bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady‐state heat transfer in a crystallizing polymer
Authors: Sifleet William L. , Dinos Nicholas , Collier John R.
Published: December 2004

The processing of polymers typically includes steps involving heat transfer, such as quenching and crystallization. The mechanical properties of a polymer are thus affected by processing conditions, such as the amount of time spent by each portion of the polymer at each temperature in the processing sequence.

This paper presents the results of a mathematical modeling study of the unsteady‐state temperatures inside a crystallizing polymer during quenching. This model differs from usual methods in including temperature dependence of induction times and kinetic processes, and in not treating the polymer as a simple, small molecule system. The model permits the prediction of the final morphological distribution within the polymer. Use of the model will aid in tailoring processing conditions to produce a product with specified morphology. The method is applicable to a wide variety of problems in polymer processing, particularly for those polymers which exhibit crystallization.
Physical properties of polymers–an introductory discussion
Authors: Smith Thor L.
Published: December 2004

Physical characteristics of isolated molecules and bulk polymers are discussed briefly. The broad spectrum of mechanical properties resulting from changes in temperature and experimental time‐scale is introduced by first considering the time‐independent properties of elastomers under large deformations and then the effect of a progressive decrease in segmental mobility, leading eventually to glassy characteristics. The phenomenological theory of linear viscoelasticity along with time‐temperature superposition is outlined, and illustrative data are presented. Finally, phenomena resulting from volumetric relaxation processes are considered briefly.
Effect of gas diffusion on creep behavior of polycarbonate
Authors: Hojo Hidemitsu , Findley William N.
Published: December 2004

Biaxial tension‐tension creep experiments were performed to study the effect of gas diffusion on creep behavior of polycarbonate. Experiments were conducted on a thin‐walled tubular specimen by applying both gas pressure and axial tension at room temperature, and measuring axial strain and gas absorption. Experiments were performed with helium, nitrogen, air, carbon dioxide and Freon‐22

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. It was found that the creep deformation was highly affected by the solubility controlled gases, carbon dioxide and Freon. The absorption measurements showed that the gas absorption behavior was clearly affected by the creep deformation of the material. Also an anomalous diffusion‐type behavior appeared even in permanent gas‐polymer systems under creep conditions. The modified superposition principle satisfactorily predicted the recovery following creep. The axial creep for the biaxial tension‐tension experiments was also computed from data previously reported for creep under combined tension and torsion of a different sample of polycarbonate.
Effects of gamma radiation on the dynamic mechanical and swelling behavior of styrene butadiene block and random copolymers
Authors: Samuels Sam L. , Wilkes Garth L.
Published: December 2004

The physical structure of a number of styrene‐butadiene copolymers were investigated via dynamic mechanical and swelling studies on uncrosslinked and gamma‐radiation cross‐linked films that had initially been solvent cast from toluene or methyl ethyl ketone. The mechanical behavior of these films before and after crosslinking was found to depend on the material history as well as the chemical structure of the copolymer, in agreement with observations made by other experimental techniques. A simple morphological interpretation was given to the dynamic mechanical spectra as a function of radiation dosage and a limited discussion of the swelling behavior is included.
Design of certain fluted mixing sections of extruder screws
Authors: Tadmor Zehev , Klein Imrich
Published: December 2004

A theoretical model is proposed, for certain barrier type fluted mixing sections of extruder screws. Screws with such mixing sections are occasionally used in plasticating extruders. With the aid of this model, these screws can now be quantitatively simulated in the design stage. Specifically the model enables the calculation of pressure change across the section as a function of geometrical configuration of the mixing section and operating conditions.

A generalized set of curves, plotted in dimensionless form, for quick manual computation is also given. With its aid, the effect of the design variables on the pressure change is discussed.

Finally, mixing section‐zones, in reference to the plasticating extrusion theory, and the state of the art of extrusion theory are very briefly discussed.
Investigation of the ductility of rolled polymers
Authors: Bahadur S. , Henkin A.
Published: December 2004

The effect of cold rolling on the mechanical properties of polymers, viz., acetal, nylon 66, poly(vinyl chloride) and polycarbonate has been studied. The yield strength, Young's modulus, and hardness increase with increasing cold work, except for a slight drop in these properties at low values of cold work. The ductility increases with rolling to a maximum and drops with further reduction. At the same time, the tensile strength increases continuously with rolling. This conspicuous occurrence of the increase in ductility with a simultaneous increase in tensile strength for polymers, unlike that in metals, is explained considering the morphological changes produced in polymers upon cold rolling. It is shown that this typical behavior is not due to the unique loading or heating and cooling cycle involved in the rolling process.
Tailoring the interface in graphite‐reinforced polycarbonate
Authors: Kardos J. L. , Cheng F. S. , Tolbert T. L.
Published: December 2004

Pronounced effects of thermal treatment on the properties of graphite fiber/polycarbonate and glass fiber/polycarbonate composites have been demonstrated and explained. At 20 volume percent loading of random‐in‐a‐plane, discontinuous fibers, both specimen strength and modulus in both fiber systems were found to increase dramatically upon molding above 260–265°C, whereas only the graphite system was further improved by subsequent annealing. In the latter case, property improvement is due to generation of a crystalline innerlayer at the interface, which apparently transfers the stresses more effectively from fiber to fiber. Regardless of the type of fiber, molding at 275°C (slightly above 260–265°C, the melting point of crystalline polycarbonate) results in improved properties due to better wetting of the fibers by the resin. Hot forming of graphite reinforced polycarbonate composites between the molding and annealing steps takes advantage of the higher processability of the unannealed material in addition to providing increased modulus and strength in the final molded article.
A rheological study of aqueous separan solutions
Authors: Blanks R. F. , Park H. C. , Patel D. R. , Hawley M. C.
Published: December 2004

The concentration dependence of the rheological response of aqueous Separan solutions was measured. The shear and primary normal stress response in steady shearing flow, and the relaxation of shear stress following cessation of steady shear flow, were measured with four different polymer solution concentrations. Two different nonlinear constitutive equations, Bird‐Carreau and Meister, were used to analyse the data. The Bird‐Carreau model fit the steady shear data very well and the parameters obtained from steady shear data allow reasonable estimates of the stress relaxation of these systems. The Meister model provided a fit of the transient stress relaxation data and could be used to estimate the steady shear response. No quantitative molecular theory was developed in this work. However, the nature of the concentration dependence of the Bird‐Carreau parameters suggests that as the polymer concentration of aqueous Separan solutions decreases from 2.0 to 0.05 weight percent the solutions should be modeled less by an entangled network theory and more as slightly overlapping hydrodynamic units. The concentration where this behavior seems to be changing appears to be about 0.25 percent by weight of polymer.
A new thickness sensor based on the Hall effect
Authors: Okuyama M. , Yagii K. , Sharda S. C. , Tschoegl N. W.
Published: December 2004

A highly sensitive thickness sensor has been developed which may be used as a continuously recording extensometer for rubbery materials. The application of the sensor for measuring volume changes in dewetting filled rubbers is also discussed. Further possible applications include the determination of Poisson's ratio on plastics.
Rheological analysis of stabilizing forces in wire‐coating dies
Authors: Tadmor Z. , Bird R. B.
Published: December 2004

A rheological analysis of a wire‐coating die is presented. The rheological forces which might play a role in the stability of the wire are estimated. In particular, consideration is given to lateral forces related to the secondary normal stress function acting on the wire which is in an eccentric position, and the hydrodynamic force related to the viscosity function acting on the wire which moves at an angle to the die axis. For the former a simple, yet general, expression was derived by solving the flow problem (without axial pressure gradient) with the Ericksen equation in bipolar coordinates. Results indicate that normal stresses stabilize the wire, i.e., tend to restore it to the central location, provided the secondary normal stress function is negative. The hydrodynamic effect tends to reduce the angle between wire and die axes, thus drawing attention to the need of perfect mechanical centering of the guider tip, since in this case this effect also reduces eccentricity. The need is stressed for further work, in particular, experimental measurement of the secondary normal stress function.
A method for estimating both the solubility parameters and molar volumes of liquids
Authors: Fedors Robert F.
Published: December 2004

The solubility parameters and molar volumes of substances can be used, in conjunction with suitable theory, to provide estimates of the thermodynamic properties of solutions; the solubility characteristics of polymer‐solvent systems and the estimation of the equilibrium uptake of liquids by polymers are examples of the type of practical problems that are amenable to treatment.

For low molecular weight liquids, the solubility parameter, δ, is conveniently calculated using the expression δ = (ΔEv/V)½, where ΔEv is the energy of vaporization at a given temperature and V is the corresponding molar volume which is calculated from the known values of molecular weight and density.

For high molecular weight polymers, the volatility is much too low for ΔEv to be obtained directly and hence recourse must be made to indirect methods for estimating δ for these materials. One such widely used method is based on Small's additive group “molar‐attraction constants” which when summed allow the estimation of δ from a knowledge of the structural formula of the material; however, the density must still be determined experimentally.

The proposed method of estimating δ, also based on group additive constants is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of the structural formula of the compound.
The solution of plastics prediction problems by thermoanlytical techniques
Authors: Bair H. E.
Published: December 2004

Often the first step in the solution of problems concerning the use of plastics involves the detailed characterization of a particular resin. Typically, a commercial plastic is composed not only of the basic resin but also of many additional additives. These additives may be such things as impact modifiers, plasticizers, flame retardants, and molding lubricants. In our laboratory we have developed thermoanalytical techniques for the determination of the morphology and composition of these multiphase materials. Specifically, we have quantitatively analyzed an ABS resin for not only the amount of SAN and BD but also the concentration of a molding lubricant (ML) in the resin. The concentration of BD and SAN was estimated calorimetrically from ΔCp measurements at Tg, and the ML level was calculated from ΔHf determinations. In addition, the shifts in Tg of both the BD and SAN phases of the ABS were studied as a function of diluent concentration. The diluents in these resins are residual monomers or other “impurities”.
A sliding scale method for rapid interpretation of rheological measurements
Authors: Ziabicki Andrzej , Szenberg George
Published: December 2004

A simple method has been developed for interpreting rheological data from virtually any of the common rheometers. The method involves the use of an overlapping scale to provide a direct readout of apparent viscosity. The procedure can accommodate data from either rotational or capillary instruments and for the conditions of either shear rate or shear stress control. The method is fully described along with several examples of its application.
Melt viscosity of poly(vinyl chloride) formulations
Authors: Utracki L. A.
Published: December 2004

Commercial, suspension‐type PVC resin, poly (vinyl chloride), molecular weight Mw × 10−4 = 8.6 ± 0.9, polydispersity Mw/Mn = 2.26, was mixed with plasticizer di(2‐ethyl hexyl)phthalate (DOP) and organo‐tin stabilizer in four different proportions. The mixtures were milled and pressed into sheets for testing. The polymer content in these samples was 97, 80, 60, and 40 wt percent. The viscoelastic properties of the materials were investigated using a Weissenberg rheogoniometer in a cone‐and‐plate, steady‐state shearing mode. The viscosities and primary normal stress difference coefficients were measured at shear rates of 10−2 ≤ \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} (sec−1) ≤ 102 and at temperatures from 151 to 246°C. The zero shear viscosities, plotted as log η0 vs 1/T (T is the absolute temperature) did not follow either a straight line dependence, reported for PVC melts at low shear rates at 170–190°C, nor was any discontinuity found near 195°C as by others; the data follows a continuous concave curve. The apparent activation energy of flow increases steeply with decreasing temperature. The data can be represented by a WLF type of equation, but the magnitudes of the parameters of this relation differ from expected values. A crossplot of log η0 (T = const.) vs log w (where w is the polymer content) also demonstrates a faster increase of η0 with w than expected from the straight line dependence. The primary normal stress difference coefficient was found to increase with w and decrease with T, paralleling the observed dependencies of η0.
The influence of crystallinity on the beta‐transition in poly(vinyl chloride)
Authors: Harrell E. Ray , Chartoff Richard P.
Published: December 2004

The effect of changes in crystallinity on the β‐transition in poly(vinyl chloride) was studied by dynamic mechanical measurements of loss tangent (tan δ) and storage modulus (E′) over the temperature range −160° to 85°C. Four frequencies were covered, 3.5, 11, 35, and 110 Hz. The data presented demonstrate that crystallinity has a significant influence on the relaxation processes involved in the β‐transition. The restrictions on segmental mobility imposed by crystallinity are most pronounced in the region between Tβ and Tg, with Tβ tending to shift to lower temperatures, Tg shifting to slightly higher temperatures, the magnitude of tan δ decreasing, and engineering tensile strength increasing. Our data also show that individual PVC resins have mechanical and physical properties which differ enough so that comparisons which are often made between them may be inconclusive. Moreover, the properties of one resin may be more sensitive to thermal treatment than those of another. We are continuing this study to establish correlations between the observed trends and other important mechanical properties such as impact strength, toughness, tensile, and compressive strength.
Crystallization of polyethylene oxide under shear
Authors: Fritzsche A. K. , Price F. P.
Published: December 2004

A concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers. This instrument allows crystallization to be followed at both constant temperature and shear rate. Several samples of polyethylene oxide (Carbowax 4000, Carbowax 20‐M, and WSR‐205) were used. A low molecular weight fraction of the Carbowax 20‐M, as well as the unfractionated material, was crystallized under shear. The WSR‐205 was studied only in a mixture with Carbowax 4000. It was shown that the kinetics of crystallization of uncrosslinked melts of polyethylene oxide are altered by shear. The induction times for the appearance of crystallinity are shorter in the sheared systems than in the quiescent melts. The Avrami exponents are also higher for crystallization in sheared melts than in quiescent systems and increase with decreasing supercooling. The high values of the Avrami exponent are attributed to the disruption of crystalline aggregates into particles larger than the critical sized nucleus. These particles will persist in the melt and continue to grow spontaneously. A continuous infusion of growing particles into the melt occurs.

At constant temperature and shear rate, the induction time of the crystallization curve is influenced by polymer molecular weight. In moderate to high molecular weight samples, the effect of shear becomes saturated at very low shear rates. Decreasing the molecular weight separates the crystallization curves. The curves from the higher shear rates appear at the shorter induction times. However, decreasing the molecular weight below that at the critical entanglement molecular weight allows the nucleation rate, strongly dependent upon the supercooling, to influence the relative positions of the sheared crystallization curves.
Crack propagation in polycarbonate
Authors: Glover A. P. , Johnson F. A. , Radon J. C.
Published: December 2004

Crack velocity measurements and fracture toughness tests have been carried out on extruded sheets of bisphenol‐A polycarbonate. Slow bend tests provided quasi‐staticK1cdata while dynamic initiation values were obtained from instrumented Charpy impact tests. In both types of tests high‐speed crack velocity measurements were made using conductive silver grids applied to the specimens. The variation ofK1cwith strain rate and temperature was found to be small and in general agreement with expectations from the relaxation properties of polycarbonate. Notch acuity was found to have little effect in that values ofK1cand crack velocity from specimens having the standard Charpy notch were similar to values obtained from sharp‐cracked specimens. Some anisotropy was present in the material and gave rise to a small variation in K1cvalues with direction of crack propagation. Crack velocity and also the fracture mode transition temperature showed considerable dependence upon orientation. It was thought that dynamic toughnessKd, was influenced more thanK1cby partial orientation of amorphous regions in the material and that the relaxation time for re‐orientation was probably significant here.
Kinetics of vapor and liquid transport in glassy polyblends of polystyrene and poly (2,6‐dimethyl 1,4‐phenylene oxide) Part II
Authors: Jacques C. H. M. , Hopfenberg H. B.
Published: December 2004

The kinetics of n‐hexane vapor and n‐hexane liquid sorption in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers were studied over a significant range of temperature and penetrant activity. The kinetics of concomitant solvent crazing, apparent at high penetrant activities, were also monitored. In all cases the kinetics of sorption and crazing obeyed predominantly Case II or relaxation‐controlled behavior. Although the rates of crazing and sorption at high activities was much more rapid in the homopolymers than in the blends, the sorption rate at lower penetrant activities increased monotonically with increasing poly(phenylene oxide) content.

These kinetic results qualitatively superimpose upon the equilibrium relationships reported in Part I of this series. Specifically, at a fixed temperature, the rate of crazing was virtually a unique function of equilibrium n‐hexane content independent of polymer composition and largely independent of penetrant activity. The coupling between rate of sorption and equilibrium penetrant content was dramatic. In limiting cases, the sorption rate increased by a factor of 10,000 apparently due to a twofold increase in equilibrium penetrant concentration. This seemingly complicated kinetic behavior is explained rather simply in terms of the equilibrium relationships between organic penetrants and polymeric glasses developed and interpreted in the first part of this series.
Antioxidant‐associated color problems in vinyl foams
Authors: Renshaw J. T. , Cannon J. A.
Published: December 2004

Investigations of chemically‐blown vinyl foam systems, based on electrical grade plasticizers, have shown that the inclusion of 2,2′‐bis (4‐hydroxyphenyl) propane (BPA) as an antioxidant results in color formation in the finished foam. Color formation appears to be due to interactions between BPA and the azodicarbonamide blowing agent. Metal ion(s) present in vinyl stabilizer/kickers are also shown to have an effect on color hue though not on color development per se. Mechanisms for the development of quinoidal and diazo color bodies, based on the reaction of BPA and azodicarbonamide are postulated. Based on these reaction mechanisms, it is shown that it is possible to choose an antioxidant that will not interact with azodicarbonamide. A rudimentary screening procedure is described for evaluating these systems.
Photochemistry in the solid phase
Authors: Guillet J. E.
Published: December 2004

Classical photochemistry is an ancient branch of chemistry, but in the past its practitioners have restricted their interest primarily to studies in the gas or liquid phases. However the practical applications of photochemistry in recent years have led to an increasing interest in photoreactions which occur in the solid phase, particularly in polymeric systems. One of the first areas of practical interest has been in stabilizing plastic and other polymeric systems against photodegradative reactions initiated by solar radiation. More recently photoreactions in polymers have been used extensively in recording and reproducing photographic and other images.
Photocrosslinkable polyphosphonates having unusual resistance to acids
Authors: Borden Douglas G.
Published: December 2004

The resistance of various linear condensation polymers to acid or base hydrolysis is dependent upon the nature of the linkages in the polymer chain. Aryl polysulfonates having a styrylketone sensitizing group have been shown to be particularly resistant to attack by strong bases. Similar phosphorouscontaining polymers have been prepared and those with the arylphosphonate, thiophosphonate, and phosphate linkages have been found resistant to attack by such acids as ferric chloride. Using a solution polymerization method, these phosphorous polymers and also those containing the phosphite, phosphonite, and phosphorane linkages may readily be prepared. A comparison has been made of the resistance of these polymers and of the corresponding polycarbonates, polysulfonates, and polyesters to various bases and to ferric chloride solutions.
Mechanism of refractive index increase in photosensitized poly(methyl methacrylate)
Authors: Bowden M. J. , Chandross E. A. , Kaminow I. P.
Published: December 2004

Poly(methyl methacrylate) prepared under special circumstances exhibits a substantial increase in refractive index after irradiation with ultraviolet light. The essential step in the preparation is peroxidation of the monomer prior to polymerization. This increase in refractive index results from a photo‐induced polymerization of unreacted monomer (1‐2 percent) within the film which produces an increase in density (and hence refractive index) in the irradiated region. It is believed that peroxides, both polymeric and monomeric, act as photoinitiators. Sensitivity depends on the concentration of photoinitiator but the absolute value of Δn depends on the amount of unreacted monomer.
Computer simulation study of images in contact and near‐contact printing
Authors: Lin B. J.
Published: December 2004

Versatile computer programs capable of simulating near‐contact images from arbitrary objects and illumination were reported. Their capability was demonstrated in examples of combinations of different types of object and illumination. From the specific examples, we were able to derive certain general rules: (1) Polychromatic illumination is always better than monochromatic illumination. (Besides observing the examples given above, polychromatic illumination also helps when standing waves in photoresist are considered.) (2) Negative masks are easier to print than positive ones. Note that a negative mask in the sense of optical diffraction means smaller dimension for transparent parts of the mask. (3) Some well designed irregularities in the mask pattern improves the image. (4) The effective depth tolerance is between the limits set by the focussing effect and the image spreading effect. (5) Holographic mask should relax flatness and exposure tolerance.
Flash exposure system for thin photoresist films
Authors: O'Hora D. E. , Beuschel W. F.
Published: December 2004

The formation of an image in a photoresist during photolithographic processing requires the exposure of the photoresist through a mask to a light source in the spectral region to which the photoresist is sensitive. The functional advantage of the flash exposure of photoresist is presented, which includes the elimination of oxygen effects, the reduction of diffraction and standing wave effects, and the enhancement of pattern‐edge acuity. The effects of both broad and narrow band sources are also shown with emphasis on proximity printing techniques. Finally, the optical, electrical and physical design parameters for a practical flash exposure system are discussed.
The interaction of 5 KeV electrons with polymers of methyl isopropenyl ketone
Authors: Levine Aaron W. , Kaplan Michael , Poliniak Eugene S.
Published: December 2004

Poly(methyl isopropenyl ketone) (PMIPK) degrades upon exposure to 5 keV electrons. Using a scanning electron microscope to expose fine‐line raster patterns in thin films of this polymer and subsequently solvent‐developing the thus‐degraded regions, sharp walled troughs are observed, the width of which is a measure of the sensitivity to degradation. Copolymers with several vinyl monomers were prepared and the sensitivities of these were similarly determined. Information relevant to the mechanism of depolymerization was obtained by comparing homopolymers with copolymers and by the use of additives in the irradiated polymer films. Examples of potential device‐fabrication techniques using PMIPK resist are given.
Vapor development of poly(olefin sulfone) resists
Authors: Bowden M. J. , Thompson L. F.
Published: December 2004

Poly(2‐methyl pentene‐1) sulfone undergoes scission followed by rapid chain depolymerization when irradiated with 5‐20 kV electrons. Several parameters which affect the rate of this process, termed vapor development, were evaluated, viz., molecular weight, dose rate, temperature, accelerating voltage and film thickness. While it was never really possible to remove 100 percent of the film, it was possible to remove > 99 percent at reasonably low doses (∼ 10−6 coul/cm−2) using high temperatures (∼ 100°C) and low accelerating voltage (5 kV). Some lithographic details of this process are also described.
A melting model for reciprocating screw injection‐molding machines
Authors: Lipshitz S. D. , Lavie R. , Tadmor Z.
Published: December 2004

A theoretical model for melting in reciprocating screw injection molding machines is proposed. The model permits the calculation of the solid bed profile as a function of time during the injection cycle. It consists of a dynamic extrusion melting model for the rotation period, a transient heat conduction model with a phase transition for the screw rest period, and a proposed model for the drifting of the beginning of melting during the injection cycle.
Elastic fracture of polystyrene solutions
Authors: Southern J. H. , Paul D. R.
Published: December 2004

Based on the assumption of a constant critical shear strain, an expression for the critical stress at the onset of entrance fracture as a function of polymer concentration has been developed. Experimental results with 10‐25 percent narrow distribution, high molecular weight polystyrene‐benzene solutions show the critical stress to be much lower than that for the polymer melt and in agreement with predicted values. This result is all the more impressive when the contrast in flow behavior at the capillary entrance for melts and solutions is observed. Instead of the rotating toroidal vortices surrounding a 90‐deg material entrance cone observed with polystyrene melt, cine movies of the solution flow birefringence patterns in the capillary entrance region reveal only a stagnant zone surrounding a narrow cone less than 20 deg. At fracture, the cone axis moves in a rotary path circulating about the capillary axis without undergoing the flow discontinuities typical of melt behavior.
Dilatometric studies of polymers undergoing high and low rate tensile deformation
Authors: Cessna L. C.
Published: December 2004

Specific volume change and stress‐strain data were obtained simultaneously during tensile deformation on several plastics known to be resistant to impact loading. Tensile deformation rates of 20 percent/minute and 106 percent/minute and temperatures of −190° to 55°C were employed. A common sequence of deformation modes was observed in all materials studied (rubber modified acrylics and styrene, ABS materials, polycarbonate, impact grade polypropylenes, and high density polyethylene). In all cases the major mode of deformation to failure at low rates and/or higher temperatures is volume conserving and primarily a shear flow process. At higher rates of deformation or lower temperatures, a transition occurs and the specific volume of the material increases in direct proportionality to the tensile strain above the apparent yield point. Volume increases of 17 to 50% were observed and these were equal to 85 percent or more of the observed tensile strain at failure. These observations indicate that microcavitation may be the major process available for the absorption of mechanical energy at impact rates in plastic materials.
Thermal expansion instability and effect on creep of a highly crosslinked polyurethane
Authors: Findley William Nichols , Reed Ray Merritt
Published: December 2004

It was found after heating that the thermal expansion of polyurethane decreased markedly in several hundred hours at constant temperature; after cooling the thermal contraction decreased with time but more slowly. The role of cross‐linking as a possible cause of this effect is discussed. Creep during the expanded phase after heating is shown to be much greater than creep after thermal expansion has stabilized at the same temperature. Experiments are described which suggest that the effect of temperature on creep results primarily from thermal expansion rather than from thermal oscillation.
A design approach to a computer‐controlled injection‐molding machine
Authors: Ma Carl Y. W.
Published: December 2004

Plastics injection molding is a complex, multi‐variable process which has not yet been clarified. The hardware controller is difficult to build without a realistic mathematical model. One powerful technique for solving such a difficulty is to employ digital control technology which can utilize sophisticated control strategies in order to optimize the system performance. Machine operation and resultant production can be tightly controlled by using computer monitoring, data storage and data logging. This paper presents elements of the various problems that process engineers may encounter in designing a computer‐controlled system for plastics injection‐molding machinery. The variables of the process and a functional analysis of process control are discussed. A hardware system design; including specification of computer, selection of peripheral devices, system design, and input/output interfacing; is presented.
Viscosity and shear modulus of PVC‐plastisols during gelation and fusion
Authors: Cayrol B. , Klason C. , Kubát J.
Published: December 2004

The Contraves balance rheometer has been used in a study of the gelation and fusion process of three DOP‐based PVC‐plastisols and the results compared with those obtained with the Brabender plastograph. The tensile properties of samples fused at different temperatures have also been determined. The rheometer results relate to the temperature dependence of the viscosity, shear modulus, and loss angle of the plastisols used. The viscosity‐ and modulus‐temperature curves are to some extent reminiscent of the torque‐temperature curves obtained with the plastograph; the fusion temperatures are slightly different. The loss‐angle‐temperature curves measured with the rheometer exhibit sharp maxima in the vicinity of the Tg‐point of the base polymer. The shear modulus decreases with time when the temperature is kept constant (above the fusion point). This effect is possibly associated with crystallite melting. The temperature necessary to reach the maximum strength plateau of films fused at various temperatures was found to agree (within 10°C) with the maximum in the modulus‐temperature curves (minimum in loss‐angle‐temperature curves) when the rheometer shear rate was sufficiently low. On the whole, the rheometer allows for better temperature control. Also, the fact that the results are given in terms of viscosity and shear modulus may have some advantage in interpreting gelation and fusion data.
Ultimate behavior of dry and water‐swollen polymer network/glass bead composites
Authors: Nicolais L. , Acierno D. , Janáček J.
Published: December 2004

Tensile properties of a poly(2‐hydroxyethyl methacrylate) (PHEMA) network filled with various amounts of glass beads, in the dry and the equilibrium water‐swollen states, have been studied below and above Tg. The temperature ranged from 5° C to 170° C and the volume fraction of the filler was up to 50 percent. In the glassy region it has been found that the temperature at which the transition from brittle to ductiel behavior occurs is increased by the presence of the filler. In the brittle zone the strength of the composites is decreased by the presence of the filler and can be predicted by using a finite element method; in the ductile zone, however, the strength of the composites reaches that of the unfilled polymer.

In the rubbery region failure envelopes have been obtained for both dry and swollen PHEMA/glass bead composites. Using a double shift procedure all the data have been superimposed to obtain universal failure envelopes for the two different states. The dependence of the shift factors on filler content is discussed.
Fluid mechanical analysis of injection mold filling
Authors: White James Lindsay
Published: December 2004

The hydrodynamics of the filling of a rectangular mold cavity by a molten polymer is considered in terms of lubrication theory. Both isothermal and nonisothermal mold filling are analyzed. The relationship of the velocity field to the cavity geometry and temperature dependence of the rheological properties is predicted. Increasing the activation energy of viscous flow increases the tendency for channeling of melt through the center of the cavity. The results are compared to the experimental observations of our previous studies.
Liquid (melt) heat capacities and heats of vaporization of oligomers of poly(hexamethylene sebacate)
Authors: Phillips J. C. , Wall L. A. , Aldridge Mary H.
Published: December 2004

The liquid heat capacities and heats of vaporization of three linear esters of poly(hexamethylene sebacate) with hexylcapped end groups (M(mol. wt.) = 370, 655, and 939) have been determined. The heats of vaporization of the oligomers measured at a mean temperature were corrected to 323.15 to 523.15°K by use of the experimental liquid (melt) heat capacities and the calculated gas heat capacities. The corrected heats of vaporization were fitted to the equation ΔHv = S(T)Mα + I(T), where the temperature dependence of the slope and intercept are represented, respectively, as S(T) = ClnT + Ko and I(T) = a T + bo, and α is an exponent. The results indicate (at corresponding molecular weights and constant temperature) that the ratio of the liquid heat capacities of the oligomer ester and the n‐alkane, and similarly the ratio of the heats of vaporization, depend on the number of carboxyl groups in the oligomer ester chain.
Effect of mold temperature on the morphology and properties of polypropylene: I. A propylene‐ethylene copolymer
Authors: Henke S. J. , Smith C. E. , Abbott R. F.
Published: December 2004

The mechanical properties of a propylene‐ethylene copolymer resin depend strongly on the mold temperature employed during injection molding. Average spherulite size correlates well with most physical properties; good impact properties are related to small average size, and high heat distortion temperatures to large average size. Tensile specimens have three distinct regions when viewed through crossed polars. The outer region (Region 1) does not contain spherulites, but Regions 2 and 3 do. The largest spherulites are found in Region 3, the center of the specimen. Region 1 has a molecular weight higher than that of the other two regions.
Polymer property enhancement by solid‐state forming
Authors: Broutman Lawrence J.
Published: December 2004

The alteration of the physical properties of a polymer by the use of forming techniques which are applied below the melt or glass transition temperature of the polymer has been discussed. The influence of cold rolling (rolling accomplished at room temperature) on the mechanical properties of amorphous polymers was first briefly reviewed (1). The specific effect of rolling on the toughness of polycarbonates, as measured by notched Izod impact strength, was discussed in detail and is summarized in (2). The role of crystallinity in further enhancing the mechanical properties of polycarbonate and the combined effect of rolling and crystallinity was also described and is discussed in more detail in (3). Other amorphous polymers were also discussed, particularly the effect of rolling on the notched Izod impact strength (4). For most polymers studied, a large increase in impact strength occurs for small reductions in thickness and a maximum occurs at a given thickness reduction beyond which the ductility of the material is exhausted. The increase in impact strength is not only a result of molecular orientation but also a function of residual stress placed in the sheet by the rolling process.

In addition to the studies on amorphous polymers, recent studies (5, 6) were described on the high‐pressure nonisothermal compression molding of linear polyethylenes. Mold pressures up to 80,000 psi were used and several different polyethylenes having various molecular weights (up to 106) were investigated. It was shown that the modulus of elasticity of polyethylene can be increased by a factor of two when the mold pressure is increased to 80,000 psi. A detailed discussion of the changes in morphology responsible for this increased stiffness is presented in (6).
Measurement of aging effects of ABS polymers
Authors: Casale A. , Salvatore O. , Pizzigoni G.
Published: December 2004

ABS (acrylonitrile‐butadiene‐styrene) plastics are one of the most common two‐phase commercial polymer systems. They consist of a continuous rigid phase (styrene‐acrylonitrile co‐polymer) in which the elastomer phase (polybutadiene grafted with styrene and acrylonitrile) is finely dispersed in the form of spherical particles. Because of their properties and relatively low cost compared to other engineering thermoplastics, ABS resins are now being used increasingly in fields of application involving severe aging. The polybutadiene content, however, poses a problem in relation to ABS aging resistance, since it is a prime site for degradative attack at double bonds and tertiary carbon atoms. The present paper presents a concise account of the methods used in our labortory for measuring ABS aging. As an example, ABS degradation during processing and during natural and artificial light aging are discussed in more detail.
Effects of mixing on polymerizations in batch reactors: Comparison of catalytic and ionizing radiation initiations
Authors: Chen H. T. , Steenrod J.
Published: December 2004

The effects of mixing on polymerizations in batch reactors are examined theoretically for initiations by thermal decomposition of catalyst and by absorption of ionizing radiation. Mathematical expressions for predicting the first three moments of the dead polymer size distribution are presented. Two extreme mixing states, perfect and no mixing, are considered. It is shown that in batch reactors mixing in any direction in which nonuniform initiations exist increases the polymerization rate and the number average molecular weight and decreases the weight average and thus the polydispersity.
A coordinate frame for helical flows
Authors: Tung T. T. , Laurence R. L.
Published: December 2004

This note presents a coordinate frame representation for the conservation laws governing fluid motion in a helical configuration as suggested by a single‐screw extruder with deep flights and by the Kenics Static Mixer. This example demonstrates the care necessary in dealing with nonorthogonal coordinate systems. The conservation equations are also presented in terms of the proper physical components, as well as the physical components of the rate of deformation tensor. The paper closes with a brief statement of the boundary conditions for flow in a static mixer.
Approximate calculation and measurement of the pressure distribution in radial flow of molten polymers between parallel discs
Authors: Winter Horst H.
Published: December 2004

The known generalized Newtonian fluid “power law” solution of the radial flow between parallel discus has been used to estimate the normal stress, the magnitude of inertia, and the temperature changes due to viscous dissipation. The flow near the wall has been found to be “nearly steady shear flow;” thus the three viscometric functions can be expected to describe the stress at the wall. Further away from the walls, however, the flow is very different from “steady shear flow.”

The temperature field in the radial flow section depends on the dimensionless parameters Nahme number, Graetz number, and ratio of inner to outer radius, as well as on the thermal initial and boundary conditions.

Experimentally the radial pressure profiles for flow of three different polyethylenes and of one polystyrene have been studied. The measured pressure profiles are about 20 percent lower than the calculated ones from the “power law” solution. This discrepancy cannot yet be explained; the effects of normal stresses, of inertia, or of viscous heating in these experiments are too small to give a measurable effect.
Fatigue crack growth in polymers. II. The interaction of mean stress, frequency, and temperature
Authors: Radon J. C. , Culver L. E.
Published: December 2004

Fatigue crack propagation was studied in large centernotched plate specimens of two polymers, poly(methyl methacrylate) and polycarbonate, under tensile cycling conditions. Tests were performed at frequencies of 0.1, 5.0, and 20 Hz, and at two temperatures, −60 and +21°C. The interaction of mean stress intensity, frequency and temperature was investigated. It was found that in tests performed at constant frequency or temperature, the fatigue crack propagation rates were dependent on both the range of the applied stress intensity factor and its mean value, Km. All propagation rates increased with increasing Km. Also, the threshold stress intensities decreased with increasing Km, suggesting very low levels of ΔK for non‐propagating cracks, certainly below the 0.4 Kc, the minimum level investigated here. In PMMA, decreasing crack growth rates with increasing frequency were established for a wide range of Km. However, in PC crack growth rates increased substantially with increasing frequency. Finally, “upper and lower transition points” were noted on crack growth curves of both materials.
Estimation of mechanical properties for rigid polyurethane foams
Authors: Menges G. , Knipschild F.
Published: December 2004

Rigid plastic foams find application in construction mainly as core materials for loaded sandwich structures—in buildings, ground vehicles, and airplanes. This work provides an equation for the mechanical behavior of polyurethane foams as a function of foam density. Starting from a model conception and the qualitative microscopic consideration of the deformation and failure mechanism, simple relations are found for the tensile, compressive and shear strength and the elastic modulus, which sufficiently express the measured results.
Elongational viscosity of microbead suspensions
Authors: Nicodemo L. , De Cindio B. , Nicolais L.
Published: December 2004

A ‘tubeless syphon’ was used as an elongational viscometer for the purpose of measuring elongational viscosities of glass bead suspensions in dilute polymer solutions. It was found that while the shear viscosities increased, the elongational viscosities decreased very sharply with increasing bead concentration. The conclusions from the present data are then compared with the observed changes in the elastic properties of two phase molten polymer systems. A double shift procedure has been successfully adopted to correlate the experimental data.
Phosphites in polyolefin process stabilization
Authors: Ray Wesley C. , Isenhart Kyle
Published: December 2004

The use of stabilizer systems containing phosphites in polyolefins is well‐established in the technical and patent literature. In addition to the known effects of improved heat and color stability for polyolfins, we have recently found that phosphite‐containing stabilizer systems impart a process stabilizing effect as evidenced by melt flow analysis. By monitoring the poly‐olefin melt flow after multiple extrusions with increasing temperature, it was found that the combination of phenolics and phosphites has a marked influence on the control of melt flow of polyolefins and the effect appears to be synergistic in operation.
Mathematical modelling and the systems approach in plastics processing: The blown film process
Authors: Petrie Christopher J. S.
Published: December 2004

As an example of a complex process, the production of blown film is analyzed. Systems descriptions are used to emphasize the importance of stating objectives clearly before process modelling. The mathematical treatment of confined and free flows is outlined, together with an account of the factors which are important in polymer melt flow. The uses and limitations of mathematical modelling are discussed briefly.