bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue failure mechanisms in polymers
Authors: Dao Kim C. , Dicken Dennis J.
Published: December 2004

Fatigue testing of polymers has revealed significant differences between the fatigue response of polymers and metals. Generally, fatigue failure in metals is a process of crack initiation, propagation, and failure. Also, fatigue damage in metals is cumulative and cycle dependent, but remains essentially independent of test frequency. Unlike that of metals, the fatigue behavior of polymers is influenced by viscoelastic effects. At high frequencies, softening and melting occur, and fatigue failure depends largely on the test frequency. At lower frequencies, fatigue failure becomes less sensitive to test frequency and results from crack initiation and propagation. These polymer characteristics arise from the production of hysteresis energy during fatigue. A portion of this energy is released as heat, some of which is dissipated, but most is absorbed in the sample, raising its temperature. This temperature rise leads to degradation of the material and a short fatigue life. Experiments were conducted to measure hysteresis energy and temperature rise for a talc‐filled polypropylene. A mathematical model was developed to calculate the energy and temperature distribution during fatigue. Correlation of the temperature rise predicted by the model with that observed experimentally provided values for the various energy terms that quantitatively defined the thermomechanical fatigue response of this polymer.
A rheometer for concentrated polymer solutions containing volatile solvents
Authors: Richards W. D. , Prud'Homme Robert K.
Published: December 2004

A new rheometer cell and integrated transducer, which is capable of performing both steady state and dynamic measurements in a controlled environment and at elevated temperatures and pressures, is described here. This cell mounts onto either the Rheometrics Mechanical Spectrometer or the Rheometrics System Four rheometer and utilizes the wide range of shear rates and frequencies available on these instruments. The unique capabilities of the rheometer and cell permit measurement of the rheological properties of concentrated polymer, solutions containing volatile solvents at temperatures above the normal boiling point of the solvent. The steady shear and dynamic properties of several polystyrene/ethylbenzene solutions having polymer concentrations greater than 50 wt percent are presented to demonstrate the performance of the rheometer.
In situ composites: Blends of isotropic polymers and thermotropic liquid crystalline polymers
Authors: Kiss Gabor
Published: December 2004

Melt blending of a variety of conventional isotropic polymers (both crystalline and amorphous) has shown that considerable reinforcement is obtained from the inclusion of thermotropic liquid crystalline polymers (LCP). When the LCP is a minor component it forms highly elongated domains parallel to the flow direction. The intrinsically high strength and stiffness of the LCP improve the mechanical properties of the resulting blend. This approach is distinguished from the common practice of filling polymers with chopped glass and carbon fibers by the fact that the reinforcing component comes into existence during processing (molding or extrusion). Many of the problems associated with fibrous fillers are avoided. For example, viscosity of the “in situ composite” is actually lower than that of the base polymer and wear on the compounding and processing equipment is reduced.
On the deformation of poly(methyl methacrylate) poly(ethylene oxide) blends: A molecular characterization by small‐angle neutron scattering
Authors: Lefebvre J‐M. R. , Porter Roger S. , Wignall G. D.
Published: December 2004

The deformation behavior of miscible amorphous/amorphous PMMA/PEO poly(methyl methacrylate)/poly(ethylene oxide) blends was compared with that of pure PMMA. Small‐angle neutron scattering experiments were performed on labeled systems made of PEO + D‐PMMA + HPMMA. Characteristic molecular parameters such as radius of gyration, Rg, molecular weight, Mw, and interaction parameter, X, were extracted from the coherent scattering cross sections, Molecular anisotropy was measured on the solid state coextruded samples, and the observed drawing efficiency is compared with, the results of shrinkage tests. In the case of PMMA/PEO blends, anomalous scattering behavior precludes any quantitative Interpretation of the scattering patterns, but revealed important structural changes upon drawing, namely a deformation‐induced phase separation.
The nucleation of microcellular thermoplastic foam with additives: Part I: Theoretical considerations
Authors: Colton J. S. , Suh N. P.
Published: December 2004

Microcellular foam is a polymeric foam with bubble sizes of 10 microns or less that is produced by saturating a polymer with gas and then utilizing the thermodynamic instabilities that result when the polymer is heated and the pressure is reduced to nucleate the cells. A model for the nucleation of microcellular foam in amorphous polymers with additives has been developed. The nucleation process depends on the solubility, concentration, and interfacial energy of any additives present. At very low levels, additives in solution act to increase the free volume of the polymer, resulting in homogeneous nucleation within the free volume Well above the solubility limit, heterogeneous nucleation dominates, as it lowers the activation energy for nucleation to levels below that for homogeneous nucleation. In the vicinity of the solubility limit of the additive, these two nucleation mechanisms compete. The polystyrene‐zinc stearate system has been chosen for experimental evaluation.
Nucleation of microcellular foam: Theory and practice
Authors: Colton Jonathan S. , Suh Nam P.
Published: December 2004

Microcellular polymer foams exhibit greatly improved mechanical properties as compared to standard foams due to the formers' small bubble size. Microcellular foams have bubbles with diameters on the order of 10 microns, volume reductions of 30 to 40 percent, and six or seven times the impact strength of solid parts. They are produced through the use of thermodynamic instabilities without the use of foaming agents. This method leads to a very uniform cell size throughout a part's cross section. A theoretical model for the nucleation of microcellular foams in thermoplastic polymers has been developed and experimentally confirmed. This model explains the effect of various additives and processing conditions on the number of bubbles nucleated. At levels of secondary constituents below their solubility limits, an increase in the concentration of the additive or the concentration of gas in solution with the polymer increases the number of bubbles nucleated. Nucleation in this region is homogeneous. Above the solubility limit of additives, nucleation is heterogeneous and takes place at the interface between second phase inclusions and the polymer. The number of bubbles nucleated is dependent on the concentration of heterogeneous nucleation sites and their relative effect on the activation energy barrier to nucleation. In the vicinity of the solubility limit, the two mechanisms compete.
Ionic impurities in water contained in plastic and pyrex bottles
Authors: Crine Jean‐Pierre
Published: December 2004

It is shown that most of the impurities in plastic bottles are not extracted by the water contained In these bottles. However, in the presence of water ions can easily be generated at 22 and 75°C in polyethylene, polypropylene, Teflon‐FEP, and Pyrex bottles. Surprisingly, relatively large amounts of fluoride ions are extracted from Teflon‐FEP bottles which contain very few contaminants. These ions greatly affect the electrical conductivity of the water which is linearly related to the ionic content. The plastic bottles containing the lowest ionic contents are those made in polypropylene and polyethylene. Sodium ions are also measured in the water contained in Pyrex bottles. It is also shown that acid rinsing of plastic containers is not a recommended cleaning technique.
Diffuse shear banded zones of blends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: McCarthy Stephen P. , Rogers C. E.
Published: December 2004

The formation, mechanical properties, thermal characteristics, and density of diffuse shear banded zones of polystyrene, poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO), and their miscible blends were studied. A significant increase in density of 0.2 to 0.3 percent was found for the diffuse shear banded zones. Differential scanning calorimetry results revealed a volume recovery process that occurs below Tg for the diffuse shear banded zones. The post‐yield‐stress drop, anelastic shear strain within the zone, and anelastic tensile strain were all found to decrease with increasing PPO content in an identical manner. The sharp shear band to diffuse shear banded zone transition was related to chain mobility, molecular packing, and free energy as manifested in the post‐yield‐stress drop. The decrease in anelastic shear strain with increasing PPO content for the blends is possibly related to the beta transition and length between entanglements.
The morphology and rheology of polymer blends containing a liquid crystalline copolyester
Authors: Blizard Kent G. , Baird Donald G.
Published: December 2004

The morphology of blends of polycarbonate and nylon 6,6 with a copolyester of 60 mole percent p‐hydroxybenzoic acid/40 mole percent poly(ethylene terephthalate) was characterized under different processing conditions. In particular, single‐screw extrusion, steady simple shear flow, and flow through a capillary were studied to determine what conditions were necessary for the development of a fibrillar morphology of the liquid crystalline polymer (LCP). Results indicate that some extensional flow is required for the coalescence and extension of the particulate LCP phase. The viscosity of the blends was determined both in a cone‐and‐plate geometry of a Rheometrics Mechanical Spectrometer at low shear rates and in the Instron Capillary Rheometer at higher rates. In general, only a small (10 or 30 percent) weight fraction of LCP was required to reduce the viscosity of the thermoplastics to that of the polymeric liquid crystal. An attempt was made to correlate the structure of the blends seen under the scanning electron microscope with the observed rheology. Not all aspects of the morphology were possible to explain in terms of the viscous properties of the blends.
Novel reinforced polymers based on blends of polystyrene and a thermotropic liquid crystalline polymer
Authors: Weiss R. A. , Huh Wansoo , Nicolais L.
Published: December 2004

A thermotropic liquid crystalline polymer (LCP), when added to polystyrene (PS), can function as both a processing aid and a reinforcing filler. Thermal, rheological, and mechanical properties of the pure components and blends containing up to 10 percent LCP are reported. The LCP used is immiscible with PS, and when an extensional component of flow is present during processing, the LCP forms an elongated fibrous phase oriented in the flow direction. This oriented phase lubricates the melt, substantially lowering the viscosity. When the processed blend is cooled, the dispersed fibrous LCP phase is preserved in the solidified material. The LCP microfibers behave like short reinforcing fibers to improve the mechanical properties of the blend; for example, at an LCP concentration of 4.5 percent, the modulus is increased about 40 percent vs. pure PS.
The essential work of plane stress ductile fracture of linear polyethylenes
Authors: Mai Y.‐W. , Cotterell B. , Horlyck R. , Vigna G.
Published: December 2004

The specific essential works of plane stress ductile tearing of several high‐ and ultrahigh‐molecular‐weight polyethylenes were obtained from deeply edge‐notched tension specimens, with either single or double notches, by extrapolating the straight line relationship between the total specific fracture work and ligament length to zero ligament. Provided the fracture morphologies of the torn ligament are not widely different, the specific essential work (we) is a material property dependent on thickness but independent of specimen geometry. The specific essential fracture work also can be identified with Jc the critical value of the J‐integral along a contour immediately bordering the fracture process zone at the crack tip. There is good agreement between the experimental we values and theoretical Jc estimates for these polyethylene materials.
Surface modifications of polymers with fluorine‐containing plasmas: Deposition versus replacement reactions
Authors: Loh I. H. , Klausner M. , Baddour R. F. , Cohen R. E.
Published: December 2004

Surfaces of polyethylene; poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), cellulose acetate butyrate, and polyoxymethylene were modified in various cold plasma reactions; feed gases to the plasma reactor were trifluoromethane, hexafluoroethane, and tetrafluoromethane. Using X‐ray photoelectron spectroscopy (ESCA) to characterize the surfaces, it was established that the plasma reactions lead to fluorinated surfaces containing CF3, CF2, and CF groups, All of these fluorinated surfaces exhibit advancing contact angles (with water) larger than 900. However, differences in the ESCA spectra, weight‐gain/‐loss measurements and scanning‐electron‐microscopy (SEM) photographs reveal that the mechanisms of fluorination in the various plasma environments are markedly different. The CF3H gas polymerizes in the gas phase of the plasma and deposits a smooth, fluorinated film on polymers and other substrates. The C2F6 plasma simultaneously etches polymers and polymerizes onto polymer surfaces. The CF4 plasma etches and reacts with the polymer surface but does not polymerize. For polyoxymethylene, the combined roughening (by etching) and fluorination of the surfaces lead to completely non‐wettable surfaces (water contact angle approximately 180°). The highly non‐wettable surfaces of these two polymers are believed to result from the physical etching and roughening at a very fine scale (approximately five micrometers) while the outermost surfaces are reacting to become highly fluorinated.
Thermal diffusivity in polymers oriented uniaxially in the solid and in the molten state
Authors: Sterzyński Tomasz , Linster Jean‐Jacques
Published: December 2004

Measurements of thermal diffusivity were carried out with semicrystalline and amorphous polymers stretched in the solid and in the molten state to different elongations. For semi‐crystalline materials two regions in the curves of the diffusivity versus the elongation can be detected. The change occurs at an elongation of 1.4 for the polymers stretched in the solid state and at an elongation of 3 for the polymers stretched in the molten state. For amorphous polystyrene the shape of the curves of thermal diffusivity versus elongation also depends on the mode of stretching. Along with thermal diffusivity measurements, wide angle X‐ray scattering investigations were also performed and give explanations for the differences in thermal behavior.
A technique for determination of stress fields in the contact loading of highly deformable polymeric materials
Authors: Reddy Narender P. , Kesavan Sunil K. , Van B. Cochran George , Brunski John B.
Published: December 2004

Soft, deformable padding materials are widely used for the fabrication of cushions and pads used to reduce contact loading stresses in several industrial and biomedical applications. This paper, presents an indentation technique that can be used to evaluate cushioning materials. The technique uses a soft‐headed indenter made of poly(vinyl chloride) gel that is impressed upon the polymer cushion to be tested. The strain fields and the high stress regimes that develop in the head are then mapped using a grid technique and finite strain theory. Results of indentation tests carried out on a number of cushions of varying stiffness are presented and analyzed.
Scale‐up of single screw extruders
Authors: Rauwendaal Chris
Published: December 2004

Scale‐up from small laboratory size extruders to large production size extruders is a procedure of great practical importance. Many scale‐up rules and theories have been proposed in the past, however it is not always clear how the different scale‐up methods will affect extruder performance. A basic analysis of scale‐up in plasticating single screw extruders is developed from which the effect of a certain scale‐up strategy on extrusion performance can be evaluated in terms of solids conveying, melting, melt conveying, mixing, residence time, heat transfer, power consumption, and specific energy consumption. Various existing scale‐up theories are evaluated and compared using the basic analysis. A number of existing scale‐up theories have some significant drawbacks, in particular with non‐constant specific energy consumption and imbalance between melting rate and pumping rate. Conditions that are desirable to achieve in scale‐up are enumerated and ranked in terms of importance. This leads to two new scale‐up methods that result in constant mechanical specific energy consumption and high throughput rates. The first scale‐up method keeps the specific surface area constant. This scale‐up should work well for high values of the Brinkman number. However, at low values of the Brinkman number, the melting rate may be insufficient. The second scale‐up method keeps the melting rate at low Brinkman number equal to the pumping rate and, thus, should be useful in cases where the first scale‐up method cannot be used.
Residual stresses in injection‐molded amorphous polymers
Authors: Siegmann A. , Kenig S. , Buchman A.
Published: December 2004

Nonisothermal flow of a polymer melt into a cold cavity and its rapid cooling give rise to the buildup of flow and thermal stresses in the molded article. In the present investigation the resultant residual stresses (RS) induced by these two sources were studied in two stages. First, the flow‐induced stresses were relaxed by proper heat treatment followed by quenching, resulting in only thermal stresses. The experimentally determined RS profiles in polysulfone and amorphous polyamide showed a parabolic shape and were correlated with the initial and final quenching temperatures, the glass transition temperature, and Biot Number. In the second stage, the combined effect of thermal‐ and flow‐induced stresses was studied using injection‐molded specimens prepared under a wide speptrum of molding conditions including melt and mold temperatures and injection rate and pressure. Results here indicated that the basic thermal‐induced parabolic RS profiles are altered by the flow‐induced stresses resulting in complicated profiles including local maxima and unbalanced RS. Finally, the tensile mechanical properties obatained for plaques molded under the various injection‐molding conditions were studied and correlated in part with the previously determined RS profiles. Results have shown that a property gradient exists as a function of distance from both the gate and surface of the molded plaque.
Structure‐property relationships in blends of linear low‐ and conventional low‐density polyethylene as blown films
Authors: Siegmann A. , Nir Y.
Published: December 2004

Three‐layer coextruded blown (either blend or composite) films, made of low‐density polyethylene and linear lowdensity polyethylene (1:1 ratio) of identical density, were compared. The tensile properties of both systems are nearly as high as those of the linear polyethylene while high strain rate properties including impact strength and tear resistance of the composite film are superior. Some structural insight was obtained by thermal analysis and thermoelastic measurements. Structure property relationships are discussed in light of the unique behavior, structure, and morphology of linear low‐density polyethylene. The two polyethylenes are only compatible to a rather limited extent mainly affecting their blend behavior. However, a strong mutual reinforcement effect was observed.
Polyurethane elastomers containing polybutadiene and aliphatic diols: Structure‐property relationships
Authors: Siegmann A. , Cohen D. , Narkis M.
Published: December 2004

The effect of aliphatic diols on the structure and some mechanical properties of polyurethane elastomers containing hydroxyl‐terminated polybutadiene and three different diisocyanates was studied. Differential scanning calorimetric studies revealed the existence of several thermal transitions, characteristic of structures of multiphased elastomers. Three transition temperatures, a subzero transition and two high temperature transitions, were found in some of the elastomers. The higher‐high temperature transition reflects ordered domains, also supported by X‐ray diffraction, Higher degree of order was achieved with longer diols. The mechanical behavior is affected by the multiphase nature of the elastomers, especially by the morphology of the hard segment domains. The structureproperty relationships for the three component polyurethane elastomers in question thus have been established.
Novel reinforced reaction injection molding (RRIM) processing: Computer‐controlled multiple‐stream RRIM production of interpenetrating polymer networks and polyurethanes
Authors: Coates P. D. , Johnson A. F. , Armitage P. D. , Hynds J. , Leadbitter J.
Published: December 2004

A four‐stream computer‐controlled reinforced reaction injection molding (RRIM) machine has been developed that attains high accuracy in dispense ratios throughout the injection period. This machine has been used for novel processing of polyurethanes, offering a route to varying product properties either throughout a shot or on a shotto‐shot basis. It also has been used for what appears to be the first production on commercial scale RRIM equipment of a polyurethane‐acrylic interpenetrating polymer network (IPN) in commercial cycle times of around 2 min.
Heat transfer during polymerization in motionless mixers
Authors: Craig T. O.
Published: December 2004

Investigation of the performance of a large‐diameter conventional motionless mixer used as a continuous reactor for styrene polymerization showed that it behaved adiabatically. Computer simulation (in which the mixer is treated as an ideal plug‐flow reactor having perfect radial mixing) predicts this tendency in terms of axial temperature profile. To avoid adiabatic polymerization, with its attendant problems of plant operability and polymer quality, the use of motionless mixers having internal heat transfer surface is indicated.
Dynamics and control of pressure in the injection molding of thermoplastics
Authors: Kamal M. R. , Patterson W. I. , Conley N. , Fara D. Abu , Lohfink G.
Published: December 2004

A detailed study was carried out to understand the dynamics of pressure variations at different points in the injection‐molding system. Thus, hydraulic, nozzle, and cavity pressures were evaluated, in addition to the pressure gradient in the cavity. Both steps and pseudorandom binary sequences (PRBS) were employed to obtain and compare dynamic models describing these variables. Subsequently, these models were employed to evaluate and select optimal controllers for the different variables.
The dynamics of peak cavity pressure in injection molding
Authors: Haber A. , Kamal M. R.
Published: December 2004

The modification of the injection‐molding machine, incorporating additional filters, an accumulator, and a servovalve, was shown to reduce the peak cavity pressure variations, in as much as the variations using the microprocessor system were random in comparison to the variations using the normal mode of operation, which exhibited nonstationarity and autoregressive behavior. If the peak hydraulic pressure could be randomized, then the peak cavity pressure variations also would be random. No closed‐loop control would be needed to control the peak cavity pressure.
Polymers as substrates and media for data storage
Authors: Kaempf G. , Loewer H. , Witman M. W.
Published: December 2004

Technological developments in the 1990s will be determined by progress in the field of microelectronics, particularly with regard to information processing and data storage. Progress in information storage is directly related to the ability to store large amounts of data in the smallest possible space, preferably in erasable form. Polymers are used as components in the standard storage systems of today: as carrier films for magnetic tapes, as photoresists and electron beam resists, and as substrates for magnetic and optical discs used for music or video replication and data storage. Storage systems with higher packing densities such as magnetooptical and phase change systems or memories based on photopolymers or polymers with liquid crystalline side chains are currently under development. In these systems, polymers will be used both as components and as actual storage materials. The development and the availability of advanced erasable memories with high storage densities could be accelerated by the availability and the system‐related modification of “intelligent” polymer materials. Worldwide activities in this interesting field have barely progressed beyond the initial stages. This progress report describes the current state of the art and compares the various developments in an attempt to forecast the possible significance of polymer memories with high data packaging densities in relation to the established technologies.
Poly(ethylene terephthalate) blends for permeability barrier applications
Authors: Subramanian P. M.
Published: December 2004

Poly(ethylene terephthalate) (PET) offers good properties as a material of choice for various packaging, electronic, and other applications. In these applications in general, the PET articles achieve improved toughness and other physical properties through molecular orientation resulting from stretching at temperatures slightly above itsTg. Without such orientation, these articles suffer from poor impact toughness. We have been investigating modifications of PET for improving toughness and retaining the permeability properties. PET having intrinsic viscosities of 0.5 to 0.7 have been modified with low modulus polymers, particularly ethylene copolymers such as ethylene‐methacrylic acid (EMAA) copolymers. The effect of crystallinity on toughness was determined. The crystallinity was established by Differential Scanning Calorimetry (DSC) techniques. Many of these modified PET compositions have good toughness and permeability barrier properties for various packaging and other controlled permeability applications such as containers and films.
Oxygen permeation of blends of copolymers of siloxanes and poly(methylmethacrylate)
Authors: Blahovici T. F. , Brown G. R.
Published: December 2004

A series of low molecular weight (≈40000) copolymers of methylmethacrylate (MMA) and 4‐(methacryloyloxy)butylpentamethyldisiloxane (MBPD) have been synthesized by free radical polymerization in dimethylformamide solution. The microstructure, as derived from 13C NMR spectra, indicates that the copolymers are about 80% syndiotactic with an overall random distribution of mers. At room temperature, copolymers rich in MMA are clear, rigid glasses but become liquid at high MBPD content. Blends of these copolymers with PMMA are all heterogeneous with visible phase separation over most of the composition range. Differential scanning calorimetry studies show the presence of two Tg's when the relative concentration of PMMA to copolymer is high. Blends of two co‐polymers of similar siloxane content produce clear films with no indication of phase separation. The permeability to oxygen at 25°C increases from 0.20 for pure PMMA to 3.0 (fmol/m·s·Pa.) for a copolymer of MMA/MBPD of the mole ratio of 3:1. Evaluation of the permeation behaviors of the blends suggests that blends rich in siloxane exist as a layered structure with the PMMA rich component dominating the observed permeability.
Additives for improving the strength, stiffness, and ductility of epoxy resins
Authors: Garton Andrew , McLean Paul D. , Stevenson William T. K. , Clark Jane N. , Daly John H.
Published: December 2004

A range of additives at 7 to 20 wt% loading can increase the stiffness and strength of crosslinked epoxy resins by up to 60%, yet the tensile specimens also fail in a ductile fashion. In additive formulations where little chemical bonding occurs between the additive and the epoxy matrix (e.g., the reaction product of 4‐hydroxyacetanilide and 1,2‐epoxy‐3‐phenoxypropane), the increase in modulus is directly related to the decrease in free volume available for segmental mobility. The increase in strength results from a combination of the increased modulus and an increased fracture energy, A ductile mode of failure occurs because the cured plastic exhibits a large increase in free volume on straining (low Poinsson's ratio). The strain‐induced increase in free volume effectively takes the sample through the glass to rubber transition. In more highly reactive formulations (e.g., the reaction product of 4‐hydroxyacetanilide and vinyl cyclohexene dioxide), chemical bonding effects complicate this simple free volume interpretation, but the occurrence of a ductile failure mode is again related to the free volume increase with strain.
Rheological properties of linear low density polyethylene/polypropylene blends. Part 2: Solid state behavior
Authors: Dumoulin M. M. , Carreau P. J. , Utracki L. A.
Published: December 2004

This second paper of a series continues the examination of the tensile properties of two series of linear low density polyethylene/polypropylene, (LLDPE/PP) blends. The blends were prepared using a twin‐screw extruder and cover the whole concentration range, An Instron Universal Tensile Tester was used to measure the tensile properties of the blends between 10 and 70°C, and the temperature and composition dependences of the modulus were examined. A comparison is established between the solid state and melt properties to underline the behavior in the PP rich region. Results of dynamic mechanical experiments and differential scanning calorimetry on the same materials are also given, and the mechanical behavior is discussed in terms of the variation of the system's crystallinity.
Effect of a separator in a sheet die on the anisotropy of tear strength of extruded medium density polyethylene
Authors: Gent A. N. , Gregory B. L. , Jeong J. , Charrier J.‐M. , Hamel F.
Published: December 2004

Sheets of medium density polyethylene (MDPE) were extruded through a slit die containing an internal separator. Thus, the melt stream was momentarily split before emerging from the die. A line of separation was evident in the extruded sheets. It is attributed to incomplete welding or healing. Measurements of tear energy Gc revealed that the extruded sheets were anisotropic and that the weld line was extremely weak after extrusion start‐up, only about 1/5 of the strength elsewhere. As extrusion continued, the strength of the weld line increased to reach that of the bulk material after about 10 min. This is attributed to an increasing temperature of the melt in the die region, aiding interdiffusion. A sample containing 30% by weight of short glass fibers showed less initial weld‐line weakness but the weld line remained weak in this case, even after long extrusion times.
The formation of polymer fibers from the rapid expansion of supercritical fluid solutions
Authors: Petersen Robert C. , Matson Dean W. , Smith Richard D.
Published: December 2004

Fibers of organic polymers (polystyrene, cellulose acetate, and polypropylene) were formed by the rapid expansion of supercritical fluid solutions through a small diameter nozzle to ambient temperature and pressure. Solutions were prepared either by dissolving the polymer directly in room temperature pentane, or in an autoclave at elevated temperatures and pressures for less soluble polymers. The fibers were collected on substrates mounted in the expansion jet. The diameters of the fibers formed (typically 1‐5 μm) were much smaller than the opening of the nozzle, although fiber diameter was observed to generally increase with nozzle diameter. The aspect ratios of the fibers, produced by this process were on the order of 103 or larger. Optimum conditions for fiber formation occurred at fluid expansion temperatures near the melting point of the polymer, with particle formation mechanisms favored at higher and lower temperatures.
Testing of a kinetics equation of mechanical degradation
Authors: Mantia Francesco P. La
Published: December 2004

A modification of the kinetics equation of mechanical degradation of Harrington and Zimm is proposed to fit experimental data taken on a molten polystyrene. This equation is applied to each molecular weight of the discretized molecular weight distribution curve, and the limiting molecular weight is determined for each molecular weight. With this modification the theoretical curves fit both Mw and Mn curves well.
Physical aging in thermosets of differing degrees of cure—master curve generation and the relation to mechanical properties
Authors: Schwartz S. A. , Bubeck R. A.
Published: December 2004

Physical aging of a thermoset system based on bisphenol‐A epoxy (DER

Trademark of The Dow Chemical Company.

383) and tetrabromobisphenol‐A cured with sulfanilamide and diaminodiphenylsulfone was studied as a function of cure history. Changes in the dynamic mechanical spectra for the thermoset system were correlated to changes in relative toughness associated with physical aging as determined by plane‐strain biaxial tension‐compression yield measurements. It was found that master curves, generated by using tan δ data obtained in the β relaxation temperature regime, are well related to the corresponding changes in mechanical properties and, hence, have predictive value. Relative toughness decreases and compressive yield increases with decreasing tan 5 because of decreased molecular segmental mobility. The relative extent of physical aging for the as‐cast thermosets was shown to be linearly related to the cure time.
Strain‐induced crystallization behavior of poly(ether ether ketone) (PEEK)
Authors: Chien Ming C. , Weiss R. A.
Published: December 2004

Strain‐induced crystallization of poly(ether ether ketone) (PEEK) was studied by the use of a parallel plate rheometer. The experimental variables included preheating time, crystallization temperature, and shear rate. The crystallization kinetics were characterized by means of an induction time defined as the time elapsed from the start of shearing to the onset of crystallization. The experimental results showed that the induction time for strain‐induced crystallization of PEEK was significantly shorter than that for crystallization under quiescent condition, and that strain‐induced crystallization was much less temperature dependent than quiescent crystallization. The activation energy for strain‐induced crystallization was found to be 0.035kcal/mole, which was considerably smaller than the reported activation energy for quiescent crystallization. Photomicrographs of the sheared specimens indicated that PEEK crystallites orient along the flow direction.
Polymer welding relations investigated by a lap shear joint method
Authors: Kline D. B. , Wool R. P.
Published: December 2004

A lap shear joint method was used to study strength development during welding of polystyrene surfaces‐ The surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface. The shear stress at failure, τf was measured at room temperature as a function of contact time, t, at constant welding temperatures up no 20°C above the glass transition temperature, Tg. The time dependence of welding could be well described by τfαt1/4. This result is in agreement with predictions of the reptation molecular dynamics model applied to inter‐diffusion at a symmetric amorphous polymer‐polymer interface. The activation energy for the thermally activated increase in strength development was determined as E = 96 kcal/mol at T = 113.5°C, which compares with E = 93,2 kcal/mole as predicted by the W‐L‐F theory using C1 = 13.7, C2 = 50 and Tg = 100°C. The polystyrene samples had molecular weights, Mn = 143,000 and Mw = 262.000. The time to achieve complete healing, t∞ ≈︁ 256 min at 118°C, was found to be of the same order of magnitude as the viscoelastic relaxation time and also with the time required for a polymer chain to diffuse a distance equal to its root mean square end‐to‐end vector.
Electrical conductivity of polymers containing carbon black
Authors: Ghofraniha Mehrdad , Salovey R.
Published: December 2004

Changes in volume resistivity with temperature of carbon‐black‐filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m2/g, the resistivity changes abruptly from 1013 to 106 ohm‐cm above 150°C. Poly(butyl methacrylate) did not show well‐defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m2/g, showed a resistivity exceeding 1013 ohm‐cm, that decreased to about 107 ohm‐cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m2/g, shows a resistivity of about 108 ohm‐cm that decreases sharply to 103 ohm‐cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network that prevents flow.
Multiple melting endotherms of poly(ethylene terephthalate)
Authors: Zhou Chixing , Clough S. B.
Published: December 2004

Poly(elhylene terephthalate) samples were isothermally crystallized from the melt on a differential scanning calorimeter. Subsequent fusion showed three endotherms under many crystallization conditions. These three peaks are attributed to melting of crystallites formed daring primary and secondary crystallization processes and to fusion of crystals formed during recrystallizatlon during the melting scan.
Elongational behavior of low density/linear low density polyethylenes
Authors: La Mantia F. P. , Valenza A. , Acierno D.
Published: December 2004

Rheological data have been collected in isothermal elongational flow for three different types of blends, made from one low density polyethylene and three linear low density samples. In addition to the transient curves, elongation at break data are also reported. The influence of the composition and of the molecular weight of the linear low density polyethylene is discussed.
Morphological studies of polycarbonate‐poly(butylene terephthalate) blends by transmission electron microscopy
Authors: Delimoy Didier , Bailly Christian , Devaux Jacques , Legras Roger
Published: December 2004

The morphology of polycarbonate (PC)‐poly(butylene terephthalate) (PBT) blends prepared by melt‐processing in an extruder or a Brabender Plastograph was studied by Transmission Electron Microscopy. Transesterification during blending was avoided by the use of di‐n‐octadecyl phosphite, an efficient transesterification inhibitor. Ruthenium tetraoxide was used to selectively stain the PC fraction. Observation of ultrathin sections revealed the biphasic nature of the blends and the partial compatibility of the polymers in the molten state. The most striking consequence of this Is the presence, of PBT crystalline lamellae growing inside the PC‐rich phase for samples annealed in the proper temperature range. A preliminary study of the morphology as a function of composition and thermal annealing was undertaken. The RuO4 staining technique was also applied to the commercial blend Xenoy CL 100 from General Electric, which was shown to contain an MBS impact modifier (a methylmethacrylate butadiene‐styrene copolymer) exclusively located In the PC‐rich phase.
Observers for optimal anticipatory control of ram velocity in injection molding
Authors: Agrawal A. R. , Pandelidis I. O.
Published: December 2004

The application of optimal anticipatory control assumes that the entire stare is available for feedback. However, in the case of injection molding this assumption is viola red due to economic considerations. For that purpose, this paper discusses the effectiveness of optimal anticipatory control using estimates of the states obtained from a dynamic system, called observer. State estimation is essential to optimal control techniques since in general the states are used in some form of feedback and the number of measurable states is usually much Jess than the actual number of state variables, limited by the availability of cheap and rugged sensors and the ease of installation. Furthermore the measurements from the existing sensors may be corrupted by significant noise. In the present paper both the stochastic and the deterministic cases are investigated for application to optimal control of ram velocity in injection molding.
Development of a mathematical model for the pultrusion of unsaturated polyester resin
Authors: Han C. D. , Chin H. B.
Published: December 2004

A mathematical model is developed for simulating the pultrusion process of unsaturated polyester resin, using a mechanistic kinetic model based on free radical polymerization. In their previous publications (Refs. 1 and 7), Han and Lee used the mechanistic model to simulate the curing behavior of unsaturated polyester resins under isothermal conditions, employing the differential scanning calorimetry data obtained for a range of single initiators and multiple initiator systems. For the sake of mathematical convenience, a pultrusion die of cylindrical geometry was considered. The mathematical model developed permits one to choose any number of initiators when predicting the distributions of the degree of cure and temperature in both the radial and axial directions of the die. The effects of material variables (e.g., the type and concentration of mixed initiators) and processing conditions (e.g., pulling speed and die temperature distribution) on the performance of the pultrusion are evaluated.
Measurement of the melting points of oligomers obtained in the manufacture of poly(ethylene terephthalate)
Authors: Yamada T. , Mizuno Y. , Imamura Y.
Published: December 2004

The melting points (Tm) were measured for oligomers obtained by a direct continuous esterification process between terephthalic acid and ethylene glycol. Multiple regression analyses of data were carried out, and an equation was obtained for predicting melting points with correlation coefficient of ∼0.99.
Molding by reactive injection of reinforced plastics
Authors: Reboredo M. M. , Rojas A. J.
Published: December 2004

A model for the molding by reactive injection of reinforced plastics for systems in which fiber glass reinforcements are placed into the molds, is proposed. It allows for the determination of processing parameters and their influence on dependent variables: conversion, temperature, and pressure. Moldability areas, where premature gelling is avoided, are defined. Operating conditions are selected to reduce cycle time, produce small load losses, and provide a fairly uniform curing stage throughout the product.
A predictive model for the mechanical behavior of particulate composites
Authors: Anderson Lori L. , Farris Richard J.
Published: December 2004

A method for predicting the stress‐strain and volumetric behavior of particulate composites from constituent properties has been developed for large values of strain. This approach allows a simple model for systems in which damage occurs without resorting to complicated constitutive equations. An energy balance derived from the first law of thermodynamics and the equations of linear elasticity calculates critical strain values at which filler particles will dewet when subjected to uniaxial tension and superimposed pressure. Calculations of critical strains over the entire strain history using reevaluated material properties accounting for the damage yield highly nonlinear stress‐strain and volumetric curves. Experimentally observed dependences on particle size, filler concentration, matrix and filler properties, and superimposed pressure are correctly predicted. The method has no adjustable parameters, and allows several idealized models of the dewetting process to be examined. Comparisons of model predictions to experimental data show good agreement.
Analysis of interfacial stresses for elastomeric disks in compression
Authors: Thornton J. S. , Montgomery R. E. , Thompson C. M. , Dillard D. A.
Published: December 2004

Relatively simple forms have been derived for obtaining the total force required to deflect a circular rubber disk of arbitrary dimensions between two rigid platens which offer Coulomb frictional resistance to flow of the rubber. The calculation of the critical radius which separates the regions of frictional adherence and restrained flow is a necessary step in the solution process. Although it cannot be solved for explicitly, an implicit form given herein converged rapidly. The solutions for force can involve differences between very large numbers as the coefficient of friction becomes small. Care should be used to evaluate these quantities in order to avoid round off errors.
Reaction kinetics of a polyurea reaction injection molding system
Authors: Pannone Mary C. , Macosko C. W.
Published: December 2004

Polyureas have the potential for Improving reaction Injection molding (RIM) productivity through shorter demo Id times and elimination of external mold release agents and post‐cure. Kinetics of urea formation are necessary for process modeling of polyurea RIM systems. Adiabatic temperature rise measurements were used to monitor the extent of reaction of an aliphatic diamine and an aromatic diamine reacting competitively with a single diisocyanate. The aliphatic diamine reacted much faster; essentially complete polymerization occurred in the RIM mixhead. A similar three‐component system was studied in dimethylacetamide and diethylene glycol dimethyl ether, and the sequential nature of the two competing reactions was confirmed. The RIM polymerization of the aromatic diamine, 3,5 diethyltoluene (2,4 and 2,6) diamine and;4,4′‐diphenylmethane diisocyanate was studied using an unreactive poly ether as the solvent. The exotherms could be fit with a third order model. Adiabatic temperature rises for all RIM experiments were in good agreement with the values predicted by heats of reaction measured in solution.
Properties of segmented block copolyurethane I. Adhesion between PET cord and rubber by polybutadiene‐polyethylene terephthalate block copolyurethane
Authors: Yamashiro Seiichi
Published: December 2004

A block Copolyurethane was synthesized by using a hydroxy‐terminated 1,2‐polybutadiene (HPBD) having vinyl side chains and a molecular weight of 2000 to 5500 as a rubber‐affinitive component, a hydroxy‐terminated poly(ethylene terephthalate) as a PET‐affinitive component, and 4,4′‐diphenylmethane diisocyanate as a chain extender. The block copolymer was mixed with a curing agent and used for the adhesion of PET cord of 1100 denier and rubber. The peak of adhesive strength was observed at the HPBD molecular weight of 4500 within the molecular weight range of 2000 to 5500.
The effects of fluids in the aircraft environment on a polyetherimide
Authors: Long Edward R. , Collins William D.
Published: December 2004

Fluid absorption studies have been made for a polyetherimide thermoplastic film and a unidirectional composite of the thermoplastic with graphite fibers immersed in water, JP4 jet fuel, ethylene glycol, and hydraulic fluid. The changes in the weight, thickness, and tensile properties were measured for the film. The changes in the flexural properties of the composite were measured for specimens whose fiber orientation was transverse to their length. Only the hydraulic fluid, which caused an erosion or dissolving of the resin at the specimen surface, affected the film's properties. Both the water and the hydraulic fluid affected the flexural properties of the composite, due to capillary absorption along the fiber‐resin interface.