bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical and relaxation properties of flame‐sprayed ethylene‐methacrylic acid copolymer
Authors: Brogan Jeffrey A. , Berndt Christopher C. , Simon George P. , Hewitt David
Published: April 2004

A range of physical and chemical properties of flame‐sprayed ethylenemethacrylic acid copolymer (EMAA) were assessed, following different processing conditions. Coatings were produced at a range of specific temperatures by varying the propane flow rate and gun traverse rate. The flame spraying process oxidizes the EMAA copolymer during processing, the extent of oxidation increasing with greater deposition temperatures. Coatings were scanned using dielectric relaxation spectroscopy at a frequency range from 102 to 106 Hz over a temperature interval of ‐20 to 85°C. The glass transition temperature (usually denoted as the β′ relaxation in this system), is attributed to the microBrownian motion of long chain segments in the amorphous phase and is found to decrease with increasing deposit temperature. The oxidation process appears to reduce the position of the β relaxation due to chain scission. The molecular weight for the EMAA powder was reduced from 22,693 g/mol to 9302 g/mol when deposited at 271°C as shown by gel permeation chromatography. Despite the decrease in chain length, the activation energies for β′ relaxation increased with increasing coating temperatures. This is attributed to the increased polarity of the oxidized coatings resulting in greater intermolecular association, which outweighs the decreased chain length.
Fibrillar morphology development of PE/PBT blends: Rheology and solvent permeability
Authors: Monticciolo A. , Cassagnau P. , Michel A.
Published: April 2004

Morphology, rheology, and permeability studies were carried out for blends of polyethylene (PE) and polybutylene terephthalate (PBT). The effect of draw ratio at the die exit of the extruder on blend morphology was investigated, and thus isotropic fibrillar morphology with different aspect ratio was obtained. The solvent barrier properties of these blends improve as the aspect ratio of the PBT fibrils increases. Rheological experiments showed that these properties can be closely related to the development of a physical network structure of the PBT fibrils. Furthermore, the elaboration of a composite polymer system PE/PBT has been made by a second extrusion processing step. This system led to anisotropic oriented PBT fibrils in the PE matrix. Thus, random oriented PBT fibrils appeared to be an effective way of improving the barrier properties of PE/PBT blends.
Partially miscible EVOH/copolyamide‐6/6.9 blends: Thermal, dynamic‐mechanical and shear rheology behavior
Authors: Nir Y. , Narkis M. , Siegmann A.
Published: April 2004

Binary blends of two random copolymers, ethylene‐vinyl‐alcohol (EVOH) consisting of different ethylene contents, and copolyamide‐6/6.9 with an approximate 1:1 comonomer ratio, have been prepared via blown film extrusion as films, 20 μm thick. Thermal, dynamic‐mechanical, and rheological properties were determined. It was found that these blends are partially miscible. The‐EVOH‐rich blends exhibit much lower miscibility than the copolyamide‐rich blends. The ethylene content in the EVOH affects the miscibility of the blends: a higher ethylene content results in a lower miscibility. This is due to fewer intermolecular hydrogen bonds between the OH group of the EVOH and the amide group of the copolyamide. The interactions between the blends' components affect their thermal, dynamic‐mechanical and their rheological behavior.
Shear rate effect on the resistivity of HIPS/LLDPE/carbon black extrudates
Authors: Breuer O. , Tchoudakov R. , Narkis M. , Siegmann A.
Published: April 2004

The effect of shear level on the structure and resultant resistivity of CB‐containing high impact polystyrene/linear low density polyethylene (HIPS/LLDPE) extrudates produced by a capillary rheometer, as a function of blend composition and CB content, was studied. The data were compared with results obtained by various processing methods such as compression molding, extrusion, and injection molding. The conductivity of systems consisting of a single polymer matrix is more sensitive to shear rate than are those with HIPS/LLDPE matrices. Increased temperature tends to increase resistivity at high shear rates, and has practically no effect at low shear rates. Capillary entrance effects determine the CB structure and resultant resistivity of the extrudates. Apparently, the combined effects of CB location and flow‐induced structuring may explain the enhanced conductivity of some of the extrudates.
Melt strength of polypropylene: Its relevance to thermoforming
Authors: Lau H. C. , Bhattacharya S. N. , Field G. J.
Published: April 2004

The melt strength of homopolymer, copolymer and high melt strength (HMS) grades of polypropylene (PP) was measured to assess the sagging resistance of PP for thermoforming applications. Acrylonitrile‐butadiene‐styrene (ABS), which can be easily processed during thermoforming, was also studied in this work. A polymer with high melt strength is considered to have a better sagging resistance. The melt strength measurements were carried out using a Gottfert “Rheotens” melt strength tester. The melt strength of the polymers increased with decreasing temperature and increasing extrusion rate. ABS generally had the highest melt strength in the low extrusion temperature region approaching the thermoforming region, indicating that it has a good sagging resistance during thermoforming. The HMS PP had significantly higher melt strength than conventional PP grades; therefore HMS PP is expected to have an improved sagging resistance. For conventional PP, melt strength was higher for the lower melt flow index (MFI) grades. A sharp increase in the melt strength was observed for conventional PP at low extrusion temperature, probably due to flow‐induced crystallization of the PP. These results indicate that to minimise the sagging problem with conventional PP, low MFI grades should be used and thermoforming should be performed at temperatures close to the melting point of PP.
Effect of holding time on high strain hysteresis loss of carbon black filled rubber vulcanizates
Authors: Kar Kamal K. , Bhowmick Anil K.
Published: April 2004

Hysteresis loss has been measured at constant stress and constant strain, at various holding times under tensile deformation of natural rubber (NR) and styrene‐butadiene rubber (SBR) vulcanizates filled with various loadings of carbon black filler. The effects of temperatures (25°C to 150°C), strain rates (3.78 × 10−5 sec−1 to 210 × 10−3 sec−1) and strain levels (20% to 300%) have been studied. Hysteresis loss and hysteresis loss ratio increase with an increase in strain rate, filler loading, strain level and holding time. It decreases with an increase of temperature. However, higher hysteresis loss and hysteresis loss ratio are observed at constant stress than at constant strain. NR and SBR vulcanizates show similar behavior. Evidence has been produced for the existence of a distinct relaxation process that occurs within first 120 second of holding time at room temperature. This process becomes less important as the strain or the temperature is increased. However, at high temperature another distinct relaxation process has been observed. The activation energy has been found to be 66.3 kJ/mole for the rates at the higher holding time, while it has been found to be 17.3 kJ/mole for the rates at the lower holding time using the data of hysteresis loss at first cycle of 40 phr black filled NR vulcanizates.
On‐line density and crystallinity of polyethylene terephthalate during melt spinning
Authors: Bansal Vishal , Shambaugh Robert L.
Published: April 2004

The density and crystallinity of polyester fiber were measured on the moving threadline during the melt spinning process. The density was calculated by applying the continuity equation at points along the length of the threadline. Experimental inputs to the equation included paralle, on‐line measurements of fiber diameter, fiber velocity, polymer mass flowrate, fiber temperature, and fiber birefringence. When spinning speeds exceeded 4500 m/min, a distinct rise in density occurred along the threadline. This rise corresponded with the rise in birefringence.
Hydrosilylation of terminal double bonds in polypropylene through reactive processing
Authors: Malz Hauke , Tzoganakis Costas
Published: April 2004

The melt‐phase hydrosilylation of terminal double bonds in polypropylene (PP) was investigated. The double bonds were generated by peroxide initiated degradation of PP in an extruder or a batch mixer. For this purpose, an organic peroxide, Lupersol 101, was employed in concentrations of 0.5–5 wt%. A hydride‐terminated polydimethylsiloxane was employed as a model substance to investigate the feasibility of hydrosilylating the terminal double bonds of the degraded polypropylene. Reactive processing experiments were carried out in a hot press, a batch mixer, and a single screw extruder. Two different reaction mechanisms were used to initiate the hydrosilylation reaction: a radical chain addition mechanism and a platinum catalyzed mechanism using Karstedt's catlyst. For the radical mechanism, it was shown that catalytic amounts of a peroxide could initiate the addition of silanes to the double bonds of the degraded polypropylene. Furthermore, it was found that both reactions, degradation and hydrosilylation, could be performed simultaneously. For the catalytic mechanism, the required stabilization of the platinum colloid formed in this mechanism was accomplished by adding t‐butylhydroperoxide as a cocatalyst. This melt‐phase hydrosilylation route may be used to produce terminally functionalized polypropylenes, and a case study involving the terminal attachment of a styrene functionality was examined.
Pressureless sintering of polycarbonate powder compacted at ambient temperature
Authors: Vick Linda W. , Kander Ronald G.
Published: April 2004

Solid‐state processing of polymer powders through compaction and sintering has potential advantages over conventional polymer processing methods. However, pressureless sintering of compacted polymer powders has been unsuccessful. In a previous paper (2), room temperature compaction of polycarbonate powder was studied to better understand the fundamental mechanisms that control polymer compaction. This paper focuses on the pressureless sintering of room temperature compacted polycarbonate powder. Thermomechanical analysis was used to characterize the dependence of dimensional recovery on time, temperature, and compaction pressure for compacts formed from both aged and unaged polycarbonate. It was found that all polycarbonate compacts exhibited irreversible expansion when heated to relatively low temperatures (∼ 50°C), with large‐scale expansion occurring near its glass transition temperature. It was concluded that irreversible expansion of polymer compacts is driven by entropic factors. Therefore, parameters that affect the degree of particle deformation during compaction also affect the degree of dimensional recovery that occurs during pressureless sintering.
Production of low‐density LLDPE foams in rotational molding
Authors: Liu Guobin , Park Chul B. , Lefas John A.
Published: April 2004

This 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

Interest 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

The 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

The 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

The 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

Microcellular 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

The 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

Neat 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

A 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

A 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

We 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

The 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

Fracture 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

A 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

Based 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

A 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

A 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

Polypyrrole 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

Extensive 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.
Formation, stability, and properties of in‐situ composites based on blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer
Authors: Machiels A. G. C. , Denys K. F. J. , Van Dam J. , De Boer A. Posthuma
Published: April 2004

This paper describes the preparation and properties of in‐situ composites based on polymers with no overlap in processing temperatures. The polymers used were Vectra A900, a thermotropic liquid crystalline copolyester (TLCP), and Arnitel em630, a thermoplastic elastomer. Blends were generated by feeding the two components from separate extruders into a Ross static mixer. Different morphologies were obtained by varying the number of mixing elements of the static mixer. Using 8 mixing elements led to a stratified morphology of Vectra layers in Arnitel, using 11 mixing elements resulted in the desired continuous fiber/matrix morphology whereas a pronounced skin‐core morphology was obtained with 14 mixing elements. It is argued that in‐situ composites can be generated by a distributive mixing process without the formation of an intermediate droplet/matrix morphology as occurs in common dispersive blending equipment. Tensile modulus and strength of all blends increased with extrudate draw ratio as a result of increased molecular orientation of the TLCP phase. The level of reinforcement, however, was lower than expected, probably due to the low temperature of drawing. Annealing and capillary instability experiments showed that above the melting point of the TLCP the fiber/matrix morphology rapidly breaks up into a droplet/matrix morphology. This process takes just a few seconds for fibers of thickness ∼ 1 μm. It is shown to be the probable cause of the skin‐core morphology obtained in case of 14 mixing elements.
Cavity pressure control during the cooling stage in thermoplastic injection molding
Authors: Gao F. , Patterson W. I. , Kamal M. R.
Published: April 2004

The evolution of cavity pressure during the injection molding cycle has a strong influence on the quality of the molded part. The injection molding cycle can be divided into three stages: filling, packing, and cooling. In a previous paper, the authors reported on the design and implementation of a strategy to control cavity pressure during filling and packing. This paper deals with cavity pressure control during the cooling phase. A coolant temperature control system has been designed for the control of cavity pressure during the cooling phase. Alternative variables have been defined to describe changes in cavity pressure during the cooling phase. The concept of controlled pressure cooling time (CPCT) has been defined and selected as the most appropriate controlled variable. The dynamics of CPCT have been studied in relation to coolant temperature. A control system for CPCT has been designed and implemented. Finally, the paper shows that the control of CPCT is an effective approach for the control of cavity pressure during cooling.
Study of thermoplastic foam sheet formation
Authors: Lee Shau‐Tarng , Ramesh N. S. , Campbell Gregory A.
Published: April 2004

This paper discusses theory and experiments on nonisothermal foam growth during foam sheet formation in an extrusion process. The extruded foam sheet expands and cools simultaneously when exposed to ambient temperature. A viscoelastic cell model in the literature was modified to include heat transfer and gas loss effects during foam sheet formation. Experiments were conducted using a twin‐screw extruder to study the effect of ambient temperature and initial sheet thickness on foam characteristics. The foam was made using low‐density polyethylene with CFC‐12 as the blowing agent. The experimental results are compared with theoretical predictions to check the validity of the model. The results reveal that heat transfer effects become important when sheet thickness decreases to the millimeter range. Agreement between theory and experiment is good when an appropriate boundary condition, to account for the gas loss, is included in the model.
Air bubble migration through a cast solution of poly(methyl methacrylate)
Authors: Schruben Dale L. , Kumble Dinesh
Published: April 2004

Transport of air (with solvent vapor) bubbles that sometimes appear in a polymer/solvent liquid are followed in the process of solvent casting the polymer. The concentration profile of the solvent in the developing casting is found to be the primary controller of bubble rise velocity. This velocity dependence on concentration is developed through experiment over the range of conditions in the casting [∼90 to 0% methylene chloride in poly(methyl methacrylate), molecular weight 300,000, and Tg 110°C]. Assumptions of quasi steady‐state and penetration type theories are used to generate this simplest model, qualitatively (and semi‐quantitatively) correct in predicting the skin layer/bubble layer/bulk layer structure in solid polymer pieces produced by the solvent casting process.
Thermal characterization and morphological study of polyphenylene sulfide–polycarbonate blends
Authors: Lim Soonho , Kim Junkyung , Park Min , Choe Chul‐Rim , Lee Jeongmin , Kim Daeheum
Published: April 2004

The thermal behavior and phase morphology of binary blends of poly(phenylene sulfide) (PPS) with polycarbonate (PC) have been investigated. Differential scanning calorimetry and dynamic mechanical thermal analysis indicate the blends are immiscible, but the glass transition temperature of PC in the blends was found to be decreased due to the degradation of the PC. The PC degradation was investigated by measuring the molecular weight of PC extracted from the blends. Rheological properties of the blends were also studied using a rheodynamic spectrometer. An inversion of the phase morphology was observed from the scanning electron microscopy and dynamic mechanical thermal analysis. The increase of crystallinity of the PPS in the blends was found from a DSC study.
Simultaneous prediction of the modulus and yield strength of binary polymer blends
Authors: Kolarik Jan
Published: April 2004

A new scheme is proposed for the simultaneous prediction of the modulus and yield (or tensile) strength of binary blends, which employs a two‐parameter equivalent box model and the data on the continuity of constituents acquired from the percolation theory. Prediction of the elastic modulus in the linear stress‐strain region assumes “perfect” interfacial adhesion; at yielding (or breaking), the upper and lower bounds have to be distinguished, those bounds being related, respectively, to the interfacial adhesion sufficient and insufficient for the transmission of the acting stress. The modulus and the upper bound of yield (or tensile) strength are monotonic functions of the blend composition within the interval delimited by the values characterizing the components. The lower bound of strengths passes through a minimum (close to the 50/50 composition) linked to the minimum sum of the continuity parameters of the constituents. Predicted dependences of the modulus and of the yield (or tensile) strength on the blend composition are in a good accord with experimental data selected from literature.
Effects of thickness on the specific essential work of fracture of rigid PVC
Authors: Levita G. , Parisi L. , Marchetti A. , Bartolommei L.
Published: April 2004

The fracture behavior of sheets of rigid poly(vinyl chloride), PVC, 2 to 10 mm thick, was investigated according to the Essential Work of Fracture (EWF) approach in order to find evidence of thickness effects. Test pieces were doubly notched and loaded in tension. Critical values of the J‐integral were measured, in three‐point bending, either complying with or violating the size requirements dictated by the ASTM 813.89 protocol. It was found that Jc did not depend on sample thickness; on the contrary, the value of the Specific Essential Work of Fracture, obtained by means of test pieces with ligaments larger than three times the thickness, was strongly affected by the sample thickness. The size of the plastic zone that developed around the ligaments was measured by optical means. At small ligaments the height of this zone linearly increased with ligament size and tended to level off at large ligaments. In the linear range, the rate of increase of the size of the plastic zone did not depend on sample thickness. It was found that the value of the Specific Essential Work of Fracture obtained by test pieces whose plastic zones were in the linear range was independent of thickness.
A calibration technique to evaluate the power‐law parameters of polymer melts using a torque‐rheometer
Authors: Marquez Alfredo , Quijano Jafet , Gaulin Marc
Published: April 2004

In this work we develop an empirical method to calibrate the measuring head of a torque‐rheometer to obtain the power‐law parameters of polymer melts. This method is based on a similar analysis developed by Lee and Purdon. However, in this work, only one geometrical parameter, with well‐defined physical limits, is needed for calibration, instead of the two arbitrary parameters proposed by the previous authors. Moreover, this parameter is closely related to the ordinate of the logarithmic relationship between the torque (MT) and the angular velocity (S1), obtained from the torque‐rheometer data. This allows us to define a calibration function for this parameter, which is used to evaluate the consistency index (m) of the melt. On the other hand, experimental results confirm the equivalence between the slope of the logarithmic values of torque and angular velocity obtained from the torque‐rheometer data and those of shear stress vs. shear rate obtained from capillary rheometry. This further highlights the feasibility of evaluating the melt flow index (n) and the consistency index (m) from the torque‐rheometer data.
Viscoelastic features of molten blends of poly(vinyl chloride)/poly(ethylene‐vinyl acetate)
Authors: Hernández R. , Del Agua J. A. , Peña J. J. , Santamaría A.
Published: April 2004

Dynamic viscoelastic measurements and extrusion rheometry results of immiscible and partially miscible PVC/EVA blends from 50 to 90 wt% in PVC are presented and compared with those of plasticized PVCs. From loss modulus data the plateau modulus, GNo, associated with entanglements, is calculated. The variation of GNo with composition is analyzed using the theory of Tsenoglou. A simple model, which accounts for the effect of a structural parameter and the effect of free volume, is used to adjust viscosity data, taken at several frequencies and shear rates. For both types of blends, best fits are obtained using a model that establishes that the free volume of each polymer is not measurably altered by the other.
Reaction injection molding: Analyzing the filling stage of a complex product with a highly viscous thermoset
Authors: Haagh G. A. A. V. , Peters G. W. M. , Meijer H. E. H.
Published: April 2004

Although numerical simulation has proved to be a useful tool to predict the filling behavior of injection molding products, few applications in reaction injection molding (RIM) have been reported. This is mainly due to the lack of appropriate descriptions of the material behavior, and to the lack of accurate material data. The analysis of the filling stage of the RIM process requires the determination of the cure kinetics and the rheological, pvT, and thermal behavior of the material, which in this study is a highly filled copolymer of ethylene and vinyl‐acetate (EVA). Since this copolymer yields some viscosity anomalies, due to the amount of filler, the rheology of a similar EVA compound with low filler content was also investigated. The viscosity of this compound can be described by a Carreau model at low conversions levels (<1%), whereas a conversion‐dependent Power‐Law model proves appropriate for higher conversion. Moreover, the viscosity behavior of both compositions is similar in the processing range. The combined Carreau/Power Law viscosity model is used for the numerical simulations of a complex product. The simulation results agree well with experimental molding results. The analysis shows that a combination of material characterization and modeling, numerical simulation, and experimental verification is necessary to make simulation programs a useful design tool for RIM products and molds.
Antiplasticization behavior of polycaprolactone/polycarbonate‐modified epoxies
Authors: Don Trong‐Ming , Bell J. P. , Narkis M.
Published: April 2004

Antiplasticization behavior was found in the polycaprolactone (PCL)/polycarbonate (PC)‐modified epoxy system, cured with an aromatic amine. The initial modulus increased and the fracture toughness and the elongation at break decreased with the addition of the PCL/PC modifier. The glass transition temperature (Tg) decreased slightly. In this system, the antiplasticization phenomenon can be explained well by the formation of hydrogen bonding between the carbonyl groups in the PCL/PC and the hydroxyl groups in the epoxy. The hydrogen bonding proportion, as analyzed from Fourier transform infrared spectra, increased with the addition of PCL/PC up to 15 parts. This is consistent with the trend observed in the mechanical properties. It was thought that for antiplasticization to occur, a strong molecular interaction is necessary for a restriction of molecular motion, in turn decreasing the free volume of the matrix and thereby causing an increase in the modulus of the material. The dynamic mechanical thermal behavior of these systems was also studied. It was found that there was no change in the molecular weights between crosslinks, which excluded the effect of crosslink density on the changes of the properties. Instead, the activation energy was increased and the peak area was decreased for the β relaxation because of the restriction of the molecular motion by hydrogen bonding. The results indirectly support the hypothesis that the motion of the 2‐hydroxypropyl ether is responsible for the β relaxation process.