ALBERT

Notes: Proteins and synthetic polypeptides undergo specific catalytic cleavage by enzymes. It is the object of this article to review the specific hydrolytic, redox, and electron transfer reactions involving enzymes and their mechanisms. The stability of the synthetic high polymers in the biochemical environments is much higher than that of proteins in general, but the increasing use of these materials in the field of surgical implants and internal prostheses has necessitated the systematic long range study of the systems in these surroundings. The enzymatic attack on the synthetic polymers has not been the subject of general study until now, but the intimate knowledge of the specificity and mode of attack of the enzymes, in case of the proteins, would pave the way towards experimental designs to elucidate the comparative stability of various synthetic plastics in these environments. The study of the correlation of the mechanical strength and the chemical structures of these polymers tested as implants in living animals is reviewed, and the suitability of several synthetic polymers for this application is discussed.

Notes: Strain gage techniques have been developed to monitor the internal stresses in epoxy resin castings. The data obtained are a measure of the stresses developed on a transducer held in the center of a mass of polymerizing epoxy resin or those caused by thermal cycling of the potted unit at intervals of storage time. Results show that the stresses developed on the transducer during the first 70 hours of room temperature polymerization reached 900 psi in axial compression. Further polymerization during storage increased the stress to 2300 psi after 12 months. During thermal cycling approximately 10,000 psi compressive stress was developed at -54°C. These stresses were relieved at 71°C but reappeared at the lower temperatures upon subsequent cooling.

Notes: The literature on radiation-induced solid state polymerization has been increasing exponentially in the last five years. Major advances have been made in retention of crystalline morphology during polymerization, in stereospecific polymerization, in modification of reactivity ratios in copolymerization and in molecular weight control of the product. However, at the present time, no commercial products have resulted from the study of radiation-induced solid state polymerization. Chemically induced polymerization techniques have been keeping abreast of this explosive development in the solid state polymerization field and have up to this time precluded the use in industry of solid state polymerization. The major potential at the present time appears to be in the area of producing fibers without additional processing.

Notes: The feasibility of monitoring curing processes in large reinforced plastics structures by electrical volume resistivity techniques has been studied. It has been found, by embedding electrodes and thermocouples within a heavy-walled structure during fabricaton and by monitoring the change is resistance during the curing process, that information indicative of the rate and extent of curing can be obtained. The resin system used in this study was Epon 826/MNA/BDMA.

Notes: The Phenomenon of draw resonance and the cyclic size fluctuation of an extruded shpae are related to basic changes in the “melt strength” (force per average cross-sectional area required to draw the molten fiber down under fixed conditions). Melt strength values are obtained by a modified rheometer which consists of a vertical chamber to melt and hold the polymers at 190-250°C, a piston for extrusion, a take-up system, a strain gauge to measure the drawdown force and a recorder for continuous force-time plots. Melt strength increases with take-off speed but not proportionally. At higher velocities, draw resonance is apparent through a sinusoidal-like variation in fiber diameter. The amplitudes of melt strength and diameter waves are correlated with molecular weight, melt viscosity, swell, melt temperature and take-off speeds.

Notes: The resistivities of commercial octyl phthalatel plasticizers have been measured after treatments of heating, drying, purification by chromatography and addition of salts. The resistivity of pure plasticizer is high but is lowered by water, acid and alcohol. The theory to explain the observations is advanced.

Notes: The behavior and appearance of ABS compounds in rheometers correlate with certain surface characteristics of extruded sheet. Three reometers were studied, each demonstrating the increase of viscosity with time of a destabilized compound over a standard ABS. This behavior shows as low gloss areas on the sheet from the destabilized compound vs uniform gloss for the standard. The Instron Capillary Rheometer proved the useful since extrudates produced can discriminate between compounds at given temperatures on the basis of gloss. The relative gloss of material tested is duplicated on extrusion as measured by a 600 Gardner glossmeter. Dynamic conditions affecting viscosity can also be predicted by the Brabender Plastigraph. Correlations developed, along with the usual physical measurements, permit appaisal of ABS compounds before commercial extrusion.

Notes: An Instron tensile tester has been modified to measure the thermal expansion of polymer films. The method greatly simplifies the experimental procedure necessary for the standard ASTM dilatometric thermal expansion measurement, particularly for thin films. Thermal expansion measurements were made for films of polyester, polycarbonates, vinyls, cellulosies, and polyolefins from room temperature up to 300°F. Second-order transition temperatures were determined by plotting thermal elongation vs temperature; the transition temperature is indicated by a change in slope. Both expansion coeffcients and transition temperatures as determined by this method give excellent agreement with values reported in the literature.

Notes: The pressure-volume-temperature behavior for both solid and molten polypropylene was determined for pressures up to 618 atmospheres. These data were measured with a newly developed compressibility device capable of obtaining precise and accurate data. Compressibilities calculated from the experimental data compared favorably to the limited existing literature data. Constants were determined for the Spencer-Gilmore polymer equation of state for both the solid and molten material.

Notes: Internal pressure measurments have been made on two common plasticizers, di-isoöctylphalate and dioctylsebacate, as a function of temperature. The ratios of internal pressure to cohesive energy density (as calculated by the method of Small) were 1.22 for dioctylsebacate and 1.17 for di-isoöctylphthalate. As in the case of simpler molecules the product of internal pressure and the square of the specific volume was constant for each plasticizer over the temperature renge studied. This implies that even in the absence of any other effects both an upper and lower critical solution temperature would be expected in mixed systems if the coefficients of thermal expansion of the components of the mixed system are sufficiently different.

Notes: Tensile stress rupture is an important engineering property of plastics required in desiging parts subject to continuous or intermittent stress over long periods of time, especially in corrosive environments. This paper presents tensile stress rupture results on polypropylene and some of their applications in a program conducted over the past several years. Among the structural and compositonal paramaters studied in this work are the effects of molecular weight, molecular weight distribution, isotactic content, polyblends, and fillers on the shape and slope of the stress rupture-time curve. Data are presented showing the interrelationships between these variables, and the agreement with current stress rupture theories is discussed.

Notes: Bulk compressibilities of a series of linear and crosslinked polymers have been measured, in a Matsuoka-Maxwell apparatus, at pressures up to 10,000 atmospheres and at temperatures to 202°C. These polymers exhibited nonlinear compressibility characteristics and a maximium compressibility of about 15% at 10,000 atmospheres. At slow loading rates, data were obtained for the amorphous polymers which could be expressed as glass-rubber phase gisgrams. The nature of the observed compressibilities are discussed and the usefulness of the data is indicated.

Notes: Residence time distribution (RTD) is a spectral property of contiuous chemical reactors. Batch reactors may be viewed as having “monodisperse” residence time distributions. This article discusses molecular weight distributions (MWDs) of polymeic materials formed in continuous and in semicontinuos process and how they are affected by reaction time distributions. All synthetic high polymers, even those Prepared in batch reaction, possess a MWD which may sometimes, for a given monomer, be altered chemically by a proper choice of catalyst and diluent. An interesting concept suggested by the present work is the prospect of “tailoring” the MWD for a given monomer-catalyst-diluent system physically by selecting appropriate reactor conditions. Hence, althought this work involves analysis the results may provide a guide to synthesis.

Notes: Thermal oxidation in linear polyethylene is mainly confined to disordered regions in which scission reactions cause crystallization and eventual deterioration of mechanical properties. Gel formation is negligible at 100°C. As degradation proceeds, comparable changes occur in the intrinsic viscosities of melt and solution-crystallized liner polymers, indicating that chain folds are regularly arranged and are resistant to oxidative scission. Breakdown is much more extensive in branched and crosslinked polymers since crosslinking retards oxidative crystallization and branching increases the volume fraction of substrate ultimately accessible to oxygen.

Notes: For a system of equivalent bonds undergoing random bond scission it is reasonable to assume that the rate of bond breaking (hence the rate of creation of new molecules) reported in the literature and data presented here demonstrate that the number of molecules created is not proportional to the time of thermal treatment hence they seem to belie this reasonable hypothesis. Other authors have adduced the presence of some non-equivalent bonds in order to account for the observed cruvature and still retain the hypothesis. Implicit in these arguments is the assumption of a steady-state concentration of reactive fragments. Our analysis explores the consequences of abandoning the steady-state assumption and shows that a quantitative explanation of the observed degradation behavior may be had by this means wihile still retaining the hypothesis of a constant probability of a bond being broken per unit time.

Notes: The factors leading to time dependnt variations of melt viscosity during capillary extrusion of thermoplastics are reviewed. An initial increase in melt viscosity has been attributed to melt elasticity while three mechanisms are cited to account for a subsequent drop in melt viscosity, which may or may not attain a steady-state value. These are frictional heational heating of the melt, increasing shear stress as the viscometer reservoir empties, and cain orientation. The relative importance of the mechanisms is examined for various melts and the importance of time effects is discussed in terms of their influence on standard flow evaluations, such as the melt index determination.

Notes: The objective of the work described herein is the experimental investigation of the velocity field of polymer melts flowing through a capillary in the regons of flow prior to and after the capillary exit. The fluids studied are branched polyethylene melts in steady laminar isothermal flow. The technique employed for the determination of the Eulerian velocity profiles is one that utilizes phototomicrogroaphy of the reflected light from tracer particles dispersed in the flowing medium.Axial acceleration of the fluid elements just before the capillary exit was observed. It was found that this accelearation is more pronounced in melts of low bulk viscosity. This observation region, non-viscometric.The translation of the velocity profiles of the fluids studied, from one resembling a parabola to that of “plug” flow, involves inflection points with minima in the velocity vector v(r, z). These minima appear near the surface of the extrudates and can not be accounted for by an existing theory.It was also found that the density of the viscoelastic fluids studied is a function of the axial position, in the region of flow investigated. The density decreases before the exit and, before it reaches an equilibuiu value at an axial position downstream equal to one or two diameters, increases beyond that value upon exit. This phenomenon is attributed to an “overshoot” in the process fo elastic recoil of the high polymer melts fron a strained structure to a random one.

Notes: An experimental investigation of the dynamic mechanical response of molten polymers was performed using the Maxwell Orthogonal Reheometer. One purpose of the study was to evaluate the effect of molecular weight distribution on the temperature dependence of viscoelastic properties. Data were obtained over a range of temperatures for both monodisperse and polydisperse materials which indicate that viscoelasticity is highly temperature dependent only for monodisperse polymers. On a molecular basis the reduction in temperature sensitivity for polydisperse materials logically can be attributed to the influence of the low molecular weight species present in a distribution on the relaxation spectrum. Since the relaxation spectrum largely determines all viscoelastic functions, the observations made from th dynamic data shown in this paper can be generalized to all viscoelastic experiments.

Notes: A simple, versatile biconical rehemoter has been developed. This device provides shear creep and creep recovery data for polymer melts over a temperature range of 200-500°F. and a range of applied shear stresses from 2 × 103 to 9 × 105 dynes/cm2.Extensive reheological data have been obtained for two samples each of polyisobutylene and high-density polyethylene. These illustrate the value of the device in obtaining data useful for predicting and understanding the processing properties of polymer melts.

Notes: A small scale screw extruder designed for laboratory extrusion studies has been developed and its performance characteristics with powder-blended rigid PVC Compounds have been investigated.The use of the extruder in determining the susceptibility of rigid PVC compounds to various die-induced viscoelastic phenomena (fracture, sharkskin, and swell) is described.An investigation of the phenomenon of “nerve” in rigid PVC extrusions has been carried out. It is concluded that nerve is associated with instabilities in the fluxing process occurring in the transition section of the extruder screw design, the operating variables of the process, and the processing characteristics of the compound.

Notes: The melt flow behavior of straight emulsion-polymerized PVC in a capillary extrusion rheometer has been found to depend upon both the molecular weight and the particle size of the sample. Observations of flow-rate, post-extrusion swell, and extrudate appearance, as functions of extrusion temperature and pressure, suggest that both molecular deformation and particle slippage are involved in the flow mechanism. The relative importance of these two modes of flow varies with extrusion conditions and with the PVC molecular weight and particle size. Particle slippage is favored by large particle size, high molecular weight, and low temperature and by a shear stress above a critical yield value. Apparent melt viscosity, swelling, and roughness are minimized under conditions corresponding to the maximum contribution of particle slippage. In the proper range of temperature and shear rate, straight emulsion PVC yields smooth, low-swell extrudates of excellent physical properties.

Notes: Re-examination of our work on internal plasticization of polyvinyl chloride leads us to suggest a number of guidelines in the synthesis of internally plasticized PVC with optimum combination of strength and low temperature properties: (1) use of comonomers of solubility parameter around 8.5 or 10.5, (2) use of a high molecular weight (long chain) comonomers in a low molar ratio, and (3) their non-uniform incorporation in the PVC chain.

Notes: A number of polymers have been “cold” extruded (i.e. at temperatures well below their normal melting temperatures) by the application of relatively high pressures. In all cases extrudates of relatively large cross-sectional area have been produced, and non-circular cross-sections have also been extruded. The extruded products has been evaluated and the results discussed. In general it has been found that whilst extrusion gives an oriented product, the increase in tensile modulus is much less than for a comparably drawn fibre. This phenomenon has been discussed in terms of the changes in crystalline structure produced by extrusion.

Notes: An analog computer-polymerizer system is described which polts continually the rate of polymerization in percent per hour and the total percent conversion. Computer components and their functions are briefly described and the polymerization vessel with its control instruments are shown. Methods of calibration and accuracy of the system are discussed.Polymerization rate curves for various initiators at various temperatures are presented. These curves show the typical autoacceleration of precipitating systems and the rate increase due to the gel effect. Experimental evidence is presented to explain the pressure drop seen in these curves at 70-75% conversion.

Notes: The influence of molecular weight and molecular weight distribution on the melt rheological behavior of two polystrenes of approximately the same weight average molecular weight, but of widely different molecular weight distribution, was determined. Then, using a series of capillaries with different length-to-diameter ratios in an Instron Capillary Rheometer, the entrance correction methods of E. B. Bagley and the relationships of W. Philippoff and F. H. Gaskins, the recoverable shear strain (SR) in the melt at the capillary wall for these mono- and polydisperse polystyrenes was determined. Shear modulus (G) and normal stress (PN) were calculated using the relationships: G = τRC/SR and PN = 2τRC SR, where τRC is the corrected shear stress at the capillary wall. These are compared to values obtained using a Weissenberg Rheogonimeter. These two polystyrenes were also injection molded into an ASTM specimen mold over a wide range of stock temperature, using a 12 OZ. in-line reciprocating screw injection press, and evaluated for mechanical property values. The effects of the elasticity parameters (SR G & PN) and their magnitude on the rheology, processability and mechanical properties of these polystyrenes are discussed.

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: 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: The viscosity of low-density crosslinked polyethylene was studied as a function of gel content and shear rate (3.75-33 sec-1). A simple model relating viscosity with gel content is suggested. It is shown that sol viscosity decreases with cross-linking propagation. The rheological parameters of the sol fraction are changed as a result, and it is natural that this effect should be utilized for flow calculations. Experimental data indicate a high degree of interaction between the sol molecules and the gel, and an experimental technique is presented for measuring it.The rheological parameters of crosslinked polyethylene are closely dependent on the gel content, viscosity and pseudoplasticity increasing with the latter.

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: The fatigue failure of thermoplastics and glass-reinforced thermoplastics is a function of cyclic stress or deflection level, test frequency, viscoelastic polymer parameters and matrix-to-fiber stress transfer. This paper reports an investigation of the modes of high frequency fatigue failure in glass-reinforced and unreinforced thermoplastics. In particular the effects and control of dissipative heating of a working specimen and the role of efficient matrix-to-fiber stress transfer are considered. A test procedure with which the severity of dissipative heating can be continuously followed and controlled during an accelerated fatigue test is described.

Notes: The flexural fatigue characteristics of boron fiber reinforced epoxy were shown to be strongly dependent on the aspect ratio of the reinforcing fibers. These composites were evaluated in a stiffness limited, constant maximum stress mode. The failure mechanism was found to be a combination of interfacial failure and brittle rupture of the matrix at 45 deg to the axis of the fibers. These fatigue cracks result in debonding of the outer fibers, thereby reducing the effective moment of inertia of the specimen.

Notes: More than seventy materials were examined for their ability to improve the performance of DTDP plasticized PVC wire formulation in a modified 105°C wire oven aging test. Twenty of these were as effective as the widely used Bisphenol A, four of which were effective at a lower concentration.

Notes: Extrapolation from data on low molecular weight n-alkanes indicates that the surface tension of polyethylene at 150°C is 26 dynes/cm. The total surface energy, γ  -  Tdγ/dT, is 51 dynes/cm and is much less dependent on chain length. The surface tension of polyethylene extrapolated to 20°C is 34 dynes/cm, consistent with the critical surface tension below which liquids will wet the polymer. The total surface energy is in reasonable accord with the incremental energy of vaporization, 1.029 kcal/mole of CH2 groups. The surface entropy is less than that of low molecular substances. This is attributed to a reduction in the opportunities for rotational isomerism at the surface.

Notes: A first order transition was observed in the temperature range of about 210°C by dilatometric studies on both isotactic and atactic polypropylene and for isotactic poly (butene-1) and poly (pentene-1). No such transition was observed for polyethylene. It was found that the transition is not due to the measurements per se, to polymer treatment, to catalyst residues, or to polymer degradation. It is suggested that the transition could be due to the disappearance of liquid crystals.

Notes: Polymer crystallization is discussed with attention given to primary nucleation, spherulite growth, and bulk crystallization. Primary nucleation is the area of least knowledge, and the authors discuss the kinetics of nuclei appearance and recent observations concerning the effects of foreign materials and surfaces. Spherulitic growth rates are discussed in general and specifically with respect to data at low degrees of supercooling in conjunction with secondary nucleation theory. The Avrami Theory and its limitations are discussed in the interpretation of bulk crystallization data. The authors propose that n = 4 in all cases and that the Avrami Theory be used for calculating the primary nucleation rate, kn, not for determining n itself.

Notes: This article is a brief review of recent work in the author's laboratory on heat stable polyaromatic heterocycles. New polymers based on 2,7-disubstituted-1,3,6,8-tetraazopyrene structure are described.Some background material on ladder or two-strand polymer structures will be discussed. This will be followed by a description of recent work aimed at producing polyquinoline types and some properties of such polymers.

Notes: The method of determining the epoxy equivalent weight of resins derived from Bis Phenol A and epichlorohydrin described by Kagarise and Weinberger has been extended to resins derived from epichlorohydrin and Tetra Brom Bis Phenol A and/or Bis Phenol A. In the infrared spectra of the latter, the characteristic aromatic band at 1610 cm-1 is replaced by a strong band at 738 cm-1, the intensity of which increases linearly with the content of Tetra Brom Bis Phenol A. The logarithm of the epoxy equivalent weight is linearly related to the ratio of the absorbance at 915 cm-1 to a linear combination of those at 1610 and 738 cm-1, respectively.

Notes: The melt viscosities of three low density polyethylenes of widely varying melt indices were studied as a function of temperature over a broad range of shear rates and shear stresses. Apparent viscosities at constant shear stress could be fitted adequately to a simple Arrhenius equation over the entire temperature range studied. However, pronounced curvature of the log ηa-1/T curves was observed for apparent viscosities at constant shear rate. The apparent activation energies for viscous flow at constant shear stress were found to decrease slowly with increasing shear stress and also to decrease with decreasing molecular weight. A temperature-shear rate superposition was demonstrated to hold, and the shift factor dependence on temperature was determined.

Notes: The interlaminar shear strength of reinforced plastic composites has long been recognized as a critical property in the structural performance of composites. However, its role in structural performance and the many factors that influence it have not been clearly elucidated. Although much attention has been given to the importance of resin-glass adhesion, little is known regarding the contribution of resin strength and composite quality. In this article it is shown that interlaminar shear strength is a direct function of both resin strength and composite void content. The curves of resin tensile strength vs interlaminar shear strength indicate a limiting value for interlaminar shear above which increases in resin tensile strength do not increase defects.

Notes: This article reports the preparation of a number of high molecular weight aromatic amide and imide polymers. An order of relative thermal stability of a series of alternative linkages between benzene rings in aromatic polymers is established on the basis of weight loss of thin films in air. It is found to agree with the stability order established by others by study of model compounds. It is further confirmed by the aging performance of laminates employing such resins. Electrical properties of the polymers were measured as a function of temperature. Change in the dissipation factor with temperature was used to determine Tg, which in turn was correlated to the minimum temperature required to produce laminates. Examples of the performance of these organic polymers in long time exposure tests at elevated temperature are given. Flexural properties of laminates aged and tested at temperatures of 600-650°F are reported.

Notes: Fatty acid salts are often added to polymers as processing aids. Although calcium stearate promoted highly reduced mixing torque requirements in polypropylene compositions, this was due largely to lowering of the polymer molecular weight. However, the amount of shear withstood without severe degradation was less. The effects of calcium stearate upon polypropylene stabilization systems were investigated by oxygen absorption studies Up to 50% stabilization was lost, particularly with metals such as copper, with 0.1% calcium stearate even in compositions protected by inhibitors. The stearate evidently reacts with transition metals or their oxides, particularly if acidic materials are present, to give metallic stearates which are extremely effective polyofin oxidation catalysts. Considering these results, the use of stearate processing aids should be avoided if property retention and stability are important in the fabricated article.

Notes: Foams are produced by mixing an epoxy resin, a primary polyamine and a trialkoxyboroxine without applied heat. The reaction heat evolved, predominantly from the reaction between the boroxine and the amine, speeds up the gelation of the epoxy resin and simultaneously evaporates methanol, a by-product, to form the foam, leading to the formation of a highly crosslinked polymer. A theory for the mechanism involves the chemical properties of intermediates, the basicity of the nitrogens, the acidity of the borons, and the mode of curing of the epoxy resin. The physical properties can be varied using different epoxies, amines and boroxines and different proportions. With a typical mixture, the foams produced have densities and thermal conductivities similar to polystyrene foam but have heat resistance up to 300°C. Adhesion to various substrates is excellent. Compression strengths are low but can be increased by the addition of fillers. The foams are self-extinguishing. Potential applications and method of dispensing the foams are suggested.

Notes: The selection of particle size distribution is based on a theoretical concept of the “close packing” of particles. The usefulness of this concept was investigated using silica as the filler in a single epoxy-hardener system. The viscosity and settling characteristics for several particle-size distributions and concentrations of silica fillers were studied. These studies show that significant decreases in the viscosities of casting formulations can be obtained using a two-component filler system which permits the use of higher filler loadigs. The increase in the ratio of coarse filler to fine filler reduced the flexural strength of the castings and increased the rate of settling in the formulations. The effect of parameters other than particle size is demonstrated by the use of non-silica fillers.

Notes: Biaxial creep tests have been performed on thin-walled tubes of polymethyl methacrylate at 116°F and 50% R.H. The tubes were loaded radially up to a specified stress state, which was then maintained for a finite time. Additional tests involved a constant stress state for a period Δt1, after which the specimen was rapidly subjected to a second stress state which was maintained for a period Δt2. The experimental apparatus and procedure are described. The results for the range of stress, temperature, and time investigated show: 1) the creep behavior can be described by the form ∊ = ∊0 + mtn, where ∊ is the strain, ∊0 is the time-independent portion of the strain, and m and n are constants; 2) n appears to be independent of stress state in the fourth quadrant (-σz axial stress, +σθ tangential stress), and m is a linear function (log-log) of effective stress. In the first quadrant (+σz +σθ), the values of m and n are dependent on stress state, the constant m being also dependent on effective stress. Since two measurements are made for tangential strain ∊0, a description of the deformation can be obtained. Some results of pre-strain history and fracture are also presented.

Notes: Epoxy-Versamid specimens were loaded in tension up to failure at different constant strain-rates and temperatures. Results revealed three modes of behavior prevailing at different temperature-strain-rate regions and associated with brittle, ductile and rubbery failure modes. The ductile region was found to be confined within a narrow band on the temperature-strain-rate plane, and is characterized by a yield plateau in the stress-strain curve and by linear dependence of yield stress on log strain rate and temperature. Yield strain seems to be almost unaffected by strain-rate, but decreases slightly with temperature rise.Analysis indicated that experimental data within the ductile region are consistent with Eyring's formulation for non-Newtonian viscoplastic flows. It leads to the evaluation of the “apparent activation energy” and activation volume for the two epoxy systems tested.Comparison with previous work indicates that the above parameters as well as yield stress and elastic modulus tend to increase with the decrease of the Versamid content in the resin.

Notes: Neither the fringed-micelle, fringed-fibril or extreme folded-chain models explain the morphological and mechanical properties of highly drawn polyethylene. The modified folded-chain model, assuming that a substantial fraction (between 5 and 30 percent) of the molecules do not fold back at the crystal surface but go through the “amorphous” surface layer and enter the next crystal, avoids the insufficiencies of the above mentioned models.The elastic modulus and tensile strength of drawn polyethylene, both increasing with draw ratio, are to a large extent the consequence of the molecules bridging the quasi-amorphous layers and interconnecting the folded-chain lamellae oriented more-or-less perpendicular to the machine direction. The folds create enough space for the accommodation of more-or-less extended tie molecules in the quasi-amorphous layers between the lamellae. Electron microscopy and calorimetry of samples as drawn, annealed and/or etched with fuming nitric acid support the model.

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: Empirical test data on low-density polyethylenes exposed to the elements for very long times are compared with results on samples of the same materials subjected to artificial “weathering” in a modified carbon arc machine.The test results conform to the expression \documentclass{article}\pagestyle{empty}\begin{document}$$ t_a = B + t_n^k $$\end{document} where ta is hours of accelerated weathering, tn years of natural exposure, and the constants B and k have values of 150 and 2.4, respectively, for the materials and test conditions involved.Earlier results are confirmed in that optimum weather resistance is found to depend on good dispersion of a fine-particle black. Protection improves with concentration up to the limit of about 5% by weight imposed by degenerative effects on mechanical properties from higher loadings of the fine channel blacks. Dependence of weatherability on molecular weight (melt index) is noted.

Notes: This discussion will illustrate some of the factors which go into the design of experiments required to solve problems in the field of plastics. Two quite diverse problems were considered. In the first case a series of experiments was described which provided a very general technique for predicting polyethylene flow behavior as a function of shear rate over a wide range of temperatures from a minimum of new data. In this case the experimentation concerned only the viscous aspect of flow and was not limited by the availability of special samples. In the second case it was desired to learn what the effect of a specific molecular structural variable was on the general melt rheological properties of polyethylene. This required the polymerization of special samples followed by detailed characterization by both solution property and melt rheological techniques.

Notes: Some properties of multilayered films are summarized in relation to the properties of the component materials. Polymers may be selected for co-extrusion into layered films to obtain various combinations of properties, such as barrier, stiffness, heat sealability, optics, and toughness. Properly chosen combinations of high and low modulus materials exhibit mutual interlayer reinforcement. Permeabilities of multilayer films can be calculated from layer geometry and individual component properties.

Notes: Spherulitic films of polybutene-1 have been stressed under biaxial tension. Direct microscopic observations indicate that the deformation is localized at the spherulite centers and at the intersections of boundaries in agreement with previous results obtained with linear polyethylene. The results demonstrate an increasing tendency for brittle failure with decreasing molecular weight. Effects of surfactants and solvents are also presented.

Notes: Common methods of calculating screw characteristics are reviewed, and predictions of performance based on these techniques are compared with those based upon the exact solution for simultaneous pressure and drag flow in a plane infinite slit. The error made in superimposing pressure and drag flow, as if each were independent of the other, is indicated. Some brief remarks are also made with regard to the effect of transverse (cross-channel) flow on the output of the extruder.

Notes: The effect of various environmental conditions, other than chemical, on the mechanical properties of amorphous polymers is considered. The response of such polymers to an applied stress or strain depends on the mobility of polymeric chains which in turn is largely a function of free volume. The free volume varies with temperature, pressure, and plasticizer concentration; in the glassy state, it also depends on thermal history and tensile strain. These concepts are reviewed and some illustrative data, primarily from the published literature, are presented. A discussion is also given of the nonlinear viscoelastic properties (in uniaxial tension) of amorphous network polymers in the rubbery state. Methods for characterizing the ultimate tensile properties of such polymers are also described. Finally, some comments are made about the mechnical characteristics of polymers in the glassy state.

Notes: The plastics industry is now coming to realize that copolymers are unique thermoplastics which have broad areas of application. It is believed that ethylene-methyl acrylate copolymers of 2 melt index may be extrusion coated to paper by a cap-coat process or by use of a chill roll with an adhesive coating. Copolymers of ethylene and vinyl monomers can be made into film by the same methods used for polyethylene. Methyl acrylate and methyl methacrylate copolymers may be processed on a wide range of molding equipment. Table VII in the article gives a list of applications for each polymer, along with expected physical properties.

Notes: The paper reviews the various classical failure theories essentially developed for metals and then seeks to show that the same theories with slight modifications could be used to describe failure of polymeric materials. These modifications consist in the consideration of the effect of rate loading on failure behavior. In addition, the paper reports experimental results on failure of two polymeric materials under uniaxial tension loading and several biaxial stress fields corresponding to pure internal pressure, internal pressure combined with tension and torque loadings and several biaxial stress fields corresponding to pure internal pressure, internal pressure cobined with tension and torque loadings. The failure behavior under various stress fields has been studied for maximum principal rates ranging from 0.05 to 60 psi. sec. The predictions based on various criteria of faliure, which considers the effect of rate of loading, are compared with the experimental results. Finally, it is shown that failure behavior under triaxial stress fields can be reasonably predicted from biaxial stress failure data.

Notes: This paper is an account of some studies of the mechanism of degradation of an uncrosslinked polyurethan prepared from poly(propylene oxide) (PPO) and 2,4-tolylene diisocyanate (TDI) at temperatures up to 320°C in a vacuum or inert atmosphere. Fractionation of polymers before and after degradation provides information about the mechanism of degradation since the molecular weight distributions obtained are dependent on the mode and sites of bond scission. A recent publication describes the column elution method of fractionation developed for undergraded and slightly degraded PPG-TDI. PPO-TDI gives essentially most probable molecular weight distributions at an initial intrinsic viscosity [η] of ∼ 0.68 dl/g and also after degradation to [η] ∼ 0.24 dl/g. This invariancy of the distribution strongly suggests a randon scission process. Other types of degradation, e.g., free-radical unzipping initiated at the chain ends, could also give invariant most probable distributions. However, such depolymerizations would be accompanied by much larger extents of volatilization than were observed for these polymers (〈5% volatilization).

Notes: A method was developed for identifying certain carbonyl compounds formed in plastics during exposure to carbon-ac or solar radiant energy. The reaction of aldehydes and certain ketones with phenylenediamines (o-, m-, p-, and N, N-dimethyl-p-) in glacial acetic acid was found to yield stable colored products whose transmittance spectra are charactersitic of the carbonyl compound. Similar colored products were also formed when exposed plastics were dissolved in acetic acid solutions of the diamine. A comparison of the spectra of solutions of the plastics with those from known carbonyl compounds facilitates identification. The method was applied to the identification of carbonyl compounds from photodegraded poly (methyl methacrylate) and cellulose acetatebutyrate.

Notes: Stress concentration effects and strengths of bonded and bolted butt joints were investigated for a glass fabric polybenzimidazole lalminate at room temperatuer and 700°F for a gloass fabric phenolic laminate at room temperature and 500°F. Specimen configurations included: (1) standard tensile specimen, (2) stress concentration specimen, (3) bolted double shear butt joint, (4) bolted single shear butt joint, (5) bonded double shear butt joint and (6) bonded single shear butt joint.Both polybenzimidazole and phenolic laminates exhibited high room temperature tensile strengths and little degradation of that strength occured as a result of elevated temperature exposure. However, low joint effencies (22 to 32%) were obtained for bolted butt joint specimens. Although bonded joints exhibited higher efficiencies, they suffered from a thermal expansion mismatch between the plastic laminate and the Inconel butt plates.

Notes: When a thermoplastic shape is extruded and drawn into a quenching medium and the drawing speed increases continuously, the cross-sectional extrudate area decreases. At a critical take-up speed, a cyclic gauge pulsation begins, becoming more pronounced with increasing drawing speed until the extrudate eventually breaks at the air-coolant in terface. This phenomenon, “draw resonance,” originates in the air gap and is independent of any melt fracture phenomena. Correlations show increasing pulsation severity with increases in speed ratio, air gap, viscosity-average molecular weight, and decreasing melt temperatures. Draw resonance occurs with polypropylene and various types of polyethylene and polystyrene. Ribbon-type and round-hole dies give equivalent results. A semi-quantitative theory is advanced is explain these phenomena in terms of thermodynamic relationships and basic molecular properties.

Notes: Certain ester-acetal derivatives of azelaaldehydic acid have been evaluated as a new type of plasticizer of PVC. In gerneral, these compouonds have high compatibility and impart excellent low-temperature, mechanical, heat- and light -stability properties to the plasticized PVC. The 2-ethylihexyl ester bis (2-methoxyethyl) acetal, in particular, appeared to have the best combination of properties for a useful plasticizer. The results indicate that a unique and useful type of plasticizer-stabilizer can be obtained from derivatives of azelaaldehydic acid.

Notes: Many rigid PVC compounds show a sharp transition from tough to brittle fracture with decreasing temperature in impact testing, and this temperature becomes a criterion of compound quality in addition to the impact strength observed at specific temperatures. This BT (brittle fracture) has been investigated individuall in commercial and experimental elastomer modified rigid PVC compounds. Factors affecting the BT include speciman thickness, composition and processing conditions. Apparently the discontinuity in impact behavior is a sudden manifestation of a gradual change, resulting in a near ten-fold decrease in notched impact strength without any obvious change in properties. The BT provides a continuous scale for comparing impact properties of compounds, and is thus more versatile and sensitive than impact tests run at a single temperature.

Notes: The determination of the state of resin advancement in asbestos-phenolic prepregs is important to the processor of this material. Many tests have been proposed for measuring this condition. In this article the follwing tests were made on the prepreg and resin extracted from the prepreg to measure advancement: viscosity, Chang Index,-infrared absorption dielectric constant, dissipation, dielectric constant, and dissipation factor, volume resistivity, and tear strength. Infrared absorption, dielectric constant, and dissipation factor correlated best and were the most sensitive indicators of resin advancement.

Notes: The application of silane coupling action produces significant improvements in physical properties in various thermpolastic resin systems. Both glass-reinforced thermoplastics and the more conventional filled thermoplastic resin systems were studied. An order of specificity between resin and coupling agent exists for thermoplastic resins similar to that of thermosets. The interaction with thermosets is considered copolymerization, wereas that with thermoplastics is not yet clearly defined. The silanes are incorporated by pre-treatment (best for glass reinforcement) or by addition during normal compounding. Fillers are added for a specific result, often with sacrifice of physical strength. Data presented show that silane addition upgrades filled thermoplastics to the level of clear resins and sometimes above. The effect of silanes on electrical properties of filled thermoplastics are also reported.

Notes: An optical method has been developed to provide quantitative results useful for characterizing the crazing of transparent plastics. The procedure consists of the detection of discontinuities in a beam of light that scans the specimen in a direction perpendicular to the line of crazing. The light is transmitted to a photomultiplier that is connected with an amplifying system and a recorder that provides a diagram of the light energy modulated by the lines of crazing. The specimen is scanner both before and after subjecting it to a treatment that causes crazing, and the crazing index is considered to be the difference between the area below the two curves.

Notes: To determine the optimum conditions for vacuum forming quality parts, a precise method of determining internal stress required development. The approach investigated was based on the shrinkage of a heated stressed part. Small stress should be proportioned to strain. By exposing loaded tensile specimens simultaneously with the formed part, the material modulus is determined. Results indicated creep which was minimized by using the correct modulus to calculate internal stress. Stresses in a normally formed part and in a part formed cool were compared at two temperatures. Values were higher in most areas of the cool-formed part and consistent at the two temperatures. This method probably can be used on other materials and possibly on injection molded parts.

Notes: The flow of polymer melts is normally laminar, but pseudoplastic in character. That is, flow rate increases in proportion to a power higher then 1, usually between 1.5 and 4, of the applied pressure difference. Viscosities are extremely high - more then a mollion times that of water - so considerable heat is generated in the flowing melt by viscous dissipation of flow energy. This mode of heat generation is put to good practial use in the screw extruder, a device that converts plastic pellets into hot melt for shaping into pipe, sheets, coatings and molded products. Equations are given for computing flow rates and viscous dissipation rates. Heating (except by viscous working) and cooling of polymers are slow processes because all these materials are poor heat conducts nad their extreme viscosities make convection impracticable. The princliples of heat transfer are reviewed, and the solutions are given for some transient-conduction problems frequenlty encountered in processing. Equations are given for judging the operation of extruders.

Notes: A method for developing long-term hydrostatic design stresses, defined as the estimated tensile stress in the wall of the pipe in the circumferential orientation due to internal hydrostatic pressure that can be applied continuously with a high degree of certainty that failure of the pipe will not occur, for thermoplastic pipe materials is described. The background information used to develop this method, data to confirm its validity, and several of its more important peculiarities are presented and discussed. The method treats hydrostatic stress-failure time test results by the method of least squares with time as the dependent variable. The long-trem performance of thermoplastic pipe materials is evaluated by stresses calculated for periods of 100,000 hours (11.43 years) and 50 years.

Notes: This article describes a general mathematical model summarized in the form of a computer program for the plasticating extruder. The model combines features of the metering-zone model previously published, the melting-zone model described in paper No. I of this series, and a feed-zone model based on an extension of known theories. It is based on theoretical models for each zone unified and improved by non-linear estimation to accurately describe the extrusion experiments.The mathematical model predicts temperature, pressure, and melt channel width profiles of the plastic being processed in the plasticating extruder as a function of design and operating variables of the machine. It enables for the first time the design of the whole machine based on temperature and pressure profiles, including new combinations of cylindrical and tapered roots.

Notes: The development of a fractional crystallization technique for characterization of polypropylenes with respect to stereoregularity is described. It is a simple technique which is attractive for routine analysis and under suitable conditions yields quantitative data with good reproducibility. Separation by fractional crystallization from hot xylene solution is shown to take place according to polymer crystallizability and is relatively independent of molecular weight. It thus represents an alternative and in some ways superior approach to the more commonly used fractional extraction method. Preliminary work indicates that the fractional crystallization method may prove of value in establishing correlations between the stereoregular nature of polypropylenes and their physical properties.

Notes: The density and tensile property changes in polypropylene resulting from various post-crystallization aging procedures are investigated with the aim of (1) establishing standard procedures for the evaluation of these properties and (2) determining which conditioning treatment will provide optimum tensile properties. The morphology and resultant tensile behavior of polypropylene are particularly sensitive to conditioning treatments in the temperature range 145-160°C. A procedure for compression molding plaques, carrying out isothermal annealing treatment in the 100-170°C range and gradual cooling is described. The dependence on annealing temperature of the density, elongation, tensile modulus and yield stress is given.

Notes: Some earlier observations on the influence of molecular weight, plasticizer, and irradiation on the thermal conductivity of polymers is reviewed. Also some new data on polystyrene and some new calculations based on the theory of Hansen and Ho are presented. These data show almost a two fold increase in the thermal conductivity of polystyrene as the molecular weight goes from 900 to 100,000. Data on the moleculer weight effect on thermal conductivity appear to be consistent with the theoretical calculations.

Notes: Whereas the creep behaviour of plastics is conventionally studied by the application of a simple step-function of stress, the stress conditions encountered in service are often much more complicated. The response of a liner viscoelastic material to a complex stess history can be calculated from the step-function response, but this is not so for plastics which are non-liner viscoelastic. The paper considers this from a mainly experimental viewpoint and underlines the general inadequacy of the current continuum echanical approach. The sections on recovery and intermittent stressing are of particular practical importance since it is under these conditions that plastic display particulary useful characteristics.

Notes: Artificial weathering devices are used extensively by the plastics industry to aid in the prediction of the weatherability of plastic matrials. Correlations between the results of outdoor and artificial weathering, however, are poor for lack of control and understanding of the exposure variables in these devices. This work summarizs some of the results of an experimental program designed to analyze the effects of variables in artificial weathering on the preoperies of selected commercial plastics. In addition to the presentation of data establishing the importance of each of the variables in artificial weathering, a discussion of the significance of these data with regard to the selection of optimum exposure cycles is given. Furthermore, some new approaches are proposed with regard to obtaining inproved correlations between the results of outdoor and artificial exposure. Model calculations based on the proposed approaches yield a surprisingly high degree of correlation between the two types of exposure.