ALBERT

Notes: Studies of polypropylene oxyluminescence show the luminous intensity to be dependent upon the degre of oxidation. The length of the low intensity level portion of the luninescence curve, or pseudo induction period, was found to be a measure of the useful stabilizer life, and the intensity of this portion indicative of the effectiveness of stabilization. The effect of peroxide decomposers was studied and results indicate that peroxide reactions are major producers of luminescence. Analysis of the accepted modes of polymer oxidation, in view of our luminescence findings, indicate that the rate of luminescence buildup should depend upon ease of R. formation and the luminous intensity should be dependent on peroxy radical concentration. The effect of tertiary-carbon content on luminescence was also investigated, and luminous intensity was found to be dependent upon the amount of polymer branching. Model Compounds having slight structural variations were examined and were found to produce different intensity-time curves during oxidation, which may be attributed to ease of formation of a reactive site and subsequent peroxy radical reactions.

Notes: Sixteen polymers containing thiazole and aromatic rings in the polymer chain were prepared and investigated for the production of fibers and films that would be useful up to about 500°C. None of these polymers was completely satisfactory. Some of the polymers gave tough fibers and films, but they had relatively low melting points (〈300°C). Other polymers did not melt below 500°C, but they did not have good fiber and film forming properties because of their low molecular weights. Fibers and films of one of the polymers (polytetramethylenephenylenethiazole) were prepared, and their physical properties, hydrolytic stabilites under acid and alkaline conditions, and resistence to ultraviolet and gamma radiations were determined.

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: Moisture present in epoxy anhyride composites may hydrolyze the anhydride and cause major changes in the mechanical and chemical properties of the final composite. Heat distortion data and infrared spectroscopy are used to analyze the changes caused by the presence of the moisture. As the concentraton of water is increased, there is a decrease in the heat distortion or gass transition temperature. The decrease is due to a change in the crosslinking network and is caused by the reduction of the functonality of the epoxy group for acid as compared to the anhydride. Where rigid specifications must be met it is essential that the moisture level in the fillers, resins, etc. be kept constant.

Notes: There is considerable literature on the behavior of polyethylene below 200°C and above 400°C. This paper presents results on both high and low density polyethylene between 2000 and 400°C, a range of practical import for various fabrication and processing steps. Practical exposure times may be short and the experimental procedures were designed to give meaningful results for times as low as 1 min. The principal effects are chain-session and oxidation. Session was isolated by applying an atmosphere of pure nitrogen and proved uite shlow at 300°C but rapid at 400°C. The course of scission and produces discoloration, odor, and rising carbonyl content. A brief discussion is given of the role of diffusion in oxidation.

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: 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 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: Tangential flow of a “power law” model fluid between two concentric cylinders is analyzed. A constant angular pressure gradient is imposed and one of the cylinders is rotating at a constant angular velocity. This type of flow is of interest in screw extrusion theory. The error in the superposition, i.e., linear addition of tangential pressure and drag flows, for a “power law” model fluid, is quantitatively calculated and plotted in the form of a correction factor. Tangential pressure flow is compared to a pressure flow between parallel plates and additional correction factor to account for the curvature is derived and plotted. The applicability of the “power law” model for flow of polymer melts in extruders is also discussed.

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: 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: Most polymers exhibit a very fluid melt rheology during extrusion and can be distorted, drawn down, and cooled without building excessive residual stresses into the product. In contrast, rigid vinyl is usually extruded as a stiff, almost selfsupporting mass. Care must be taken to prevent the formation ot oriented stresses in the product which will be relieved during long periods of exposure resulting in dimensional instability and related loss of physical properties. A newly developed method of in-line annealing has shown to be an effective means of relieving oriented stresses developed during extrusion. By use of this instrumented technique, rigid vinyl products can be controlled to much tighter shrinkage specifications in a single step process, thereby eliminating post-annealing treatments.

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: Commercial films, elastomers, and fibers have valuable in-use properties below 300°C. Astronautic requirements, however, may evaentually call for materials that withstand 500 hrs at 300°C or 100 hrs at 500°C while fully retaining their useful properties. The most significant advances in the synthesis and preparation of heat resistant polymer have been made since 1959 with new synthetic methods such as interfacial polymerization, cyclopolymerization, and intramolecular polymer post-cyclopolymerization, and intramolecular olymer post-cyclization reactions. It is the purpose of this paper to discuss the structural relationships among those heat resistant, orgainc polymers that were reported to give strong films and fibers. Those heat resistant polymers, which have not yet been fabricated into films and fibers are not included in this review.

Notes: Monodisperse and polydisperse polystyrenes of equal weight average molecular weight (Mw) are evaluated for melt flow behavior in an Instron capillary rheometer and for injection molding behavior in a 12 ounce in-line reciprocationg screw injection molding machine. The influence of molecular weight distribution on the shape of the flow curves is deconstrated over a wide range of shear rate and temperature. The influence is also reflected in injection molding behavior as defined by pressure to fill or flash the mold at a given melt temperature. Studies of capillary rheometer data for correlation with injection moling beghavior indicate poor agreement when low shear rate viscosity data are used. Good agrement is foun using high shear rate viscosity data in the range 103 to 104 sec-1 Striking crossover points on melt rheology and injection colding area diagram curvs are found with the monodisperse and polydisperse polystyrenes of the same M These crossovers shift with melt temperature and make possible the determination of a “controlling shear rate” for the injection molding process. This is found to be 3500 sec-1 for short shot and 6200 sec-1 for flash with the ASTM test specimen mold used in this study.

Notes: The stress-strain characteristic of polymeric binders and solid propellants are dependent on the crosslink density, molecular weight between crosslinks, molecular weight distribution in the binder formulation, volume fraction of filler, and the interaction between the binder and filler particles. This investigation is directed toward elucidation of solid propellant microscopic response and failure mechanisms through characterization of the constitutive effects of crosslink density, molecular weight distribution and curing agent ratio in the binder formulation, and filler fraction. This was accomplished on the ERLA/PBAA propellant system through investigation of three binder formulations with the same curing agent ratio but different crosslink densities; five binder formulations with different curing agent ratios; and four formulations with up to 69.9% by volume of filler.Uniaxial stress-strain characteristics were determined on each formulation at displacement rates of 0.2 to 20.0 in/min at isothermal test conditions ranging from 75 to -90°F. The failure characteristics of a viscoelastic material represent a curve in the three-dimensional space of stress, strain, and time. The ultimate property data on each formulation are presented as projections of this failure curve on the stress-strain, stress-time, and strain-time planes, respectively. Relationships are developed for the dependence of the stress-time, strain-time, and stress-strain failure envelopes on the volume fraction of bound rubber, crosslink density, molecular weight distribution and curing agent ration in the binder component, and the volume fraction of filler.

Notes: Two independent methods for predicting the deformation of free openings of arbitrary shape in a viscoelastic plate are illustrated.The first method is experimental and is based on the interference of two systems of lines representing the initial and final positions of the material. To demonstrate the moire method, the creep compliance function for polymethylmethacrylate is determined as preliminary information. This function is used as input data in the ensuing theoretical analysis to insure realistic viscoelastic behavior.The second method involves techniques to approximate viscoelastic displacements from known elasticity solutions and known material properties.The methods are applied to two examples: (1) The square hole - to determine the motion of an opening of complicated shape; and (2) an ellipse loaded at 45° - to indicate qualitative agreement with an existing prediction of the motion of cracks in a viscous plate.

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: Considerable progress has been made in the past 20 years in the synthesis, characterization and fabrication of plastics. Previous SPE Award winners, such as Mark, Natta, and Marvel dealt largely with synthesis; Flory with characterization; Alfrey and Du Bois with fabrication. One of the still unsolved problems lies in the realm of relating mechanical properties, such as impact strenght and creep to molecular structure.The design enginner who wishes to use a plastic part is concerned primarily with how some property such as impact strenght varies with temperature, speed of test, test method, etc. The polymer scientist must know why. Through knowing why, he may be able to design better plastics.This paper attempts to survey some of the world-wide progress made in this area in the past 10 years. The ultimate goal is to understand these mechanical properties in terms of internal molecular motions which occur in solid polymers. Internal motion can be detected by electrical, electromagnetic and dynamic mechanical measurements. When these three methods are applied on a given polymer over a range of temperatures, insights can be gained as to the variation of impact strength and other properties with temperature and frequency for that same polymer. These three fundamental methods, which require very small samples (less than 50 grams), can provide insight into the practical behavior of plastic materials over the wide range of temperatures and frequencies encountered in the real world.

Notes: A knowledge of the variation of melt viscosity of thermoplastic polymers with both shear rate and temperature is of considerable importance to plastics engineers as well as to polymer rheologists. The actual measurement of melt viscosity at a large number of temperatures and shear rates is frequently a tedious and time-consuming task. A technique has been developed, based upon the applicability of shear rate-temperature superposition, for predicting the flow curves of a number of olefin polymers and copolymers at various temperatures from experimental data obtained at one temperature for the material in question. The experimental validity for superimposing log shear stress - log shear rate curves at different temperatures along the log shear rate axis has been established for both high and low density polyethylenes, polypropylene, polybutene-1, and poly (ethylene vinyl acetate) copolymers. The temperature dependence of the resultant shift factors has been determined for each system, and the method of utilizing this information to predict viscosities as a function of temperature and shear rate is discussed.

Notes: A dynamic mechanical study has been made of an ethylenemethacrylic acid copolymer containing 4.1 mole per cent of methacrylic acid units and its sodium, lithium and calcium salts. On the basis of the results and related physical chemical studies it is proposed that the structures of the ionized copolymers consist of three distinct phases - a crystalline polyethylene phase, an amorphous polyethylene phase, and an ionic phase consisting of ionic domains. It is further proposed that the unionized acid copolymer consists of two phases - a crystalline polyethylene phase and an amorphous phase consisting of polyethylene crosslined with hydrogen bonded, carboxylic acid dimers.

Notes: The true stress-true strain behavior of polyoxymethylene, n(-CH2O), as an example of a bulk semi-crystalline polymer, has been investigated for constant hydrostatic environmental pressures from 1 atmosphere to 8 kilobars with the principal objectives of elucidating the factors controlling flow and fracture. Experiments were conducted in uniaxial tension at room temperature and constant strain rate. The tensile observations were supplemented by measurements of bulk compressibility and stress relaxation behavior at pressure.In contrast with metals and inorganic compounds, the modulus, yield stress and fracture stress of POM increase strongly with pressure by a factor of approximately three at 8 kilobars. The modulus increase is shown from the stress relaxation measurements to be associated with a pressure-induced increase in the β-transition temperature which points to the potential usefulness of the concept of pressure-temperature super-position of mechanical behavior. The characteristics of the pressure dependence of the yield stress demonstrate that yield criteria based on continum mechanics considerations, including the Mohr or Coulomb-Navier criterion, are not valid for general deformation (non-plane strain) conditions in this polymer. The concept of a critical volume change determining the initiation of yielding is suggested to be applicable to semi-crystalline polymers. Comparison with analogous changes in yield stress with temperature points to an increasing contribution to the control of yielding by the initially disordered regions with increasing pressure or decreasing temperature. The fracture behavior observed at pressure eliminates the concepts of a critical stress as a fracture criterion for POM and of a simple reduction in normal stress at points of stress concentration as the principal effect of the applied pressure on fracture.

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: 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: 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: Thermal conductivity curves for the 0°C to 170°C temperature region are presented for six irradiated low density polyethylene samples (radiation doses from 0 to 3100 megarads) and one irradiated high density sample (120 megarad dose). In agreement with data in the literature for unirradiated polyethylene, the thermal conductivity values for lightly irradiated polyethylene are found to decrease with increasing temperature in the elevated temperature region where the crystallites begin to melt. Beyond the crystalline melting point, test results for lightly irradiated and crosslinked samples indicate that the thermal conductivity is almost independent of temperature. Although radiation doses of less than 250 megarads produce only small changes in the thermal conductivity, higher radiation doses result in a significant lowering of the conductivity in the room temperature region and an increase of the conductivity at temperatures above the melting point. The decrease in conductivity at low temperatures is considered to be a result of disordering of the crystallites by the radiation, and the increase above the melting point is attributed primarily to radiation induced crosslinking.

Notes: Unsaturated polymers thermally degrade by a number of different mechanisms depending on the structure of the polymer and the experimental conditions. By use of deuterium tagging it was shown that polyisobutylene degrades stepwise from the end by a cyclic unimolecular mechanism. Volatile products from isotactic polypropylene contained 75% propane at 340°, 64% n-pentane at 375° and 49% propylene plus 12% isobutylene at 495°. Polyethylene was shown to give mostly propylene at lower temperatures but gave a 60% yield of ethylene at 600°.

Notes: Recent studies of the morphology of semicrystalline polymers have demonstrated the inadequacy of the familiar fringed micelle concept. It is now generally recognized that polyolefins crystallize in a spherulitic form having a skeletal structure of coherent crystals with a fibrous habit. Crystallization occurs in two stages: (1) spherulitic growth of crystalline lamellae, and (2) partial crystallization of residual melt in regions between lamellae. The dependence of modulus on degree of crystallinity in polyethylene indicates that the crystalline network carries much of the elastic energy acquired when the plastic is subjected to stress. Two of the mechanical transitions are also related to morphological structure. The high temperature or α transition is attributed to motion within lamellae while the intermediate or β transition is attributed to motion in disordered regions between lamellae.

Notes: Many plastic articles when exposed outdoors deteriorate first at points of highest stress. Consequently, weathering of polyolefins under stress speeds the deterioration and hence the evaluation of ultraviolet stabilizers used to retard it. Cracking of the stressed polyolefin specimens denotes failure and is a direct measure of the minimum useful outdoor lifetime of the materials, whereas in other methods the change in some property, such as elongation, is used to predict the useful lifetime. In this work, the results of nine years of natural and artificial weathering illustrate the usefulness of the stresscracking method for evaluating polyethylene and polypropylene compositions. The evaluation of compositions by this method was found to correlate with that made by measuring the loss of elongation during outdoor weathering.

Notes: Fracture surfaces record the kinetics of failure at two levels in the structure of polymeric solids. The first is evidenced by the formation of geometric markings resulting from the interaction of the primary fracture front with secondary fractures developing radially just ahead of the primary fracture. These markings are often visible to the unaided eye and have minimal dimensions in the micron range. The second fracture phenomenon appears to involve the orientation of molecular chains or bundles. Such orientation manifests itself in the interference-color producing film found on the fracture surfaces of poly (methylmethacrylate) and polystyrene. It is also apparent in the free or adherent film found on the surfaces of large fractured crazes. Some evidence is presented for the existence in these films of chain bundles 30A or less in diameter. It would seem that similar mechanisms are operating in the production of “craze matter” and of fracture surface films.

Notes: This article presents data on outdoor weathering of unfilled epoxy resins. The data have been accumulated after five years of weathering. The anhydride cured epoxy resin system was least affected by outdoor exposure. In addition, systems with higher deflection temperatures were more resistant to attack by outdoor exposure than those of lower deflection temperatures. It was also evident that heat curing is better than curing at room temperature. Hardness, for all systems, decreased with exposure time. Microscopic examination of the exposed systems showed that surface change closely correlated with changes obtained in the mechanical and electrical properties tested in this program. Systems showing the greatest change also had the worst surface appearance.

Notes: There has been a marked increase in the interest shown in the field of characterization of polymeric materials via dynamic techniques, so much so that symposia devoted exclusively to “dynamic” properties of materials are now commonplace (1, 2). This article provides both a frame of reference with regard to the wide variety of “dynamic” test techniques now in use, and…as well…dynamic test data for a wide range of polymers. Particular emphasis will be placed upon the difference in function of varying test techniques and the applicability of data obtained for specific R & D vs engineering applications. For the purposes of the presentation an arbitrary distinction will be made between “dynamic” tests of the cyclic type and “dynamic” tests of the unidirectional type.

Notes: The balance of engineering properties of rubber-modified polystyrene make it attractive for many applications, but it is difficult for the design engineer to relate laboratory data to service requirements because of differences in strain rates, temperatures, etc. Data are presented which show how the toughness and stiffness of an appliance-grade, impact polystyrene vary with impact velocity (or loading rate), temperature, fabrication method, and pigment level. The ability to survive multi-axial impact loads is strongly dependent on loading rate; a maximum in energy-absorbing ability was observed in the range 500-2000 in./in./min, where the failure mechanism changed from ductile to brittle.

Notes: The authors previously reported work on the kinetics and mechanism of the uncatalyzed thermal oxidation of isotactic polypropylene. The data, obtained form infrared absorption spectra of the carbonyl region, was utilized in developing the theoretical expressions presented. This paper summarizes this work and presents further evidence which substantiates the derived expressions. The additional evidence is obtained from infrared absorption spectra involving the apparent hydroperoxy region and from measurements on the rate of formation of volatile products. Some recent pertinent literature is also discussed.

Notes: The time-dependent mechanical behavior of solid polymers can be classified into linear viscoelastic, nonlinear viscoelastic and rheological types. The linear viscoelastic theory has now been worked out in detail, and applies with particular success to amorphous polymers above their glass transition temperature. Examples of systems falling outside this category are principally discussed, including glassy, composite, and crystalline materials. These systems are characterized by the fact that structure and structural changes are playing a major role in the mechanical behavior. Specific theories must be developed in the future which adequately treat this type of behavior.

Notes: The thermal degradation of polytetrafluoroethylene has been investigated in a closed system as a function of the nature of the surface of the reaction vessel wall. Reproducible results cannot be obtained in a stainless steel vessel as metal fluoride is continuously formed and a stable fluoride is not formed on the wall. Quartz spoon reaction vessels coated with calcium fluoride give a few reproducible runs, before the coating has to be renewed. If the dimerization of the monomer, which takes place very rapidly around 600°C, is considered, first order rates are obtained up to about 75% monomer formation. The kinetics is briefly discussed on the basis of random initiation followed by depropagation with a relatively short kinetic chain length and disproportionation as termination reaction.

Notes: There are essentially two ways to arrive at high softening polymers: crystallization and cross linking. The first approach leads to thermoplastic materials which have a more or less sharp and reversible melting point; the second produces three dimensional unmeltable networks which are thermosetting and can support very high temperatures without degradation. Factors which affect the mechanical behavior of a polymer exposed to high temperatures are degradation and cross linking. The first process is caused by scission of the chain molecules. The second process, cross linking, ties individual polymer chains into a rigid network, increases the molecular weight and leads to a very hard, brittle product which can neither be melted nor dissolved. The stability of a polymer against oxidation is always improved by the addition of an oxygen scavenger which reacts with oxygen in preference to the polymer and also by the addition of a UV absorber.

Notes: Creep experiments under combined tension and torsion loading are reported for tubular specimens of polyvinyl chloride copolymer. Experiments include a sequence of several combinations of tension and torsion on each specimen with abrupt changes between combinations, including reversal of sense of torsion, recovery and reloading after recovery.Results show a strong path and time dependence for the strain and for the direction of the strain-rate vector at constant state of stress following a change in state of biaxial stress.The character of the results is described reasonably well by the Boltzmann superposition principle of linear viscoelasticity using a constitutive equation of the form: Examples are given of the use of this equation for common states of stress.Better agreement with the data is obtained from a similar but non-linear equation employing hyperbolic sine functions of stress.

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: Uniaxial tension tests to, the yield point were performed on poly(hexamethylene adipamide) (nylon 6,6) as a function of temperature from 21 to 200°C at a strain rate of 2 min-1. At 21 and 60°C, measurements were also made at strain rates from 0.02 to 8 min-1. Using simple rate theory, reasonable values of activation volume were obtained, but the simple theory is inadequate to determine the activation energy. The yield-strain temperature dependence changes at 160°C as a result of a reversible crystal-crystal transition. Because of this behavior of the yield strain, the yield energy is not a linear function of temperature, as observed for several other polymers.

Notes: In extruding thick polymeric objects such as bars, voids may form as a consequence of fast cooling. As is well known, this phenomenon is due to volume contraction of the inner zone which takes place when the external “shell” is already solidified. Recent experimental results on this effect show the influence of various parameters such as polymer melt viscosity, bar diameter, and operating pressure upon a critical extrusion velocity above which voids are detected. A detailed analysis of the phenomena which are thought to be relevant is presented and compared with the experimental results.

Notes: Measurements of the resistance force to a wide range of contact loadings have been performed on poly(methylmethacrylate), polycarbonate, and epoxy specimens. Rigid spherical indenters of 4.5, 9, and 18 mm diameter, as well as cones of various apex angles, were driven into thick specimens at constant velocity over the range 0.005 to 150000 mm/min. The objective of this study was to develop a data base useful for the understanding and analysis of the phenomena involved when polymeric solids are impacted by small hard bodies. Spheres and cones were used because these symmetrical shapes offer the best chance for analysis in terms of viscoelastic extensions of the classical Hertz elastic contact problem. Measurements covered penetration depths from first detection of contact, where the strains are smallest and the material response should most likely be interpretable in terms of linear viscoelastic analysis, to much greater depths where the strains far exceed the yield values. The observations are tabulated, as are the values of parameters that allow the data to be modeled to within experimental error. These parameters fit into a specially developed empirical law designed to facilitate subsequent treatment of the data using Laplace transform methods. An analysis is offered to try to sort out time-dependent force relaxation from depth-dependent force increase during the progress of the penetration. The results of the response at small penetration depths are in broad accord with published relaxation moduli. However, the dependence of force upon indenter geometry does not follow simple expectation.

Notes: Morphological studies have been carried out on a thermotropic liquid crystalline copolyester based on poly(ethylene terephthalate) (PET) and para hydroxybenzoate (PHB) that has been subjected to different types of flow histories. Wide angle X-ray scattering investigations and chemical etching (n-propylamine is the etchant) in conjunction with electron microscopy studies conducted on end gated injection molded plaques of the 60 percent PHB and 80 percent PHB copolyesters indicate that a highly oriented skin region and a less oriented core region is present. Chemical etching studies performed on microtomed layers of end gated and center gated plaques show that the etching is less pronounced in the skin region and is more pronounced in the core. The microtomed layers of the end gated injection molded plaques when analyzed by ESCA indicate the presence of a “PHB rich” skin region and a “PET” rich core region. Biaxial orientation, as denoted by WAXS measurements, is observed when the 60 percent PHB copolyester is squeezed between lubricated parallel plates.

Notes: Test results are presented for a matrix type phase change thermal storage tile module with no surface covering, intended to transfer heat directly to and from room air at small temperature differences. Heat is stored and released by melting and freezing mixtures of fatty acids, which constitute up to half the weight of the tile. The polymeric matrices tested were powders or granules of poly(vinyl chloride) (PVC), poly (vinyl acetate) (PVAc), poly(vinyl alcohol) (PVA), vinyl acetate-vinyl chloride copolymer (VAc-VC), and high density polyethylene (HDPE). The tiles keep their shape and dimensions without any weeping of liquid fatty acid, up to 37 or 51°C, depending on their composition. In the case of PVC and PVA, infrared spectra and differential scanning calorimetry indicate interactions between the polymer and the fatty acids, which may increase the surface tension and allow larger matrix pores before weeping begins. Some of the tiles were reinforced with glass fibers, and others with cellulose fibers. The best mechanical properties were obtained with 5 percent of long (85 to110 mm) glass fibers. Paraffin chloride and antimony trioxide served as satisfactory fire retardants.

Notes: Sorption isotherms show that epoxide prepolymers sorb water in increasing amounts as the temperature decreases and the water vapor concentration increases. Below Tg the behavior is typical of a Fickian transport combined with a relaxation process. Diffusion coefficients as function of sorption rates provide temperature shift factors from which the activation energy for diffusion is 35.3 KJ/mol. Combined effect of temperature and water concentration is described by a second order polynomial.

Notes: The subject of crazing in crystalline polymers is reviewed and specific consideration given to crazing in polypropylene (PP). Tensile tests conducted over a wide spectrum of temperatures and strain rates indicate that, for a given test temperature, there exists a critical strain rate above which crazing is the dominant deformation mode of PP. Similarly, for a given strain rate, there exists a critical temperature which demarcates crazing from shear yielding as the characteristic process of deformation. High deformation rates and low temperatures favor crazing, while low rates and high temperatures favor shear yielding. Crazes in crystalline PP were found to be morphologically similar to those in glassy polymers: high reflectivity, large area-to-thickness ratio, and planarity. They have a higher tendency to bifurcate than those in glassy polymers. Two types of craze fibrils could be identified: those parallel to σ11, and the randomly oriented interconnecting fibrils. It is demonstrated that microtome-trimming at low temperature followed by suitable chemical treatment is an effective technique of sample preparation for SEM examination of craze morphology in crystalline polymers. Further evidence has been provided that crazes in spherulitic polymers do not in general follow an interspherulitie path, but propagate through spherulites. The length of a craze in PP is not restricted to one spherulite diameter, nor does it grow radially.

Notes: Random multiblock copolymers of bisphenol-A-polycarbonate and poly(dimethylsiloxane) were hot-pressed or solvent cast into films which were studied by dynamic mechanical methods over the range 11 to 110 hertz (Hz) and 100 to more than 2200 Hz, respectively. The samples were studied also by differential-scanning calorimetry. The two phases are separated well in spite of the low-molecular weights of the blocks. This separation is altered by thermal history and by the solvent medium when solvent casting is used to prepare the films. The damping properties do not vary greatly with frequency. Damping is greatest near the glass-transition temperatures of the two components. The expansion of the block copolymer with heat appears to be retarded by the polycarbonate phase until the glass transition of that phase is approached.

Notes: Simha's equation of state provides the relation between reduced pressure, temperature, and volume (P̃, T̃, and Ṽ, respectively) and the occupied site fraction, y = y (P̃, T̃). The latter theoretical parameter combines the P and T effects on the occupied and unoccupied (“free volume”) part of the model liquid. It can be computed for each liquid once the thermodynamic reducing parameters are known. Empirical correlation between published zero shear viscosity data, η = η (P, T), and y indicates that for n-paraffins and molten polymers η is a single parameter function: η = η (y). The mathematical form of this dependence was explicitly given for n-paraffins. However, for polymers the correlation depends on molecular weight, molecular weight distribution, branching, composition, etc. In Practical terms, η = η (y) should be determined for each polymer by measuring the temperature dependence of η in as wide a range of T as possible. Then pressure effect on η can be determined from η = η(y) plot, knowing the y = y(P̃, T̃) relation.

Notes: A mathematical model of the dynamics and heat transfer of the film embossing process has been developed. The thermal analysis around the preheat roll is determined from an unsteady, two-dimensional heat conduction equation along with appropriate boundary conditions by neglecting the curvature of the preheat roll and choosing a Lagrangian reference frame. The heat transfer occurring between the preheat roll and the embossing rolls is based on a one-dimensional analysis, including both convective and radiative effects. The deformation occurring in the nip region is analyzed for two different situations. For the case where the surface features are small in comparison with the film thickness, a modified one-dimennsional calendering analysis is given, accounting for the irregular geometry of the embossing roll surface. For the case where the polymer does not make complete contact with the surface of the engraved channel, the local deformation is determined by means of a simple one-dimensional cavity filling model. The required pressure distribution is determined by means of a simple one-dimensional cavity filling model, The required pressure distribution is determined by means of a conventional calendering analysis. The analysis for the case of a Newtonian and power-law model is presented in detail. The model yields qualitatively correct results and is computationally simple.

Notes: The physical properties of finished polymer blend composites are, in general, strongly influenced by the heterogeneity of the blend and the distribution of ingredients (especially reinforcement fillers) in each of the polymer phases. In this article, we review and update a processing technology specifically for the processing of multiphase rubber blend compounds in order to produce blend compounds with more desirable properties for practical applications. The basic concept is centered on the controlled-ingredient-distribution mixing (CIDM) process. The improvements in the following properties of rubber blend compounds are discussed: crack growth resistance, heat buildup, oil swelling, covulcanization, green strength, and permeability.

Notes: Measurements have been made of the recovery of polyethylene samples from bending deformations of varying severity. The amount of spring-back from a severe bend is quite different for different densities (degrees of crystallinity), especially at short times after release, being much greater for lower-density polyethylenes. Short-term spring-back measurements thus afford a simple and rapid means of determining the approximate density. Immediate recovery is small, 5 to 15 percent, and is in rough accord with expectations for elastic-plastic solids. A major protracted recovery process follows. It is accelerated by raising the temperature, in reasonable agreement with the WLF relation for segmental mobility. It is therefore attributed to retarded molecular motions in the amorphous fraction. Final recovery is greater for lower-density materials, but it is incomplete even after very long times or for mild degrees of bending. Thus, some irreversible processes appear to take place, even when bending strains as low as 3 percent are imposed.

Notes: Fatigue crack propagation (FCP) rates are studied in 6 mm thick specimens of high density polyethylene (HDPE) containing razor notches, Centrally-notched plates and single-edg notched bars are subjected to sinusoidal tension-compressio or tension-zero cycling at 0.5 or 2.0 Hz under load control a room temperature; crack growth is monitored using a travelling microscope. After many thousands of cycles with no observable damage at the tip of the razor notch, a craze like zone begins to form. This zone grows slowly until it reaches the length characteristic of a mature crack at the same ΔK. Crack growth proper then begins. The number of cycles to initiate crack growth falls linearly with increasing ΔK at the razor notch Subsequent crack growth is determined both by the current value of ΔK and by loading history. When ΔK is increasing, FCP rates follow a standard Paris law curve. However, reduced, FCP rates are observed following an overload.

Notes: The solid-phase flow behavior of polymers is very important in the mechanical performance and testing of solid polymers and in solid-phase forming. This paper includes an extensive characterization of the solid-phase flow curve for a wide range of commercially important polymers. Rigid semicrystalline, ductile semicrystalline, tough ductile amorphous, and two-phase ductile amorphous resins were studied in both tension and compression. It is clearly shown that semicrystalline polymers normally exhibit a load drop upon yielding due only to geometrical strain softening while the amorphous polymers exhibit yield drops due to material strain softening. New flow equations are given that closely model the observed behavior for all types of materials, over the entire range of strain.

Notes: A new rapidly crystallizing aromatic-aliphatic polyamide has been developed by reacting 4,4′-methylene bis(phenylisocyanate) (MDI) with aliphatic dicarboxylic acids. The polymer has a Tg of 130°C and Tm, of 290°C. Glass reinforced resin shows better flexural creep resistance at high stress levels (3000 psi) at elevated temperatures (75°C) than most reinforced semicrystalline commercial polymers i.e., nylons, thermoplastic polyesters and acetal because of its high Tg. Glass reinforced polyamide can be injection molded on conventional equipment to afford flexural moduli in excess of 1,000,000 psi and HDT's as high as 250°C at 264 psi. Because of the high level of crystallinity these parts will not dissolve or swell in most organic solvents and this aromatic aliphatic polyamide is also far less sensitive to moisture than commercial nylons.

Notes: Shear sensitivities of molten polymers may be determined from measurements made on individual samples subjected in one test to a series of either increasing or decreasing shear rates. Many polymers, including polyesters, degrade when molten. If the effect of degradation is significant, and is ignored during data analysis, a significant error could result. The magnitude of the error depends directly on the magnitude of the reaction rate constant for degradation, which differs from polymer to polymer and which increases as temperature increases. In rheological characterization of molten polymers, one should know or determine the degradation behavior of the polymer being investigated and then account for it in the data analysis. Experimental results for poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are presented and discussed. Ways to account for degradation in shear sensitivity measurements are also presented.

Notes: Dumb-bell specimens and rectangular boxes were used to study phase separation effects occurring in injection molding of glass-bead and glass-fiber-filled thermoplastics. The separation effects were more pronounced with beads than with fibers and they increase with increasing bead diameter. The filler distribution is further influenced by mold geometry, filler concentration, matrix material, and processing conditions. If the use of fillers, which promote inhomogeneity, is unavoidable it is possible to improve the distribution of the rigid phase by a favorable choice of injection speed and melt temperature. With the theories available at present a qualitative interpretation of the origin of the observed separation phenomena is feasible.

Notes: The kinetics of the activated anionic polymerization of caprolactam to nylon 6 was studied by the adiabatic temperature rise technique. This allowed very rapid reaction conditions to be studied. The polymerization was activated by diisocyanate and catalyzed by sodium caprolactamate, produced in situ by the addition of sodium hydride. The temperature rise measurements were used to generate Arrhenius curves of the rate data. Several isocyanates were investigated, all giving similar rate curves. The reaction rate was reduced, however, when the activator concentration exceeded the catalyst concentration. To model the actual rapid molding conditions, time vs. temperature reaction profiles were measured for thin plaque castings. In these reaction profiles, two successive exotherms were observed. The first was the polymerization exotherm, and the second was determined to be the crystallization peak. This second exotherm allowed the direct observation of crystallization times within the closed molds. The crystallization times were found to depend strongly on the mold temperature and to a lesser extent on the monomer temperature. The crystallization times were minimized at a 150°C mold temperature. At higher temperatures, the crystallization rate was significantly slower, while at lower temperatures, the slow rate of polymer formation delayed the onset of crystallization. This study has demonstrated the value of using temperature monitoring as a means of studying the polymerization and crystallization behavior of nylon.

Notes: An overview of the use of polyesters for containers is presented. The market for polyethylene terephthalate container resin should reach 760 million pounds by 1989. Diethylene glycol, a polymerization by-product, and other comonomers reduce the polymer melting point and crystallization tendency, yielding wider container processing latitude. The effect of these modifications on creep and tensile strength is discussed. Improved gaseous barrier approaches and hot-fillable container opportunities are presented, Newer applications for thermoplastic polyester containers are summarized.