bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production of low‐density LLDPE foams in rotational molding
Authors: Liu Guobin , Park Chul B. , Lefas John A. 
Published: April 2004

AbstractThis paper describes plastic foam processing for the manufacture of LLDPE foams in rotomolding. In order to better understand the mechanisms of foaming, a fundamental study on the foaming process in rotomolding has been conducted. First, the decomposition behavior of the chemical blowing agents was studied by a thermogravimetric analyzer (TGA). The zero‐shear viscosity of LLDPEs was measured using a rotational stress rheometer. Also, an optical microscope with a hot stage was used to study cell nucleation, growth, coalescence, and coarsening in LLDPE melts, which provide an improved understanding of the foaming dynamics with a chemical blowing agent in rotational molding. Finally, the actual foaming behavior in rotomolding has also been studied. The experimental results indicate that the amount of blowing agent, the heating time, and the processing temperature play important roles in determining the cell morphology in rotational foam molding.
On the stability of reactive extrusion
Authors: Janssen L. P. B. M. 
Published: April 2004

AbstractInterest in reactive extrusion has grown considerably during the last decade. The instabilities that may occur during polymerization in extruders can pose severe limitations on the process and on its scalability. They manifest themselves as severe fluctuations in throughput and product quality or as dual steady states, one at low conversion and one at high conversion. These instabilities may be of thermal, hydrodynamic, or chemical nature. In this paper the possible sources of instabilities are identified in a qualitative way and some possibilities to prevent them are given. Because some of the instabilities are dependent on the scale of the equipment, experiment design is important when a reactive extrusion process has to be developed on laboratory equipment and successively scaled up to larger machines.
Weld line morphology of injection molded polypropylene
Authors: Mielewski D. F. , Bauer D. R. , Schmitz P. J. , Van Oene H. 
Published: April 2004

AbstractThe weakness of plastics at weld lines provides serious difficulties for the design and long term durability of injection molded parts. The goal of this work was to identify the cause of weld line weakness in polypropylene (PP) systems. The morphology of weld lines in a high molecular weight PP has been studied. It was found that the PP contains a hindered phenolic antioxidant additive that is not soluble in the polymer at the standard processing conditions. Transmission electron microscopy (TEM) pictures reveal the additive existing as a dispersed phase in the bulk polymer. Even though very small concentrations of this additive are normally used, (0.1–0.5%) large quantities were found at weld lines in a band approximately 100 nm wide and penetrating about 10 μm into the surface of the part, hindering strength development at the weld line. X‐ray photoelectron spectroscopy (XPS) results confirm enhanced concentrations of antioxidant on the flow front and mold wall surface of short shot samples. The mechanical properties (Izod impact, tensile strength) are measured for samples molded at various processing conditions, varying amounts of antioxidant additive and with and without weld lines. The results are consistent with the presence of the additive playing a key role in strength development at PP weld lines.
Spin coating of thin and ultrathin polymer films
Authors: Hall David B. , Underhill Patrick , Torkelson John M. 
Published: April 2004

AbstractThe spin coating of thin (> 200 nm thick) and ultrathin (< 200 nm thick) polymer films is examined in several solvents of varying volatility over a broad range of polymer solution concentrations and spin speeds. Experimentally measured film thicknesses are compared with a simple model proposed by Bornside, Macosko, and Scriven, which predicts film thickness based on the initial properties of the polymer solution, solvent, and spin speed. This model is found to predict film thickness values within 10% over the entire range of conditions explored, which gave film thicknesses from 10 nm to 33 μ:m. The model underpredicts film thickness for cases in which a very volatile solvent is used or the initial concentration of polymer is high, while overpredicting film thickness for cases in which a low volatility solvent is used or the initial polymer concentration is very low. These deviations are a consequence of how the model decouples fluid flow and solvent evaporation.
The vibration welding of poly(phenylene oxide)/poly(phenylene sulfide) blends
Authors: Stokes Vijay K. 
Published: April 2004

AbstractThe weldability of three blends of poly(phenylene oxide) and poly(phenylene sulfide), each with a different level or type of impact modifier, is assessed through 120 and 240 Hz vibration welds. The type of impact modifier is shown to have a large effect on the strength and ductility of welds. Weld strength in these blends is shown to be sensitive to the weld frequency; higher weld strengths are attained at the higher weld frequency. In these three blends, maximum relative weld strengths of about 70%, 85%, and 87% have been demonstrated at a weld frequency of 240 Hz. The highest weld strength in each of these three blends is achieved at different weld pressures.
Compressive behavior of microcellular polystyrene foams processed in supercritical carbon dioxide
Authors: Arora Kelyn A. , Lesser Alan J. , McCarthy Thomas J. 
Published: April 2004

AbstractMicrocellular polystyrene foams have been prepared using supercritical carbon dioxide as the foaming agent. The cellular structures resulting from this process have been shown to have a significant effect on the corresponding mechanical properties of the foams. Compression tests were performed on highly expanded foams having oriented, anisotropic cells. For these materials an anisotropic foam model can be used to predict the effect of cell size and shape on the compressive yield stress. Beyond yield, the foams deformed heterogeneously under a constant stress. Microstructural investigations of the heterogeneous deformation indicate that the dominant mechanisms are progressive microcellular collapse followed by foam densification. The phenomenon is compared to the development of a stable neck commonly observed in polymers subjected to uniaxial tension, and a model that describes the densification process is formulated from simple energy balance considerations.
Curing study of a preimidized photosensitive polyimide
Authors: Rich David C. , Sichel Enid K. , Cebe Peggy 
Published: April 2004

AbstractThe effects of curing on removal of solvent and the development of chemical crosslinks were studied in a preimidized, intrinsically photosensitive polyimide. The polymer, Probimide 412, was in solution of γ‐butyrolactone (GBL), and spun cast or doctor bladed to form samples for analysis. The films were systematically studied from soft (100°C) to hard bake (400°C), as the effects of cure environment (i.e., air vs. nitrogen) and UV exposure were monitored. The samples were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA). The index of refraction was measured by waveguide propagation mode determination. TGA results show that there is a distribution of solvent removal temperatures, probably due to polymer‐solvent binding. Solvent is removed from the polymer as it is thermally cured from ∼150°C to 300°C, and UV curing aids in the removal of solvent. Chemical crosslinks induced by both thermal and UV curing increase the refractive index and darken the material. Crosslinking broadens the glass transition and reinforces the rubbery modulus. FTIR results show that thermally induced crosslinking occurs in the polymer at 400°C in nitrogen and at 300°C in air but does not occur appreciably at 300°C in nitrogen or at any lower temperature. Ultraviolet curing also crosslinks the polymer and is caused by hydrogen abstraction from alkyl substituents and subsequent crosslinking at the benzophenone carbonyl group. During thermal curing, although there is evidence from FTIR spectroscopy that a similar reaction may occur, there are probably multiple reactions simultaneously taking place.
Particle and polymer chain orientation development in thermoformed talc‐filled thermoplastics
Authors: Suh Chang Ho , White James L. 
Published: April 2004

AbstractNeat and talc particle‐filled thermoplastic cones have been fabricated by thermoforming of compression molded sheets. The orientation of talc particles and polymer chains of thermoformed talc‐filled thermoplastics are investigated using the wide angle X‐ray diffraction pole figure technique. The levels of orientation of both talc particles and polymer chains are represented in terms of orientation factors. The talc particles were highly oriented by the compression molding and the subsequent thermoforming, and the orientation factors of talc particles of thermoformed talc‐filled thermoplastics are of order −0.9. The c‐axis of the talc particles orients perpendicular to the surface of the thermoformed parts, which means that the surface of the talc particles is parallel to the surface of the thermoformed parts.
A structural model for the catalytic polymerization of ethylene using chromium catalysts. Part I: Description and solution
Authors: Estenoz Diana A. , Chiovetta Mario G. 
Published: April 2004

AbstractA mathematical model for the polymerization of ethylene using silica‐supported chromium catalysts is presented. The fundamentals for the physical and chemical representation of the phenomenon are detailed. The emerging mathematical problem is attached and solved using a multiple moving‐boundary numerical scheme. Predictions are made using the model for the cases of low and high activity catalysts tested by experiments, and the results used to evaluate the model. The main feature of the model is its structural nature: catalyst characterization and morphology data are used to create a physical scheme that does not require the assumptions concerning particle geometry, usually made in models. The initial catalyst fragmentation process is modeled using a pore‐structure scheme based upon porosimetry data. The whole fragmentation sequence is treated as a set of steps that follow the actual rupture process of the initial solid into fragments with irregular shapes. Parameters are evaluated from data for the initial support, and time evolution is followed using a realistic interpretation of the pore filling process. A novel application of moving‐boundary solution techniques permits a relatively simple mathematical scheme to handle the transport and reaction processes that take place in the polymerizing particle. Only the results obtained for the experimental laboratory conditions are analyzed. In subsequent parts, the case of thermal effects typical of industrial conditions will be discussed. The results obtained are in excellent agreement with the experimental data.
A structural model for the catalytic polymerization of ethylene using chromium catalysts. Part II: Thermal effects
Authors: Estenoz Diana A. , Chiovetta Mario G. 
Published: April 2004

AbstractA mathematical model, including energy balances and thermal effects, for the polymerization of ethylene using silica‐supported chromium catalysts is presented. The model is based on a previous work, with the main feature being its structural nature. Catalyst characterization and morphology data are used directly in a physical scheme that does not require the assumptions concerning particle geometry found in other models in the literature. Predictions are made using the model for the cases of high activity catalysts under experimental (laboratory) and industrial reactor conditions. Catalyst fragmentation is modeled as a set of steps that follow the actual rupture process of the initial solid into fragments with irregular shapes. Parameters are evaluated from experimental data for the initial support. From modeling results, mass transfer control is not observed. Neither external mass transport phenomena, nor internal diffusive processes become restrictive for polymerization although monomer concentration decay exists. Temperature rise is relevant because of the high catalyst activity and monomer concentration typical of industrial systems. However, under controlled polymerization conditions, temperature elevation is important but not critical to polymer production. The limiting step in the energy transport process in the particle is the external transfer. The results obtained show a strong influence of reactor conditions upon polymerization reaction and polymer properties, and are in good agreement with the available data.
Impact strength improvement of polystyrene by dispersion of rigid particulate
Authors: Mitsui S. , Kihara H. , Yoshimi S. , Okamoto Y. 
Published: April 2004

AbstractWe have discovered that the impact strength of polystyrene is increased by the addition of rigid particles several microns in diameter and at concentrations of 0.01 ∼ 1 wt%. As examples, we used barium sulfate particles and crosslinked polystyrene beads. From the observation of real‐time deformation of polystyrene incorporating the rigid particles, and from finite element analysis, it is clear that the impact improvement mechanism is related to the formation of voids or peeling layers, and successive extension of crazes from the voids or peeling layers.
Study of oscillation signals in instrumented charpy impact testing
Authors: Aggag Gamal , Takahashi Kiyoshi 
Published: April 2004

AbstractThe effects of mechanical and electrical filtering were examined for signals obtained from a strain gauge installed at a dart of an impact tester. Mechanical filtering was provided by placing a thin rubber sheet on the impacted surface of the specimens. The electrical filtering was done using a 3 kHz low‐pass filtering circuit in the strain amplifier. It was shown from the results for polycarbonate Charpy specimens that mechanical filtering with a thickness of 0.5 and 1.0 mm gives good reliability for the impact velocity at both 2.8 and 4.0 m/s, not only in reducing the inertial oscillation effect but also in correctly providing values of impact energy.
The application of fracture mechanics to materials selection
Authors: Huang Donald D. 
Published: April 2004

AbstractFracture mechanics methodologies have been applied in the area of materials selection. The abilities of fracture mechanics to differentiate materials on the basis of their crack growth behavior and to incorporate fracture toughness results into rational schemes for fracture prevention are described. While a single fracture toughness value adequately describes the fracture behavior of linear elastic polymers, it is generally inappropriate for elastic plastic polymers. For these materials, the entire crack growth resistance curve should be considered.
Fracture toughness characterization of a PC/ABS blend under different strain rates by various J‐integral methods
Authors: Lu Ming‐Luen , Chiou Kuo‐Chan , Chang Feng‐Chih 
Published: April 2004

AbstractA published, nonconventionalJ‐integral method, based on the hysteresis energy and the ASTM E813 methods, has been employed to test the fracture toughness of a polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) blend. The criticalJvalues (JIc) at crosshead speeds ranging from 0.5 to 20 mm/min obtained from the hysteresis energy method are ∼10 to 20% higher than those obtained from the E813–81 method and ∼50 to 70% lower than those obtained from the E813–87 method. However, the hysteresis energy method results in comparableJIcvalues with a modified ASTM E813–87 method when the 0.2 mm offset line is replaced with a 0.1 mm offset line. The critical displacements in terms of the onset of crack initiation, determined from the plots of hysteresis energy vs. displacement, hysteresis ratio vs. displacement, and the true crack growth length vs. displacement, are fairly close in value. This indicates the critical crack initiation and the correspondingJIcobtained from this hysteresis energy method indeed represent the actual physical event of the onset of crack initiation.
Crack‐tip fields for porous solids with pressure‐sensitive matrices and for rubber‐modified epoxies
Authors: Jeong H.‐Y. , Pan J. 
Published: April 2004

AbstractBased on a set of constitutive relations developed for porous solids with rate‐dependent pressure‐sensitive matrices, the stress, strain and void volume fraction distributions are investigated near the crack tip with a finite root radius under mode I, plane strain, and small‐scale yielding conditions. A rubber‐modified epoxy is taken as our model. The rubber particles are taken as the void volume fraction from the view of stress‐carrying capacity when the epoxy is subject to extensive plastic deformation. The set of constitutive relations for porous solids is based on a generalized Gurson yield criterion for porous solids with pressure‐sensitive matrices. The set of constitutive relations has been implemented into finite element code ABAQUS to investigate the near‐tip field of a crack in porous solids. Our numerical results indicate that the plastic zones, the intense straining zones, and large void volume fraction contours are long and narrow ahead of a crack tip in porous solids with moderately large initial void volume fractions. The strain softening and subsequent hardening of the matrices also make these zones more concentrated ahead of the tip. As the initial void volume fraction or the pressure sensitivity of the matrices increases with a decrease of plastic dilatancy, these zones become more elongated ahead of the tip. The cavitation of the rubber particles in the rubber‐modified epoxy is also considered via a stress‐controlled void nucleation model. The numerical results for the rubber‐modified epoxy based on the nucleation criterion show that the shape and size of the intense straining and cavitation zones agree well with the corresponding experimental results.
Micromechanical modeling of crack‐tip rubber particle cavitational process in polymer toughening
Authors: Sue Hung‐Jue , Yee Albert F. 
Published: April 2004

AbstractA simple micromechanical modeling of the rubber particle cavitational process at the crack tip was conducted using the combination of Irwin's crack tip stress intensity factor analysis, slip‐line field theory, and Dewey's closed‐form elastic solution. This unique micromechanical modeling provides fruitful insights concerning the possible role(s) the rubber particles play in front of a constrained (plane‐strain) crack tip. The cavitation of the rubber particles at the tip of the crack causes the redistribution of the stress and strain fields around the cavitated rubber particles. This, in turn, alters the stress state the surrounding matrix experiences. Consequently, the fracture process is affected by the rubber particle cavitational event. The results of the micromechanical analyses suggest that both the preexisting holes and the occurrence of cavitation in the rubber particles in front of the crack serve (i) to relieve the plane‐strain constraint, (ii) to promote shear yielding of the matrix, and (iii) as stress concentrators. The major difference between the preexisting holes and the rubber particle cavitational event lies on the sudden buildup of the octahedral stress component upon the cavitation of rubber particles in the crack tip region. Experimental observations of toughening mechanisms of various rubber‐modified polymers support this micromechanical analyses.
Fatigue of hybrid epoxy composites: Epoxies containing rubber and hollow glass spheres
Authors: Azimi H. R. , Pearson R. A. , Hertzberg R. W. 
Published: April 2004

AbstractA diglycidyl ether of bisphenol A (DGEBA) epoxy resin was modified by incorporation of varying concentrations of hollow glass spheres (HGS) and/or reactive liquid rubber (CTBN). The fatigue crack propagation (FCP) behavior and mechanisms of such materials were studied in detail. A synergistic phenomenon reported for static fracture toughness was also observed in the FCP resistance of such composites. Optical microscopy studies revealed that the interactions between the stress fields of the crack‐tip process zone and HGS cause plastic‐zone branching, which in turn gave rise to synergistic toughening. It is also shown that process zone ‐ second phase particle interactions cause a transition in FCP behavior of rubber‐modified epoxy polymers, similar to that observed in metal alloys. Consequently, the process zone toughening mechanisms are active only above a certain stress intensity range. Conversely, FCP resistance of both modified and unmodified epoxies were the same below the transition.
The effect of process parameters on the morphology of polypyrrole coatings formed on carbon fibers
Authors: Wood Greg A. , Iroh Jude O. 
Published: April 2004

AbstractPolypyrrole coatings have been electropolymerized onto carbon fibers. Several process parameters, including the type of electrolyte, the monomer concentration, the electrolyte concentration, the applied voltage, and the electropolymerization time were systematically varied, and their effect on the morphology and composition of the coatings assessed. The SEM micrographs of the coated samples revealed several distinguishable morphologies. The presence of the counterion, derived from the electrolyte, in the coatings was confirmed by EDAX analysis, elemental analysis, and infrared spectroscopy. The doping and formation of the polypyrrole coatings occurred concuriently. The morphology of the coatings was greatly influenced by the type of electrolyte, electrolyte concentration, and the applied voltage.
Statistical analysis of product variability associated with continuous and cut sheet thermoforming operations
Authors: Ryan Michael E. , Stephenson Martin J. , Grosser Kevin , Karadin Larry J. , Kaknes Paul 
Published: April 2004

AbstractExtensive published data exist with regard to the variation of part weight and dimensions for products manufactured by injection molding and blow molding. Relatively little information is available with regard to thermoformed parts. Such data are of considerable practical and theoretical value in establishing realistic processing targets in commercial processing operations. Experimental data have been systematically collected over an extended time from three continuous roll‐fed thermoforming processes, as well as a cut sheet forming process. Two of the continuous processes studied were high‐volume production lines. One of the operations produced 16‐ounce drinking cups from a blend of a styrene‐butadiene block copolymer with polystyrene. The other commercial continuous process manufactured tubs from high‐density polyethylene. The third process studied involved a pilot plant test former used to produce 10‐ounce drinking cups from the styrenebutadiene/polystyrene blend material. All three continuous processes employ plug assist in conjunction with a multi‐cavity mold. The measured parameters included the weight of individual parts, and the wall thickness measured at several different locations. The cut sheet forming process employed a plug assist with a single‐cavity mold for the production of a scanner cover. The polymer used consisted of a blend of an acrylic and a poly(vinyl chloride) resin. The deformation and wall thickness of the scanner cover were measured at several different locations.