bluuebunny/crossref_metadata_2025 huggingface dataset:
Mesostructure development during molding of sheet molding compounds
Authors: Mei T. , Piggott M. R.
Published: April 2004

Experiments have been carried out with sheet molding compounds in which the amount of shear developed during molding was varied by changing the charge size. The effects of pressure and temperature were also investigated. The moldings were characterized by their mesostructures and the influence of the mesostructures on the Izod toughness and flexural strength was examined. It was found that high degrees of shear resulted in fiber orientation and the spreading of the fiber bundles. However, this did not improve properties, and it was concluded that for optimum properties, small amounts of shear were desirable.
A simple technique for grafting poly(methyl methacrylate) onto glass fabric
Authors: Sailaja R. R. N. , Kumar Anil
Published: April 2004

We have developed a two‐step technique for synthesizing dichlorosuccinyl peroxide at room temperature, starting from succinic anhydride. It reacts with silanated glass fabric or beads at room temperature. The macroinitiator thus formed can be used for the polymerization of methyl methacrylate, MMA. We show that the MMA is grafted to the surface of glass giving a chemically bonded ultrathin coating, as confirmed by the FTIR analysis and electron micrography.
Development and characterization of high‐performance polybenzoxazine composites
Authors: Shen Shyan Bob , Ishida Hatsuo
Published: April 2004

To develop high‐performance composites with high temperature resistance, two newly synthesized polybenzoxazines were successfully cured with carbon fiber to obtain composites with 60 vol% fiber. Results from differential scanning calorimetry studies were used to modify the benzoxazine monomers to improve processability in terms of melting point and solubility. The density and void content of these composites were measured. Dynamic mechanical tests were performed to determine the glass transition temperature (Tg) and the activation enthalpy of the glass transition process for these two composites. The effect of cure temperature on the Tg of the composites was investigated. Thermal characteristics were studied by means of dynamic mechanical analysis in terms of isothermal aging, decomposition temperature from thermogravimetric analysis, and storage moduli change at high temperatures. Mechanical evaluations of these composites were conducted by flexural and interlaminar shear tests. The mechanical and thermal properties of these two composites exceed bismaleimide composites and compete with polyimide composites, while exhibiting easier processability than polyimides.
Development and hot‐melt impregnation of a model controlled flow prepreg system
Authors: Hayes Brian S. , Seferis James C. , Chen Judy S.
Published: April 2004

A controlled‐flow epoxy‐based model prepreg resin system was developed. The formulation of the model controlled‐flow resin was designed from performance information obtained from a commercially available controlled‐flow resin, presently used in the aircraft industry. Thermoanalytical techniques including rheometry were used to provide the necessary information to develop the model system along with a formulation methodology developed by Seferis and co‐workers. The model resin formulation, which was a combination of tetraglycidyl ether of methylenedianiline (TGMDA), diglycidyl ether of bisphenol‐A (DGEBA), carboxyl‐modified butadiene/acrylonitrile rubber (CMBN), carboxyl‐terminated butadiene/acrylonitrile rubber (CTBN), bisphenol‐A (BPA), diaminodiphenyl sulfone (DDS), and dicyandiamide (DICY), was hot‐melt impregnated into unidirectional carbon fibers on a laboratory scale hot‐melt prepreg machine. A two‐parameter, three‐level design of experiments was performed on the prepreg processing parameters in which impregnation temperature and pressure were varied. Thus, a total of nine different experimental prepregs were produced and characterized by resin content, extent of impregnation, and tack. The results from the characterization of the nine experimental prepregs are compared with the effects of the prepreg processing conditions. These results are also compared with the results generated for the commercial controlled‐flow resin. Collectively, this work provides a fundamental basis by which the analysis and rational utilization of controlled‐flow matrix prepregs can be effected.
Evaluation of interlaminar‐toughened poly(etherlmide)‐modified epoxy/carbon fiber composites
Authors: Woo E. M. , Mao K. L.
Published: April 2004

Amorphous poly(ether imide) has been used as interlaminar toughening particulate agent in laminated carbon fiber/epoxy composites. Mode I and Mode II delamination fracture toughness was characterized using the double cantilever beam (DCB) and end‐notched flexure (ENF) specimens. The delamination surface was examined using a scanning electron microscopy (SEM) to investigate relationships between the morphology and properties. The results revealed that the PEI‐modified composites exhibited a significantly increased fracture toughness, which increased with the PEI content.GICwas improved from 165 to 540 J/m2(at 1 mm/min crosshead speed).GIICwas improved more significantly from 290 to 1300 J/m2. It is believed that these values could be further improved if the processing cycle were to be optimized.
Phthalonitrile‐carbon fiber composites
Authors: Sastri Satya B. , Armistead James P. , Keller Teddy M.
Published: April 2004

Phthalonitrile polymers offer promise as matrix materials for advanced composite applications. The phthalonitrile monomer is readily converted to a highly crosslinked thermosetting polymer in the presence of thermally stable organic amine catalysts. Rheometric studies were conducted to elucidate the optimum amine concentration for composite formulations. High quality composite panels were processed in an autoclave using unsized IM7 carbon fibers. Mechanical properties of the phthalonitrile/carbon composite are either better than or comparable to the state‐of‐the‐art PMR‐15 composites. Dynamic mechanical analysis reveal that samples postcured at elevated temperatures (375°C) do not exhibit a glass transition temperature up to 450°C and also retain °90% of their initial modulus at 450°C. Flame resistance of phthalonitrile/carbon composites, evaluated by cone calorimetric studies, excels over that of other polymeric composites for marine applications. The composites also show low water uptake, <1% after exposure to water for 16 months.
Pultrusion of epoxy matrix composites: Pulling force model and thermal stress analysis
Authors: Moschiar S. M. , Reboredo M. M. , Larrondo H. , Vazquez A.
Published: April 2004

Pultrusion processing for epoxy resin with glass, carbon, and DuPont Kevlar fibers has been modeled. The model has three submodels: heat transfer, pressure, and force. The validity of the model was verified by comparison of results obtained on the glass fiber/epoxy system with experimental values in the literature. The application of the model permitted an explanation of the difference in behavior between polyester and epoxy resins. Different process variables were studied. Increasing the pulling velocities increases force values. The influence of the fiber content was analyzed. Different wall temperature profiles were used and the residual thermal stresses were calculated. The use of different fibers (glass, carbon, and Kevlar) was simulated under the same process conditions. The higher pulling force was obtained for composites with carbon fibers.
Coupled analysis of injection molding filling and fiber orientation, including in‐plane velocity gradient effect
Authors: Chung S. T. , Kwon T. H.
Published: April 2004

On injection molding of short fiber reinforced plastics, fiber orientation during mold filling is determined by the flow field and the interactions between the fibers. The flow field is, in turn, affected by the orientation of fibers. The Dinh and Armstrong rheological equation of state for semiconcentrated fiber suspensions was incorporated into the coupled analysis of mold filling flow and fiber orientation. The viscous shear stress and extra shear stress due to fibers dominate the momentum balance in the coupled Hele‐Shaw flow approximation, but the extra in‐plane stretching stress terms could be of the same order as those shear stress terms, for large in‐plane stretching of suspensions of large particle number. Therefore, a new pressure equation, governing the mold filling process, was derived, including the stresses due to the in‐plane velocity gradients. The mold filling simulation was then performed by solving the new pressure equation and the energy equation via a finite element/finite difference method, as well as evolution equations for the second‐order orientation tensor via the fourth‐order Runge‐Kutta method. The effects of stresses due to the in‐plane velocity gradient on pressure, velocity, and fiber orientation fields were investigated in the center‐gated radial diverging flow in the cases of both an isothermal Newtonian fluid matrix and a nonisothermal polymeric matrix. In particular, the in‐plane velocity gradient effect on the fiber orientation was found to be significant near the gate, and more notably for the case of a nonisothermal polymer matrix.
Fiber/Matrix mechanical interaction in carbon fiber/bismaleimide model composites
Authors: Favre J.‐P. , Auvray M.‐H. , Chéneau‐Henry P. , Galiotis C. , Vlattas C. , Paipetis A. , Pegoraro M. , Severini F. , Di Landro L. , Yuan Liju
Published: April 2004

The fiber/matrix interaction of high modulus (M40) and intermediate modulus (T800) carbon fibers with a bismaleimide resin has been studied by means of three micromechanical techniques involving a single fiber, namely, fragmentation, Raman spectroscopy, and pullout. A number of chemical treatments aimed at improving the fiber/matrix stress transfer at elevated temperature were tested. The stress transfer proved to be reduced by the temperature in the same way for all interfacial conditions. The limitations to the micromechanical characterization of model composites in temperature are emphasized.
Control of polymer properties by melt vibration technology: A review
Authors: Ibar J. P.
Published: April 2004

This paper reviews the technology of melt vibration (more specifically at low frequency) to reduce viscosity during processing of plastics and to enhance mechanical performance of the solidified parts. The effect of vibration frequency and amplitude on melt viscosity is explained in terms of shear‐thinning criteria. The effect of pressure and temperature on shear thinning is also reviewed to predict how these variables interfere with melt vibration. Practical applications of the principles of melt vibration are provided in injection molding, extrusion and compression molding/thermoforming, from reduction of viscosity to lowering processing temperature and pressure to the elimination of melt defects and weld lines, to the enhancement of mechanical properties, stiffness and strength, by modification of the amorphous and semicrystalline texture and orientational state. Commercially available equipments are reviewed. Results showing the effect of melt vibration during processing for two classical polymers, polystyrene and polypropylene, are discussed. The paper concludes on the remaining challenges to bring the benefits of the new technology to full commercialization.
3D finite element method for the simulation of the filling stage in injection molding
Authors: Hétu J.‐F. , Gao D. M. , Garcia‐Rejon A. , Salloum G.
Published: April 2004

During the molding of industrial parts using injection molding, the molten polymer flow through converging and diverging sections as well as in areas presenting thickness and flow direction changes. A good understanding of the flow behavior and thermal history is important in order to optimize the part design and molding conditions. This is particularly true in the case of automotive and electronic applications where the coupled phenomena of fluid flow and heat transfer determine to a large extent the final properties of the part. This paper presents a 3D finite element model capable of predicting the velocity, pressure, and temperature fields, as well as the position of the flow fronts. The velocity and pressure fields are governed by the generalized Stokes equations. The fluid behavior is predicted through the Carreau Law and Arrhenius constitutive models. These equations are solved using a Galerkin formulation. A mixed formulation is used to satisfy the continuity equation. The tracking of the flow front is modeled by using a pseudo‐concentration method and the model equations are solved using a Petrov‐Galerkin formulation. The validity of the method has been tested through the analysis of the flow in simple geometries. Its practical relevance has been proven through the analysis of an industrial part.
A study of extrudate distortion in controlled‐rheology polypropylenes
Authors: Baik Jae Jin , Tzoganakis Costas
Published: April 2004

The melt fracture characteristics of controlled‐rheology polypropylenes (CRPP) were studied by means of capillary rheometry experiments. CRPPs were produced through reactive extrusion of a commodity polypropylene resin using various peroxide concentrations. These materials exhibited lower molecular weights and narrower molecular weight distributions than those of the starting commodity resin. The CRPP materials studied were found to exhibit only gross melt fracture. At extremely high shear rates and relatively low temperatures, a sigmoidal flexure was observed in the flow curve of certain CRPPs. Generally, it was found that the severity of melt fracture decreased with increasing shear rate for a given material and temperature and in some cases, the extrudates exhibited completely smooth surfaces. Also, the severity of surface distortions was reduced when high L/D dies were employed at a given shear rate. The critical shear stress for the melt fracture onset was found to increase with decreasing molecular weight and polydispersity, and correlations have been developed between the critical stress values and the polymer polydispersity and shear compliance.
Toughening of unsaturated polyester with rubber particles. Part II: Fracture behavior
Authors: Maspoch M. L. L. , Martinez A. B.
Published: April 2004

Fracture behavior of rubber‐modified unsaturated polyester is studied. Unsaturated polyester was modified by the addition of different rubbers; liquid rubbers (BFGoodrich Hycar) and high molecular weight rubbers. Values of stress‐intensity factor Klc and fracture energy Glc were determined using a double‐torsion test. Young's modulus was determined in flexural. Increases in toughness were recorded when there was adhesion in the particle‐matrix interface. The toughening mechanism was identified. Whitening was not observed. Crack propagation changed from stick‐slip to continuous manner when volume fraction of Hycar VTBN increased.
Thermoforming of liquid crystalline polymer sheets
Authors: Mogilevsky M. , Siegmann A. , Kenig S.
Published: April 2004

Liquid crystalline polymer (LCP) extruded sheets were further processed by the conventional thermoforming method. The available processing temperature range was defined through the structural, thermal, and elevated temperature mechanical characterization of the extruded sheet. This temperature range was found for LCP to be quite narrow, in the proximity of the crystal‐mesophase transition. The structural changes imposed on the LCP sheet during forming and its thermal stability were investigated using wide angle X‐ray diffraction, mainly for the determination of the chain orientation distribution, DSC, and dynamic mechanical analysis. Thermoforming onto a symmetrical male mold was found to enhance the orientation in the extrusion machine direction and even change the preferred orientation in the extrusion transverse direction to orientation along the thermoforming direction. Annealing at the thermoforming temperature range results in a more ordered and thermally stable structure accompanied by just a slight orientation loss.
Variable temperature cure polyetherimide epoxy‐based prepreg systems
Authors: Hayes Brian S. , Seferis James C.
Published: April 2004

This work identifies the necessary attributes of variable temperature cure epoxybased prepreg systems as they relate to high performance prepreg systems capable for composite repair. Model polyetherimide epoxy blend resins were developed and hot‐melt impregnated into woven carbon fabric and compared with a commercial prepreg system. It was found that when the PEI content was increased from 0 to 14 wt% in the base resin of the prepregs, the GIC and GIIC fracture toughness increased by over 70%. The fracture toughness was found to be similar when the model prepreg was cured at either 121°C or 177°C, a result of only a 9% difference in conversion and complete phase separation of the PEI at both cure temperatures. Void content in vacuum cured laminates were found to decrease as the PEI content was increased because of a large quantity of resin in the interstitial areas between the longitudinal and transverse tows. A comparison of the model and commercial prepreg system demonstrated many similarities and some significant differences. For example, the commercial prepreg had a 15% difference in conversion when cured at 121°C versus 177°C and very little PEI phase separation after both cure cycles. As a result, a significant difference in GIIC for the commercial prepreg was observed for the two cure temperatures.
High weissenberg number simulation of an annular extrudate swell using the differential type constitutive equation
Authors: Tanoue Shuichi , Kajiwara Toshihisa , Iemoto Yoshiyuki , Funatsu Kazumori
Published: April 2004

Annular extrudate swell simulations at high Weissenberg numbers were made using a differential type constitutive equation. The streamline‐upwinding method with a sub‐element for extra stress components, which is called SU4 × 4, is one of the best mixed finite element methods for computation of viscoelastic flows. Planar and capillary extrudate swell calculations at high Weissenberg numbers (We > 1000) were accomplished by SU4 × 4. However, annular extrudate swell simulations at high We by SU4 × 4 were not successful. The calculated We was less than about 4. A new calculation technique using a Newton‐Raphson discretization of the equation of motion was developed. This technique is called a “new under‐relaxation method.” The calculated We of annular extrudate swell simulation by the new under‐relaxation method with SU4 × 4 was about 6∼250 times larger than those by SU4 × 4. Reasonable calculation results were obtained in an annular flow and a capillary extrudate swell by this method, and the reliability and the utility of the new under‐relaxation method are shown. It is now possible to consider the swell shapes of annular extrudate under industrially useful conditions. The calculated swelling ratios were also compared with experimental ones.
Correlation between microhardness and optical anisotropies and crystallinity in lamellar regenerated cellulose
Authors: Pinto Gabriel , Lorenzo Vicente
Published: April 2004

An experimental study about the effect of the crystallinity on the birefringence and microhardness of regenerated cellulose tubular films is reported. The degrees of crystallinity of samples varied between 0.53 and 0.66. It was demonstrated that for the polymeric films studied there was an excellent agreement between crystallinity and optical and microhardness anisotropies, showing that micro‐indentation hardness, scarcely used but rapid and nondestructive, is a suitable technique for characterizing the degree of order in this polymer.
Modular tangential counter‐rotating twin screw extrusion: Determination of screw pumping characteristics of modules and composite machine behavior
Authors: Bang Dae‐Suk , Hong Myung‐Hyuk , White James L.
Published: April 2004

Extensive experimental studies of a starved flow modular tangential screw extruder are described. Die pressures and fill factor profiles along the screw axis are measured and used to determine screw characteristic curves Q vs. ΔP/L for individual screw elements of varying designs in a Leistritz twin screw extruder. Superior pumping characteristics of matched as opposed to staggered elements is found. The experimental screw characteristic curves are compared with the results of mathematical simulations of the flow. Agreement is generally good.
Thermomechanical studies on newly developed copolyester thin films. Part I: Thermal expansion coefficients
Authors: Shi Frank F. , Economy James
Published: April 2004

In this paper, the in‐plane linear coefficients of thermal expansion (CTE) (αx and αy) of a newly developed family of all aromatic and aromatic/aliphatic copolyester thermoset films prepared from spin coating were measured. The volumetric CTEs (β) were determined by a Pressure‐Volume‐Temperature (PVT) technique (1). Based on the difference between the volumetric CTEs and the sum of the in‐plane linear CTEs, the out‐of‐plane linear CTEs (αz) were calculated. The effects of film processing, including film coating and curing, on the CTEs are discussed. It was found that the linear CTEs varied significantly with the processing conditions, the volumetric CTEs were essentially constant, and the out‐of‐plane linear CTEs (αz) of the spin coated films were higher than the in‐plane linear CTEs (αx, y).
Formation and characterization of cast and biaxially stretched poly(butylene terephthalate) film
Authors: Song Kwangjin , White James L.
Published: April 2004

An experimental study of structure development in cast film exhibited only α‐form crystallites and relatively low crystallinities (Xc = 3.5–14%), while biaxially stretched films showed a mixed character of both α‐ and β‐form crystallites with crystallinities of 20–30%. Crystal perfection increases with uniaxial deformation. Biaxiality causes a decrease both in crystal perfection and crystallinity of the films. Annealing increases crystallinity. The orientation of the films has been determined by refractive indices and WAXS pole figures. Polymer chains orient rapidly to the machine direction (MD) with uniaxial stretching. Increasing biaxiality causes an increase in population of TD‐oriented crystals. The planarity of the film increases with simultaneous transverse stretching. The phenyl rings orient into the plane of the film. Annealing further increased the orientation of the films.
Characterization of novel thermoplastic polymers with phenolphthalein in their backbone chains
Authors: Wu Chi
Published: April 2004

Different molecular weight phenolphthalein poly(ether ketone) (PEK‐C) and phenolphthalein poly(ether sulfone) (PES‐C) fractions in chloroform (CHCl3) were studied by static and dynamic laser light scattering (LLS). The dynamic LLS revealed that both the PEK‐C and PES‐C samples contain some large polymer clusters formed in the process of polymerization. These large clusters can be removed by filtering the solution with a 0.1‐μm filter. The positive second virial coefficient (A2) shows that CHCl3is a good solvent for these polymers at room temperature. The persistence length and the Flory characteristic ratio of these polymers in CHCl3at 25°C are ∼2 nm and ∼3, respectively, which indicate that these polymer chains are flexible. A combination of static and dynamic LLS results, namely the weight‐average molecular weight from static LLS and the line‐width distribution from dynamic LLS, lead to two calibrations between the translational diffusion coefficient (D) and molecular weight (M):D= 2.20 × 10−4M−0.56for PEK‐C andD= 2.45 × 10−4M−0.55for PES‐C in CHCl3. Using these calibrations, we are able to estimate not only the molecular weight distributions of these fractionated polymers, but also unfractionated PEK‐C and PES‐C samples.
Additive modification of the polymerization and properties of an acrylic bone cement
Authors: Yang Jen‐Ming , Shyu Jiing‐Shen , Chen Hsin‐Lung
Published: April 2004

A commercial surgical bone cement has been modified by adding tricalcium phosphate (TCP), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA). The effects of the addition of TCP, HEMA, and EGDMA on the vinyl polymerization kinetics and thermal stability of the bone cement have been evaluated. The reaction rate constants (k) were determined from a kinetic analysis. The separate and combined effects of TCP, HEMA, and EGDMA contents on the rate and the heat of polymerization can be explained by the frequency factor and the activation energy. The decomposition temperture of the modified acrylic bone cement was studied by thermogravimetry. The decomposition temperature increased with TCP content, whereas HEMA and EGDMA had little effect on the decomposition temperature.
“In‐out” recursive probability modeling of branched step‐growth polymerizations
Authors: Miller Douglas R. , Sarmoria Claudia
Published: April 2004

This paper presents the derivation of mathematical formulae for molecular and network parameters of branched step‐growth polymerizations. Weight‐average molecular weight, gel point, and weight fractions of soluble, pendant and elastically‐effective material in a gel are derived. The direct “in‐out” recursive analysis of Macosko and Miller is applied to four general step‐growth polymerization systems. The method is introduced using the simple case of Af homopolymerization. Two new systems are then modeled; a homopolymerization of AfBg monomers with two types of reactive groups, and an Af+Bg+Ch terpolymerization. The fourth system presented is a general Af+Bg copolymerization of polydispersed reactants; we have partially analyzed this system before, but we give a new and complete presentation here to show the generality of the “in‐out” analysis. We also survey some additional polymer systems that have been analyzed in the literature. Then, we discuss limitations of this modeling approach, the use of the models and their implementation in software. We give two numerical examples: a silicone rubber system and a segmented polyurethane network system. Appendices present the small amount of elementary probability theory and polymer distribution theory needed to support the analysis. This paper serves as an introduction to the “in‐out” method; after reading this paper, the reader should be able to apply the “in‐out” method to many step‐growth polymer systems.
Dynamic and isothermal thermogravimetric analysis of a polycyanurate thermosetting system
Authors: Zacharia R. E. , Simon S. L.
Published: April 2004

Isothermal and dynamic thermogravimetric analysis (TGA) were performed on a polycyanurate thermosetting material. The effects on thermal stability of the copper naphthenate catalyst were studied by comparing two systems with different amounts of catalyst. Tests were performed isothermally at temperatures ranging from 200°C to 240°C for times up to one week. Dynamic tests were also performed at rates from 0.1°C/min to 40°C/min at temperatures ranging from 180°C to 600°C. It is found that increasing the concentration of copper increased the weight loss in isothermal tests, but did not affect the overall activation energy. Conversely, in dynamic tests, copper concentration had no effect on weight loss. The results demonstrate the difficulties of extrapolating dynamic TGA data to use conditions in order to predict long‐term thermal stability.
Two‐stage crystallization kinetics modeling of a miscible blend system containing crystallizable poly(butylene terephthalate)
Authors: Woo Eamor M. , Yau Shang N.
Published: April 2004

A modified two‐stage kinetic model is proposed to describe the crystallization/solidification from the melt state of a miscible binary blend system comprising amorphous poly(ether imide) (PEI) and crystallizable poly(butylene terephthalate) (PBT). Differential scanning calorimetry (DSC) was employed to monitor the isothermal melt‐crystallization of the PBT/PEI blends. A nonlinear regression method was adopted for estimating the kinetic parameters in accordance with the modified two‐stage series‐parallel model in comparison with the Avrami model. The results suggested that the crystallization of the PEI/PBT blends could be more precisely described by using the modified model, which properly takes into account the changing mechanisms from early to later stage of crystallization. For practical applications, an optimal temperature window for solidifying PEI/PBT miscible blends may be determined by utilizing this model.
Simultaneous interpenetrating polymer networks of epoxy and N‐phenylmaleimide‐styrene copolymers
Authors: Sung Po‐Hou , Chao Wei‐Liang , Chen Yun‐Yuan
Published: April 2004

Ductile thermoplastic N‐phenylmaleimide‐styrene copolymers (PMS) have been introduced into diglycidyl ether of bisphenol A (epoxy) by a simultaneous polymerization technique. The tensile strength and fracture toughness increased with increasing PMS content and reached a maximum value at a PMS/epoxy ratio of about 20/80 (w/w). The mechanical properties decreased significantly beyond that ratio, because of phase inversion.
Non‐isothermal polymer crystallization kinetics and Avrami master curves
Authors: Lambrigger Markus
Published: April 2004

The kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. It is shown in this paper that, in the case of non‐isothermal crystallization kinetics with constant heating or cooling rates, an apparent m‐order reaction model is approximately equivalent to the nucleation and growth model of Avrami in the vicinity of the inflection points of the corresponding crystallization curves. Since the apparent m‐order reaction model is defined for every real, positive apparent reaction‐order m, a distinct Avrami index n, which is valid for the characterization of isothermal and non‐isothermal crystallization experiments with constant heating or cooling rates, can always be related to any apparent reaction‐order m. Therefore, two types of Avrami master curves, which are dependent merely on the Avrami index n and which describe the isothermal polymer crystallization thoroughly, can be obtained by performing non‐isothermal experiments with constant heating or cooling rates.
The influence of extrusion parameters on the mechanical properties of polypropylene sheet
Authors: Macauley N. J. , Harkin‐Jones E. M. A. , Murphy W. R.
Published: April 2004

Extruded thermoplastic sheet is widely used in the production of thin‐gauge tubs and containers for the food and beverage industry using the thermoforming process. The production of high quality thermoformed parts is critically dependent on the standard of extruded sheet feedstock used. The extrusion process itself imparts a thermal history to the sheet, and this in turn partly dictates its subsequent thermoformability. This paper assesses the influence of various extrusion parameters on the mechanical and morphological properties of polypropylene sheet, with a view to defining the optimum extrusion conditions for polypropylene. The extrusion parameters under consideration are chill‐roll temperature, line speed, sheet thickness and melt temperature.
The mechanism of triallylcyanurate as a coagent in EPDM peroxide vulcanization
Authors: Murgić Zlata Hrnjak , Jelenčć Jasenka , Murgić Leonard
Published: April 2004

The reaction mechanism of ethylene‐propylene‐diene (EPDM) peroxide vulcanization, in the presence of triallylcyanurate (TAC), as a coagent, was studied by IR spectroscopy and equilibrium swelling technique. Coagent TAC is added in EPDM polymer to prevent the scission of polymer chains during the curing process. Because of this incompatibility with polymer, TAC was supposed to reside in small domains. To establish the existence of coagent bridges, the cleavage of ether linkages in the vulcanizates was made. After that treatment, IR measurements proved incorporation of coagent in polymer network. Measurements of allyl absorbances and the s‐triazine ring indicated that crosslink efficiency is enhanced and homopolymerization and cyclization take place in the presence of the coagent. In addition, the swelling results and IR measurements confirmed that the properties of the polymer, such as molecular mass and molecular mass distribution, will determine which of these reactions will predominate during the vulcanization process.
Compatibility in binary blends of thermotropic liquid crystal polymers
Authors: Stachowski M. J. , Dibenedetto A. T.
Published: April 2004

The compatibilization by transesterification of aromatic thermotropic liquid crystal polyesters (Ar‐TLCP's) and TLCP's containing aliphatic ethylene‐terephthalate (ET) linkages has been studied. Three Ar‐TLCP's were mixed with two p(ET/HBA)'s, each having different extents of blockiness, to form a series of binary blends (Bin‐TLCP's). The morphology and physical properties of the resultant Bin‐TLCP's depend on the block structures, compositions, viscosities, and susceptibility to transesterification of the components. In this work, the influence of TLCP block structure and transesterification on the compatibility of the components of the Bin‐TLCP's is described.
Influence of impurities on mechanical properties of recycled glass fiber reinforced polyamide 66
Authors: Eriksson P.‐A. , Albertsson A.‐C. , Boydell P. , Månson J.‐A. E.
Published: April 2004

This work investigates the influences of impurities on the durability and the reliability of the mechanical properties of recycled glass fiber reinforced polyamide 66. A critical size‐concentration zone could be determined based on changes in tensile properties of samples containing untreated glass beads of different size and concentrations, which were used as simulated impurities in in‐plant reprocessed material. Characterization of samples based on recyclate from post‐use radiator end‐caps, which contained residues of EPDM rubber, showed that the tensile strength was almost unaffected by rubber particles up to an equivalent diameter, d, of ∼700 μm. However, a significant strength reduction commenced for rubber particles larger than 1200–1300 μm, and the strength showed a correlation with d−1/2. Furthermore, large simulated impurities (425–590 μm) in in‐plant material and rubber residues in post‐use recyclate showed a negative effect on the mechanical reliability.
Study on void formation in resin transfer molding
Authors: Chang Chih‐Yuan , Hourng Lih‐Wu
Published: April 2004

A 2‐D model has been developed for the transverse impregnation of a resin into a unidirectional packed fiber mat. The model takes into account two types of flow, macro‐flow around the fiber bundles and micro‐flow around the fibers in the bundles, which occur simultaneously. Both flows are described by Darcy's law. Results show that if the ratio of permeability of the macro‐flow to the micro‐flow is more than 20, an elliptic type void is formed within the fiber bundle, and the void will shrink and disappear if vacuum assistance is applied in the mold. The capillary effect was also investigated by use of a numerical simulation based on a body‐fitted finite element method and by experiment. A correlation between the capillary force and other parameters is proposed for the XT‐D/O unidirectional fiber mat. The quasi‐equilibrium capillary effect is limited to when the modified capillary number is about O(10−4).
Conductive elastomeric foams prepared by in situ vapor phase polymerization of pyrrole and copolymerization of pyrrole and N‐methylpyrrole
Authors: Fu Yueping , Weiss R. A. , Gan Poh Poh , Bessette Michael D.
Published: April 2004

Electrically conductive elastomer foams were prepared by in situ vapor phase copolymerization of pyrrole and N‐methylpyrrole within preformed polyurethane foams. The conductive polymer is formed within the dense polymer phase of the foam, and the conductivity of the composite foam ranged from 10−1 to 10−7 S/cm. The conductvity depended on the density of the foam, the amount of conducting polymer incorporated, and the copolymer composition. Replacing with N‐methylpyrrole in the copolymer lowered the conductivity.
The degradation of high impact polystyrene with and without starch in concentrated activated sludge
Authors: Jasso G. C. F. , González‐Ortiz L. J. , Contreras J. R. , Mendizábal M. E. , Mora G. J.
Published: April 2004

Disposal of plastic solid waste is primarily accomplished by landfilling, degradation, and recycling. Degradation is highly justified in some applications. In this work, high impact polystyrene blended with starch (16–32% weight) in a “V” mixer is degraded in concentrated activated sludge for 12 weeks. Samples of 0.75 mm thickness were obtained in ribbon geometry by single screw extrusion. Mechanical degradation was determined by stress‐strain tests. Gel permeation chromatography measurements established changes towards lower polymer molecular weights. Scanning electron microscopy examination showed the presence of microorganisms in the polymer samples, as well as changes in polymer morphology in areas near holes produced in samples. Results demonstrate the utility of concentrated activated sludge in polymer degradation and the effectiveness of starch inclusion as a filler to accelerate the structural molecular changes.
A study of sub‐Tg heat flow transition of cured epoxy resin
Authors: Chen Xiangxu , Li Shanjun
Published: April 2004

The physical aging behavior of fully and partially cured epoxy resins based on diglycidyl ether of bisphenol A(DGEBA) has been investigated by differential scanning calorimetry (DSC). A sub‐Tg heat flow transition (Tg1) could not be attributed to the phase separation or dynamic mechanical relaxation, as reported in the literature. In both fully and partially cured epoxy resins, it occurs only when the cooling rate is higher than that having the lowest Tg in the DSC scan. Therefore, it could be attributed to the motion of the internal stress‐relaxed molecular chain.
Thermomechanical studies on newly developed copolyester thin films. Part II: Thermal and intrinsic stress
Authors: Shi Frank F. , Economy James
Published: April 2004

Thermal stresses were determined by a wafer bending technique for a newly developed family of all‐aromatic and aromatic/aliphatic copolyester thermosetting films prepared by spin coating. The intrinsic stresses of the films were also estimated for T > Tg (glass transition temperature). The effects of chemical structure and film processing conditions on thermal stresses are discussed. Thermal stresses varied with temperature and processing conditions, and the variations were dependent upon the chemical structures and Tg of the copolyester films. The Tg's of different copolyesters were also estimated from thermal stress‐temperature curves.
Kinetics of polyesterification of adipic acid with 1,3‐butanediol
Authors: Bacaloglu Radu , Fisch Michael , Biesiada Keith
Published: April 2004

The kinetics of non‐catalyzed, acid catalyzed and alkyltin catalyzed polyesterification of adipic acid with 1, 3‐butanediol as a model for polymeric ester synthesis was followed at 180°C and 215°C by monitoring of carboxyl, hydroxyl, and water content of the reaction system. The rate constants of the three processes were calculated using a simulation method. The process is kinetically controlled during the first 4–10 h (down to AV ≅ 20 mg KOH/g, conversion 95%) and then thermodynamically controlled by elimination of water from the system. Methyltin derivatives, especially trichloride, are more active catalysts but dibutyltin oxide can be used with good results. The model study suggests that addition of the catalyst at the beginning of the process and applying a vacuum (pressure 60 Torr) will reduce the reaction time in half, compared with adding catalyst at AV ≅ 20 mg KOH/g and using no vacuum.
Theoretical analysis of the thermally induced delamination of polymeric coatings in double‐coated optical fibers
Authors: Shiue Sham‐Tsong
Published: April 2004

To maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double‐coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double‐coated optical fibers to minimize the thermally induced coating's delamination is also discussed.
The effect of surface tension on extrudate swell from square and rectangular channels
Authors: Gifford W. A.
Published: April 2004

The effect of surface tension on extrudate swell of a Newtonian fluid from square and rectangular channels is presented. Surface tension decreases extrudate cross‐sections in all cases examined. The influence on the shapes of final extrudate profiles is found to be greater for channels with higher aspect ratios. Surface tension has the greatest influence on the swell of the longer side of the extrudate while that of the shorter side is virtually unaffected. The effect of the capillary number can be significant and in certain cases should be considered in the design of extrusion dies.
Free volume, mobility, and structural relaxations in poly(ethylene oxide)/poly(methyl methacrylate) blends
Authors: Wästlund C. , Schmidt M. , Schantz S. , Maurer F. H. J.
Published: April 2004

Time‐dependent structural relaxations in a melt‐mixed 38/62 vol% poly(ethylene oxide)/atactic poly(methyl methacrylate) blend were studied using several techniques: differential scanning calorimetry, pressure‐volume‐temperature analysis, positron annihilation lifetime spectroscopy, dynamic mechanical analysis, and solid‐state nuclear magnetic resonance. The internal volume (free volume hole size) and the external volume (specific volume) of the blend are found to decrease with aging time. The time scale of the volume changes is the same, suggesting that internal and external volumes can be calculated from each other. Increasing mobility of poly(ethylene oxide), composition fluctuations, and shifting glass transition temperatures are observed upon aging. Phase separation in terms of spinodal decomposition below an upper critical solution temperature occurs within minutes and results in two amorphous phases of different composition. Subsequent crystallization then causes further structural changes.
Barium sulfate–filled blends of polypropylene and poly(styrene‐co‐acrylonitrile)—dynamic mechanical melt state properties and interlayer effects
Authors: Hammer Claes O. , Maurer Frans H. J.
Published: April 2004

Different microstructures were obtained as a result of the chemical character of the polymer phases in barium sulfate–filled blends of polypropylene (PP) and poly(styrene‐co‐acrylonitrile) (SAN). The microstructure was controlled with the aid of low molecular mass maleic anhydride–grafted polypropylene (PP‐g‐MAH), which seems to form an interlayer around the filler particles resulting in controlling of the polymer phase in which the filler is occluded. The variation of the properties as a function of the concentration of PP‐g‐MAH with different amounts of grafted maleic anhydride and the average filler size was found to be due to a change of the microstructure. A low molecular weight PP‐g‐MAH interlayer around the filler particles occluded in the PP phase, dilution of the filler when occluded in the PP matrix phase of low viscosity as compared with SAN and filler network formation were found to be of importance for the dynamic mechanical properties. A theoretical model, the interlayer model, was used to simulate the dynamic mechanical properties of the filled blends.
Process studies in precision injection molding. II: Morphology and precision in liquid crystal polymers
Authors: Liu C. , Manzione L. T.
Published: April 2004

Precision injection molding is an important technology for improving productivity and lowering costs in fields such as electronics, photonics, and medical plastics by allowing the substitution of molded plastics for more expensive metal and ceramic parts. The work in this phase of the program examines correlations between morphology and precision of injection molded liquid crystal polymers. The materials were poly(benzoate naphthoate) polymers with several different filler packages including glass fibers and minerals. These materials show a distinct skin/core morphology in which the relative amounts of skin and core vary with process parameters. The precision of the parts is affected by this ratio of skin to core.
Shear and extensional flow of a thermotropic liquid crystalline polymer
Authors: Pickles A. P. , Gibson A. G.
Published: April 2004

The flow of a thermotropic liquid crystalline polymer (unfilled and glass fiber filled) was studied using a capillary rheometer and an instrumented injection molding machine. Despite different thermal histories, the techniques gave similar results. From 330 to 350°C, viscosity was independent of temperature. At 340°C, where most measurements were carried out, pronounced shear‐thinning occurred and the shear flow curves were nonlinear, the power law exponent decreasing from 0.51 at a shear rate of 10 s−1 to 0.35 at 104 s−1. A previously reported model was used to derive elongational flow curves from die entry pressure data. Because of the nonlinearity of the flow curves, quadratic log‐stress vs. log‐strain rate plots were needed to model behavior over the strain rate region studied. The elongational flow curves were similar in shape to the shear flow curves, with an effective Trouton ratio of 30. Despite orientation and structure present in the melt, the extensional viscosities and Trouton ratios were within the range found with normal thermoplastic melts. The results suggest that extensional flow may be inhomogeneous, the flowing units possibly being partially ordered domains.
Extrusion of polypropylene. Part I: Melt rheology
Authors: Brandao J. , Spieth E. , Lekakou C.
Published: April 2004

This paper considers the rheology of extruded polypropylene regarding melt flow index, shear viscosity, and die swell. Two grades of polypropylene are studied with differences in the molecular weight and rheology. An Instron capillary rheometer is used for the measurement of viscosity and die swell. A range of shear rates and temperatures is covered in these measurements. Die swell is also measured in polypropylene extruded through a commercial single screw extruder where the effect of varying conditions of cooling and annealing on die swell are tested. A detailed theoretical analysis is carried out for the die swell. Analytical expressions are employed for the description of viscosity and die swell with empirical constants which are determined from the experimental data.
Polymerization of styrene in a continuous filled tubular reactor
Authors: Yoon Won Jung , Choi Kyu Yong
Published: April 2004

Free radical solution polymerization of styrene has been studied using a binary mixture of symmetrical bifunctional initiators in a filled tubular reactor packed with static mixers. Owing to intensive radial mixing induced by the static mixers, a near plug flow pattern was obtained in the reactor with some axial dispersion effect. The axial mass dispersion coefficient was determined from the residence time distribution experiment and a dynamic axial dispersion model has been developed and solved to investigate steady state and transient behavior of the filled tubular reactor. With a solvent volume fraction of 0.3, the monomer conversion up to 70% was obtained without fouling problems in the temperature range 90 to 120°C. The experimental filled tubular reactor was operated under various reaction conditions and a reasonably good agreement between the model and the experimental data was obtained without using any adjustable parameters.