bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure‐property relationships in thermoplastic elastomers: I. Segmented polyether‐polyurethanes
Authors: Woo Edward J. , Farber G , Farris Richard J. , Lillya C. Peter , Chien James C. W. 
Published: December 2004

AbstractSegmented poly(ether‐b‐urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′‐diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene‐2, 4‐diisocyanate (TDI). The chain extenders were symmetric N, N′‐bis(2‐hydroxyethyl) terephthalamide (BT) and N, N′‐bis(2‐hydroxyethyl)‐hydroquinone (BH) unsymmetric N, N′‐bis(2‐hydroxyethyl)isophthalamide, and linear aliphatic 1, 4‐butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment Tg, there are transitions which occur in the regions −56 to −36°C (Ta), 70 to 90°C (Tb), and 138 to 168°C (Tm). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of Ta are ∼ −51 C and −56°C for the MDI‐BT and HDI‐BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI‐BT or BI and MDI‐B polyurethane have composition‐independent Ta values of −41 and −36°C, respectively. These materials probably have considerable “domain‐bound‐ary‐mixing”. At low hard segment content the MDI‐B polymers behave as non‐crosslinked elastomers. Only the MDI‐BI polymers have Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing‐in‐domains” and is supported by morphology observed by microscopy. The next higher transition, Tb, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI‐BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI‐BI polymers disappeared at 130°C. The Tb values are 70, 83 to 90, and 100°C for the MDI‐B, HDI‐BT, and HDI‐BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI‐BT systems which decompose before melting. Thermal decomposition is a two‐stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI‐BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.
Some properties of silane‐grafted moisture‐crosslinked polyethylene
Authors: Narkis M. , Tzur A. , Vaxman A. , Fritz H. G. 
Published: December 2004

AbstractSilane‐grafted polyethylene materials are processed in conventional thermoplastic fabrication machines. The shaped articles are then crosslinked in water by the formation of Si‐O‐Si crosslinks. This paper represents studies on the crosslinking progress in different environments at various temperatures. Molecular orientation is shown to become permanent and mostly irrecoverable even at 150°C, in the silane‐grafted solid state crosslinked specimens (the crosslinking temperature in water is well below the polymer melting temperature). These frozen molecular orientations have a significant effect on the tensile properties of the crosslinked materials causing higher yield stresses and lower elongations at break. The thermal and tensile properties of some silane‐grafted crosslinked polyethylene samples and peroxide‐crosslinked materials are compared and analyzed.
Thermal analysis of photocurable materials
Authors: Appelt B. K. , Abadie M. J. M. 
Published: December 2004

AbstractPhotocurable materials such as photoresists, UV‐curable inks and paints, etc., can be analyzed by a variety of techniques. Commonly, these analyses are performed in a discontinuous mode, i.e., samples are exposed to light for varying times and subsequently they are subjected to analysis. Rates of reaction, conversion, etc., are determined from the residual functionalities; in the case of differential scanning calorimetry, these parameters are derived from the residual heat of reaction. In order to determine “photo speed” or sensitivity, a number of exposures of varying duration are necessary to obtain rates of reaction. By combining an exposure unit with a differential scanning calorimeter, the photoreaction can now he observed in situ. Determination of speed or rate of reaction is reduced to a single experiment. As a consequence, effects of wavelength, intensity, temperature, and environment are quickly examined as is demonstrated here for a photoresist. During the second scan residual exotherms can be used to determine reaction extend or formation of new thermally active products. Conversion may be limited if Tg rises during polymerization to exceed exposure temperatures. In addition, the formation of inaccessable functionalities has to be accounted for during evaluation.
Minimum end time policies for batchwise radical chain polymerization, part V—multicomponent copolymerization with one charge of comonomers
Authors: Chen Show‐An , Lee Song‐Tai 
Published: December 2004

AbstractFor batchwise radical chain solution multicomponent copolymerization, the minimum end time problem for the predetermined monomer conversion and number average molecular weight has been studied by considering the initiator concentration (or feed rate) and temperature as the two control variables. Applying the maximum principle and “unit segment treatment” (by which the co‐polymerization can be treated as homo‐polymerization in the kinetic analysis), it is found that for initiator addition processes the optimal initiator addition policy is to make the rate of initiation constant for the optimal temperature variation case, and the initiator concentration constant for the isothermal case as in homo‐polymerization. For single charge of initiator processes, the optimal initial initiator concentration is such that it should be maintained at the lowest possible value (by which the polymerization is strongly dead‐end) for the optimal temperature variation case without chain transfer steps, and at some optimal value (by which the polymerization is near dead‐end) for the best isothermal case.
Glass fiber‐filled thermoplastics. I. Wall and processing effects on rheological properties
Authors: Chung Bin , Cohen Claude 
Published: December 2004

AbstractA systematic study of wall effects on the shear viscosity of short glass fiber‐filled polypropylene and polystyrene is presented. The dependence of these effects on capillary radius, shear rate, temperature, and polymer matrix is examined. The “true” viscosity curves of these materials (free from wall effects) can be obtained by an extrapolation procedure. Breakage of glass fibers in the high shear‐rate processes of extrusion and injection molding lead to an appreciable reduction of the viscosity of these materials and is probably the more important effect to take into account in these processes.
Glass fiber‐filled thermoplastics. II. Cavity filling and fiber orientation in injection molding
Authors: Sanou Muneharu , Chung Bin , Cohen Claude 
Published: December 2004

AbstractMold filling of a rectangular cavity of three different thick nesses fed from a reservoir is studied for unfilled and glass fiber‐filled polypropylene and polystyrene. The shapes of flow fronts studied by short‐shots are affected predominantly by the thickness of the cavity with other parameters playing a less important role. Pressure drop versus volumetric flow rate inside the thinnest cavity is studied experimentally and predictions are made from a computer simulation of mold filling. The orientation of fibers in the cavity is examined using a reflect‐type microscope and the orientation is found to depend on cavity thickness, melt temperature, fiber content, and to a lesser extent, on volumetric flow rate. In the thinnest cavity, where the flow is quasi‐unidirectional, the fibers remain in the plane of flow oriented either along the flow direction or perpendicular to it, except in the region near the flow front, where they follow a “fountain” flow behavior.
Mechanical properties of polypropylene filled with calcium carbonate
Authors: Mitsuishi Kazuta , Kodama Soji , Kawasaki Hitoshi 
Published: December 2004

AbstractThe tensile behavior of polypropylene (PP) filled with calcium carbonate particles has been studied using a tensile test. In particular, the effect of strain rate, filler content, and filler size upon the elastic modulus, yield stress, and strain of surface‐modified and unmodified particles‐filled PP were investigated. The results indicated that the elastic modulus and yield stress of an unmodified system were increased with an increase of strain rate and filler content, and with a decrease of filler size. The yield strain was decreased with an increase of filler content, and with a decrease of filler size, but did not depend on the strain rate. Although the dependence of elastic modulus on the filler size was maintained even by the surface‐modified fillers, that dependence on the strain rate and filler content was decreased by such fillers. This may be because the modifier is present at the interface of filler and polymer matrix.
Separating polymer solutions using high pressure lower critical solution temperature (LCST) phenomena
Authors: McClellan Alan K. , McHugh Mark A. 
Published: December 2004

AbstractA lower critical solution temperature (LCST) phase split can be used as an alternative to steam stripping for separating polymer solutions, By adding a supercritical fluid (SCF) additive to the polymer solution, the LCST can be lowered, thus minimizing the possibility of polymer degradation and also reducing the thermal energy requirements for the process. Experimental results for the poly(ethylene‐co‐propylene)‐hexane‐SCF ethylene system are shown as an example of the type of phase behavior observed with polymer‐solvent‐SCF additive solutions. Adding 20 percent (w/w) ethylene to the polymer solution lowers the temperature of the LCST by 109°C. The addition of 30 percent (w/w) ethylene to the polymer solution lowers the temperature of the LCST curve sufficiently to merge this curve with the upper critical solution temperature (UCST) curve. When the lower critical end point (LCEP) is plotted against the critical temperature of the solvent the data for poly(ethylenie‐co‐propylene)‐solvent systems are well represented by a single curve. A more fundamental modeling approach is needed to estimate the pressure of the LCEP and the concentration of SCF additive necessary to merge the LCST and the UCST curves. Patterson's theory of corresponding states can be used for these calculations.
Binary alloys of nylon 6 and ethylene‐methacrylic acid copolymers: Morphological, thermal and mechanical analysis
Authors: Macknight W. J. , Lenz R. W. , Musto P. V. , Somani R. J. 
Published: December 2004

AbstractThe morphology and mechanical properties of binary blends of nylon 6 (N6), as the major component, and ethylene‐methacrylic acid copolymers (E/MAA), as the minor component, have been analyzed. It was found that the methacrylic acid content of the copolymer used as the second component has a profound effect upon the properties of the resulting blends. In particular, with increasing methacrylic acid content, the size of the domains of the E/MAA dispersed phase in the N6 matrix decreased in a regular fashion while the ultimate tensile properties increased regularly. This behavior has been attributed to a series of chemical and physico‐chemical interactions taking place between the two components. The interactions are due to the presence of the acid functionality on the copolymer and do not occur when this functionality is absent. Chemical analysis of the blends was performed to confirm that chemical modification took place during the blending process.
Phase behavior studies of polyarylate/copolyester blends by thermal and dynamic mechanical analysis
Authors: Golovoy A. , Cheung M.‐F. 
Published: December 2004

AbstractThe phase behavior of polyarylate blends with a copolyester based on poly(1,4‐cyclohexanedimethylene/ethylene terephthalate) was studied by differential scanning calorimetry and dynamic mechanical analysis. A single glass‐transition temperature was observed over the entire composition range. Up to 30% weight polyarylate, the copolyester crystallized readily and its melting point did not change with blend composition. This indicates that transesterification, if it occurred, was negligible. The thermal and dynamic results also suggest a weak polymer‐polymer interaction in this system.
Microscopic studies of segmented urethanes with different hard segment content
Authors: Foks Janina , Janik Helena 
Published: December 2004

AbstractThe morphology of a series of segmented polyurethanes (PUs) has been characterized by means of optical and electron microscopies. Use of a two step replica from cryogenically fractured surface appeared to be a very useful technique to characterize the morphology of segmented PUs. The materials contain poly(ethylene adipate) glycol (PEA) as a soft segment and a hard segment derived from 4,4′‐diphenylmethane diisocyanate (MDI) and butane diol (BDO). Changes in morphology have been observed as a result of the increase of the hard segment content in the series of polyurethanes. The greater the proportion of the hard segment content, the greater the number of grain aggregates on the fracture surface in the sample under investigation. PUs with the hard segment content of 22% are not crystalline and have no grain aggregates on the fracture surface. PUs with the hard segment content above 50% are anisotropic in the whole volume under polarized light and their fracture surface is grainy over almost the whole area. Two types of grain aggregates dispersed in spherulite‐like matrix have been observed for PUs of 32–50% of hard segment content. Two types of the anisotropic structure in some PUs have been found. The comparison of microscopic and thermal analysis results shows the inhomogeneous distribution of the soft and hard segments in some PUs similar to that found by Chang, et al., in the PU system based on poly(propylene oxide) endcapped with poly(ethylene oxide) as a soft segment.
Knit lines structure in injection molding of nylon 6: Relation to first solidified sample cross section
Authors: Titomanlio G. , Piccarolo S. , Rallis A. 
Published: December 2004

AbstractThe effect of processing variables on the knit line structure of nylon 6 samples was investigated. Either local sample thickening or grooves were observed at the knit lines for samples injected with mold conditioning temperatures of 130° and 30°C respectively. The results also indicate that shrinkage venting, either to or from the weld zone, is the dominant mechanism for knit line formation, which is thus related to the position where complete cross section solidification first takes place.
Effect of shear modification on the rheological behavior of two low‐density polyethylene (LDPE) grades
Authors: Ritzau G. , Ram A. , Izrailov L. 
Published: December 2004

AbstractShear modification treatment represents a special shearing history affecting mainly the elastic behavior of polymer melts. This process has been attributed to reversible physical changes in the entanglement structure of the polymer chain network. Shear modification studies were performed for two well‐characterized low‐density polyethylene (LDPE) grades differing in molecular weight distribution and degree of long chain branching. The shear working of the material was carried out using a specially designed shearing unit producing definable amounts of pure shear in a continuous process. Measurements of the dynamic storage modulus, G′, steady‐state shear compliance; Je, extrudate swell, melt flow index, and the extensional behavior (Rheotens test) indicate that primarily properties associated with the elasticity of the melt are reduced in value. The observed reduction is found to correlate with the mean specific energy dissipated during sample preparation. Comparing the two LDPE grades showed that higher degrees of modification can be obtained at lower energy input levels for the more highly branched grade. Reversibility tests were performed and complete recovery of the initial material behavior was observed. Comparison of measurement results for samples prepared using the shearing unit presented here and a Brabender Plasticorder indicates that the degree of modification depends not only on the molecular structure of the polymer but also on the manner in which the shearing history is imposed upon the material.
Kinetic studies of a composite thermoset cure reaction—application in pultrusion simulations
Authors: Ng Hendra , Manas‐Zloczower Ica 
Published: December 2004

AbstractA mechanistic kinetic model based on the concept of free radical polymerization and corrected for diffusion controlled reactions was used to describe the curing behavior of an unsaturated polyester resin. Kinetic parameters for the model were obtained from dynamic differential scanning calorimetry (DSC) scans using a multiple regression technique. The presence of kaolinite or fiber glass in the system does not affect the progression of the reaction. The results obtained from the kinetic studies were used to simulate the influence of system composition on temperature and conversion profiles inside a pultrusion die. The results of the simulations show that kaolinite and fiber glass act as heat sinks for the composite system reducing the peak exotherm and delaying curing progression.
Fracture behavior of oriented poly(ether‐ether‐ketone) (PEEK)
Authors: Wu Gwo‐Mei , Schultz J. M. 
Published: December 2004

AbstractPoly(ether‐ether‐ketone) (PEEK) is a newly developed engineering thermoplastic with potentially vast application in advanced composites due to its exceptional performance. It is thus desired to understand the relationship between physical processing, microstructure and fracture in this semicrystalline polymer. Both oriented and unoriented PEEK were mechanically characterized using static test of three‐point bend specimens. The molecular chain orientation was imposed using a rolltrusion technique. The effects of thickness, strain rate, Initial crack length ratio, and orientation on fracture toughness (Kc) are investigated. The crystallinity is also examined by density measurement. The degree of orientation is determined qualitatively by wide‐angle X‐ray scattering diffraction patterns and quantitatively by further measurement using an image analysis system. Fractographic analysis, using scanning electron microscopy, provides precise information about the mode of fracture, Results indicate that both the modulus and the fracture toughness are remarkedly increased in the direction of drawing (T‐type) as opposed to the transverse direction (L‐type).
Dependence of melt temperature on screw speed and size in extrusion
Authors: Guo Y. , Chung C. I. 
Published: December 2004

AbstractMelt temperature in an extrusion process can significantly influence production rate, product quality, and yield. However, prediction of melt temperature is extremely difficult because errors in the predictions of output rate, screw power, and heat transfer, which are used to calculate melt temperature, cumulatively cause a very large error in the prediction of melt temperature. This paper analyzed the overall energy balance of an extruder and developed a simple equation to predict the melt temperature of a projected extruder in scale‐up as a function of screw diameter, depth, and speed based on the experimental results of an experimental extruder and the polymeroperties. The predicted melt temperatures agreed reasonably with the measured values reported in a previous scale‐up study.
Alternate derivation of the effective medium conductance above and below the critical fill in a metal‐filled polymer
Authors: Schruben Dale L. 
Published: December 2004

AbstractHerein is more detail to microscopic aspects of electron transport through a conductor‐filled polymer than has yet been considered in the literature (irrespective of quantum mechanical tunneling and thermal expansion). Some of these details only clarify earlier theories, but others lead to new discoveries such as the cubic conduction path coordination number z = 18 (contrasted with the classical geometric coordination number of z = 6). New also are simplified derivations of the high and low fill asymptotes of the master equation for conductance as a function of fill fraction in the effective medium theory of conductor‐filled polymers.
Orientation and crystalline morphology of blow molded polyethylene bottles
Authors: Choi Kyung‐Ju , Spruiell Joseph E. , White James L. 
Published: December 2004

AbstractA study was carried out of the development of orientation during processing of conventional blow molded bottles made from low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE). The level of molecular orientation was found to be relatively low in all of the polyethylene bottles examined; it increased with increasing inflation pressure and decreasing extrusion temperature. Pole figures for the HDPE bottles indicated a slight a‐axis orientation toward the circumferential direction of the bottle. The b‐axes, which correspond to the lamellar growth direction, tend to be parallel to the bottle thickness direction. A comparison was made of the structure developed in blow molded bottles and blown films. The results for both films and bottles indicate that crystallization during processing involves both an increase in level of molecular orientation and an increased tendency toward biaxiality. Based on pole figures and small angle X‐ray scattering patterns, a morphological model for HDPE blow molded bottles is proposed.
Screw design in injection molding
Authors: Verbraak C. P. J. M. , Meijer H. E. H. 
Published: December 2004

AbstractThe performance of screws of advanced design in injection molding has been investigated with respect to four different objectives: (1) improvement of distributive mixing; (2) improvement of dispersive mixing; (3) increase of plasticating capacity; and (4) reduction of inhomogeneity of melt temperature.The screws used are three zone screws with different compression ratios, screws with pineapple or Maddock/Egan mixing elements, with one or two channel barrier sections, with static mixers mounted in the valve or in the nozzle, or with combinations of these different elements. The best mixing quality is obtained with multi‐channel Maddock sections. The highest plasticating capacity and, consequently, the shortest cycle times are achieved with the barrier screws. Temperature measurements show that these screws improve melt homogeneity considerably with a relatively small loss of plasticating time. In all cases, increasing the back pressure gives inferior results compared with improvement of the screw design.