary with each of the four stabilizer systems, and are related to the effectiveness of the particular formulations used.The ratio of t1500 for copolymers to the basic t1500 value for PVC homopolymers at the same intrinsic viscosity (molecular weight) is a practical measure of relative processability, trel, which is characteristic of PVC resin types and independent of stabilizer systems.

Notes: There is an increasing body of evidence showing that, for a variety of copolymers, there are significant changes in the copolymer composition over the molecular weight distribution of the polymer. In this work, we have polymerized the copolymer poly(styrene-methyl methacrylate) using ethylaluminum sesquichloride as the initiator. The copolymers produced were fractionated using a semiprep gel permeation chromatograph. The composition of the fractions was determined using infrared spectroscopy. Results show that the percent methyl methacrylate of the copolymers was higher at both the low- and high-molecular-weight regions of the polymers.

Notes: A model is proposed for the flow, reaction, and heat transfer during compression molding of thin, flat parts. The isothermal Newtonian version of the model is implemented using the finite element method, and is capable of handling arbitrary planar geometries. Automated mesh expansion and boundary condition modification allow the simulation to run without operator interaction. The model accurately predicts mold filling pattern for non-Newtonian and non-isothermal flows.

Notes: Some of today's modern screws contain melt-separating secondary (barrier) flights in the transition zone. With increasing utilization of barrier screws, the availability of proper and accurate design methods for the melting zone remains of paramount importance. A modified version of a mathematical model developed by the authors previously is applied to two most common types of barrier screws, viz. - The Mailefer screw (varying pitch and constant depth); - The Barr screw (constant pitch and varying depth). The present analysis provides valuable insight into the operating principles of these screws. A comparative study is presented demonstrating the possible advantages and disadvantages of the Maillefer and Barr screws in relation to conventional compression screws.

Notes: The effects of shearing conditions (i.e., shear temperature and shear rate) on the degree of orientation of polyethylene (Marlex 6006) and to what extent the induced orientation could be relaxed were examined in this study. Two types of samples were prepared: namely, SIC (shear-induced crystallization) and non-SIC samples. The SIC samples show induction times and possess a high degree of c-axis orientation along the shear direction. The induced orientation of SIC samples can be relaxed to a small extent but does not reach a steady value. Non-SIC samples do not show induction times and they show low degrees of c-axis orientation. The induced orientation of non-SIC samples can be relaxed to a steady state value with an activation energy of 90 kJ/mole. Our results also indicate that, when the shear temperature is at and above 145°C, polyethylene can be sheared up to 200X without introducing any significant molecular orientation even at very high shear rates.

Notes: Prediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τs) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down-channel velocity also requires the calculation of τs. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τs extremely difficult.As a first step of developing a reasonable mathematical model for calculating τs, experimental measurements of τs were made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τs on metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τs could not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τs must be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting conditions.

Notes: The notch sensitivity of high-density polyethylene (HDPE), polypropylene (PP), and polybutylene (PB) was evaluated using uniaxial tensile deformation and fractographic analysis. Each polyolefin was tested at relatively low and high molecular weights (MW). Only the lower MW HDPE was found to be clearly notch-sensitive. The lower MW PP exhibited some tendency toward notch sensitivity. The lower and higher MW PB, the higher MW HDPE, and the higher MW PP displayed notch strengthening. Whereas PB showed similar notched tensile performance regardless of molecular weight, both HDPE and PP showed higher susceptibility to notch sensitivity at lower molecular weights (and concomitant higher crystallinity). Tendencies toward notch sensitivity or notch stengthening were evidenced in the failure modes of these materials.

Notes: The mechanical response of integral-skin rigid polyurethane foam, with an average density of 300 to 700 kg/m3, to constant rate and creep loading was determined. Sandwich specimens were modeled by layers of a core material and two skins, whose secant moduli had been determined experimentally by separate tests and approximated by linear functions of the density. The effective rigidities of the sandwich in tension and flexure were calculated and compared favorably to experimental measurements. The sandwich structure improved the flexural rigidity of homogeneous foam by a factor of more than 2.20. Tensile creep tests of sandwich specimens at relatively low stress levels (up to about 38 percent of their strength) showed that the creep was nonlinear, but a single creep curve could represent creep of specimens of various densities, provided the relative load on them was the same. A limited number of flexural creep tests led to similar conclusions, but the creep rate was smaller than in tension. Results from torsion tests of core material, compressive tests of sandwich specimens, and tension and compression tests of nonskin rigid foam are included in this article.

Notes: It is shown that the Williams-Landel-Ferry equation can be taken to describe the temperature dependence of viscosity of an amine-cured epoxy resin. Furthermore, for this resin system, the two parameters of the W-L-F equation can be expressed simply as functions of hardener concentration. Since the hardener concentration decreases with advancement, and since the reaction rate equation for advancement is readily determined and known, the viscosity can be calculated over any temperature (cure) cycle.

Notes: In recent years the spinning speeds of poly(ethylene terephthalate) (PET) fiber have increased to the point that significant structural development is being observed in the spun yarn. At even higher speeds significant crystallization has been obtained. Data characterizing these yarns will be presented and discussed showing the development of crystals and that the onset of this phenomena is related to the stress at the “freeze point.” The “freeze point” rises from around Tg at low speeds to the order of 200°C at high speeds. The spinline itself has been characterized by velocity and orientation profiles which show the crystallization process is extremely rapid, occurring over a few centimenters of the spinline.

Notes: The value of tmax in differential scanning calorimetry is correlated with the crystallization kinetics of poly(ethylene terephthalate) (PET). The Avrami exponent, n, obtained varies as a result of a change in slope of the curve at the point tn, a secondary crystallization transition. The plot of tn vs. tmax shows a linear relationship. The rate of crystallization depends upon both molecular weight and crystallization temperature. Under a nucleation controlling step, the plot of log tmax vs. \documentclass{article}\pagestyle{empty}\begin{document}$ t_{\max } vs.\frac{1}{{T^2 \Delta T}} $\end{document}gives a linear relationship. Theoretical concepts of the treatment are discussed.

Notes: Polypropylene, polystyrene, EP (ethylene/propylene) rubber, and bromobutyl rubber were blended under standardized conditions and the sizes of minor phase domains determined by Quantimet analysis. Dispersion effectiveness was found to depend on the melt viscosities of components under mixing conditions and on their “compatibilty” as inferred here from surface-tension data. Dispersion was optimized when components wet readily at contact surfaces and when melt viscosities were similar. Shear heating during dispersion appeared to offer an empirical index of component compatibilty. Apparent melt viscosities of the blends further reflected the component compatibility factor.

Notes: The finite element technique is applied to analytically predict the response of a disc made of BPA-polycarbonate during a displacement-controlled puncture test with a hemispherical indenter. The analysis includes effects of contact load, large displacements and rotations, and large strains and material yielding. Two general topics are addressed with this analysis. First, it is shown that the load-displacement behavior of impacted, BPA-polycarbonate plates can be accurately predicted over a wide range of engineering interest (strains up to 30 percent) using a bilinear representation of the stress-strain curve and flow theory of plasticity. For this purpose, the von Mises criterion is applied to define yielding in a generalized biaxial stress state, and strain rate effects are incorporated through the use of a yield stress consistent with the initial strain rate during the test. Second, in order to broaden the understanding of results associated with this widely used test, a number of mechanical and material effects are discussed, including large displacements, friction at the clamped support and indenter head, and clamping pressure at the support. Lack of agreement between the present analysis and experimental results with regard to ultimate load at puncture suggests that strain hardening and strain rate hardening of the material during the high-strain portion of the test (30 percent-60 percent) must be more accurately modeled for improved predictive capability.

Notes: This article concerns itself with the prediction of effective diffusion coefficients of small permeants in binary polymer blends of varying degrees of miscibility and microstructural order. Several models have been critically evaluated with the help of previously published experimental data and in terms of consistency of morphological information provided by small permeants serving as morphological probes. Completely random, two-phase media have been modeled in terms of Effective Medium Theory with the coordination number (z) describing the average morphology. A comprehensive analysis of experimental data has shown a correlation between z and various physical situations. Near the percolation threshold, z attains a maximum value while, above it, z tends to decrease with increasing content of the conductive component. Accurate predictions of effective diffusivity can be made for volume fractions between 0.3 and 0.8 by letting z = 6. Evidence for phase inversion was studied in terms of models with ordered microstructure and transport data.

Notes: Our laboratory recently published several analytical equations that can be used to predict the melting rate of fully compacted solid polymers sliding on a heated metal surface, modeling the melting mechanism inside an extruder. These equations were obtained by seeking asymptotic solutions to the differential equations describing the melting mechanism, temperature, and shear-dependent viscosity of polymer melts. Following the same asymptotic approach, we successfully developed accompanying analytical equations for predicting the stress required to slide fully compacted solid polymers on a heated metal surface. The accuracy of these analytical stress equations was found to be reasonable, although not fully satisfactory, by comparing their predictions to the experimentally measured values. The accuracy of the stress calculation is directly related to the accuracy of the viscosity values at high shear rates. The consideration of the temperature and shear dependencies of melt viscosity is most important for accurate prediction of the stress, just as it is for the melting rate. The stress not only depends on the melt rheological properties of the polymer but also on the thermodynamic properties.

Notes: A simple empirical relationship exists between the thickness and the solvent-evaporation rate of spin-coated thin films. The thickness of a film formed from an organic solvent solution can be approximated by the relationship\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (E\lambda /C_p)^{0.60} $\end{document}, where μ is the viscosity of the coating solution, ω is the rotation speed, E is the solvent-evaporation rate, λ is the latent heat of evaporation, Cp is the heat capacity of the solvent, and K0 is a constant for volatile organic solvents. A similar relationship for aqueous polymer solutions is\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (1.0 - RH)^{0.60} $\end{document}, where RH is the relative humidity of air around the spin coater and Ka is a constant for aqueous solutions. These relationships are helpful in understanding the mechanism of thin-film formation in spin coating.

Notes: This paper discusses the most important input parameters affecting the conventional injection-molding process and describes a closed-loop control system for determining the interaction between ten process inputs and three output parameters. The input parameters are: back pressure, holding pressure, injection time, open mold time, shot size, clamping pressure, injection pressure, screw speed, and boost cut-off. The output parameters studied are: part weight, maximum cavity pressure, and maximum mold deflection.