bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of extrudate distortion in controlled‐rheology polypropylenes
Authors: Baik Jae Jin , Tzoganakis Costas 
Published: April 2004

AbstractThe 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

AbstractFracture 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

AbstractLiquid 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

AbstractThis 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

AbstractAnnular 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

AbstractAn 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

AbstractExtensive 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

AbstractIn 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

AbstractAn 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

AbstractDifferent 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

AbstractA 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

AbstractThis 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

AbstractIsothermal 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

AbstractA 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

AbstractDuctile 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

AbstractThe 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

AbstractExtruded 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractA 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

AbstractElectrically 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.