bluuebunny/crossref_metadata_2025 huggingface dataset:
Sol‐Gel transition and crystallization kinetics of ultra‐high molecular weight polyethylene/decalin solution
Authors: Jo Won Ho , Kwon Ick Hwan , Seoul Chang
Published: December 2004

The gel melting temperature and crystallization kinetics of ultra‐high molecular weight polyethylene (UHMW‐PE)/decalin systems were investigated. Two methods were used to determine gel melting temperature; thermomechanical analysis (TMA) with a penetration probe and differential scanning calorimetry (DSC). The melting points determined from TMA and DSC were in good agreement, indicating that the crystallization of UHME‐PE is an essential step for gelation. The gel melting temperature increases with UHMW‐PE concentration. The change in gel melting temperature with composition results from interaction of the components in the amorphous phase. The gelation and crystallization rates increase with decreasing UHMW‐PE concentration.
Physical aging in poly(methyl methacrylate)poly(styrene‐co‐acrylonitrile) blends. Part II: Enthalpy relaxation
Authors: Mijović J. , Ho T. , Kwei T. K.
Published: December 2004

An investigation of the effect of physical aging on excess enthalpy of compatible polymer blends was carried out. Poly(methyl methacrylate) (PMMA) and poly(styrene‐co‐acrylonitrile) (SAN) were chosen for this study. Blends of different ratios of PMMA and SAN were physically aged at different times and temperatures below their glass transition (Tg) and then subjected to enthalpy relaxation measurement in a differential scanning calorimeter (DSC). An improved procedure was developed and, employed to analyze the data. The error associated with the calculation of the normalized deviation in enthalpy, known as the “Φ” function, was below 4%. The relaxation was observed to proceed faster at higher aging temperature. It was also found that at higher aging temperatures of Tg – 20 and Tg– 35°C, enthalpy relaxation in SAN‐rich blends proceeds faster than in PMMA rich blends, while at the low aging temperature of Tg– 50°C the rate of relaxation becomes independent of the composition.
Ultrasonic welding of thermoplastics in the far‐field
Authors: Benatar Avraham , Cheng Zhang
Published: December 2004

In far‐field ultrasonic welding of plastic parts the distance between the ultrasonic horn and the joint is greater than 6 mm. This study investigated the farfield ultrasonic welding of amorphous (acrylo butadiene styrene and polystyrene) and semicrystalline (polyethylene and polypropylene) polymers. Far‐field welding worked well for amorphous polymers. Weld strength improved substantially with increasing amplitude of vibration at the joint interface. Increasing the weld pressure and/or the weld time also resulted in higher weld strengths. Far‐field ultrasonic welding was not successful for semicrystalline polymers. The parts melted and deformed at the horn/part interface with little or no melting at the joint interface. A model for wave propagation in viscoelastic materials, which was developed to predict the vibration amplitude experienced at the joint interface, indicates that increasing the length of the samples to a half a wavelength should improve the far‐field welding of semicrystalline polymers by maximizing the amplitude of vibration at the joint interface.
Ultrasonic welding of PEEK graphite APC‐2 composites
Authors: Benatar Avraham , Gutowski Timothy G.
Published: December 2004

The ultrasonic welding process is modeled using a five part model that includes mechanics and vibration of the parts, viscoelastic heating, heat transfer, flow and wetting, and intermolecular diffusion. The model predicts that melting and flow occur in steps, which has been confirmed by experiments. The model also indicates the possibility of monitoring joint quality by measuring the dynamic mechanical impedance of the parts during welding, which has also been verified experimentally by indirectly monitoring the magnitude of the impedance. via measurements of both the power and the acceleration of the base. When the melt fronts of the energy directors meet, at the end of welding, the dynamic impedance of the composites' interface is shown to rise rapidly. This raises the possibility of developing closed loop control procedures for the ultrasonic welding of thermoplastic composites. Ultrasonic welding of polyetheretherketone (PEEK) graphite APC‐2 composites produced joints with excellent strengths.
Fracture mechanics parameters for polystyrene under high speed impact
Authors: Cook D. G. , Rudin A. , Plumtree A.
Published: December 2004

A series of commercial polystyrenes was tested using an instrumented impact tester to determine the fracture toughness Kc and critical strain energy release rate Gc. Over the range of Mw, 201,000 to 336,000, Kc increased from 1.38 MN/m3/2 to 1.76 MN/m3/2and Gc from 0.92 kJ/m2 to 1.60 kJ/m2. A linear correlation for Kc and Gc was seen with melt index, and an inverse relationship was obtained against molecular weight. Examination of the fracture surfaces revealed the presence of crack growth bands corresponding to the crack tip plastic zone size. It is suggested that these bands are the consequence of variations in crack growth along crazes that form in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances. The spacing of these bands corresponds to the craze length formed in the plastic zone, and the band spacing increases with molecular weight.
Mathematical modeling of the in‐mold coating process
Authors: Castro J. M. , Griffith R. M.
Published: December 2004

Fiber glass reinforced polyester parts compression molded from sheet molding compound (SMC) are prone to such surface inconsistencies as porosity and sinks. Even though it appears that some of these defects could be eliminated by techniques such as vacuum molding, the resulting surface, with current technology, is not yet consistently up to automotive standards for exterior body panels. In‐mold coating (IMC) of SMC, is designed to fill porosity, reduce sinks, and furnish a primer‐like coating, thus upgrading the part surface to automotive standards. As a consequence, IMC is generally an integral part of the molding cycle when producing compression molded SMC exterior automotive body panels. Most commonly, in‐mold coating is injected after opening the press slightly so as to separate the mold cavity and the exterior surface of the part to make room for the coating. A second approach is to let the hydraulic pressure of the injected IMC open the mold. Here, we present a mathematical model of the process and show application in predicting injection pressures, fill times, and filling patterns. A comparison with experimental results is also presented. Cycle times required for IMC injection methods is also discussed.
Structural heterogeneity in epoxies
Authors: Wu Wen‐Li , Hu Jiann‐Tsun , Hunston Donald L.
Published: December 2004

The effects of different cure procedures on the structure and properties of epoxy samples made from diglycidyl ether of bisphenol A (DGEBA) and mixtures of two linear aliphatic diamines were studied. The elastic modulus, fracture toughness, impact resistance, and glass transition temperature were determined for various cure schemes. The morphologies of the cured resins were characterized with small angle X‐ray scattering. The results show that samples with the same average morphology (molecular network structure) have similar elastic moduli and glass transition temperatures. If some heterogeneity is introduced in the molecular network structure without changing the average structure, however, the experiments indicate that the toughness can be increased without significantly sacrificing other properties.
Optimization of injection molding design. Part II: Molding conditions optimization
Authors: Pandelidis Ioannis , Zou Qin
Published: December 2004

The quality of an injection molded part is affected by many factors. These include geometric parameters associated with the mold design and the cooling system design as well as process parameters such as the molding conditions during the filling phase. In the companion paper, the problem of automatic optimization of gate location was addressed. In this paper, a methodology for molding condition optimization is presented. The optimization problem can be broken into three parts. An approximate feasible molding space (AFMS) is first determined to constrain the search space for the optimization algorithm. Quality is quantified as a function of flow simulation outputs and constitutes the objective function that must be minimized. The resulting optimization is solved by iterative search in the constrained space based on numerical optimization algorithms. The proposed methodology is not dependent on any particular simulation package and may be applied for any thermoplastic material and any complex mold geometry.
Functionalization of ethylene‐propylene rubber via melt mixing
Authors: Wu C. H. , Su A. C.
Published: December 2004

Grafting of maleic anhydride (MAH) onto ethylene‐propylene rubber (EPR) of apppoximately unitary ethylene/propylene molar ratio was performed by melt mixing in a laboratory‐scale internal mixer with the addition of dicumyl peroxide (DCP) as an initiator. Concurrent with the graft reaction, the simultaneous presence of DCP and MAH enhanced the cross‐linking of EPR chains as suggested by the emergence of a cure peak in the mixing torque, curve and supported by dynamic rheological evidence; the DCP‐induced chain scission, however, remained important. The height of the cure peak increased consistently with the amounts of DCP and MAH in the reaction mixture. At the end of ca. 30 min of melt mixing, the gel content (determined via xylene extraction) of the functionalized EPR increased with the height of cure peak but then levelled off in the vicinity of ca. 50 wt%. The limited gel content was attributed to the competition from DCP‐initiated scission reaction. This competition resulted in a wide distribution of chain connectivity, ranging from highly degraded short chains to partially cross‐linked chains. At low DCP levels, the extent of grafting (estimated by means of Fourier‐transform infrared spectroscopy) increased with the MAH content and then remained at a plateau value; at higher DCP levels, the plateau appeared to have already been reached even at the lowest MAH content (i.e., 0.5 phr) here. The limited extent of grafting was attributed to the immiscible nature and the low diffusion rate of MAH in EPR.
The interparticulate friction behavior of acetal copolymer pellets with bilobal and trilobal cross‐sections
Authors: Liu Chia‐Ying , O'Brien Keith T.
Published: December 2004

The interparticulate friction coefficient has been measured for a range of pellet cross‐sections. This measurement is postulated as representing the integrity of the solid bed in plasticating extrusion, reciprocating‐screw injection molding and extrusion blow molding. The value of the interparticulate friction coefficient has been found to be consistently greater for profiled pellet cross‐sections such as bilobal and trilobal than for conventional pellets with circular cross‐sections. It is postulated that this result means that solids beds formed from pellets with profiled cross‐sections are less likely to fracture, or break‐up, than are solids beds formed with conventional pellets, during plasticating extrusion, reciprocating‐screw injection molding and extrusion blow molding. It is further postulated that this will result in surge inhibition, and allow the manufacturing units to run faster with fewer operational problems. The effects of normal load, pellet geometry, polymer molecular weight and agitation of the bed are also presented. In addition to the measurement of the interparticulate friction coefficients, the manufacturing procedures for profiled pellets are explained.
Prediction of gel‐time in the cure of unsaturated polyester resins: Phenomenological modeling vs. statistical analysis
Authors: Muzumdar Shailesh V. , Lee L. James
Published: December 2004

A series of kinetic and rheological measurements were carried out using a differential scanning calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). The effects of temperature, inhibitor level, initiator level, and initiator type on the curing of unsaturated polyester resins were investigated. Two models based on the free radical polymerization mechanism were developed for predicting the time to reach liquid‐solid transition. These models adapted a concept that gelation occurred at a critical radical concentration. The applicability of these models was compared to that of a statistical analysis.
Stiffness of polyoxymethylene whiskers/polyoxymethylene resin composite films
Authors: Zahran R. R.
Published: December 2004

This paper presents a refinement of an erroneous, recently published analysis of the mechanical properties of polyoxymethylene (POM) whisker/POM resin composite system. Furthermore, it extends the applicability of the molecular composite model to isotropic POM resins. It is shown that using the Halpin‐Tsai equation, coupled with the laminate theory, is highly superior to using the Nielsen‐generalized Halpin‐Tsai equation for predicting the modulus of the whisker/resin system. The comparison between the experimental tensile modulus data and the predicted results, as functions of the whisker volume content, yields a good agreement to better than 15%.
Transcrystallinity phenomena in fiber‐reinforced polypropylene. II: Morphology, thermal and mechanical properties relationships
Authors: Avella Maurizio , Martuscelli Ezio , Pascucci Beniamino , Raimo Maria
Published: December 2004

The effect of short‐length carbon and Kevlar fibers on the crystallization of isotactic polypropylene (iPP) in composites prepared by compression molding has been investigated. The tendency of carbon and Kevlar fibers to nucleate the iPP during isothermal and nonisothermal crystallization has been evaluated by differential scanning calorimetry. The influence of different thermal histories used to prepare the unreinforced and reinforced samples on the crystallization parameters of iPP was examined. In addition, the tensile behavior was related to the resulting morphologies of the samples. It was observed that the crystallinity content, obtained by using different thermal treatments (slowly cooling or quenching), gives rise to different morphologies by influencing the mechanical behavior of materials as well. Moreover, the composites obtained by slow cooling seem to present a better fibber/matrix adhesion then that found in quenched samples. Possible underlying microstructures, which can explain the properties and the morphological characteristics, are also discussed.
The grafting of maleic anhydride on high density polyethylene in an extruder
Authors: Ganzeveld K. J. , Janssen L. P. B. M.
Published: December 2004

The grafting of maleic anhydride (MAH) on high density polyethylene in a counter‐rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non‐linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.
Optimization of stabilizer formulations for polyolefin processing
Authors: Pearson L. Timothy , Sousa Marcia
Published: December 2004

An approach to formulation is presented that is based on a statistical experimental design package for use on a personal computer. The total level of phosphite + hindered phenol, and the ratio of phosphite to hindered phenol are used as experimental variables. The approach was tested on extrusions of polypropylene using melt flow retention and yellowness index as observed variables. A quadratic model gave a satisfactory fit to the data for both variables. Contour plots are presented of the performance of the systems for two commercially available hindered phenols and two polypropylene samples. The largest difference between the resins is in the degree of color generation on extrusion. For both hindered phenols, a resin made using “3rd generation” or “high activity” catalyst gave lowest color development on extrusion. There were also small differences in the response of the melt flow of the resins to phosphite level.
The kinetics of photo‐oxidation of low‐density polyethylene films
Authors: Carvalho M. E. S. , Cruz‐Pinto J. J. C.
Published: December 2004

The kinetics of the accelerated photo‐oxidation of low‐density polyethylene (LDPE) films has been studied within a range of temperatures, using an ultraviolet radiation enclosure. A simple, lumped parameter, kinetic model was developed to interpret the results of measurements of carbonyl and hydroperoxide absorbances as functions of time; the model predicts, with reasonable accuracy, the general experimental behavior and also that both the formation of hydroperoxides and carbonyl Norrish‐I reactions are important initiation steps. Slightly more complex models may thus have the potential of interpreting other fine details of the degradation behavior, namely the generation of other chemical species and the chain scission and cross‐linking processes, which are directly related to changes in the mechanical properties.
Ultrasonic welding using tie‐layer materials. part II: Factors affecting the lap‐shear strength of ultrasonic welds
Authors: Ramarathnam G. , North T. H. , Woodhams R. T.
Published: December 2004

The influence of tie‐layer Melt Flow Index on the lap‐shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie‐layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap‐shear strength properties were obtained using tie‐layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie‐layers, hot spot formation and concomitant changes in fusion zone and heat‐affected‐zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie‐layers were used, the mode of failure during lap‐shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie‐layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo‐oxidative processes.
A study of the residual microstress at the matrix interface in filled epoxy resins
Authors: Wang Hong‐Bing , Li Shan‐Jun , Zhou Hong‐Wei , Yu Tong‐Yin , Jin Xiao‐Wei
Published: December 2004

Using the technique of photoelasticity, we have studied in detail the magnitude of the residual microstress at the matrix interface between epoxy resin and rubber particles or glass beads. A spheric stress‐optic equation applicable to these composites was derived. The photoelastic figures induced by the interfacial residual microstresses and the factors affecting the intensity of light are discussed. The experimental results show that the residual microstresses at the matrix interface are independent of the particle size of rubbers or glass beads, but depend on the nature of fillers, which have different thermal expansion coefficients and mechanical properties. Thermal history and interfacial chemical bonding of filled epoxy resins have distinct effects on the residual interfacial microstresses and the matrix internal stresses.
Thermal shock resistance of flat plastic integrated circuit packages
Authors: Kojima Yoshitsugu , Ohta Takashi , Matsushita Mitsumasa , Takahara Minoru , Kurauchi Toshio
Published: December 2004

Flat packages (FPs) were formed from epoxy molding compounds with various physical properties using a transfer molding machine. The compounds were prepared by changing kinds and amounts of additives and addition methods. The thermal shock test was carried out by the following procedures. The plastic package was soaked alternately in liquid nitrogen (−196°) and in liquid solder (200°) in the cycle of 140s. The median life to crack initiation was defined to be the cycles when half of the specimens exhibited crack initiation. According to linear fracture mechanics, the following expression was obtained relating the median life N, thermal stress σt, and strength σb; N = C/σ·(σb/σt)m. We found the linear relation between logarithm of Nσ and logarithm of σb/σt for various packages, and estimated the values of C and m as 5 × 104 MPa2 and 5.5, respectively. The value of m was the same as that obtained for a dual‐in‐line package.
Computer simulation of thermoforming in complex shapes
Authors: Kouba K. , Bartos O. , Vlachopoulos J.
Published: December 2004

A finite element analysis of thermoforming based on the thin membrane approximation is presented. Triangular elements with adaptive mesh refinement are used to describe deformed shapes in complex geometries. Viscoelastic effects are assumed to be negligible, and Ogden's model is used to express the material response. The results are in good agreement with previous simulations and some experimental data available in the literature. The combination of adaptive mesh refinement near corners and edges, inclusion of slip or no‐slip conditions as required on mold walls, and an efficient equation solver allow simulation of thermoforming in complex geometrical shapes at reasonable computer times on a personal computer.
Cure of epoxy resins containing epoxidized polyols
Authors: Podgaiz P. , Riccardi C. C. , Williams R. J. J.
Published: December 2004

A commercial epoxy resin, consisting of a mixture of diepoxides based on diglycidyl ether of bisphenol‐A (DGEBA) and containing an epoxidized polypropylene glycol as reactive diluent, was characterized by 1HNMR, FTIR, SEC, and chemical analysis. The kinetics of the cure with ethylenediamine (EDA) was catalyzed by the (OH) groups present in a large amount in the commercial formulation. A second order kinetic behavior gave an accurate fitting of results obtained by different experimental techniques (DSC in dynamic and isothermal modes and SEC in the pregel stage). The activation energy was E = 59.1 kJ/mol (14.1 kcal/mol), in very close agreement with values reported for the catalytic mechanism of the DGEBA‐EDA polymerization. From the gel conversion and the critical stoichiometric ratio for samples containing an epoxy excess it was found that the average functionality of epoxidized species was f = 1.58.
Rheology and morphology of some thermoplastic blends with a liquid crystalline copolyester
Authors: Ajji A. , Gignac P. A.
Published: December 2004

Liquid crystalline polymers (LCPs) are known for their high performance properties. However, owing to their high cost, research efforts are much oriented to their use as reinforcements for different thermoplastics. In this study, we investigated the morphology, mechanical and dynamic rheological properties of blends of a 60/40 para hydroxybenzoic acid–ethylene terephthalate copolyester LCP (PHB/PET) with poly(butylene terephthalate) (PBT), poly(hexamethylene terphthalate) (PHMT), and polycarbonate (PC). Addition of up to 30 wt% of LCP to the different thermoplastics was performed in a Haake Rheomix mixer at 300°C. The dynamic rheological properties of the blends showed significant changes upon the addition of LCP, but no improvement in the mechanical properties was observed. The rheological properties of the blends below the nematic transition temperature of the LCP (210°C) were similar to those of solid filled thermoplastics. At 270°C, at which the LCP is in the nematic phase, the viscosity of LCP blends with PC blends decreased, whereas that obtained with PBT blends was increased. This is interpreted as being due to the differences in viscosity and interfacial tension between the components and to a possible reaction between the LCP and the thermoplastics.
Kinetic model for the curing reaction of a tetraglycidyl diamino diphenyl methane/diamino diphenyl sulfone (TGDDM/DDS) epoxy resin system
Authors: Lee Sung‐Nung , Chiu Ming‐Tsung , Lin Ho‐Sheng
Published: December 2004

A kinetic model based on reaction mechanisms was proposed for the description of the curing behavior of a TGDDM/DDS resin system. The characteristic of this model is the separation of the non‐autocatalytic part from the autocatalytic part of the reaction, so the model can match the well‐established pseudo second order reaction mechanism, as proposed by many other studies about the epoxide/amine reaction. The present model was compared with two other widely used models for the autocatalytic curing behavior of epoxide/amine system, i.e., an equation based on a single rate constant and another based on pure phenomenological analysis, by using DSC data. It was found that the reaction rate calculated from this new model can fit the DSC empirical result much better than those calculated from the other two models. Parallel studies on some other resins, such as the DGEBA/m‐PDA system, also proved the superiority of this kinetic model. Results have revealed that the new model was valid for most of the epoxide/1o‐amine systems studied. A discrepancy did appear as the epoxide/amine molar ratio and/or the isothermal curing temperature reached certain limits, owing to the occurrence of side reactions.
The effects of thermomechanical coupling on the cold drawing process of glassy polymers
Authors: Boyce M. C. , Montagut E. L. , Argon A. S.
Published: December 2004

The source and the effects of strain‐induced heating on the stress‐strain behavior and corresponding cold drawing process of glassy polymers are investigated. The nature of dissipative and stored components of work are discussed where only 50 to 80% of the mechanical work of glassy polymers has been found to be dissipative. This phenomenon is demonstrated to be well‐modeled by considering a portion of the work to be stored as strain‐induced molecular orientation in the polymer that evokes a back stress tensor. The results of the modeling are found to be consistent with experimental measurements reported in the literature. The constitutive and corresponding heat generation model are used in fully thermomechanically coupled finite element analysis of the cold drawing of glassy polymers. The influence of applied elongation rate on the resulting temperature rise, heat transfer, thermal softening, and fiber geometry are presented, together with a full complement of the deformation field parameters related to the propagating shoulders of the drawn neck.
Influence of thickness and processing history on fatigue fracture of nylon 66. Part II: Crack tip morphology
Authors: Wyzgoski Michael G. , Novak Glen E.
Published: December 2004

Fatigue crack propagation rates in injection molded nylon 66 were previously shown to be strongly affected by prior processing history. To provide a physical basis for the observed acceleration in crack growth rates, microtomed sections were cut through the tips of stable fatigue cracks and examined by optical microscopy. A reduction in spherulite size occurs with reprocessing along with an accompanying decrease in the amount of deformation at the crack tip. For the initially processed nylon 66 this deformation consists of a vast array of independently initiated craze‐like zones. Patchy type regions observed on the fatigue fracture surface are similar in size to the initially formed crazed zones. Crack advance occurs by the breakdown and coalescence of the crazed regions via matrix shearing. The extensive damage zone is believed to result in a reduction in stress intensity at the crack tip thereby reducing the crack propagation rates. For the reprocessed nylon 66, one observes fewer crazes and a sharper fatigue crack tip with a consequent acceleration in crack propagation rates and a smoother fracture surface.
High orientation of toughened chalk‐filled isotactic polypropylene: Preparation and properties
Authors: Galeski A. , Kryszewski M. , Kowalewski T.
Published: December 2004

Chalk‐filled isotactic polypropylene (iPP) toughened by modifying the interfaces with liquid oligomer of ethylene oxide was subjected to high deformation at elevated temperature. Oriented chalk‐filled material exhibits interesting properties: high concentration of open interconnected pores, high elastic modulus, high tensile strength, ability to absorb large quantities of liquids, white color and roughness of the surface. A continuous process for the production of oriented, toughened, chalk‐filled isotactic polypropylene is described. The stretching ratios which can be achieved range from 4 to 8 for modified chalk concentrations with compositions of 60 and 40 wt%, respectively. Solid state extruded, toughened, chalk‐filled iPP prepared for comparison exhibits similar morphology and properties as drawn toughened chalk‐filled iPP although it contains much less voids.
Model filled polymers. XIII: Mixing and time‐dependent rheological behavior of polymer melts containing crosslinked polymeric particles
Authors: Sun L. , Park M. , Aklonis J. J. , Salovey R.
Published: December 2004

The rheological properties of polystyrene (PS) and poly(methyl methacrylate) (PMMA) composites filled with monodisperse sized crosslinked polymeric particles are sensitive to processing history and chemical composition. Particles compatible with the matrix, such as PMMA or copolystyrene‐vinylphenol in a PMMA matrix, are randomly dispersed on mixing, yielding (almost) Newtonian fluids. Particles incompatible with the matrix, such as PS or copolystyrene‐acetoxystyrene in PMMA, produce composites whose steady shear viscosities depend on shear rate and whose dynamic moduli are elevated at low frequency. Particles in incompatible composites tend to cluster, producing a structure that is destroyed at high shear rates and that reforms on aging at elevated temperatures.
Photoinitiated crosslinking of low density polyethylene. V: Orientation in stretched samples
Authors: Qing Yan , Rånby Bengt
Published: December 2004

Low density polyethylene (LDPE) is extruded, stretched, and photocrosslinked at different temperatures with different stretch rations in a continuous production line. Three different sequences are adopted: crosslinking before drawing, crosslinking after drawing, and crosslinking during drawing. The effect of drawing is studied by measuring the tensile properties. The increase of tensile strength and the decrease of elongation at break after stretching are related to chain orientation in crystalline morphology measured by X‐ray diffraction. Thermal analysis by differential scanning calorimetry (DSC) supports these results. Owing to chain relaxation, the effects of orientation by stretching are significant only when the samples are drawn at a temperature not much higher than the melting point. Annealing of the drawn samples at a temperature above the melting point shows that the orientation in a crosslinked sample is retained for a much longer time than in an uncrosslinked sample. For the crosslinked samples, it is found that crosslinking after or during drawing gives a material with lower shrinkage upon heating; however, crosslinking before drawing gives a heat‐shrinkable material.
Injection molding of unsaturated polyester compounds
Authors: Blanc R. , Agassant J. F. , Vincent M.
Published: December 2004

A bulk‐molding compound made of unsaturated polyester resin, glass fiber, calcium carbonate fillers, and low profile additives is studied. The viscosity of the compound in the absence of cure reaction is measured by capillary rheometry. The compound exhibits a shear‐thinning behavior. Injection molding in a rectangular plaque equipped with pressure transducers shows that the crosslinking reaction can begin during mold filling for low flow rate or high mold temperature. Fiber orientation in the plaque is complex as the reinforcement appears under two aspects, bundles or filaments. Their lengths and orientations are different. A layered structure throughout the thickness is observed at the mold entrance, whereas the orientation becomes progressively unidirectional in the plaque. Two fiber‐free layers near the the mold walls are observed. A numerical simulation of mold filling assuming inelastic non‐Newtonian kinetic dependent behavior is presented. The results agree well with pressure measurements. A simplified decoupled fiber motion calculation is finally proposed. A qualitative explanation of the basic phenomena which induce fiber orientation is presented.
Some considerations on equation of state and phase relations: Polymer solutions and blends
Authors: Xie Hankun , Nies Erik , Stroeks Alexander , Simha Robert
Published: December 2004

We review briefly the general assumptions underlying hole theories of the configurational thermodynamic functions for single and multiconstituent systems. From the original Simha‐Somcynsky theory several important modifications have recently evolved. First, there is a revision of the combinatorial entropy originating from the mixing of segments and holes in the spirit of Huggins's theory. With consistent additional modifications of the configurational free energy, quantitatively significant consequences for certain aspects of phase equilibria can arise. Finally, allowance for nonrandom mixing of constituents species and holes has been made. We illustrate the theory's potentials first in terms of pressure‐volume‐temperature (PVT) data for high and low molar mass species and their miscible mixtures. The influence of PVT properties on the miscibility behavior of solutions and blends is examined next. Of particular concern are the connections between predictability of lower from upper mixing spinodals, pressure effects, and the binary interaction χ‐function.
Interfacial grafting and crosslinking by free radical reactions in polymer blends
Authors: Lambla Morand , Seadan Manus
Published: December 2004

Relevant developments in polymer blends based on immiscible products have shown how efficient the amphiphilic species are in improving mechanical properties and morphological stabilization throughout successive processing steps. However, it appears that the amount of compatilizer that has to be introduced for reaching the expected level of global properties is largely higher than the calculated concentration based on the interfacial area. In order to obtain the required concentration of amphiphilic copolymer at the interface, it seems of interest to test the possibility of creating these species by in situ reactivity at the interface. As most of the polymers are hydrocarbon compounds, they are subjected to free radical reactivity by hydrogen abstraction on the different hydrocarbon sites, which may lead to crosslinking or grafting. Therefore, this work deals with reciprocal free radical reactivity of two immiscible semicrystalline homopolymers, namely, low density polyethylene (LDPE) and polyamide‐11 (PA‐11). The reaction has to occur mainly at the interface, where the resulting grafted copolymer has to be anchored for final stabilization of the biphasic system. Different analytical techniques help in characterizing the reacted blend and determining the level of interfacial grafting.
Compatibilized blends of polyamide‐6 and polyethylene
Authors: Padwa Allen R.
Published: December 2004

An increasing number of polymer alloys made by reactive processing of a compatibilizer precursor (CP) to form the compatibilizer in situ have appeared in recent years. Literature reports on compatibilization studies have focused on interactions of chemistry‐morphology, processing‐morphology, morphology‐rheology, morphology‐properties, etc. In commercial alloys, the interaction of chemistry and processing results in a material that has a balance of physical properties and rheological behavior. To maximize the contribution of each phase, it is of interest to be near the phase inversion region. In this work, maleic anhydride functionalized polyethylene is used as an effective CP for polyamide/polyethylene blends. In blends containing 50% nylon 6, the melt viscosity of the alloy increases exponentially as the ratio of CP to polyethylene increases though the morphology remains dispersed polyamide 6. High ratios of CP/PE are desired for toughness, alloys containing lesser amounts of CP exhibit better processability. The balance of toughness and processability is shown to be affected by the molecular weight of the CP.
Fluid mechanics of the formation of polymer blends. Part I: Formation of lamellar structures
Authors: Lindt J. T. , Ghosh A. K.
Published: December 2004

This paper deals with the early stages of blend morphology development as occurs in a screw extruder. Using combinations of similar polymers (polystyrene and styrene‐butadiene copolymer) and dissimilar polymers (PS and EVA) as model systems, it has been concluded that during melting the scale of segregation between the blend components is reduced by orders of magnitude within fraction of a second residence time. During the early stages of morphology development, the melting pellets produce fine lamellar structures (thickness of the order of μm) that extend over much of the melting zone before being broken up by capillary forces. The origin and the deformation history of the lamellar structures have been successfully interpreted by a new theory.
Spatial depth profiling of chromophores in thin polymer films using photopyroelectric spectroscopy
Authors: Prystay M. C. , Power J. F.
Published: December 2004

Frequency domain photopyroelectric effect spectrometry (FD‐PPES) is a recent spectroscopic technique that may be used to recover depth profiles of optical absorption in thin films on a noncontact and nondestructive basis. In this work a series of well characterized thermally homogeneous samples were prepared that exhibited continuous or discrete subsurface profiles of optical absorption. Multifrequency FD‐PPES measurements made on these samples were compared to theory using a heat transfer model, which we have developed for a multilayer thermally homogeneous absorber. Excellent agreement between experiment and theory was obtained for these model studies. While both phase and magnitude channels of the FD‐PPES response give depth profiling information, the phase response is especially sensitive to variations in the subsurface profile of optical absorption. By means of the phase response it is possible to determine the number and spatial positions of absorbers in a series of discrete absorbing layers. The FD‐PPES. technique has excellent potential for analysis and nondestructive evaluation of polymer films.
Glass transition temperatures in bismaleimide‐based resin systems
Authors: Tungare A. V. , Martin G. C.
Published: December 2004

The glass transition temperatures in bismaleimide‐based resins were investigated using different stoichiometric ratios of 1, 1′‐(methylenedi‐4, 1‐phenylene)bismaleimide (BMI) and 4, 4′‐methylenedianiline (MDA). The resin cure involves a low temperature primary amine addition to the maleimide double bonds and a high temperature homopolymerization of the maleimide double bonds. The network topology and the glass transition temperature changes with resin composition and curing conditions were determined using differential scanning calorimetry (DSC). An empirical model was used to relate the glass transition temperature to the extents of the amine addition and the homopolymerization reactions in 1:1 and 2:1 BMI:MDA resins. The changes in thermal properties with resin post‐cure were also examined.
Plasma polymerized tetramethyl germanium films deposited at elevated substrate temperatures
Authors: Sadhir R. K. , Saunders H. E. , Byers W. A.
Published: December 2004

Thin plasma polymerized films of tetramethyl germanium are deposited at various substrate temperatures. The influence of substrate temperature on the deposition rate, composition, structure, and electrical properties of the films is discussed. With an increase in the substrate temperature from 25°C to 150°C under similar plasma deposition conditions, the conductivity of the film increased by four orders of magnitude. Films of plasma polymerized tetramethyl germanium deposited at 150°C show typical semiconducting behavior (increasing conductivity with increasing temperature) and have a sheet conductivity of 1.0 × 10−6 S cm−1 at 25°C. There is a direct correlation between the conductivity and the composition of the films, i.e., the higher the conductivity the higher the ratio of germanium to carbon at the surface. At deposition temperatures of 25 and 75°C the germanium to carbon ratio was essentially the same, but at a deposition temperature of 150°C, this ratio was considerably higher.
Effect of catalyst on the reactive processing of polyesters with epoxy‐functional polymers
Authors: Stewart M. E. , George S. E. , Miller R. L. , Paul D. R.
Published: December 2004

The objective this work was to determine the effects of selected polyester catalysts on the reaction of a polyester with epoxy functional polymers. Polyesters containing various catalyst metals were melt blended with either an ethylene‐co‐glycidyl methacrylate or a styrene‐co‐glycidyl methacrylate copolymer. The viscosities of the blends were monitored as a function of mixing time using torque rheometry. In addition, the molecular weight distributions of selected samples were analyzed using gel permeation chromatography. Both the torque rheometry and the gel permeation chromatography results indicate that the polyester reacts with epoxy functional polymers. This reaction occurs under conditions and at processing times which are readily obtainable in conventional melt processing equipment. Furthermore, the reaction kinetics of polyesters with glycidyl methacrylate copolymers are dramatically affected by the nature of the catalyst system used to prepare the polyester. Under the conditions used, antimony catalysts are particularly effective at promoting the reaction between polyesters and the epoxy functionality and the activity of the catalysts studied appears to decrease in the following order: antimony > gallium > tin ≃ titanium > germanium. Manipulation of the polyester catalyst system may offer a method to control the extent of reaction obtained in reactive processing of polyesters with epoxy functional compounds.
Impact toughened blends of styrene‐maleic anhydride copolymer, polyethylene, and ethylene‐propylene copolymer
Authors: Datta S. , Dharmarajan N. , Ver Strate G. , Ban L.
Published: December 2004

Impact‐toughened, compatibilized binary blends of styrene‐maleic anhydride (SMA) copolymer/amine functionalized ethylene‐propylene (amine‐EP) polymer and ternary blends consisting of SMA/amine‐EP/high density polyethylene (HDPE) are described. In both blends 0.02 to 4 μm range rubbery inclusions, which toughen the SMA matrix, are formed. SMA sub‐inclusions exist in the amine‐EP phase. In the ternary blend substantially all of the polyethylene is embedded in the EP phase. Compatibilization of the SMA and the commingled polyolefin phase is promoted by a graft copolymer formed by the reaction of amine groups on the EP with the maleic anhydride groups on the SMA. We describe the morphology, rheology, aging characteristics and impact properties of these blends. SMA modification by SMA‐g‐(amine‐EP) polymers formed in situ in the melt, with HDPE, has not been previously reported.
Plasticity and fracture initiation in rubber‐toughened poly(methyl methacrylate)
Authors: Gloaguen J. M. , Steer P. , Gaillard P. , Wrotecki C. , Lefebvre J. M.
Published: December 2004

The deformation behavior of rubber toughened poly(methylmethacrylate), RT‐PMMA, has been investigated in terms of the ability of the material to nucleate plasticity. Work‐hardening rate parameter K measurements in the early stages of the nonelastic response in a constant strain‐rate test are used to probe the development of micro shear zones as a function of rubber volume fraction. The results reveal the existence of a sharp transition from difficult to easy shear band nucleation for a critical rubber volume fraction Vc. This abrupt change in mechanical behavior also shows in the evolution of the critical stress intensity factor K measured at the onset of crack initiation. These findings are discussed in terms of the morphological parameters of the blends.
Characterization and analysis of defects in extruded/coagulated films of heterocyclic aromatic polymers for nonlinear optics studies
Authors: Mehta R. , Lee C. Y.‐C.
Published: December 2004

The high degree of electron delocalization in heterocyclic aromatic molecules makes this class of chemistry ideal for hyperpolarizability and NLO (nonlinear optics) polymer developments. This type of polymer is usually insoluble in common solvents and is not amenable to common optical film processing techniques like spin coating. A study of the approach in using an acidic solution extrusion followed by coagulation for optical quality film forming is reported in this paper. The polymers studied are: PBZT, (poly (p‐phenylene benzobisthiazole)); 6F‐PBO (polybenzobisoxazole containing hexaflorinated moities); and Zytel 330 (an amorphous nylon). Some of the resulting films showed an improved optical quality while others showed an extremely poor optical quality over the films used in a previous study. The optically clear films, however, were not of wave‐guiding quality. The defects in the films that would cause light scattering were characterized and the probable causes of these defects were discussed. The defects were: (a) optically inferior morphology, (b) micro‐voids, (c) macro‐voids, (d) solid particles, (e) lines in the transverse direction, and (f) lines in the machine direction. Identification and classification of these defects will help additional efforts in the future for improving the optical quality of heterocyclic aromatic polymer films.
Properties and morphology of oriented ternary blends of poly(ethylene terephthalate), high density polyethylene, and compatibilizing agent
Authors: Sambaru Prasad , Jabarin S. A.
Published: December 2004

Oriented blends of poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) with and without compatibilizing agent have been studied with regard to orientation temperature, stretch rate, extension ratio, mode of orientation, and blend composition. These oriented blends have been characterized using infrared spectroscopy and differential scanning calorimetry. The tensile and tensile impact properties were also investigated. The results show that blends with compatibilizer show strain hardening upon orientation, whereas the blend without compatibilizer does not strain harden upon orientation. The blends with less PET content have been difficult to orient. The morphology of these blends show fibril structure, highly oriented in the direction of stretch. Infrared measurements show that PET within the blend has undergone strain induced crystallization upon orientation. It has also been observed that the mechanical properties, such as the modulus and ultimate stress, show improvement upon orientation. Simultaneously stretched blends show better physical properties than sequentially oriented blends.