bluuebunny/crossref_metadata_2025 huggingface dataset:
Warm hydrostatic extrusion of polyethylene
Authors: Bigg D. M. , Smith E. G. , Epstein M. M. , Fiorentino R. J.
Published: December 2004

Hydrostatic extrusion of high density polyethylene at an extrusion ratio of 15:1 was investigated in the temperature range between 100 and 134°C. A thin‐walled tube was extruded having a tensile strength of 370 MPa and a tensile modulus of 10 GPa. The extrusion rate was limited by severe extrudate distortion which occurs at a limiting shear stress under stick‐slip conditions. Even during steady extrusion wall slip was evident. At a constant extrusion speed, the extrusion pressure was found to be very sensitive to the extrusion temperature. An increase from 120 to 125°C reduced the extrusion pressure by half. Various thermal pretreatments of the starting billets were found to have little effect on the extrusion behavior and physical properties of the extrudate.
Effects of some liquids on the creep behavior of high impact polystyrene
Authors: McCammond D. , Hoa V. S.
Published: December 2004

The effects of seventeen different fluids on polystyrene is investigated. The fluids are divided into three groups by their effect on the unstressed polymer, namely dissolving, softening, and non‐softening fluids. The accelerated rates of creep of the polymer when immersed in the dissolving fluids are shown to be due to the reduction in the load‐bearing area resulting from dissolution at the surface, The increase in creep strain rates (relative to that in air) when exposed to the softening fluids result from the combined effects of: (i) the accumulated deformation of numerous crazes; (ii) the reduction in stiffness of the surface layer due to the softening effect of the fluid; and (iii) the swelling of the softened layer. In the case of the non‐softening fluids, the creep rates “accelerated” after a specific delay time which is a function of the applied stress. For these fluids there exists a critical stress below which crazing does not occur. This critical stress is shown to increase with increasing difference between fluid and polymer solubility parameters.
Crazing of fibrous polymers
Authors: Carton A. , Carlsson D. J. , Stepaniak R. F. , Wiles D. M.
Published: December 2004

Highly oriented filaments of nylon 6 and polypropylene (PP) are shown to craze when deformed slowly at room temperature. A marked yield point occurs at 20‐40 percent elongation. After this point extensive voiding occurs until at fracture the overall density is reduced by ∽25 percent for PP and ∽15 percent for nylon 6. SAXS analysis indicates that for PP the voids are elongated in the fiber axis while for nylon 6 voiding occurs both parallel and perpendicular to the fiber axis. Optical and electron microscopy show typical craze structures. The use of etching demonstrates that crazing occurs across the whole filament cross section. This yielding behavior is shown to be associated with the use of a low temperature of drawing during fiber production and becomes less important when a higher temperature of drawing or a separate annealing step are used. The crazing mechanism is thought to involve progressive separation of interfibril boundaries with the production of elongated voids.
Elongational flow of polymer melts
Authors: Johnson Eric D. , Middleman Stanley
Published: December 2004

A new technique is described whereby the rate of collapse of an air bubble within a molten polymer may be measured without the need for visual observation. The method involves use of a high speed recording dilatometer, From such data it is possible to measure an apparent elongational viscosity of the melt, and such measurements are presented for two polyethylenes (Tennite, a low density PE, and Plaskon, a high density PE), Limitations of the methods are discussed. This is one of a series of papers (1‐3) documenting our development of a new experimental technique, and the corresponding mathematical modeling, whereby one may measure the elongational viscosity of polymeric viscoelastic fluids. Previous experimental work was confined to transparent fluids, since the technique depended on high‐speed motion picture photography of the collapse of an air bubble within the fluid. In this paper we describe an attempt, largely successful, to develop a new experimental system which permits the study of molten polymers, including opaque fluids. Sample results are presented for both a low and a high density polyethylene.
Prediction of rheological properties of well‐characterized branched polyethylenes from the distribution of molecular weight and long chain branches
Authors: Pedersen Sven , Ram Arie
Published: December 2004

An empirical model suggested earlier by B. H. Bersted predicting the rheological properties of linear polyethylene from the molecular weight distribution is modified to account for the rheological properties in steady shear flow of branched polyethylene as well. The shear dependent viscosity, the steady shear compliance, and extrudate swell could be calculated from the distributions of molecular weight and long‐chain branching in good agreement with experimental data for eight commercial low density polyethylenes. Tanner's equation was used to calculated die‐swell from the modified Bersted model. The steady shear compliance was found to be related to \documentclass{article}\pagestyle{empty}\begin{document}$(\overline {gM} )_z .(\overline {gM} )_{z + 1} /(\overline {gM} )_w^2 .$\end{document}.
A cooling time model for plastics processing operations
Authors: Dietz Wolfgang
Published: December 2004

The cooling of a crystallizing polymer is analyzed taking into account the effect of pressure drop on the energy balance. Thermal conductivity and diffusivity of a low density polyethylene are determined at pressures between 0.1 and 150 MPa (1 and 1500 bars). Using a pressure, volume, temperature‐diagram, a complete set of material functions could be obtained. A numerical cooling model based on these material functions was established and tested experimentally. Good agreement between the model and experiment was obtained. The numerical algorithm of the model can be adapted easily to plastics processing operations, e.g., injection molding, blow molding, and extrusion.
Heat transfer to molten polymers flowing through tubes
Authors: Hulatt M. , Wilkinson W. L.
Published: December 2004

A theoretical and experimental study of heat transfer to polymer melts flowing through circular tubes is presented. The mathematical model provides for shear heating and expansion cooling effects, and also heat of reaction during flow for various wall boundary conditions. Experimental results, obtained using low density polyethylene, show reproducible temperature and velocity profiles. The measured inlet melt temperature profile and the axial wall temperature profile provide the boundary conditions for the calculations. The experimental data confirm the predictions of the magnitude of the shear heating and expansion cooling effects during tube flow.
Swelling‐controlled, constant rate delivery systems
Authors: Hopfenberg H. B. , Hsu K. C.
Published: December 2004

Materials and conditions required for constant rate absorption of a liquid into a glassy polymer (Case II transport) have been exploited to produce prototype devices for constant rate delivery of a solute, molecularly dispersed within the polymer, to the surrounding liquid environment. Absorption of n‐hexane in polystyrene films, containing between one and two percent of Sudan Red IV dye, resulted in constant rate liberation of the colored solute to the surrounding fluid. The rate of dye release was controlled by the constant rate absorption of n‐hexane in these dye‐containing films. Companion experiments involving microtome sectioning and photomicrographic recording of dye‐loaded films, consequent to immersion in n‐hexane for various time intervals, revealed that the unpenetrated central core retained the dye originally dispersed within the film sample and, conversely, the swollen outer regions were completely denuded of dye consequent to n‐hexane penetration. The constant rate advance of the microscopically observable sharp boundary, between dye‐containing and dye‐denuded polymer, was quantitatively consistent with the independently determined kinetics of dye accumulation in the supernatant n‐hexane. These results indicate that diffusion of invading n‐hexane to the relaxing boundary and back diffusion of dye in the previously swollen outer shell are both rapid compared with the rate‐determining Case II transport of n‐hexane in these dye‐containing films. The delivery of Sudan Red IV to the n‐hexane was not confounded by an initial burst of solute, typically common to so‐called membrane‐reservoir controlled delivery devices. Swelling‐induced delivery from glassy matrices appears useful, therefore, for the design of monolithic devices for constant rate delivery over the entire course of the delivery cycle. The concept is not limited to monolithic devices; membrane‐reservoir devices could be constructed involving a glassy, solute‐containing reservoir which could be activated by penetration of invading liquid consequent to placement in a suitable fluid environment. Development of devices, suitable for swelling‐controlled release of drugs to target organs, will be based upon glassy, hydrophilic polymeric hosts.
Effects of the state of stress on the toughness of polycarbonate
Authors: Petrie S. P. , Dibenedetto A. T. , Miltz J.
Published: December 2004

It is shown that the mechanical properties of polycarbonate are controlled by the state of stress of the test specimen. Whereas the yield stress of the material is relatively insensitive to the state of stress, the tendency of the material to microcavitate is strongly dependent on the residual stresses in the surfaces of a test specimen. The effects of quenching, annealing, post notching, solvent swelling and rate of testing on the modulus of toughness are all related to the state of compression on the free surfaces. The mechanism of deformation is shown by cinematography to consist of the nucleation of a shear band followed by microcavitation along the propagating band. Maximum toughness is obtained by suppressing microcavitation so as to promote shear yielding. When microcavitation occurs, it is the competition between propagating the microcavitation throughout the material and the generation of microcracks in the advancing shear band that controls the ultimate elongation.
Aramid fiber‐reinforced ionomer
Authors: Alesi Anthony L. , Litman Alan M. , Mitchell Douglas F.
Published: December 2004

Chopped aramid fiber reinforced ionomer formulations were investigated as prototypes of military armor materials effective in providing protection against munition fragments. The dependence of ballistic impact resistance upon fiber openness was demonstrated by radiographs. Concentrations of 30 percent or less by volume of 1/4 and 1/2 in. fibers were injection moldable, However, the greater than optimum dispersion of fibers as a result of extrusion compounding or of the injection molding itself resulted in lower ballistic resistance and in usually lower tensile and flexural strength properties than were achieved by compression molding: Compression molding of suitably opened 1/4, 1/2 and 2 in. fibers produced rigid materials with fiber contents as high as 90 percent by volume. Ballistic impact resistance increased linearly with fiber content.
Fiber‐foam: A rheological phenomenon and a novel product
Authors: Cole E. A. , Cogswell F. N. , Huxtable J. , Turner S.
Published: December 2004

When certain molten thermoplastics containing glass fibers up to 20 mm in length are extruded through an orifice, the extrudate has a frothy texture and solidifies into an irregular open‐cell structure. The effect is apparently caused by the recovery of the fibers from distortions arising in the region of converging flow near the entry to the orifice. The effect is particularly pronounced in systems with melt viscosities between 50 and 500 Ns/m2. Polypropylene, as an example, containing weight fractions of about 0.25 of glass fibers can be extruded through a zero‐length die 2 mm in diameter to give “ropes” that can be readily formed into flat sheets or three‐dimensional shapes because of adhesion between the still molten polymer in the newly extruded rope. Such sheets can then be bonded to other materials to make a variety of laminates. A range of bonding techniques is available and the rough surface texture of the ropes provides a useful mechanical key for bonding with grossly dissimilar materials. Fiber‐foam is highly resistant to fracture and has a modulus in the range expected by a simple model for the foam.
Aspects of the yield behavior in poly(ethylene terephthalate) fibers
Authors: Sweet G. E. , Bell J. P.
Published: December 2004

The yield behavior during cold drawing of commercially spun poly(ethylene terephthalate) (PET) filament yarn was investigated. Microscopic examination revealed the presence of inherent flaws within the spun filaments; these act as points for localized stress concentration. These inhomogeneities appear to be either internal cracks or crazes developed during the fiber melt spinning process. During elongation, stress magnification at these flaws results in shear band formation, indicating the onset of inhomogeneous yielding. At the yield bend in the load‐elongation curve a circumferential crack propagates within these shear band regions. This yield crack develops into the classical neck geometry which further localizes additional plastic deformation within the sample at the neck.
The influence of structure on the failure of isotactic polypropylene films
Authors: Samuels Robert Joel
Published: December 2004

The failure behavior of uniaxially‐oriented isotactic polypropylene films has been examined over a wide range of rates and temperatures. Above the glass transition temperature the failure behavior is observed to be a direct function of the initial noncrystalline orientation state of the film. Below the glass transition temperature (−80°C, −196°C), both the crystalline and noncrystalline regions contribute to the failure.
Viscoelastic measurements of PVC plastisol during gelation and fusion
Authors: Nakajima N. , Ward D. W. , Collins E. A.
Published: December 2004

This work is concerned with the change of viscoelastic properties of poly(vinyl chloride) (PVC) plastisol during heating. The system changes from a suspension of solid particles in a liquid medium to a swollen gel and further to a fused state as the temperature is raised. The Rheometrics mechanical spectrometer was used in the oscillatory mode at 0.1 Hz. The temperature of the sample was raised in a controlled manner to 195°C. During gelation, the viscosity increased rapidly about three decades. There was a similar increase of the elastic modulus. After reaching a maximum, both viscosity and elastic modulus decreased rapidly with the progress of fusion. The viscoelastic properties depended somewhat on the heating rate. At 170‐195°C, it took a few minutes for the moduli to reach steady values. Continued heating, for several minutes at 195°C, did not change the moduli any further. The temperature range of the decomposition of a blowing agent in the plastisol foam formulation was determined. Over this temperature range, the viscoelastic properties change very rapidly. Quantitative estimates were made for the decrease of moduli during this period.
Thermal response of composite panels
Authors: Kourtides Demetrius A. , Gilwee William J. , Parker John A.
Published: December 2004

The thermochemical and flammability characteristics of laminating resins and composites currently in use and others being considered for use as aircraft interior panels are described. The properties studied included: (a) limiting oxygen index of the composite constituents; (b) fire containment capability of the composite; (c) smoke evolution from the composite; (d) thermogravimetric analysis; (e) composition of the volatile products of thermal degradation; and (f) relative toxicity of the volatile products of pyrolysis. The performance of hightemperature laminating resins such as modified phenolics, polyimides and bismaleimides is compared with the performance of epoxies. The relationship of increased fire safety with the use of polymers with high anaerobic char yield is shown. Processing parameters of the state‐of‐the‐art epoxy resin and the advanced resin composites are detailed.
Some corrosion mechanisms in attack of resin and resin‐glass laminates
Authors: Allen R. C.
Published: December 2004

In contrast to metallic corrosion where electrochemical corrosion mechanisms are dominant, a variety of mechanisms play a role in degradation of fiber reinforced plastic (FRP) structures. Attack may occur by physical or chemical means or by a combination of both. Although some actions of particular attacking species may be quite specific, there are a number of general corrosion mechanisms and broad guidelines that can be established in order to choose a resin suitable for a particular service. Corrosion mechanisms are illustrated by interactions of environments with vinyl ester resins. Attack in non‐aqueous media is often related to chemical similarity between attacking specie and the resin. Among chemically similar resins, the extent of this type of attack is often influenced by the crosslink density of the resin. It is shown that the solubility parameter of the attacking specie is useful in predicting suitability of a resin for service, if the resin has been evaluated by a test sequence in organic media of varying solubility parameters. In aqueous media it is found that physical attack can occur by means of an osmotic permeation of the resin by water. Degradation by pure water is often more severe than that caused by ionic solutions. Such physical attack can cause delamination and blistering of laminates and must be regarded as a potentially serious corrosive mechanism, although not primarily chemical in nature. In addition to physical attack, chemical attack can occur. Saponification by sodium hydroxide and oxidation by sodium hypochlorite are discussed in some detail as examples. It is shown that in both these cases the chemical corrosive process may be inhibited by controlling the physical corrosion process due to water.
The thermal expansion of reinforced nylon‐6 composites through the matrix glass transition temperature
Authors: Segal Leon
Published: December 2004

The coefficient of thermal expansion (CTE) of nylon‐6 reinforced with particulate filler, short glass fibers, and long‐to‐continuous glass fibers was measured between −30 and 170°C. As the reinforcement level, the reinforcement aspect ratio, or degree of orientation increases, the linear CTE decreases. The Tg range for the composite system is equal to the Tg for the pure nylon‐6 matrix. An unexpected result is observed when the nylon‐6 is reinforced with long or continuous glass fibers in random planar orientation and the weight fraction of reinforcement exceeds 10 percent. In this case, the longitudinal linear CTE (parallel to the plane of the fibers) above the Tg is lower than the longitudinal linear CTE below the Tg. Analysis of the mathematical descriptions of composite thermal behavior indicates that an extremely low composite modulus in the transverse direction above the Tg may be a cause for this low CTE. The differences in CTE between short fiber and long fiber reinforced compositions indicate that the critical fiber length for thermal stress transfer may be higher than the critical fiber length for mechanical stress transfer.
An ultrasonic‐acoustic technique for nondestructive evaluation of fiber composite quality
Authors: Vary Alex , Bowles Kenneth J.
Published: December 2004

This report describes an ultrasonic‐acoustic technique used to measure a “stress wave factor” in order to nondestructively assess the quality of composite structures. In a prior study this factor was found effective in evaluating the interlaminar shear strength of fiber‐reinforced composites. Details of the method used to measure the stress wave factor are described. In addition, frequency spectra of the stress waves are analyzed in order to indicate the nature of the wave phenomena involved. The stress wave factor can be measured with simple contact probes requiring only one‐side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus, in many cases, measure material properties in directions assumed by actual loads. Moreover, the technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite polyimide composite panels and results obtained are compared with through transmission immersion ultrasonic scans.
Flow of polymers with pressure‐dependent viscosity in injection molding dies
Authors: Lord Herbert A.
Published: December 2004

Considerable effort has been expended recently by a number of researchers to develop methods of simulating the flow of polymers in injection molding dies. The computer models developed by these researchers provide the mold designer with useful quantitative information concerning the predicted effect of design parameters on mold, filling characteristics. This paper will describe some recent work which is aimed at increasing the usefulness of these models by more accurately describing the flow behavior of those polymers, such as polycarbonate resins, which exhibit a strong effect of pressure on viscosity.
Review of forging, stamping, and other solid‐phase forming processes
Authors: Kulkarni K. M.
Published: December 2004

In the last ten years, a considerable amount of work has been conducted on many different processes distinct from common plastics processing methods such as injection molding, extrusion, and compression molding. Perhaps the most common feature of these new techniques is that they resemble more the methods used for fabricating metallic materials in solid phase. However, there is a lack of uniform terminology. More importantly, the commercial acceptance and applicability of these processes have been slow. This review attempts to summarize the important findings of various publications and, whenever possible, to give information about potential or actual industrial applications. The purpose is to provide a brief overview of the state‐of‐the‐art of the whole technology. Advantages, disadvantages, and the need for more work are pointed out as they relate to different processes and to crystalline and amorphous materials. A few instances where material was heated beyond the melting temperature by a small amount are included in the review when the processing method was similar to solid‐phase forming.
Time constants for moisture diffusion through a permeable barrier into an airspace
Authors: Pinnes Edward L.
Published: December 2004

This paper arose from a study of the use of polymeric materials to protect humidity‐sensitive items from damp ambient conditions. A one‐dimensional model for the Fickian diffusion of moisture through a permeable wall into a volume of air is considered. The humidity in the airspace asymptotically approaches equilibrium with the exterior, and the time constant is defined as the time to reach 1–1/e of its ultimate value. Exact and approximate solutions are considered. Depending on the system geometry and properties, the time constant is either permeability‐controlled or diffusivity‐controlled, or somewhere in between. Under certain conditions, there exists an optimum combination of airspace depth and wall thickness that maximizes the time constant.
Physiochemical quality assurance methods for composite matrix resins
Authors: May C. A. , Hadad D. K. , Browning C. E.
Published: December 2004

Fiber reinforced composite structures have gained a significant position as materials of construction for the aerospace industry. It thus follows that large expenditures of funds and human lives are dependent on the reliability of these products. An important step in gaining confidence in a part is knowing that the starting prepreg has the same chemical formulation in each lot of material and that each lot has been processed in the same manner. This can be accomplished by physiochemical characterization. The techniques described herein were developed for 177°C (350°F) epoxy matrix systems. However, the methods form a basis for developing similar procedures for other types of matrices.
Orientation in injection molded polystyrene
Authors: Kamal Musa R. , Tan Victor
Published: December 2004

The ultimate properties of injection‐molded thermoplastics articles are controlled to a large extent by flow and heat transfer phenomena that take place during the injection‐molding process. In fact, the thermo‐mechanical history of the melt during the molding process leads to a non‐uniform distribution of many of the critical properties of the molding. Birefringence has been employed as an indirect measure of the distribution of frozen stresses or strains in amorphous polymers. The present study employs birefringence to study the development of frozen stresses in injection‐molded polystyrene. In general, orientation in the flow direction is much greater than the orientation in the transverse direction of the moldings. In the vicinity, of the gate, where mold filling is characterized by spreading radial flow of the melt, the hoop stresses (planar deformation) at the melt front give rise to high orientation in the transverse direction. It appears that relaxation phenomena are not very important during the filling stage; however, they become more, important in the packing and pressure holding stages. With the aid of the appropriate rheo‐optical relationship, it is shown that the distribution of frozen‐in orientation in injection‐molded polystyrene may be estimated on the basis of data relating to pressure variations during the filling stage.
Poly(vinyl chloride), Part II: Effect of polymerization temperature and molecular weight on the glass transition and melting point of poly(vinyl chloride)
Authors: Daniels Charles A. , Collins Edward A.
Published: December 2004

A detailed study was made of the thermal behavior of poly(vinyl chloride) (PVC) homopolymers, whose chain length and structure were independently manipulated. Normal PVC polymerizations are made at temperatures, the selection of which determines the polymer chain length. In the case of PVC, this choice of temperature also determines its syndiotacticity, and so, its glass transition temperature, and in many ways, its processibility. The ability to understand how to control chain structure and length in PVC is critical in designing polymers for selected specific end use conditions. The thermal spectrum is known to be one measure of how polymers will perform. This study reveals how such controlled chain length/structure PVCs are characterized by thermal methods, and how one can separate individually the effects of syndiotacticity and molecular weight on thermal properties of poly(vinyl chloride).
An experimental study of the influence of carbon black on the rheological properties of a polystyrene melt
Authors: Lobe Vincent M. , White James L.
Published: December 2004

A broad range of experiments on carbon black filled polystyrene melts shows the reinforcing effect of the filler. This study represents one of the most extensive investigations of a series of highly filled polymer melts. Stress relaxation and dynamic experiments characterize the small strain behavior while the steady state shear viscosity, normal stresses, and elongational flow experiments describe the large strain deformation rate response. Extrudate swell and unconstrained shrinkage of extrudates are also measured. Highly filled systems exhibit yield values. This is seen in the dynamic experiments and in the shear and elongational viscosities. Viscosity does not level off at finite values with decreasing deformation rate but continues to increase in an approximately inverse manner. This corresponds to yield values of order 5 × 105 dynes/cm2. The storage modulus also does not tend to zero at low frequencies. The small strain dynamic properties and stress relaxation results suggest high memories for small strain experiments. Txtrudate swell values are however small and the systems exhibit minimal delayed recovery. The implications of this are considered. Generally it is argued that at volume loadings between 10 and 20 percent, the system takes on the characteristics of a gel and the response is similar to that of a Schwedoff body.
The torsion pendulum in the investigation of polymer
Authors: Heijboer J.
Published: December 2004

The early history of the use of the torsion pendulum in the investigation of polymers is described together with the development of dynamic mechanical testing at TNO. Examples are listed of studies of structure‐property relationships by means of the torsion pendulum. Techniques using supported. Samples are compared with those using unsupported samples, particular attention being paid to the advantages and restrictions of torsional braid analysis (TBA). The comprehensive application of TBA by Professor Gillham is reviewed; a few TBA results are compared with our torsion pendulum measurements. A rheologist's view on the so‐called liquid‐liquid transition (Tn) in polymer melts, as observed by TBA, is presented.
Effect of cure history on dynamic mechanical properties of an epoxy resin
Authors: Lewis A. F. , Doyle M. J. , Gillham J. K.
Published: December 2004

The effect of cure history on the dynamic thermomechanical properties of a high temperature curing epoxy resin has been studied using torsional braid analysis. In isothermal cures “full cure” is not possible except at temperatures above the maximum glass transition temperature (Tg) of the cured resin, hence the necessity of a “post‐cure” after lower temperature isothermal cures. The highest Tg and maximum cross‐linking in the cured resin was for a linear heating rate of 0.05°C/min from 30 to 200°C; higher heating rates lead to lower glass transition temperatures.
Interaction of water with macromolecules by dynamic mechanical analysis
Authors: Hiltner Anne
Published: December 2004

The dynamic mechanical relaxation of macromolecules is found to be very sensitive to the presence of water which is strongly associated with the macromolecule. Polymers with the amide group exhibit a characteristic loss process (β or β2) in the region of 200K which is associated with the amide‐water complex. Changes in the relaxation parameters with water content permit the stoichiometry of the interaction to be determined. Polymers with ionic groups on the side chain exhibit a higher temperature relaxation (β1) associated with side chain motion. This relaxation is also affected by the presence of water. Analysis of the effect of water on the loss parameters of the β2 and β1 processes has provided insight into the nature of the interaction of water with complex biological macromolecules.
Contributions of torsional braid analysis to Tu
Authors: Boyer Raymond F.
Published: December 2004

The accomplishments of Borden Award Winner John K. Gillham and his colleagues using Torsional Braid Analysis (TBA) and Differential Scanning Calorimetry (DSC) to investigate the Tg and T > Tg or Tu regions of anionic and thermal poly styrenes (PS) are evaluated and related to work on PS and other polymers and to controversies surrounding TBA and the Tu transition. Arguments are presented to refute the contention that Tu by TBA is an artifact produced by the braid and the contention that Tu has a relaxational nature but no thermodynamic basis. Two distinct behavior patterns are found for Tu vs log M̄n plots: quasi‐static methods such as DSC on fused films show Tu to level off above Mc and approach an asymptotic value of ∼435K; dynamic methods involving melt flow show that Tu increases without limit above Mc because of entanglements. A compilation is presented of 25 investigations of Tu on polybutadiene, poly(methyl methacrylate) (PMMA), PS, plasticized PS, and atactic polypropylene, involving twenty experimental techniques. The behavior of zero shear melt viscosity for PS is summarized. Gillham's work has not only led to clarification of many isolated papers in the literature but has also inspired various parallel experimental and literature studies on Tu. We conclude that Tu is a molecular level transition which, like Tg, exhibits both kinetic (relaxational) and thermodynamic aspects. It is shown that heat capacity should be a more sensitive method than dilatometry for studying the Tu transition.
Fourier transform infrared spectroscopic study of transitions above Tg in atactic polystyrene
Authors: Enns John B. , Boyer R. F. , Ishida Hatsuo , Koenig J. L.
Published: December 2004

Fourier transform infrared spectroscopy (FT‐IR) has been applied to the study of the molecular mechanisms of transitions of atactic polystyrene above Tg. Intensity measurements of vibrational modes as a function of temperature revealed two transitions above Tg, which are designated as Tu and T′u. T′u is independent of molecular weight as opposed to the molecular weight dependent Tu whose behavior is similar to Tg. Infrared measurements are more sensitive to T′u than Tu. Conformationally sensitive bands show that T′u may be related to disruption of local order where there is a negligible barrier to conformational change.
The influence of drawing, twisting, heat setting and untwisting on the structure and mechanical properties of melt spun polypropylene filament
Authors: Kitao Toshio , Spruiell Joseph E. , White James L.
Published: December 2004

The changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was noted.
Some performance aspects of the extruder as a reactor
Authors: Siadat B. , Malone M. , Middleman S.
Published: December 2004

Continuous flow reactors are increasingly utilized for polymerization. Two aspects of reactor performance are considered here, with major emphasis on the screw extruder as a reactor. First, the effect of residence time distribution is discussed, and comparative calculations are made for several flow reactors using a simple model for a polycondensation reaction. We conclude that the extruder behaves nearly as a plug flow reactor. Second, the effect of viscous heating in the extruder is accounted for, in the limiting case of adiabatic operation. A model for the effect of heating on conversion is developed, and some implications for scale‐up are noted.
Simultaneous interpenetrating networks based on castor oil elastorners and polystyrene. IV. Stress‐strain and impact loading behavior
Authors: Devia N. , Manson J. A. , Sperling L. H. , Conde A.
Published: December 2004

The stress‐strain and impact loading behavior of simultaneous interpenetrating networks (SIN's) based on three elastomers derived from polymerized castor oil and polystyrene was studied. The elastomers included the sebacic acid polyester, the 2,4‐tolylene diisocyanate (TDI) polyurethane, and the mixed sebacic acid‐TDI poly(ester‐urethane). Both toughened plastic and reinforced elastomer compositions were prepared. Stress‐strain measurements and Izod impact studies were carried out at room temperature. Both the plastic and the elastomeric SIN's proved tougher than their corrresponding homopolymer networks. Elongations to break of about 8 to 16 percent were found for the plastics, while the elastomers ranged from 55 to 125 percent. The castor oil polyester elastomer toughened plastic yielded the greatest improvement in impact resistance, having a value of 68 J/m.
Sintering behavior of poly(methyl methacrylate) particles
Authors: Narkis M.
Published: December 2004

The sintering behavior of poly(methyl methacrylate) (PMMA) particles was studied by photographic, means and mechanical testing. Interpretation of the data gives the sequence of events taking place during high temperature sintering (without pre‐compaction). Optical observations, show essentially two main sintering regions while mechanical studies also give an intermediate transition zone separating these two regions. It is suggested that the flow mechanisms involved in the sintering process are viscoelastfc flow in the lower temperature range and shorter times and non‐Newtonian viscous flow in the higher temperature range and longer times.
Wall thickness distribution in thermoforming
Authors: Rosenzweig N. , Narkis M. , Tadmor Z.
Published: December 2004

This paper presents an isothermal, one‐dimensional model predicting wall‐thickness profiles of vacuum‐ or pressure‐formed products. After formulating a set of simplifying assumptions theoretical analyses of forming into conical and truncated (deep and shallow) molds are presented and discussed. Fair agreement is found between previously reported experimental results and the proposed theoretical models.
Grüneisen functions of semicrystalline polymers
Authors: Shen Mitchel
Published: December 2004

The current, and rather incomplete, understanding of the role of amorphous contribution to the Grüneisen functions of semicrystalline polymers is reviewed. There are two kinds of Grüneisen functions. The microscopic mode Grüneisenr parameter is a measure of the volume dependence of lattice frequencies in a solid. Their magnitudes vary with the specific mode. The macroscopic Grüneisen constant relates the mechanical and thermal parameters in solids. It is a weighted average of mode Grüneisen parameters. At a given temperature there is only one Grüneisen constant for a material. Because the various experimental techniques often favor certain lattice modes, there is a great variation in the literature values of Grüneisen functions for polymeric solids., For semicrystalline polymers, the degree of crystallinity and thermal history also affect the measured magnitudes. In this work a unified derivation of the existing equations will be given. Current theoretical models for the Grüneisen constants are described. The available literature data on Grüneisen constants of semicrystalline polymers, principally polyethylene, will be discussed.
Interpretation of the dynamic mechanical response of heterogeneous polymer blends in terms of continuum models
Authors: Dickie R. A.
Published: December 2004

Dynamic mechanical measurements have been widely used for characterization of polymer blends and composites. This paper discusses application of continuum models to interpretation of the dynamic mechanical response of isotropic microscopically heterogeneous polymer blends. The models typically predict shifts in apparent glass transition temperature (location of principal loss tangent maximum) for each blend constituent. Experimentally observed shifts in the apparent glass transition of heterogeneous blend constituents may thus arise at least partly for mechanical reasons rather than because of changes in the properties or glass transition temperature of the blend constituents. It is suggested that, for heterogeneous blends of well characterized phase morphology, changes in glass transition behavior of blend constituents be determined by comparison of measured and calculated loss tangent maxima. For two‐component blends, the loss tangent at the temperature at which the loss tangents of the blend constituents are equal may be useful as a further diagnostic tool for changes in loss mechanisius.
Non‐isothermal phenomena in polymer engineering and science: A review. Part II: Non‐isothermal phenomena in polymer deformation
Authors: Stolin A. M. , Merzhanov A. G. , Malkin A. Ya.
Published: December 2004

Thermal phenomena in deformation of solids and flows are reviewed. Regularities common to all these phenomena as well as their characteristic features and consequences important for science and engineering are reported. The analogy between thermal phenomena in polymer mechanics and in chemical reaction is noted.
Towards an understanding of the heat distortion temperature of thermoplastics
Authors: Takemori Michael T.
Published: December 2004

A systematic understanding of the heat distortion temperature (HDT) of amorphous and semi‐crystalline polymers is possible through a direct correlation with the modulustemperature behavior. For amorphous polymers, the precipitous drop in modulus at the glass transition temperature makes the HDT a well‐defined, reproducible and predictable property. Furthermore, the addition of reinforcing fillers has a negligible effect on the HDT of the amorphous polymer. For semi‐crystalline polymers, however, the exact opposite may hold true. The modulus exhibits a “plateau” region between the glass transition and the melting transition. Hence the HDT often is difficult to predict, is sensitive to thermal history and may be greatly increased through the addition of fillers. More importantly, the HDT may not be an accurate measure of the upper use temperature for semi‐crystalline polymers in load bearing situations since considerable stiffness may still be retained even upon exceeding the HDT.
Thermal transition behavior of polybutadiene containing polyurethanes
Authors: Schneider N. S. , Matton R. W.
Published: December 2004

The thermal transition behavior of a series of hydroxy terminated polybutadiene (HTPBD) containing segmented polyurethanes has been studied by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). Four transition regions are observed; the soft segment Tg, at −74°C, two hard segment transitions T1, at 40°C and T2 at 103°C and a softening region by TMA at 180°C, presumed to arise from the dissociation of allophonate bonding, The low Tg, only 7°C higher than the Tg of free HTPBD, indicates nearly complete phase segregation despite the amorphous nature of the hard segment structure. The dependence of T1, on hard segment length and thermal cycling suggests that it represents domains consisting primarily of shorter hard segments units. Factors contributing to the rather low mechanical properties of HTPBD polyurethanes are also discussed.
Mechanical, thermal, and electrical properties of metal fiber‐filled polymer composites
Authors: Bigg Donald M.
Published: December 2004

The critical concentration at which a metal‐filled composite becomes electrically conductive can be dramatically reduced by adding the metal as randomly dispersed fibers. The higher the aspect ratio of the fibers, the lower the concentration needed to induce electrical conductance. Composites exhibiting resistivities below 20 ohm‐cm have been produced with less than 8 volume percent aluminum fibers, having an aspect ratio of 24:1. At low fiber loadings the tensile strength of the composites is similar to that of the unfilled polymer. The thermal properties of these composites are shown to increase monotonically in accordance with the theoretical development of Nielsen.
Studies on wire coating extrusion. II. The rheology of wire coating coextrusion
Authors: Han Chang Dae , Rao D. A.
Published: December 2004

An experimental and theoretical study of wire coating coextrusion through a pressure‐type die was carried out. For the experimental study, the wire coating apparatus employed was the same as that described in Part I of this series (14), except for the newly constructed coextrusion die. The die was provided with three melt pressure transducers along the axial direction, which permitted us to determine the pressure gradient in the die. It was found that a reduction in pressure gradient was realized when a lower viscosity polymer was coextruded with a high viscosity polymer. The materials used for the coextrusion were combinations of low‐density polyethylene, high‐density polyethylene, polystyrene, and two different commercially available thermoplastic rubbers (UniRoyal TPR‐1900 and Shell Kraton G 2701). The use of a high shrinking (crystalline) polymer inside a low shrinking (amorphous) polymer was found to give rise to distorted coatings (non‐circular cross section of the coated wire). The interface between the coextruded layers was examined under a magnifying lens, and it was found that under certain processing conditions, the interface was highly irregular. Experimental correlations were obtained to explain the onset of an unstable interface in terms of the rheological properties of the individual components being coextruded, and of the processing variables. It was found that interfacial instability occurs when the shear stress and the viscosity ratio (also elasticity ratio) of the two components at the interface exceed certain critical values. For the theoretical study, using a power‐law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymers being coextruded. Solution of the system of equations permitted us to predict the velocity profile and shear stress distributions of two molten polymers inside a pressure‐type wire coating coextrusion die. Comparisons were made between the experimental and theoretically predicted volumetric flow rates. The comparison was found to be reasonably good with certain systems. The discrepancy between the experimentally obtained and the theoretically predicted volumetric flow rates was attributed to interface migration and interfacial instability.
Characterization and continuous extrusion of isotropic and anisotropic poly(p‐phenylene terephthalamide)/sulfuric acid solutions to form ribbons and blown film
Authors: Aoki Hiroshi , Onogi Yoshihiko , White James L. , Fellers John F.
Published: December 2004

An experimental characterization and processing study of redissolved Kevlar® and poly(p‐phenylene terephthalamide)/sulfuric acid solutions is reported. Polarized light microscopy studies show the development of an anisotropic phase. When two phases coexist, negatively birefringent spherulites are observed. At higher concentrations, a single phase of coalescing spherulites is seen and following melting and subsequent cooling, nematic (threadlike) structures are observed. Viscosity and normal stresses were measured at various concentrations and temperatures. A yield stress is exhibited at room temperature. Both room temperature and 60°C viscosity vs concentration curves display maxima. The solution in concentration ranges from 2 to 12 percent have been extruded as ribbons and as annular blown tubular film. Processing variables and problems are discussed. Wide angle X‐ray scattering patterns of films show orientation. Tensile properties have been measured on films.