bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoinitiated crosslinking of low density polyethylene. IV: Continuous extrusion application
Authors: Qing Yan , Rånby Bengt 
Published: December 2004

AbstractA new continuous method is developed to crosslink polyethylene, based on a photoinitiated radical reaction. An experimental production line for low density polyethylene (LDPE) extrudate is constructed with a Brabender® extruder and an “Irradiation Unit” on line. Some new initiators of benzophenone derivatives are prepared to overcome the volatility of benzophenone and increase its compatibility with the polymer matrix. Extraction and gel swelling experiments are performed to characterize the crosslinking of the product and the results are quite satisfactory: under the conditions used, crosslinking can be optimized to about 65% gel content within 5 to 15 s irradiation time, corresponding to a production rate of about 1.5 to 0.5 m/min, respectively. The dynamic mechanical properties of the crosslinked polymer are measured through the melting region and the effects of crosslinking are demonstrated. Without affecting the rate of crosslinking, the stability against thermal oxidation of the crosslinked products is greatly improved by adding stabilizers to the compounds before crosslinking.
Blends of modified polycarbonate and high density polyethylene
Authors: Mekhilef N. , Kadi A. Ait , Ajji A. 
Published: December 2004

AbstractIn this work, blends of polycarbonate and a high density polyethylene were investigated through their morphology, mechanical properties, and the effect of compatibilizers: a copolymer styrene‐butadiene‐styrene and an ionomer. Blending was performed in the melt state at 220°C, and the concentration of the compatibilizers was varied from 1% to 5% by weight. In the case of the copolymer modified blend, the results showed no change in the mechanical properties compared to the neat blend, whereas the morphology showed that the copolymer might interact with only one phase. For the ionomer, the addition of 1% increased the Young's modulus and the tensile strength of the blend. For the morphology, a large change in the size of the dispersed phase (polyethylene) is observed. This was attributed to the compatibility of the ethylene group of the ionomer with the minor phase, and the reaction between the carbonate group of polycarbonate (PC) and the acid group of the ionomer. An investigation on the binary blends of PC and the ionomer showed the occurrence of a chemical reaction that might be of a transesterification type. Differential scanning calorimetry and Fourier transform infrared techniques were used to characterize these blends.
Influence of thickness and processing history on fatigue fracture of nylon 66. Part I: Crack propagation measurements
Authors: Wyzgoski Michael G. , Novak Glen E. 
Published: December 2004

AbstractThe influence of sample thickness on fatigue crack propagation rates in injection molded nylon 66 was determined by preparing 12.7 mm thick plaques along with more conventional 3.0 mm thick samples. Initial results suggested a large effect of thickness as the crack propagation rates were accelerated in the thicker samples and the stress dependence was also increased. Since the calculated thickness for a plane stress to plane strain transition in nylon 66 is 9.0 mm, it was thought that these results were related to the stress state at the crack tip. However, a more thorough study of the thicker plaques has now demonstrated that neither the magnitude nor the stress dependence of the fatigue crack growth rates is necessarily changed under plane strain conditions as similar results can be obtained for thick and thin plaques. It is suggested that the earlier results were confounded by a previously unrecognized processing history effect which does accelerate fatigue fracture. The latter effect is shown by thermal analysis and optical microscopy to be related to a rearrangement of the polymer network during melt processing.
Constitutive modeling and simulation of energy absorbing polyurethane foam under impact loading
Authors: Sherwood James A. , Frost Colin C. 
Published: December 2004

AbstractThe compressive‐stress strain response of polyurethane foam under uniaxial compressive impact loading has been studied. The development of a uniaxial constitutive model from strain rate controlled compression tests is detailed. Density and temperature functions have been added to the integral power model proposed by Schwaber, Meincke, and Nagy. The model assumes that the effects of density, temperature, strain and strain rate on stress are separable functions. The model correlated well with actual static compression tests and was used successfully to predict the impact response of energy absorbing polyurethane foam under uniaxial compressive loading.
Elastic moduli of semicrystalline polyethylenes compared with theoretical micromechanical models for composites
Authors: Janzen Jay 
Published: December 2004

AbstractA large collection of data on Young's modulus and density of unfilled polyethylenes at ambient conditions has been compared with various competing theoretical mixing rules developed for composite micromechanics. The objective was to see if such theories usefully predict the dependence of stiffness on crystalline content in an archetypal isotropic semicrystalline thermoplastic polymer above its glass trnsition temperature. It was found that the self‐consistent scheme derived by Hill and Budiansky from continuum micromechanics appears to have valid application to this system. The scheme naturally and coherently incorporates information on bulk and shear moduli and Poisson's ratios, while giving a good account of the main trend in the Young's modulus data. Conversely, other theoretical models frequently invoked in the polymer literature were explicitly found to be unsuitable for representing principal features of modulus‐density relationships dectated by the data.
Indentation behavior of polymer coatings on glass
Authors: Ritter J. E. , Sioui D. R. , Lardner T. J. 
Published: December 2004

AbstractFor relatively soft polymer coatings on soda‐lime glass substrates the indentation load increases substantially when the indenter penetrates into the glass substrate since the glass can now directly support some of the indenter load. A model for the indentation load‐depth behavior is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile‐up of coating material underneath the indenter. The model predicts the indentation behavior as a function of coating and substrate hardnesses and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda‐lime glass substrates shows good agreement.
Effectiveness of polymer coatings on reducing indention damage in glass
Authors: Ritter J. E. , Gu W. , Lardner T. J. 
Published: December 2004

AbstractPolymer coatings are widely used to protect glass from indentation damage. A model for the strength degradation that occurs when a sharp indenter penetrates through the coating is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile‐up of coating material underneath the indenter. The model predicts the strength degradation as a function of indentation load, coating and substrate hardnesses, and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda‐lime glass substrates shows good agreement.
Effect of melt history on the crystallization kinetics of poly(phenylene sulfide)
Authors: Mehl Nathan A. , Rebenfeld Ludwig 
Published: December 2004

AbstractDifferential scanning calorimetry (DSC) was used to study the effects of melt history on the isothermal crystallization kinetics of poly(phenylene sulfide) (PPS). Crystallization of the polymer was shown to be permanently altered by both the time and the temperature spent in the melt. Suggested explanations are nonequilibrium melting, chain scission, chain extension, and crosslinking. Molecular weight was also shown to affect the rates of these processes, PPS of lower molecular weight being more susceptible to the observed changes.
The separate roles of phase structure and interfacial adhesion in toughening a brittle polymer
Authors: Liu N. C. , Baker W. E. 
Published: December 2004

AbstractThe effects of rubber particle size and rubber/matrix adhesion on the impact properties of a brittle polymer have been separated using polystyrene (PS)/acrylonitrile‐butadiene rubber (NBR) as a model system in which interfacial chemical reaction could be controlled. It has been proven that the interfacial adhesion between the rubber phase and the PS matrix not only greatly aids in reducing the rubber particle size but also plays a further role in improving the impact properties of the matrix polymer. The impact energies of PS/NBR blends with interfacial chemical bonding are four to ten times as high as those without interfacial bonding for the same average rubber particle size. However, at temperatures below the glass transition temperature of the rubber, there is no difference in impact energies with or without interfacial chemical bonding. It has been found that the optimum rubber particle size for toughening PS is influenced by interfacial adhesion. Smaller optimum rubber particle size is observed for blends with greater amounts of interfacial chemical bonding.
Use of T1ρH as a probe for polymer blend phase structure
Authors: Natansohn A. 
Published: December 2004

AbstractT1ρH′ the proton spin‐lattice relaxation time in the rotating frame, can be used as a probe for polymer blend miscibility in the same way the glass transition temperature (Tg) is used. T1ρH has some advantages over Tg. It is indicative of the separate phases at a level of a few nanometers, below what Tg can distinguish. Also, T1ρH is the only parameter related to the local proton density in a sample. This paper shows a few examples of T1ρH investigations, including thermally reversible blends, phase separated composites, and mixtures of polymers with small molecules.
Rheological properties of corona modified cellulose/polyethylene composites
Authors: Dong S. , Sapieha S. , Schreiber H. P. 
Published: December 2004

AbstractThe rheological behavior of wood fiber/polyethylene composites made of corona treated constituents was investigated. Corona treatment of one or both of the constituents resulted in decreased melt viscosities relative to compounds containing untreated materials. The reduction of melt viscosity may originate from low molecular weight moieties formed on the surfaces of both polyethylene and cellulose during corona treatment. These may act as lubricants at interfaces. Also it was found that the corona treatment of fibers leads to higher packing volumes; this may result from a reduction in fiber length when treated fibers are processed under high shear conditions. As a result these fibers perturb the normal flow pattern in the melt to a lesser degree than the longer fibers of untreated cellulose.
Extrudate swell of high density polyethylene. Part I: Aspects of molecular structure and rheological characterization methods
Authors: Koopmans R. J. 
Published: December 2004

AbstractTwo high density polyethylene (HDPE) resins–samples 801 and 802–both nominally the same material, as they are taken from successive batches of the same commercial grade, are characterized for their molecular structure and rheological properties. Gel permeation chromatography (GPC) and low angle laser light scattering (LALLS) results must be interpreted in combination with rheological data to show the presence of somewhat more high molecular weight material in 802 that in 801. Small amplitude oscillatory shear, steady shear, and capillary shear measurements performed in different laboratories show consistently higher shear viscosity values at low shear rates for sample 802. Extensional viscosity measurements show similar results. The interpretation of rheological data in terms of molecular structure could be complicated by the possible presence of long chain branching (LCB). The zero shear viscosity and discrete relaxation spectrum is estimated for both samples. The small rheological difference between 801 and 802 forms the basic information for understanding their time dependent extrudate swell behavior, as will be described in Part II.
Extrudate swell of high density polyethylene. Part II: Time dependency and effects of cooling and sagging
Authors: Koopmans R. J. 
Published: December 2004

AbstractFor two high density polyethylene resins, the isothermal time dependency of extrudate swell has been measured. Very minor differences in the large molecular weight part of the molecular weight distribution, hardly detectable with gel permeation chromatography and low angle laser light scattering techniques, dramatically influence the time dependency of extrudate swell as well as the maximum swell attainable. The presence of larger molecules in sample 802 than in 801 is reflected in a lower short time (after seconds) and a larger long time (after minutes) or maximum extrudate swell value. Extruding the polymers through a capillary die L:D = 30:2 mm into air at ambient temperature allows only the short time swelling behavior to be observed, because cooling and sagging of the strand.
Morphology development in polymer blends
Authors: Sundararaj Uttandaraman , Macosko C. W. , Rolando R. J. , Chan H. T. 
Published: December 2004

AbstractThe major morphological changes during polymer blending occur during the initial softening stage. This work explains the evolution of phase morphology of polymer blends from pellets to submicron particles in a co‐rotating twin‐screw extruder. The extruder was opened and blend samples were taken along its length. The major phase component was extracted by means of a selective solvent so that the dispersed phase morphology could be viewed directly by using scanning electron microscopy. The two systems studied were 80:20 polystyrene/amorphous polyamide and 80:20 polystyrene/polypropylene. In both systems, the initial morphology consisted of sheets of dispersed phase. Holes form in the sheets, and these holes grow as a result of interfacial tension forces until they coalesce with each other, forming thin ligaments. These fluid ligaments are unstable and break up via mixer shear forces. Very large changes in dispersed phase size are observed during the softening stage. The particle size changes less after the polymers are completely melted. The extruder results are compared to results from a batch mixer. The same dispersed phase sheeting mechanism is seen in the initial morphology in the batch mixer and the breakup of the dispersed phase domains parallels the breakup seen in the extruder.
Development of polymer blend morphology during compounding in a twin‐screw extruder. Part III: Experimental procedure and preliminary results
Authors: Bordereau V. , Carrega M. , Shi Z. H. , Utracki L. A. , Sammut P. 
Published: December 2004

AbstractCurrently, selection of screw configurations as well as the operating conditions for compounding polymer blends with desired morphology in a co‐rotating twinscrew extruder is an art based on experience. In this paper a quenching section of a twin‐screw extruder is described. The section may replace any segment of the extruder barrel. It allows, on the one hand, a regular operation of the machine, and on the other, a rapid quenching and removal of blend specimens for morphology analysis from any place along the extruder barrel and at any time of the blending. The experimental observation of development during compounding of polymer blends enables verification and improvement of the theoretical model, aimed at predicting and controlling the size and polydispersity of the minor phase. Development of the predictive model for blend morphology will provide a valuable guide to the polymer processing industry. The preliminary data were collected using polystyrene/high density polyethylene (PS/HDPE) blends at low concentration of the dispersed phase, 5 wt% of either PS or HDPE. It was observed that the viscosity ratio, blend composition, screw configuration, temperature, throughput, and screw speed significantly influence the blend morphology.
Cyclic deformation and relaxation characteristics in polypropylene
Authors: Ariyama Takashi 
Published: December 2004

AbstractCyclic deformation and stress relaxation after cyclic preloading in polypropylene were investigated by using an electrohydraulic, servocontrolled testing machine. The cyclic deformation tests were performed under various sets of strain rate, number of cycles, and strain amplitude in the as‐received sample and a quenched sample. The stress relaxation tests were made after a cyclic preloading in both samples. The distinctive shape of the hysteresis loop, termed a propeller‐like shape, is characteristic of the as‐received polypropylene with large spherulites, in marked contrast to the behavior of metals. The curves at strain amplitudes from ± 1.5% to ± 5% indicate a propeller‐like shape; these loops change into the steady state response as the number of cycles (N) is increased up to N = 30 to 50. The drop of stress in relaxation tests for the quenched samples is smaller than that for the as‐received samples at the same strain levels. This stress drop behavior reflects the difference of spherulite structure. The stress relaxation behavior depends on the morphology, the predetermined strain amplitude, and the process of the tests.
Nondestructive quantitative determination of starch content in polyethylene by solid state NMR and FTIR
Authors: Tikuisis T. , Axelson D. E. , Sharma A. 
Published: December 2004

AbstractFourier transform infrared spectroscopy (FTIR) and carbon‐13 solid state nuclear magnetic resonance spectroscopy (NMR) were used quantitatively (and non‐destructively) to determine the starch content in a series of starch filled polyethylene samples (nominal addition levels range from 3 to 6 wt%). Data acquisition times (including sample preparation and instrument analysis) were typically a few minutes for both techniques. Current methodologies for starch analysis in polyethylene are based upon wet chemical techniques (gravimetric or enzyme analysis). The proposed methods offer several advantages over these traditional methods: they are less labor intensive, do not require chemical reagents, are relatively insensitive to changes in the sample matrix, and are fast.
Self‐Reinforced composites of two thermotropic liquid crystalline polymers
Authors: Akhtar S. , Isayev A. I. 
Published: December 2004

AbstractBlends of two thermotropic liquid crystalline polymers (LCP) based on 6‐oxy‐2‐naphthoyl and p‐oxybenzoyl moieties and p‐oxybenzoyl, terephthaloyl and hydroquinone moieties have been studied. The blends were prepared by melt mixing using a twin screw extruder. Thermal, rheological, mechanical, and morphological studies were carried out. Based on the dynamic mechanical thermal analysis and the morphological observations, the blends are found to be immiscible. The viscosity ratios of pure LCP melts exceed values of 10 over a wide range of shear rates, with the viscosity of the blends lying between those of the pure components. The prepared blends are shown to be self‐reinforced composites in which one LCP enhances the molecular orientation of the other. Studies of the injection molded bars by scanning electron microscopy indicate a complicated hierarchical morphology with microfibrils of submicron level in diameter, bundled, and intertwined into fibrils of a substantially larger diameter. Due to self reinforcement, impact and tensile properties of the blends show significant synergism when compared to those of the pure LCP components. The properties obtained are remarkably higher than those known for any high performance engineering thermoplastics.
Analysis of unsaturated polyester‐polyurethane interpenetrating polymer networks II: Phase separation behavior
Authors: Lee Sun Suk , Kim Sung Chul 
Published: December 2004

AbstractThe phase separation behavior of unsaturated polyester (UPE)‐polyurethane (PU) interpenetrating polymer networks (IPNs) was investigated by light scattering measurements during simultaneous polymerization. The scattered light intensity change with time showed the formation of the dispersed domains, and the average domain correlation length could be calculated from the angle of maximum scattering intensify. It was noted that the dominant phase separation process was spinodal decomposition due to fast reaction. The morphology observed by the transmission electron micrographs for various process conditions showed similar results as obtained from the light scattering experiment.
Electronic structure of polyaromatic nitrogen compounds: Surface analytical and electro‐optical investigations
Authors: Kessel R. , Stöckert D. , Schultze J. W. 
Published: December 2004

AbstractThe polymers of the aromatic nitrogen compounds N‐methyl‐pyrrole (P‐N‐Me‐PPY), carbazole (PCarb), and aniline (PANI) have been investigated with electro‐optical and surface analytical methods. The in‐situ reflection spectra indicate the formation of polarons or bipolarons during electrochemical oxidation, depending on polymer type. The absorption bands can be attributed to changes in the electronic structure with regard to the applied potential. Photocurrent spectra of P‐N‐Me‐PPY and PCarb show a p‐type semiconducting behaviour for the polymers in the reduced state. The transition to the oxidized state with quasi‐metallic properties is indicated by a significant shift in the Fermi level energy and can be followed with XPS and UPS measurements.
Blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer. I: Mechanical properties and morphology
Authors: Verhoogt H. , Langelaan H. C. , Van Dam J. , de Boer A. Posthuma 
Published: December 2004

AbstractBlends of a thermotropic liquid crystalline polymer (LCP), Vectra A900, and a thermoplastic elastomer, Kraton G1650, were made on a single screw extruder. During extrusion, fibers of the LCP are formed under influence of shearing and elongating forces. The stiffness and tensile strength of the elastomer are greatly improved by the addition of the LCP. The modulus of elasticity of blends containing up to 20% LCP can be described well with the Halpin‐Tsai equation. Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) measurements show that the polymers are immiscible, but the DMTA results show a shift of the glass transition temperature of the elastomeric block of the Kraton polymer. This shift may be attributed to a layer of elastomer adsorbed on the LCP particles.
Melt elasticity of incompatible blends of poly(butylene terephthalate)(PBT) and polyamide 6 (PA6)
Authors: Wakita Naoki 
Published: December 2004

AbstractThe extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi‐empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.