bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parameters affecting process efficiency of peroxide‐initiated controlled degradation of polypropylene
Authors: Ryu S. H. , Gogos C. G. , Xanthos M. 
Published: April 2003

AbstractParameters affecting the process efficiency of the peroxide‐initiated controlled degradation of polypropylene, such as concentration of peroxide, reaction temperature, and reaction time, are investigated under in situ uniform, microsegregation, and macrosegregation conditions. Reactions were carried out under static (no mixing) and dynamic conditions on model samples and samples processed in batch mixers, respectively. As expected, MW and MWD decrease with increasing peroxide concentration. Low‐ and mid‐MW fractions increase at the expense of the high‐MW fractions. Localization of peroxide occurs under macrosegregation conditions and causes overall loss of peroxide efficiency and side reactions. MW and MWD undergo no further change after three to four times the half‐life of the peroxide. A kinetic model developed using the quasisteady‐state approximation on free radicals successfully simulates the degradation reaction kinetics for peroxide uniformly mixed. The method of moments is used to calculate the molecular weight averages. The results of this work confirm the importance of mixing uniformity as a parameter controlling the product characteristics in reactive processing.
Experimental analysis of the thermoplastic film embossing process
Authors: Haber A. , Kamal M. R. 
Published: April 2003

AbstractFilm embossing is a mechanical process in which a flat film is transformed into an embossed product. During the process, thermal and stress fields are applied to the polymer, causing changes in the microstructure and physical dimensions of the material. The engineering analysis of the process requires the study of various aspects relating to the characterization of the microstructure before and after embossing. A variety of experimental techniques were employed to characterize the properties and microstructure of embossed films in relation to: crystallinity, orientation, mechanical properties, and dimensions of the embossed films. Mathematical models were also developed to predict the temperature, stress, and deformation in the plastic films during embossing. The thermal treatment of the plastic film was shown to be the most significant factor in the process. The important aspects influencing the thermal treatment include the radiation heater temperature, preheat roll temperature, line velocity, and film thickness. In general, the heat transfer mathematical model predictions were in agreement with the experimental data. The stress and deformation analysis suggested that the embossing pressure and the rubber layer on the backup roll are significant factors in determining the dimensions and stress distribution in the nip region. © 1992 John Wiley & Sons, Inc.
Reactive polymers for blend compatibilization
Authors: Liu N. C. , Baker W. E. 
Published: April 2003

AbstractBlending of immiscible polymers offers attractive opportunities for developing new materials with useful combinations of properties. However, simple blends often have poor mechanical properties and unstable morphologies. Compatibilization of such blends is necessary. Preformed graft or block copolymers have been traditionally added to act as compatibilizers. Another route, however, is to generate these copolymer compatibilizers in situ during melt blending using functionalized polymers. In this review, a variety of reactive polymers that have been utilized in the reactive compatibilization of polymer blends is examined. They are classified into six major categories according to the types of reactive groups they have, namely, maleic anhydride, carboxylic acids, carboxylic acid derivatives, primary and secondary amines, hydroxyl and epoxide, and reactive groups capable of ionic bonding. Their preparation methods and applications and the chemical reactions they undergo during melt blending are presented. © 1992 John Wiley & Sons, Inc.
Peroxide modified polyolefin blends—Part II: Effects on LDPE/PP blends with polymer components of dissimilar initial viscosities
Authors: Yu D. W. , Xanthos M. , Gogos C. G. 
Published: April 2003

AbstractBlends of high viscosity polypropylene (PP) and low viscosity low density polyethylene (LDPE) were prepared in the Brabender batch intensive mixer. The rheological mismatch of these immiscible blend components resulted in coarse blend morphologies and poor mechanical properties. By reacting these blends with 1800 ppm Lupersol 101 peroxide at 180°C, the morphology became much finer and, at 50/50 weight ratio, assumed co‐continuous phase structure. As a result, the mechanical properties improved significantly. The above observations are attributable to the fact that the peroxide reaction at this level of concentration removes the rheological disparity of the blend components, a condition that is more favorable for efficient dispersive mixing. It has been frequently stated that the scale and uniformity of dispersive mixing affects the uniformity and controllability of reactions occuring in molten blends. This work shows, for the first time, that reactions with peroxides alter the blend morphology in a beneficial manner. The two phenomena are, therefore, mutually dependent. © 1992 John Wiley & Sons, Inc.
Advances in injection molding of fiber‐reinforced thermoplastics during 1991—Part I: Materials and processing
Authors: Kelleher Paul G. 
Published: April 2003

AbstractThis is the first part of a survey of developments reported in the open literature during 1991 on the subject of injection molding of fiber‐reinforced thermoplastics. Topics discussed include materials, polymers, reinforcing fibers and composite properties, advances in the injection molding process, fiber breakage, shrinkage, and warpage, as well as alternatives to the injection molding process. © 1992 John Wiley & Sons, Inc.
Synthesis of polystyrene and styrene copolymers by reactive extrusion
Authors: Michaeli W. , Grefenstein A. , Frings W. 
Published: April 2003

AbstractDue to the ever growing and more complex demands on the properties of polymer materials, raw material producers and plastic processing industries are more and more interested in the continuous synthesis and modification of polymers. In this article the production of polystyrene and styrene–isoprene copolymers by anionic s‐butylithium initiated bulk polymerization in a co‐rotating close intermeshing twin screw extruder is described. In spite of high reaction temperatures of above 200°C the polystyrene stays “living,” which makes it possible to modify it in the melt by adding more monomers. The following processing methods were developed and analyzed: (1) homopolymerization of styrene; (2) copolymerization of styrene–isoprene monomer mixtures; (3) sequential polymerization of styrene and isoprene. The polymerized material resulting from the above‐mentioned processes differed considerably in structural features and final properties depending on the process parameters. As for homopolymerization of styrene, the influence of the process parameters screw rotation speed and screw geometry on the range of molecular weight distribution was investigated. Products made according to the two copolymerization methods were analyzed with regard to their structure and mechanical properties. The tests revealed that for sequential copolymerization the temperature in the polymerization zone has a decisive influence on the product quality. The influence of the screw rotation speed is less important. © 1993 John Wiley & Sons, Inc.
Biaxial orientation of poly(ethylene terephthalate). Part I: Nature of the stress—strain curves
Authors: Chandran Prashant , Jabarin Saleh 
Published: April 2003

AbstractThe orientation characteristics of extruded poly(ethylene terephthalate) (homopolymer) sheets are discussed with respect to: mode of extension (simultaneous versus sequential), strain rate, stretch ratio, and temperature. The nature of the stress–strain curve recorded during the process of extension, and its dependence on the parameters of extension mentioned above, are analyzed. Results show that for specimens stretched in the biaxial simultaneous mode, the stress–strain curve is concave upward, which is typical for amorphous polymeric materials. Strain‐hardening occurs at high planar extensions, and is accompanied by a steep rise in the stress measured during stretching. The magnitude of this stress increases with increasing strain rate and extension ratios, but decreases with increasing temperature of stretching. During biaxial sequential extension, the stress–strain curve is concave upward at low strain rates or at high temperatures of stretching, but becomes convex upward at higher strain rates or lower temperatures. The curve also changes from concave to convex upward at high limiting extension ratios in the first direction. The convex upward nature of the stress‐strain curve is typical of semi‐crystalline materials, indicating the occurrence of strain‐induced crystallization during stretching in the first direction. Again, the level of stress, measured during stretching, increases with increasing strain rate and limiting extension ratio in the first direction, while it decreases with increasing temperature of stretching. © 1993 John Wiley & Sons, Inc.
Biaxial orientation of poly(ethylene terephthalate). Part III: Comparative structure and property changes resulting from simultaneous and sequential orientation
Authors: Chandran Prashant , Jabarin Saleh 
Published: April 2003

AbstractCommercial operations for producing Poly(ethylene Terephthalate) (PET), Blow molded oriented containers and films, usually involve stretching PET either in simultaneous or sequential modes. The specific orientation characteristics of these two modes are studied with respect to the stress‐strain curves and the strain‐hardening parameter. Degree of orientation, crystallinity, and physical properties are studied for each mode as functions of stretch ratio and temperature. The relationships among physical properties, orientation, and below molding characteristics are studies. © 1993 John Wiley & Sons, Inc.
Chemical products from cured unsaturated polyesters
Authors: Tesoro G. , Wu Y. 
Published: April 2003

AbstractRecovery of value from cured unsaturated polyesters, other than the approach of grinding the resin and blending it with virgin resin for applications of minor importance, has been difficult. The long established position of the resins in the marketplace, their complex composition, and economic considerations have been major obstacles. This article reports results obtained on recovery of soluble, well‐characterized products from cured resins by neutral hydrolysis and on some experimental applications of the products. © 1993 by John Wiley & Sons, Inc.
Incremental drawing for controlling synthetic fiber structure, properties, and productivity
Authors: Sussman M. V. 
Published: April 2003

AbstractThe “Incremental Draw Process” (“IDP”)“Incremental Draw Processing”* and “IDP”* are trademarks and designations for fiber orientation and elongation processes owned and patented by M. V. Sussman, Ph.D., P.E., and licensed through Arthur D. Little Enterprises, Acorn Park, Cambridge, MA 02140.
is a newly commercialized technique that controls stress and temperature profiles during high speed drawing of synthetic polymer fibers. Fiber is drawn on a single pair of shaped rolls through a large number of small draw increments within a compact space. Draw zone length and residence time are increased substantially, allowing time for morphological change. Stress relaxation between draw increments and adjustment of temperature, tension, and rate of deformation (draw) at each draw increment more effectively control stress induced crystal growth and amorphous orientation. Ultra‐orientation, improved tensile modules high tenacity, low break elongation, and low boil‐off shrinkage have been produced. Because rates of plastic deformation during drawing are drastically reduced, high fiber throughput speeds are possible, allowing direct coupling to high speed spinning lines.Commercial applications include both textile and ultra‐high strength industrial fiber production. Limited drawing of liquid crystal fibers has been demonstrated. © 1993 John Wiley & Sons, Inc.
Computer simulations on polysilanes: A new method for modeling the energetics and dynamics of their thermochromic transitions
Authors: Welsh William J. 
Published: April 2003

AbstractThe present article summarizes the author's recent work on the computer‐based molecular modeling of polysilanes [‐SiR2‐]. First, conformational energies were calculated by molecular mechanics on model compounds for poly(dimethylsilane) (PDMS), poly(diethylsilane) (PDES), and poly(di‐n‐hexylsilane) (PDHS). Discrepancies in conformational preferences between calculated and experimental results are attributed to factors not accounted for in these calculations, such as electronic stabilization and packing forces. Second, molecular dynamics simulations carried out on a model compound for PDHS suggest the presence of an abrupt “gas phase” thermochromic transition, analogous to the abrupt thermochromic transitions observed for PDHS both in solution and in the solid state. Third, we develop a methodology for testing Schweizer's theory of polysilane thermochromism based on the existence of a unique polymer‐solvent conformation‐dependent stabilization energy present in conjugated chains. In his treatment of the polysilanes, Schweizer adopted reasonable estimated values for this stabilization energy term VD. Presented here is a derivation of an analytical expression for VD based on a first‐principles approach. © 1993 by John Wiley & Sons, Inc.
A review of polyethylene–polypropylene blends and their compatibilization
Authors: Teh J. W. , Rudin Alfred , Keung John C. 
Published: April 2003

AbstractA major stream of post‐consumer plastics is a commingled blend of polyethylenes and polypropylenes, which usually exhibits lower performance compared with that of the homopolymers due to the incompatible nature of polyethylenes and polypropylenes. Various studies have been carried out to characterize the structure, morphology, mechanical, thermal, and rheological behavior of this blend. The effect of processing, modification, and compatibilization have also been studied by various workers. This article is a review of the work done on polyethylene–polypropylene blends to help in the understanding of this important blend. © 1994 John Wiley & Sons, Inc.
Self‐tuning cavity pressure control of injection molding filling
Authors: Gao F. , Patterson W. Ian , Kamal M. R. 
Published: April 2003

AbstractCavity pressure is an important process parameter for injection molding control. However, the nonlinear and time‐varying behavior of cavity pressure cause some difficulties in implementing a control system based on commonly used linear, time‐invariant design strategies. In this work, the nonlinearity and time‐varying characteristics of cavity pressure are examined for the mold filling phase. A self‐tuning controller has been developed, implemented, and tested for both regulating and tracking purposes over a wide range of conditions. It is found that the proposed control system can automatically adapt itself to different operating conditions, yielding quite accurate control. © 1994 John Wiley & Sons, Inc.
Oxidative effects of ozone on the aging of structural silicone elastomers
Authors: Keshavaraj Ramesh , Tock Richard W. 
Published: April 2003

AbstractThe changes in the physical properties of three different commercial silicone sealants used in structural glazing applications were monitored as a function of various aging factors. The variables included, simultaneous exposure to ozone and moisture in which the pH of the moisture was maintained at discrete levels of 3 and 11. The extremes of the pH range represent recorded values for acid rain (pH = 3) and basic cleaning solutions (pH = 11), respectively. A second portion of the study involved studying the effect of loading on the sealant performance. The experimental coupons were cut from cast sheets of DC‐790, DC‐995, and DC‐983. An Instron tester was used to measure the changes in the engineering properties such as Young's modulus, relaxation time, and ultimate tensile stress of the test samples as a function of time of exposure to the different variables. Unexposed samples, kept at ambient laboratory conditions, were used as the control. Results of these tests indicate that the Young's modulus of the samples decreases during an initial period as a result of their exposure. After this initial decrease the sample moduli showed a steady increase with time. Surface cracking was observed during the initial period, even though the moduli continued to increase. Moreover, the acid and ozone appear to act synergistically in the deterioration of the sealant. Samples exposed to the higher pH level did not show this kind of behavior. The effect of tensile loading on the sealant was significant only for DC‐983, the high modulus formulation. This was perhaps because of the creation of high stress centers. The medium modulus material exhibited good resistance to the synergistic effects causing deterioration. Ozone resulted in discoloration, softening, and change in structure in the low modulus formulation. Although the ozone did not react aggressively with silicone, its slow attack or degradation should still be of concern. In spite of the use of inhibitors, severe and acute cracks appeared on the surface of the rubber material at angles of ninety degrees across the line of tension. It is hoped that these accelerated test results can lead to more informed decisions concerning silicone sealant life following their exposure to ozone and acid precipitation. © 1994 John Wiley & Sons, Inc.
Extrusion die design for viscoplastic fluids
Authors: Liu Li‐Dah , Wen Shu‐Heng , Liu Ta‐Jo 
Published: April 2003

AbstractWe propose to apply two approaches to analyze the design and performance of extrusion dies that deliver wide and thin uniform sheets and films of fluids with yield stress. The first approach is based on the one‐dimensional lubrication approximation and the second approach is the three‐dimensional finite element simulation. The performance of a T‐die and a coat‐hanger die has been under investigation. The effects of two dimensionless groups, the Reynolds number Re and the Bingham number Bi, on lateral flow uniformity have been examined. Several design variations, such as opening the end of the manifold and inserting a choker bar into a die, have also been studied. © 1994 John Wiley & Sons, Inc.
Mechanical properties of polycarbonate–polysulfone and polycarbonate–polyetherimide blends
Authors: Kohlman William G. , Petrie Stephen P. 
Published: April 2003

AbstractFive, ten, and twenty percent by weight blends of polysulfone in polycarbonate and polyetherimide in polycarbonate were produced by melt blending. The materials were injection molded into plaques. Mechanical analysis consisting of tensile, pendulum impact, and ballistic impact testing was conducted using the plaques or samples machined from the plaques. The average impact strength and percentage of ductile failures decreased with increasing composition of polysulfone and polyetherimide. The tensile test results indicate that a relationship exists between the percent composition and the yield strength for the blends with the blends showing an improvement in tensile strength. The ballistic testing results show that a possibly linear relationship exists between the percent composition and the critical velocity for complete penetration. Differential scanning calorimetry was conducted to measure the glass transition temperatures of the materials. The presence of two glass transition temperatures and lack of transparency have indicated that the blends are immiscible. © 1995 John Wiley & Sons, Inc.
Recent developments in in‐line spectroscopy/microscopy for monitoring extrusion processes
Authors: Xanthos M. , Patel S. H. 
Published: April 2003

AbstractOn‐line/in‐line measurement technologies are increasingly finding uses for controlling the quality of polymeric materials during all phases of production and for minimizing waste in the form of off‐spec materials. In addition to commercial/developmental sensors for rheological or spectroscopic monitoring of extrusion processes, prototype instruments have been recently developed for in‐line optical monitoring of multiphase polymer melts. In this article, examples of developments in in‐line/on‐line Fourier Transform Infrared (FTIR) and Near Infrared (NIR) spectroscopy and optical microscopy and their applications to extrusion processes will be presented. © 1995 John Wiley & Sons, Inc.
The dissolution/reprecipitation technique applied on high‐density polyethylene: I. Model recycling experiments
Authors: Poulakis J. G. , Papaspyrides C. D. 
Published: April 2003

AbstractA model dissolution/reprecipitation process is studied for the recycling of high‐density polyethylene (HDPE). The process proposed basically comprises dissolution of the plastic in an appropriate solvent, reprecipitation by using a nonsolvent, thorough washing of the material obtained, and drying. The solvent mixtures involved are separated by distillation for further reuse. Toluene/acetone was tried as a potential solvent/nonsolvent pair and proved to be very satisfactory, similarly to the case of recycling low‐density polyethylene. Further investigation was focused on the effect of sample history through successive recycling cycles. The recycled grades were evaluated in terms of the following properties: melt flow index (MFI), molecular weight, crystallinity, mechanical performance in tensile mode, and grain size analysis. In all cases the recycled polymer exhibited excellent retention of its properties. © 1995 John Wiley & Sons, Inc.
Engineering analysis and design of twin‐screw extruders for reactive extrusion
Authors: Michaeli W. , Grefenstein A. 
Published: April 2003

AbstractProcess developments in reactive extrusion or reactive compounding are largely carried out in closely intermeshing corotating twin‐screw extruders. The aim of this article is to present an analytical process model for this reactor type in order to facilitate the design of screw geometry and the settings of process parameters. Taking simultaneously into account aspects of flow behavior, heat transfer, thermodynamics, physics, and chemistry, a powerful mathematical model has been developed which was compared with practical results (e.g., residence time, pressure buildup, drive energy, bulk temperature, and conversion) on lab and production scale machines. The experiments were mostly carried out for the anionic bulk polymerizations of nylon 6 and polystyrene. Furthermore the reactive blending of nylon 6 and polyethyleneterephthalate was examined. Based on these chemical systems the practical use of computer‐aided process design will be discussed. © 1995 John Wiley & Sons, Inc.
Further thoughts on the relationship between economic value added and stock market performance
Authors: Sparling David , Turvey Calum G. 
Published: April 2003

AbstractAs authors of a previous study questioning the strength of the relationship between EVA and shareholder value, and in light of the arguments posed by Keefe and Roush, we revisit the relationship between EVA and shareholder return and reexamine the evidence and issues surrounding the use of EVA as a tool for valuing investments. Using the Stern Stewart Fortune 1000 data, we examine two potential relationships for 33 food companies listed in the database. The first is between the absolute level of EVA in 2000 and 3‐, 5‐, and 10‐year shareholder returns. The second is between 3‐, 5‐, and 10‐year mean percentage changes EVA and 3‐, 5‐, and 10‐year shareholder returns. The correlations found were extremely weak in all instances tested. [EconLit citations: 9120, 9320, M410, Q130]. © 2003 Wiley Periodicals, Inc. Agribusiness 19: 255–267, 2003.