bluuebunny/crossref_metadata_2025 huggingface dataset:
The injection molding of thermoplastics part II: Experimental test of the model
Authors: Kamal M. R. , Kenig S.
Published: December 2004

Experimental studies have been conducted with a 2 1/3 oz reciprocating‐screw injection molding machine to check the validity of a proposed theoretical model for injection molding. A semi‐circular cavity has been employed in the study to achieve spreading radial flow during the filling stage. Both high speed photography and pressure transducer measurements have been employed to obtain data on polyethylene. The photographic studies confirm the existence of spreading radial flow throughout the filling stage, and are in very good agreement with data obtained with the transducer on the progression of the melt front in the cavity. The results show that the proposed theoretical model yields predictions which are in good agreement with experimental data for all stages of the injection molding cycle with polyethylene. The model also predicts a composite pressure‐time curve for the overall cycle which is similar to those reported in the literature and which satisfactorily represents the data obtained in this study. It is also possible to predict a short shot under selected molding conditions in agreement with observation. The main problems in the application of the model arise during the filling stage near the cavity entrance where viscoelastic and end effects are important and where some of the assumptions inherent in the model may not be valid.
Uniaxial extension of polyvinyl chloride in the high‐elastic state
Authors: Vinogradov G. V. , Fikhman V. D. , Alekseyeva V. M.
Published: December 2004

The dependence of true stress on the extension ratio of PVC threads has been determined for a wide range of extension rates. Since the polymer subjected to deformation was in the high‐elastic state (at temperatures from 90 to 160°), the deformations were predominantly high‐elastic. The dependence of true stress on the amount of high‐elastic deformation is described by the Mooney‐Rivlin equation.

Relaxation moduli have been found on the basis of measurements of stress relaxation at constant deformation after various extension ratios were attained at different rates. Within the limits of deformation regimes at which the true stress is an increasing function of extension ratio the relaxation moduli do not depend on extension ratio and rate of extension. This enables one to arrive at a master curve of the relaxation modulus versus relaxation time with the reservation indicated above concerning the increasing character of the dependence of true stress on extension ratio. The relaxation spectrum represented by the high‐elasticity plateau has been determined from the relaxation moduli according to the first approximation.

The experimental data for a very wide range of deformation regimes and temperatures are presented in the form of an invariant dependence of the ratio of true stress to the rate of deformation on the product of deformation time by extension ratio.

The ultimate strength of the specimens frozen rapidly after the attainment of definite extension ratios is determined by the accumulated high‐elastic deformation.
Critical regimes of shear in linear polymers
Authors: Vinogradov G. V. , Insarova N. I. , Boiko B. B. , Borisenkova E. K.
Published: December 2004

The state of the problem of elastic turbulence is critically discussed. It is shown that the development of elastic turbulence is associated with the transition of polymer systems to the high elastic state.

Model experiments with a narrow‐MWD polybutadiene have been carried out. The method of vizualization of the flow in a flat slit with the aid of circular‐polarized light has been used. The results of polarization‐optical investigation are compared with the results of capillary viscometry and dynamic measurements at small amplitudes. It is shown, in accordance with theoretical predictions, that when a polymer passes from the fluid to the high elastic state with an increase in the shear rate, it ceases to behave as a fluid under shear. This is accompanied by various forms of flow perturbation at the duct exit and entrance and inside the duct. Perturbations at the duct entrance and exit are due to stress concentration in these zones. The transition of a polymer to the high elastic state near the walls inside the duct gives rise to the “stick‐slip” process or to continuous slippage along the duct walls, depending on the velocity of polymer movement. This can be clearly traced by the changes in the interference band pattern. Still higher velocities result in an intensive process of continuity break (rupture) in the polymer and in its chaotic movement in the duct as an aggregate of irregularly shaped lumps, which, relaxing, may form a continuous body again. Attention is drawn to the significance of these observations for a quantitative description of the viscosity anomaly of polymer systems and of the relationship between the viscosity anomaly with various flow irregularities and perturbations in such systems.
Some factors influencing cooling rates of rotationally molded parts
Authors: Throne James L.
Published: December 2004

Recently, rotational molding engineers, concerned with warpage and uneven cooling in parts, have been “pre‐cooling” the mold in forced draft air after removal from the oven and prior to water quenching to removal temperature. In this paper, we analyze some of the factors that influence the rate of heat removal from an amorphous plastic in a metal mold. We find that mold thickness and thermal diffusivity, convection heat transfer coefficient of the cooling fluid, the thermal properties of the plastic and the initial, final and “freezing” temperatures of the plastic influence this cooling rate and the corresponding rate of volumetric shrinkage. We illustrate our analysis with several examples and discuss some guidelines in detail.
Prediction of polymer processing characteristics using the C. W. Brabender plasti‐corder torque rheometer
Authors: Allen Edward O. , Williams Robert F.
Published: December 2004

The Brabender Plasti‐Corder is shown to be an effective tool for predicting the processing characteristics of thermoplastic polymers. Procedures for determining the molding temperature range, the relative melt viscosity over a continuous temperature range, and the stability of molding and experimental curtain coating materials are presented.

Molding temperature ranges can be determined by first establishing the Brabender torque which corresponds to the maximum viscosity at which a material will just fill the cavity in a particular injection system under full injection pressure and maximum injection rate. This torque is constant for any material to be molded in this system. A Brabender torque‐temperature curve is then obtained on the pertinent resin and the temperature which corresponds to the torque associated with the maximum viscosity is the minimum molding temperature. Maximum molding temperature is the temperature at which the log of the torque deviates from a linear dependence on temperature.

The stability of thermoplastic compositions can be shown by a Brabender torque‐time curve at constant temperature. An unstable polymer shows decreasing torque with time if the decomposition predominantly consists of chain scission.
Solids conveying in screw extruders part III: The delay zone
Authors: Kacir L. , Tadmor Z.
Published: December 2004

A theoretical model was developed for the newly‐defined delay zone of the plasticating screw extruder. The delay zone starts at the end of the solids conveying zone, i.e. at the point where the solid plug surface contacting the barrel melts and forms a film of melt up to where the steady state melting mechanism starts to operate. The model permits the film thickness and pressure profiles in this zone to be calculated. Published results were used to support the validity of the model. The results indicate that the film thickness at the end of the delay zone is several times the flight clearance. Finally, a criteria, based on the final value of the film thickness, is suggested to calculate the length of the delay zone.
Energy transport to molten flowing polymer systems: I. Development of an apparatus to obtain temperature profiles
Authors: Saltuk Ismail , Siskovic Nandor , Griskey Richard G.
Published: December 2004

An improved apparatus for studying temperature profiles in molten, flowing polymers has been developed. The apparatus incorporates modifications and improvements of earlier temperature profile devices. In addition, this unit made it possible to study temperature profile development as a function of axial flow length. Data taken with the apparatus were found not only to be precise and highly reproducible but also to show the proper trends with respect to physical behavior.
The bending of polymers under tension as related to a deep drawing process
Authors: Buettner William B. , Marshall D. I. , Manson John A.
Published: December 2004

Two engineering plastics, an acrylonitrile‐butadiene‐styrene resin (ABS resin, Cycolac MS) and a rigid polyvinyl chloride resin (PVC resin, Dacovin 2082) were investigated to determine the effects of cold working. In particular, the “bending under tension” stress system of a deep drawing process was considered. The object was to determine the effect of the blank‐holder pressure, the ratio of the punch radius to the material thickness, the speed of deformation and the temperature of deformation. The stress‐strain characteristics of the deformed and undeformed material were markedly different. Upper yield points were lower in the deformed specimens, the tensile strengths were decreased by 10 to 15% and the %‐elongation at break was higher—up to double the values for underformed specimens. An analysis indicated that these effects can be attributed to non‐homogeneous yielding. The results also indicated that crazing plays an important role in permitting an ABS material to permanently conform to a radius with no geometric constraints.
The particle flow of polystyrene during capillary extrusion
Authors: Nielsen K. Strange
Published: December 2004

The melt flow of emulsion polymerized polystyrene has been investigated in accordance with the particle flow concepts developed by Berens and Folt. Particles were found to be present in the extrudate up to 210°C and resins with larger particles were found to have lower viscosities. The molecular weight appears to have no significant effect on the melt viscosity above a certain molecular weight. The energy of activation for viscous flow at 190°C and at shear stress of 5 × 105 dynes/cm2 was found to be 29–33 kcal/mol depending on type of resin.
The macroscopic volume changes of selected polymers subjected to uniform tensile deformation
Authors: Powers John M. , Caddell Robert M.
Published: December 2004

High density polyethylene (PE), polycarbonate (PC), and polymethylmethacrylate (PMMA) were subjected to uniaxial tensile deformation up to the onset of instability or necking. Simultaneous readings of longitudinal extension and transverse contraction (width and thickness) were obtained continuously during the loading period. From these data, plots of longitudinal versus “average” transverse strain were produced and it was found that the trends were neither constant nor linear over the full strain range employed. Additional plots of per cent volume change versus longitudinal strain indicate that the PMMA and PC show a maximum volume increase of about 0.6% while PE shows a maximum volume decrease on the order of 2.5%. Similar volume decreases have been noted by others and it would appear that structural changes are the most likely cause of this behavior.
Evaluation of melt flow as a measure of low density polyethylene processability into blown films
Authors: Plochocki Andrew , Czarnecki Lech
Published: December 2004

Melt capillary flow and extrudate swelling for low density polyethylenes (LDPE), differing in ease of heavy‐duty, blownfilm extrusion, have been employed as processability criteria. LDPE of good processability is characterized by a unique combination of melt fluidity, temperature, shear rate dependence and melt elasticity. These characteristics of flow are correlated with LDPE film blowing process variables such as maximum take‐up speed, film thickness scatter, and extruder temperatures profile. Intuitively, these melt flow criteria should be extended to Trouton's viscosity and the tensile strength of the melt. The limited development of the elongation viscometry techniques, however, has limited their application.
Effect of rubber particle size on deformation mechanisms in glassy epoxy
Authors: Sultan Jacques N. , McGarry Frederick J.
Published: December 2004

When tested in tension, a cross‐linked epoxy resin can be made to exhibit shear yielding. A modified von Mises criterion, τ = τ0 − μP describes the yielding behavior of the same resin under a biaxial stress system, indicating that the flow of the material is pressure sensitive.

Butadien‐acrylonitrile elastomer particles suspended in the cross‐linked epoxy matrix induce large local deformations when the composite material is stressed. Particles a few hundred Angstroms in diameter cause the glassy matrix to exhibit shear banding, and the macroscopic failure envelope of such a system follows a modified von Mises criterion similar to that of the matrix resin. It was found that the coefficient of internal friction, τ, and the activation energy for yielding are approximately the same for the two cases. With larger particles (5‐15,000 Å diam) the failure mode changes as shown by the macroscopic yield envelope and the associated activation energy. Electron micrographs of the fracture surfaces show microcavitation, similar to crazing around each particle; the deformed glassy polymer around each particle retracts upon heating the matrix above its Tg. The fracture surface work value of the unmodified matrix is 1.75 × 105 ergs/cm2. With 10 pph small particles, the value increases to 3.32 × 105 and with 10 pph of large particles, to 15.48 × 105 ergs/cm2.
Synergism in thermal stabilization of polyvinyl chloride
Authors: Deanin Rudolph D. , Landers James F. , Byczko Richard W. , Linzer Ira
Published: December 2004

Plasticized polyvinyl chloride was thermally stabilized by barium, cadmium, and zinc laurates, epoxidized soybean oil, and monoalkyl diaryl phosphite, and by combinations of these stabilizers. Of 26 possible combinations, 18 showed some improvement, 8 showed useful improvement, 7 showed marked improvement, and 3 systems were outstanding. Of the 26 combinations, 10 showed distinct synergism, based mainly upon combinations of Group II‐B metals with Group II‐A metals, “secondary” stabilizers, or both. Combinations of Group II‐B metals with “secondary” stabilizers were particularly interesting and promising.
The mechanical behavior of thermoplastic materials in the deep drawing process
Authors: Evans Robert E.
Published: December 2004

This study presents a mechanical analysis of the deep drawing of thermoplastics in the glassy state. A theoretical stress analysis is conducted by applying principles of classical plasticity together with several assumptions. A simple model is presented relating drawing performance with the mechanical properties of the plastic measured under the conditions of the fabrication operation. An experimental procedure is described for evaluating the drawability of a plastic. Data on thirteen thermoplastics are used to demonstrate the applicability of the theory developed.
Low temperature transitions in a crosslinked urethane
Authors: Wischmann Kenneth B. , Brassell Gilbert W.
Published: December 2004

We have investigated the low temperature transitions in a urethane prepolymer crosslinked with various amines and triols by measuring their dynamic mechanical properties over a temperature range of 25°C to approximately − 190°C. In the formulations studied, a low temperature transition was observed near − 140°C and the transition was shown to be related to the electronic and steric influences of the curing agent structure at the crosslink site. A quantitative relationship was demonstrated between the low temperature transition peak intensity and the polymer's crosslink density. The above relationships were derived from torsion pendulum and solvent swell experimentation.
The effect of flake aspect ratio on the flexural properties of mica reinforced plastics
Authors: Lusis J. , Woodhams R. T. , Xanthos M.
Published: December 2004

Two naturally occurring micas, phlogopite and muscovite, were ground and classified according to their average aspect ratios (flake equivalent diameter to thickness ratio). These flakes were then used to reinforce a polystyrene copolymer and a polyester resin. The compression molded test pieces were tested in flexure and the flexural strengths and flexural moduli determined for each aspect ratio. The experimental results indicate a strong dependence of strength and modulus on the flake aspect ratio up to a value of 100–200 for these systems. At high volume fractions, 0.6 to 0.7, high aspect ratio mica composites yielded flexural strengths of 35–45,000 psi with flexural moduli of 10–14 million psi. Notched Izod values were in the range of 0.5–1.4 ft lb per inch of notch. These results were compared with the theoretical treatments of Padawer and Beecher, and Riley.
Model filler reinforcement studies by small angle X‐ray scattering
Authors: Myers M. E. , McIntyre D.
Published: December 2004

Polybutadiene rubbers, filled with polydichlorostyrene or polystyrene latices having spherical diameters of approximately 500Å, were examined by small angle x‐ray scattering. The filler latices were examined by x‐ray scattering as a function of strain. The sample elongations ranged up to 400 percent. An analysis of the scattering of the polydichlorostyrene filler latices showed that there was deformation of the filler particles up to 25 percent. Such a deformation is not expected on the basis of the mechanical properties of bulk glassy polydichlorostyrene. However, deformation into ellipsoids of revolution is consistent with the x‐ray evidence. The deformation of the latices is reasonable.
Viscoelastic properties of heterophase blends of homopolymers and block copolymers
Authors: Choi G. , Kaya A. , Shen M.
Published: December 2004

Stress relaxation and dynamic mechanical measurements were carried out for two types of heterophase polyblends. One is obtained by blending homopolymers of butadiene and styrene (high impact polystyrene or HIPS); the other by blending homopolymer of butadiene with a triblock copolymer of styrene‐butadiene‐styrene (SBS/B). It was found that for HIPS, time temperature superposition is difficult, and the shift factors cannot be adequately interpreted by a reasonable model. For SBS/B it is impossible to carry out superposition. Modulus‐temperature and loss tangent curves determined by dynamic mechanical experiments indicate the presence of new transition near −40°C. Possible mechanisms giving rise to this new transition are discussed.
Flow behavior of well characterized polyethylene melts
Authors: Miltz Joseph , Ram Arie
Published: December 2004

A careful characterization and rheological study of low density polyethylene (LDPE) reveals that long‐chain branching (LCB) plays a decisive role. At constant molecular weight (M̄w) higher LCB reduces the Newtonian viscosity ηo and the shear sensitivity, increases the activation energy Eo, and finally delays transition to pseudoplastic flow to higher shear rates and the onset of melt fracture to higher shear stresses (τd). The flow parameters ηo, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma _{cr} $\end{document}cr, τd, and the derived flow relaxation times are uniquely correlatable by means of a modified molecular weight (gM̄w) incorporating the LCB effect. High density polyethylene are less shear sensitive than their low‐density counterparts, have a lower activation energy, fracture at higher shear stress levels and cannot be regarded as branchless LDPE's.
Effect of an epoxidized novolac resin anhydride structure on the properties of resin
Authors: Johnson Ronald E. , Fricke A. L.
Published: December 2004

The properties of an epoxidized novolac resin cured with two homologous series of substituted succinic anhydrides (alkenyl and alkyl) have been determined and the effects of anhydride structure on properties have been evaluated. Substituted succinic anhydrides yield cured resins with lower strengths, lower heat distortion temperatures, and lower moduli. Use of substituted succinic anhydrides could broaden the range of application of alicyclic anhydrides to include those requiring a more flexible resin. Effects of specific elements of anhydride structure have been consistently interpreted from properties measurements and from aging and solvent resistance studies.
The mechanical properties of high‐density rigid polyurethane foams in compression: I. Modulus
Authors: Phillips P. J. , Waterman N. R.
Published: December 2004

A series of rigid polyurethane foams of densities varying from 65 kg/m−3 to 400 kg/m−3 have been tested in compression as a function of rate and temperature. It has been found that a linear relation exists between density and modulus if the data is referred to a constant thermodynamic temperature.
Morphology of a polyurethane‐polyacrylate interpenetrating polymer network
Authors: Frisch K. C. , Klempner D. , Migdal S. , Frisch H. L. , Ghiradella H.
Published: December 2004

Interpenetrating polymer networks of the SIN type (simultaneous interpenetrating networks) composed of a polyacrylate and a polyurethane were prepared. They were made by mixing several concentrations of the linear polymer and prepolymer in solution, together with their respective chain extending and crosslinking agents and catalysts, casting films and curing them in situ. The morphology was studied by differential scanning calorimetry and electron microscopy in order to determine the extent of chain entanglement of the two networks (interpenetration). It was found that little or no phase separation occurred, thus implying extensive interpenetration.
The plasticating process in injection molding
Authors: Donovan R. C.
Published: December 2004

A mathematical representation of the plasticating process in a reciprocating‐screw injection‐molding machine has been formulated as a design tool for simulating the effect of processing parameters on the melting performance, the melt temperature, and the pressure profile. Comparisons with experimental data on low density polyethylene (LDPE), acrylonitrile butadiene styrene (ABS), and polyvinyl chloride (PVC) under a wide variety of processing conditions are described.
The surface area of bulk poly(vinyl chloride)
Authors: Salovey R. , Cortellucci R. , Roaldi A.
Published: December 2004

The porosity of poly (vinyl chloride) (PVC) resin particles produced in bulk polymerization is sensitive to polymerization conditions. Using scanning electron microscopy, 60μ spherical beads of PVC are shown to be composed of loosely packed 1μ spherical subparticles. This complex morphology is characterized by a variability in surface area. The surface area of bulk PVC materials can be measured by a chromatographic technique. The elution time of n‐octane as a probe molecule on PVC packed columns is simply related to PVC surface area. At approximately constant particle size (measured by Coulter counter and optical microscopy), surface areas measured by argon adsorption are correlated to chromatographic elution times. The bulk density, plastisol viscosity and pore volume (from mercury penetration porosimetry) are determined and related to specific surface area.
Chemical thickening of low profile polyester resin systems
Authors: Volgstadt F. R. , Sieglaff C. L.
Published: December 2004

Low profile polyesters and sheet molding compounds, SMC, are two of many resin‐glass composites that have been commercialized in the past few years. They have evolved through application of earlier technologies and have opened up possibilities for fiber‐reinforced plastics. Because of rapid growth, insufficient time has been spent documenting the technical aspects of making SMC. Techniques are thus described that we have used to characterize the rheological properties of the resin mix during its transition from liquid‐like (viscous) behavior of the initial formulation through the solid‐like (elastic) behavior of the resultant SMC.
Prediction and evaluation of the susceptibilities of glassy thermoplastics to environmental stress cracking
Authors: Henry L. F.
Published: December 2004

Glassy, amorphous thermoplastics experience a nearly universal susceptibility to crack and craze formation in the combined presence of stress and a chemical environment. This susceptibility has been evaluated for styrene‐acrylonitrile copolymers according to the factors which effect craze initiation and those which limit the rates of flaw propagation. Molecular weight, styrene‐acrylonitrile ratio, rubber content, and rubber phase morphology are variables which were found to affect flaw initiation and propagation. Fundamental characterization of the chemical parameters which control the initiation of craze formation in polysulfone and polycarbonate is also presented. In particular, “3‐dimensional” solubility parameters have been observed to be a reasonable means of characterizing susceptibility to environmental stress cracking.
Prediction of diallyl phthalate molding performance from laboratory tests I. Characterization and quality control of diallyl phthalate compounds
Authors: Slysh Roman , Hettinger Arthur C. , Guyler Karl E.
Published: December 2004

The purpose of this study was two‐fold:

To determine the relationship between the composition and curing characteristics of glass‐reinforced diallyl phthalate (DAP) compounds and their molding performance.

To develop quality control tests in order to assure their satisfactory processing.

DAP compounds were analyzed with regard to composition, flow, curing characteristics, and heat stability. Tests involving “Spiral of Archimedes” and differential scanning calorimetry (DSC) were used to determine the flow and curing characteristics, respectively. A Brabender torque rheometer was employed to measure both flow and curing properties of DAP. The results obtained indicate that curing properties are of major importance in controlling the DAP processing. Good correlation was observed between the Brabender processing time, the onset curing temperature as measured by DSC, and the molding performance. A computer program was developed capable of calculating the kinetic parameters from the dynamic DSC scan of uncured DAP compounds. The curing data obtained from this method agree with those determined by isothermal DSC. A method based on the penetration of a hot metallic cone has been developed to measure rapidly the percent cure of molded DAP parts. The above mentioned techniques are recommended for the quality control of DAP molding compounds.
Phenylation of PVC with triphenylaluminum and related model reactions
Authors: Kennedy Joseph P. , Ichikawa M.
Published: December 2004

It was theorized that the heat stability of PVC may be improved by exchanging the “weak” (allylic and tertiary) chlorines by groups of higher bond strength, e.g., phenyl. Thus PVC was phenylated by ϕ3Al in carbon disulfide slurry for various times (1 to 5 hrs) and temperatures (from −30 to +45°C). The ϕ3Al concentration, temperature and time of ϕ3Al treatment greatly affect the ultimate heat stability of PVC. Significant improvement in the heat stability was obtained by treating PVC in carbon disulfide at 25°C for 1 hr. The mechanism of phenylation was studied by model experiments in which the possible structural irregularities in PVC were simulated by small molecule chlorine compounds, i.e., 3‐chloro‐1‐butene, 1,3‐dichloro‐1‐butene, 4‐choro‐2‐pentene were models for terminal and inchain allylic chlorines, t‐butyl chloride was the model for tertiary chlorine at branch site, and isopropyl chloride simulated regular secondary chlorines. The reactions between ϕ3Al and these chlorides were carried out at 35°C for various times and the NMR spectra were analyzed. The ϕ3Al + tBuCl reaction in carbon disulfide gives t‐butylbenzene (Wurtz coupling) and isobutylene oligomers. Evidently ϕ3Al (or the ϕ2AlCl formed) dehydrochlorinates tBuCl to isobutylene which rapidly oligomerizes in the presence of Lewis acids. In aromatic diluents, i.e., benzene, chlorobenzene, and o‐chlorotoluene, Friedel‐Crafts t‐butylation of the diluent occurs; in mesitylene t‐butylation is absent presumably because of steric hindrance and small amounts of t‐butylbenzene are formed by Wurtz coupling. All the allyl chlorides examined are rapidly phenylated by ϕ3Al in carbon disulfide at 35°C and yield the expected products: 3‐chloro‐1‐butene → 1‐phenyl‐2‐butene; 1,3‐dichloro‐1‐butene → 1‐chloro‐3‐phenyl‐1‐butene; 4‐chloro‐2‐pentene → 4‐phenyl‐2‐pentene. The kinetics of phenylation by ϕ3Al of model compounds have been studied and the following rate constants were obtained: kallyl = too fast to measure, ktBuCl = 1.0, and kiPrCl = 9 × 10−4 l/mole min. Evidently the rate of the ϕ3Al + RCl reaction is mainly determined by the stability of the R⊕ intermediate: substituted allylic⊕ ≫ tertiary⊕ ≫ secondary⊕.
The influence of stabilizers on the fusion of rigid poly(vinyl chloride)
Authors: Kulås Finn Ragnar , Thorshaug Niels Peter
Published: December 2004

It is known that the fusion rate of rigid PVC in an extruder partly depends upon the lubricants that are used. In the present study it is shown that different stabilizers have a great influence upon the rate of fusion of rigid PVC. Results from extrusion experiments and the Brabender Plastograph strongly indicate that a correlation exists between rapid melting in the extruder and the melt viscosity‐temperature relation of the polymer blend. The reason why certain stabilizers cause a more rapid fusion of the PVC is attributed to the chemical structure of the stabilizers.
Strain history of the melt in film blowing
Authors: Farber Robert , Dealy John
Published: December 2004

Techniques have been developed for measuring the strain and thermal histories of fluid elements as they move from the die lips to the freeze line. Motion pictures were analyzed to determine the rates of extension in the machine and transverse directions. A radiation pyrometer was used to measure the temperature of the film. These techniques were used to study the film blowing of polyethylene; a 2.5‐in. diameter die was used, and blow‐up ratios in the range of 1.8 to 3.4 were employed. Film thickness ranged from 2 to 4 mils. The maximum measured extensional strain rates in both the transverse and machine direction were in the range of 0.15 to 0.6 sec−1. Standard shrinkage and impact tests were performed on the finished films, and an attempt was made to correlate the results with several simple empirical norms of the strain history. No correlation could be discerned. The results of this study are inconsistent with some popular ideas about the origin of orientation in blow films, but they are consistent with some recently published data on the influence of deformation on orientation in melt‐drawn capillary extrudate.
Superdrawn crystalline polymers: A new class of high‐strength fiber
Authors: Clark E. S. , Scott L. S.
Published: December 2004

A new kind of acetal fiber has been discovered which has a tensile strength of 1.7 GPa (250,000 psi) and an elastic modulus of 35 GPa (5 × 106psi). This fiber is produced by a special two‐stage drawing process in the solid state which requires careful control of deformation rate and temperature. Previously known drawn fibers are reported to consist of folded‐chain blocks joined by a limited number of tie‐molecules. It is hypothesized that the second stage of the novel drawing process eliminates the lamella (block) surfaces which act as strength‐limiting stress concentrators. A new type of fiber is created in which any remaining chain‐folds are distributed as defects in a continuous crystal matrix. It is the continuity of the crystal matrix which is believed responsible for the remarkable properties of the fiber.
The effect of sudden strain‐rate change on the yield behavior of bisphenol‐A polycarbonate
Authors: Yee Albert F. , Detorres Pablo D.
Published: December 2004

We wish to investigate the path dependence of yield processes in glassy polymers and to understand this dependence, if any, in terms of molecular mechanisms. To this end the effect of sudden strain‐rate change on the yield behavior of bisphenol‐A polycarbonate has been investigated. In the experiment, a specimen was initially deformed at a constant elongation rate R1; at an elongation Δlc the rate was suddenly changed to another constant elongation rate R2. R1 was either lower or higher than R2. The yield stress subsequent to the rate change was found to be lower than if the entire deformation was at R1. These results can be satisfactorily explained in terms of Robertson's theory of the yielding of glassy polymers if it is assumed that the “bond flexing” in his theory manifests itself in anelastic deformation.
The significance of capillary rheology testing temperature for predicting PVC extrudability
Authors: Shah Pravin L.
Published: December 2004

A rheological investigation of the saturated fatty acids as lubricants for PVC was made in a Sieglaff‐McKelvey rheometer over a wide temperature range. Results reveal that with an increase in carbon chain, fatty acids became more effective in reducing the melt viscosity of PVC. It was also discovered that the maximum viscosity variation due to these materials was observed at 350°F. At test temperatures of 400°F and above, no major viscosity differences were observed. Furthermore, the changes in the melt viscosity were more pronounced at shear rates less than 200 sec−1. The usefulness of the measured viscosity variations at the critical test temperature of 350°F was shown by extrusion. An excellent correlation between the apparent melt viscosity and extrusion melt temperature was found. The criticalness of the test temperature in assessing the effect of lubricants on PVC flow is discussed.
Viscometric behavior of high‐density polyethylene solutions at high temperatures
Authors: Brockmeier N. F. , Westphal S. P.
Published: December 2004

The steady shear viscosities of high density polyethylene disolved in highly branched isoparaffin solvents have been measured with a high‐pressure autoclave viscometer at temperatures ranging from 150 to 250°C and over a range of shear rates from 0.02 to 170 sec−1. Laboratory measurements on solutions ranging from 15 to 67 wt percent polymer were used to develop and calibrate a mathematical model for solution viscosity intended for a range of from 10 to 100 wt percent polymer. The foundation for the model consists fo two equations: the modified Martin equation is used to describe the effect of concentration, and the Sabia equation is used to describe pseudoplastic behavior. The model correlates viscosities that can range over nine orders of magnitude with sufficient accuracy for most process design work, averaging less than 10 percent error. Both the data and the model indicate that at constant stress the activation energies (EA) for the effect of temperature on viscosity are higher for solutions in the midrange of composition than for either of the pure components. This peak in EA is related to the density difference between polymer and solvent.
Blade‐coating of a viscoelastic fluid
Authors: Greener Yehuda , Middleman Stanley
Published: December 2004

A theory is presented which describes the dynamics of blade‐coating of a viscoelstic fluid onto a moving sheet. The method begins with the usual “lubrication” approximation, and develops the solution as a perturbation about the Newtonian case. Viscoelasticity is described by an empirical constitutive equation which shows non‐Newtonian viscosity and finite normal stress behavior consistent with typical observations of polymeric fluids. Theoretical results indicate a small increase in coating thickness due to departure from Newtonian behavior, and a significant decrease in the magnitude of the pressure developed under the blade. Consequently, the blade loading can be reduced significantly by viscoelastic effects. The results for the loading may be an artifact of the specific constitutive model, since it can be shown that some viscoelastic fluids, specifically an “elastic Newtonian” fluid, would exhibit increased loading relative to the inelastic Newtonian case.
Packing and discharge in injection molding
Authors: Koita Y. T.
Published: December 2004

In a reciprocating‐screw injection‐molding machine, the screw or plunger forces the plastic into the mold. It remains in the forward position under pressure for a fixed time during which plastic flow into the mold or ‘packing’ takes place. After the timer runs out, the screw moves back while rotating thus releasing the pressure on the plastic in the mold. At this time, if the gate has not frozen, flow of plastic out of the mold or ‘discharge’ takes place. In this study, clear rigid PVC, poly (vinyl chloride), was molded with varying amounts of packing and discharge. Photoelastic stress patterns for parts observed between cross‐polaroids suggested that packing and discharge give rise to high frozen stresses due to molecular orientation in the gate area. Mechanical strength tests on the molded parts show that these high stresses are a source of weakness. Short forward times for the plunger significantly improve the mechanical properties of the parts in the gate area and at the same time have a significant influence on part dimensions, especially in the gate vicinity. Laminations observed at the gate interface can also be reduced by controlling the extent of molecular orientation introduced by packing and discharge.
A theory of roll coating of viscous and viscoelastic fluids
Authors: Greener Yehuda , Middleman Stanley
Published: December 2004

A theory for roll coating of a fluid onto a moving sheet is developed utilizing the usual “lubrication approximations.” The effects of fluid and operating parameters on coating thickness and pressure distribution are determined for a Newtonian fluid, and for a purely viscous non‐Newtonian fluid obeying the Power Law. The results for these cases are obtained analytically, and are rather straightforward.

A viscoelastic fluid is considered, of a type which shows typical non‐Newtonian shear behavior observed in polymer melts and solutions and which also exhibits normal stress behavior. Analytical solutions are not possible, but a perturbation method, using a viscoelastic perturbation parameter related to a Deborah number, yields an approximate solution. Only terms to first order in the perturbation parameter are given. Subject to that degree of approximation, the following conclusions are drawn:

Non‐Newtonian shear behavior reduces the pressure distribution, and increases the coating thickness.

Elasticity of the type usually observed in polymer solutions makes only a minor contribution to the roll‐separating (load‐carrying) force. The contribution is positive, but smaller than the corresponding negative contribution due to the non‐Newtonian shear effects.

An increase in load‐carrying capacity would require a different viscoelastic fluid than the type considered here—one that is essentially Newtonian in shear but, independently, capable of developing significant normal stresses.
Role of singlet oxygen in photo‐oxidative degradation and photostabilization of polymers
Authors: Rabek J. F. , R̊anby B.
Published: December 2004

Evidence is presented that singlet oxygen may have an important role in the photo‐oxidation of polymers. Increased attention is being paid to singlet oxygen as a possible reactive intermediate in the initiation step of the photodegradation of polymers. Singlet oxygen may be produced by energy transfer either from impurities or internal groups after excitation, e.g. carbonyl groups, which are present in commercial polymers. As a consequence, reactions of singlet oxygen may also be important in the stabilization of polymers, e.g. leading to search for new and more effective antioxidants.
Ultra‐high molecular weight high‐density polyethylene as a gear material
Authors: Yelle Henri , Poupard Maurice
Published: December 2004

Tests have been made for use of a high‐density polyethylene of ultra‐high molecular weight as a gear material. The gears had a diametral pitch of 10 and 30 teeth. They were tested in mesh with a steel gear of the same size in two operating conditions: (1) in still air without lubrication, and (2) in oil with generous lubrication.

The effects of speed, temperature, and initial lubrication on the load capacity of the gears were tested and an equation was developed to express the limits of these gears operating without lubrication. In the lubricated conditions, the influence of oil flow and its temperature on the gear teeth temperature were evaluated. The wear of the plastic gear was measured in both operating conditions and wear rate was calculated as a function of the load and gear life. Curves are presented suggesting design limits of the gears in the two operating conditions. There are also recommendations on the center distance setting and the backlash to use.
The flow behavior and impact strength of poly(butylene‐terephthalate) as a function of several processing variables
Authors: Van Der Wielen Michael P.
Published: December 2004

The flow behavior of poly (butylene‐terephthalate) (PBT) has been investigated using a capillary extrusion rheometer. The behavior was measured as a function of temperature, moisture content, and residence time of the molten polymer in the rheometer barrel. The temperature and moisture dependence of PBT are compared with polycarbonate. The notched Izod impact strength of injection‐molded PBT is also reported as a function of moisture content and residence time at processing temperatures.
The detection of structure in amorphous polymers by electron microscopy: Particle flow
Authors: Chapoy L. L. , Sørensen A.
Published: December 2004

During the last several years there has been considerable interest in the occurrence of structure in certain bulk polymers normally thought to be structurally homogeneous. Specifically, it has been proposed that polymers produced by emulsion polymerization may retain a particle structure in the bulk state. This has been demonstrated by both rheological measurements and by electron microscopy. In this work we show conclusively that at least part of the particle structure observed by electron microscopy for polystyrene is an intrinsic feature of the fracture surface and is in no way related to the history of the sample.
Characterization of advanced composite materials for structural design
Authors: Waddoups M. E.
Published: December 2004

Our preliminary characterization of advanced composite materials has been conducted simultaneously with the development of large‐scale primary and secondary aircraft structures. We have demonstrated significant advantages over metal structure on a one‐to‐one basis. Our efficiency levels gained to date demonstrate that we have extracted about fifty percent of the maximum potential advantage. Recovery of the remaining efficiency will result from understanding material characteristics and development of advanced design concepts. We will develop and demonstrate a summary format for viewing the structural response of monolithic metals and polymers and then document the observed responses of advanced composites within the format. Our data show that the addition of high‐modulus fibers into a polymeric matrix produces a physically distinct material with substantial advantage over unreinforced polymers. The unique properties of composite materials yield a significant advantage in physical properties and in design. Full advantage of material orientation has yet to be developed in a practical design but through examples we can illustrate the potential. We develop two examples: (1) stress concentration control through buffer stripping and (2) fracture control through buffer stripping. The impact of composite material characteristics as aircraft materials and design methods is also reviewed.
Sorption kinetics and equilibria in annealed glassy polyblends
Authors: Hopfenberg H. B. , Stannett V. T. , Folk G. M.
Published: December 2004

The sorption kinetics and equilibria of n‐hexane in glassy polyblends of polystyrene and poly(2,6 dimethyl‐1,4 phenylene oxide) were studied as a function of annealing conditions. Cast film samples were annealed 20°C above their respective glass transition temperatures for two hours and twenty‐four hours. The rate of relaxation‐controlled (Case II) sorption of n‐hexane in these films was reduced markedly consequent to annealing. The effect of annealing on the sorption kinetics and the independently determined film densities was more pronounced for the poly(phenylene oxide)‐rich samples. Although sorption rates were reduced by as much as a factor of 100, the sorption equilibrium was insignificantly affected by annealing. Super Case II transport was observed for the slow absorbing annealed samples whereas the more rapid sorption in the unannealed samples followed ideal Case II kinetics. The more pronounced effects of annealing for the poly(phenylene oxide)‐rich samples on sorption rates and film densities were explained by considering the increasing difference between the film Tg and the drying temperature used in the original film preparation for the poly(phenylene oxide)‐rich samples. These results suggest that glassy polymers, cast and dried well below their glass transition temperatures, will be subject to large long‐term reductions in absorption rates and specific volume. Moreover, residual, excess free volume significantly affects relaxation‐controlled absorption of vapors in partially annealed glassy polymers.
World‐wide weathering of poly(vinyl chloride)
Authors: Szabo Emery , Lally Robert E.
Published: December 2004

In order to determine the effect of outdoor aging in various areas of the world, poly(vinyl chloride), PVC, compositions were exposed at test sites in Australia, Canada, England, Germany, South Africa, and in Piscataway, New Jersey. These results are related to the climatological data from the different test sites. The data obtained show the effects of a three‐year period of exposure on clear and filled, flexible and rigid PVC compositions. The merits of various types of additives are shown in respect to the outdoor aging properties of PVC compounds. It was observed that the exposure conditions vary from severe for Australia and South Africa to mild for England. However, the general results obtained throughout the world correlate well with those from the exposure site in New Jersey.
Crazing in glassy polymers: Studies on polymer‐glass bead composites
Authors: Narkis M.
Published: December 2004

Stress‐strain curves of glass bead‐filled glassy polymers show a slope discontinuity related to crazing in the matrix. This discontinuity serves as basis for a simple method for determining εp′ the critical strain in the polymer to initiate crazing. The stress at the discontinuity (σD) is governed by the nature of the dispersed particles acting as stress concentrators. The two parameters, εp′ and σD, (neither of which is a function of the filler content) have the following values in ascending order σ = 1540, 1750, 1880, 2390 and 3300 psi for polystyrene, ABS, poly(vinyl chloride), SAN and poly(phenylene oxide) respectively; εp = 0.63, 0.72, 0.81, 1.10 and 1.67 percent for poly(vinyl chloride), polystyrene, SAN, ABS and poly(phenylene oxide) respectively. In coupled particulate systems, (σD) is increased and apparently vaies with the efficiency of the coupling agent. The modulus of a particulate system can be predicted by a one‐parameter equation.
An analysis of caprolactam polymerization
Authors: Tirrell M. V. , Pearson G. H. , Weiss R. A. , Laurence R. L.
Published: December 2004

A versatile model for ε‐caprolactam polymerization is presented. A deterministic, mathematical basis for obtaining the most probable distribution of molecular weights in batch polymerization is developed. Continuous polycaproamide production has been modeled and shown to give othe than most probable distribution in many cases. The effect of adding monofunctional agents has been investigated. Results of some preliminary studies toward determining the optimal reactor configuration are presented.