bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeabilities and water vapor transmission rates for commercial polymer films
Authors: Tock Richard Wm. 
Published: April 2003

AbstractHigh molecular weight polymers have become well established as packaging or container materials. Unlike metallic and ceramic barriers, however, polymer films are known for their semipermeable nature; that is, they permit small gaseous and vapor molecules to migrate through their atomic/molecular structures. Since the intrusion of oxygen/water from the surrounding air or the loss of water/carbon dioxide from a packaged product can be detrimental to the shelf life of the product, the steady state transmission rate of a polymer film has become an important property characteristic of polymers to be used for packaging.An attempt has been made in this study to review the transmission data of commercially available polymer films. The three molecular species O2, CO2, and H2O were of particular interest. Since these permeability data vary over five orders of magnitude, several log‐log plots were constructed in order to assist decision making in film selections. Data for 34 different polymers are given. The effects of order or crystallinity, the presence of plasticizers, and the effects of laminated layering are discernible. It is the latter modification (laminating) that possesses demonstrable potential for improving the barrier properties of polymer films used for packaging purposes.
Pressure drop for molten polymer flow through tapered dies
Authors: Vlachopoulos J. , Scott P. S. 
Published: April 2003

AbstractSome approximate equations for the calculation of pressure drop for polymer melt flow through slightly tapered dies are presented. These include equations for pressure drop in a truncated cone, converging flat plates, and a converging annulus. The predicted values obtained from these equations are compared to the results of a finite element simulation for two‐dimensional flow of a power‐law fluid and some experimental data available in the literature. It is concluded that the approximate equations can be used for pressure drop calculations for dies of small taper angles and when entry, exit, and viscous dissipation effects are negligible.
Quality assurance for fiber‐reinforced composites
Authors: Frick A. , Pöllet P. , Eyerer P. 
Published: April 2003

AbstractTo ensure the growing use of high‐performance composites such as carbon‐fiber‐reinforced plastics (CFRP), the quality properties of these materials must be guaranteed. This goal can be reached through a quality assurance concept which still has to be developed. The individual steps of such a development are indicated. Flaws occuring in fiber‐rein‐forced composites are discussed, taking into consideration the manufacturing process, and the nondestructive and slightly destructive test methods suitable for flaw selected flaws are given as examples.
The development of phase morphology and polymer chain orientation in the processing of incompatible polymer blends
Authors: White James L. , Min Kyonsuku 
Published: April 2003

AbstractA critical review is presented of experimental research on development of phase morphology and polymer chain orientation in disperse two phase flow of polymer melts. It is shown that, in stratified flow, phase morphology variations are primarily caused by viscosity differences between the two phases. For disperse two‐phase flow, the phase morphology is strongly influenced by the interfacial tension as well as the viscosity ratio. This appears to be through the capillarity or Taylor number. Large interfacial tensions and small shear stresses or matrix viscosities lead to coarse phase morphologies and phase growth under quiescent conditions. Interface modification additives (compatibilizers) may be interpreted in terms of reduction of interfacial tensions. Applications to polymer processing operations and interpretation of rheological properties are described. The development of orientation of individual polymers in blends is reviewed. It is shown that chain orientation develops differently for the individual components in both compatible and incompatible blend systems. In incompatible systems, an addition of a second polymer to a crystallizing melt would appear to reduce the levels of eventual crystalline orientation in the latter, if the former shows sharp viscosity rises prior to the crystallization.
Extruder scale‐up in a corotating twin‐screw extrusion compounding process
Authors: Agur Enno E. 
Published: April 2003

AbstractThe effects of processing conditions and extruder scale are examined for a compounding process involving fully intermeshing corotating twin‐screw extruders. A systematic experimental study involving a matrix of two independent variables (extruder throughput rate and screw rotational speed) was conducted on two different size twin‐screw extruders using a styrene copolymer and carbon black. Several process parameters were examined including melt temperature at the die, motor power, residence time distribution, and carbon black concentration in the extrudate. The residence time distribution data were fit to a three‐parameter plug flow/stirred tank model to obtain a time delay, a time constant, and a mean residence time for each extrusion condition. At low screw speeds, as utilized in many compounding processes, the mean residence time dropped only slightly with increasing screw diameter (for comparable screw length/screw diameter ratios). The carbon black concentrations as measured in the extrudate pellets were within ±5% of mean value, indicating that the extruder damped out the high frequency noise caused by feed rate fluctuations in the individual polymer and carbon black feeders.
Mathematical modeling of injection mold filling: A review
Authors: Mavridis H. , Hrymak A. N. , Vlachopoulos J. 
Published: April 2003

AbstractThe flow of molten polymers in molds is described by the conservation of mass, momentum, and energy. Several simplifications have been proposed in the last 40 years. The early models were essentially unidirectional approximations. More recently, the Hele–Shaw flow approximation has been used together with the appropriate analytical or numerical methods. Current developments include commercially available computer software based on network models for flow simulation in complex molds and modern sophisticated finite element solution of the complete conservation equations that give insight to fountain flow and small scale phenomena.
Flow patterns in the calender gap of a counterrotating twin screw extruder
Authors: Speur J. A. , Mavridis H. , Vlachopoulos J. , Janssen L. P. B. M. 
Published: April 2003

AbstractThe finite element method was employed to examine the flow details in the calender gap of a counterrotating twin screw extruder. For Newtonian fluids a vortex is predicted at the entry of the calender gap. Calculations show that the vortex intensity is determined uniquely by the value of relative throughput and disappears when it exceeds 24%, for the geometrical configurations examined. Shear thinning behavior of the fluid reduces the vortex intensity. Approximate equations for the pressure drop based on the lubrication approximation are compared with the finite element results and prove accurate for engineering calculations.
The glass transition in novolac phenolic molding compounds and the kinetics of its development during cure and postcure. II
Authors: Landi Vincent R. 
Published: April 2003

AbstractThe change in onset temperature of the glass transition in a novolac phenolic molding compound was related to the time and temperature of cure. A mathematical model consisting of a single function of time and temperature fit glass transition onset temperature ranging from 87 to 242°C. These glass transition temperatures had developed during molding at temperatures from 132 to 218°C at times of 10–1800 s. The same model predicted the glass transition and onset temperature of samples postcured to a glass transition temperature of 287°C. The mathematical model resulted from a kinetic rate law treatment. This treatment, however, did not include a secondary reaction which causes a small exotherm above 210°C in DSC testing. The resulting rate law still appears to provide a useful approximation of the development of the Tg and the cure rate in novolac phenolic molding compounds over practical molding and postcure conditions.
Chemical coatings in the eighties: How are they new?
Authors: Pilcher G. R. 
Published: April 2003

AbstractThe Chemical Coatings industry is examined with regard to its progress in the field of “Compliance (lower VOC) Coatings,” with emphasis on new technologies, applications systems, and ultimate goals. Various technological areas are grouped, and discussed with regard to perceived strengths, draw‐backs, and potential future developments.
Injection welding of polyamides
Authors: Maskus Peter , Gähwiler H. U. 
Published: April 2003

AbstractIn the following article, we will discuss welding of polyamides inside the injection mold. This process is called injection welding. The process of injection welding makes it possible to bond polyamides with quite different characteristics together without adhesive. In this way, one can achieve economic as well as constructional advantages. We will discuss two different methods in this article. In the first process, two melts are injected onto each other simultaneously; with the second technique, the melt is injected onto a thermoplastic insert. The weld line strengths of injection‐welded parts depend on material and process conditions. With an amorphous polyamide, the weld line strength can be attained up to the full tensile strength of the material, while a glass‐fiber‐reinforced polyamide falls back onto the tensile strength of the basic polymer. Injection welding achieves the greatest weld line strength when two melt streams are colliding together with the highest possible injection pressure. If a melt is injected onto an insert, the temperature of the melt should be as high as possible.
Composite models of modular intermeshing corotating and tangential counter‐rotating twin screw extruders
Authors: White James L. , Szydlowski Witold 
Published: April 2003

AbstractComposite models of the flow rate and pressure profiles in modular intermeshing corotating and tangenital counter‐rotating twin screw extruders are developed. The simulation of the intermeshing corotating machine involves both screw and kneading disc elements, including left‐ and right‐handed sections. The conditions under which starvation behavior develops in sections of the screws are discussed.
Development of dispersion in the mixing of calcium carbonate into polymer blends in an internal mixer
Authors: Suetsugu Yoshiyuki , White James L. , Kyu Thein 
Published: April 2003

AbstractAn experimental study of agglomeration tendency and the compounding of calcium carbonates of varying particle size into polypropylene and polystyrene melts in an internal mixer and in a two roll mill is described. The tendency of particles to agglomerate was studied using the sedimentation volume method. Agglomeration increased with decreasing particle size. It was sharply reduced by coating with stearic acid. Agglomerate size distributions in thermoplastic matrices were measured using optical microscopy. The greatest problems in dispersing fillers were with the smallest particles. One unexpected result with the polystyrene compounds was that the number of large agglomerates of the smallest particles actually increased with time. This was associated with uncoated small CaCO3 particles clinging to the chamber walls of the internal mixer and being only gradually incorporated. The phenomenon was less pronounced in the polypropylene compounds. Generally large agglomerates were broken down with increased mixing. Stearic acid coating reduced the number of large agglomerates.
Orientation, crystallization, and haze development in tubular film extrusion
Authors: White James L. , Cakmak Mukerrem 
Published: April 2003

AbstractA critical review of research on the development of crystallinity, orientation, and haze in tubular film is presented. We examine the basic methods of characterization of polymer films and interpretation of experimental techniques. Most studies in the literature relate to polyethylene, polystyrene, and polypropylene tubular film. Polymer chain and crystallographic axis orientation have been studied using X‐ray diffraction and birefringence. We critically discuss the representation of such data using biaxial orientation factors. The data appears correlatable in terms of expressing orientation as a function of applied stresses at solidification. It appears that film haze is predominantly caused by surface roughness. This is largely associated with the crystallization of the melt on the process line.
Inorganic superconducting materials formulated in cured polymers
Authors: VanWoert H. C. , Brumlik G. C. 
Published: April 2003

AbstractFine clusters of inorganic compounds (all lowtemperature superconductors) were mixed thoroughly with polymerizing epoxy or urethane monomers. The resulting composites were cured. These polymer composites were formulated at room temperature and pressure. The electrical resistivity of the synthesized composites were measured at room temperature and pressure. Further resistivity measurements were carried out at room temperaturehigh pressure and room pressure–liquid nitrogen temperature. Significant drops in resistivity were found for composites measured at high pressure and liquid nitrogen temperature. Composites in both epoxy and urethane polymers when subjected to pressures of up to 2000 psi had drops in resistivity of up to 6 orders magnitude. Also, composites in urethane when subjected to liquid nitrogen temperature had drops in resistivity of 6 orders in magnitude. In contrast, composites made up in two types of epoxy polymer when subjected to liquid nitrogen temperature had drops of only up to eightfold.
Compression molding of composites: Mold heating system design
Authors: Upadhyay R. K. 
Published: April 2003

AbstractIn compression molding of composite parts, it is important to minimize the temperature variation in the part during processing for consistent quality. A mold heating analysis and optimization scheme has been developed that allows computation of temperature variation on the mold/part surface, and optimizes the location and power of heaters. The heat transfer coefficients for a given mold can also be theoretically calculated. The validation of the analysis was carried out by two sets of experiments: the first one measured the heat loss from the mold under different boundary conditions, and the second one the temperature variation on mold/part boundary for theoretically determined power histories for a specified temperature history. The experimental data compared well with theory and provide a satisfactory validation of the analysis. The present work provides a useful tool to a design engineer and allows the mold heating system design on a scientific basis, thus eliminating the trial and error approach.
Solid bed compaction and frictional drag during melting in a simulated plasticating extruder
Authors: Hwang Chii‐Guang , McKelvey James M. 
Published: April 2003

AbstractSolid bed transport has an important effect on the over all performance of a plasticating extruder. The coefficient of friction and density are the properties of the solid bed that govern its transport in the feed section of the screw. These properties have been measured, as a function of temperature and pressure, for eight common thermoplastic materials in an apparatus that simulates solid bed motion and compaction in a plasticating extruder and the results have been interpreted phenomenologically.
Properties of three types of crosslinked polyethylene
Authors: Venkatraman S. , Kleiner L. 
Published: April 2003

AbstractThe same base resin, a HDPE with vinyl–silane units grafted along the backbone, was subjected to three different types of crosslinking: (a) using peroxides and heat, (b) using a catalyst under high humidity, and (c) using high‐energy radiation. Macroscopic properties, such as tensile behavior‐at‐break, shear modulus, gel content, and crystallinity were measured for all three types of crosslinked material. Although the mechanical and rheological properties appear to indicate differences in distribution of crosslinks, the major differences are seen for the degree of crystallinity. These differences are rationalized on the basis of the mechanism of crosslinking and the resultant location of crosslink sites.
Reactive extrusion of polymers: A review
Authors: Tzoganakis Costas 
Published: April 2003

AbstractDuring the last 30 years the plastics industry has experienced enormous rates of growth. Due to an increasing demand for high performance plastic materials, the use of extruders as continuous flow reactors for polymers has attracted considerable attention in polymerization and polymer modification applications. This paper is an attempt to present a survey of recent literature on the reactive extrusion of polymers. Experimental and modeling studies for various polymer systems are reviewed and some rheological, modeling, and design aspects of reactive extrusion systems are addressed.
Mechanical properties of prestressed thermoplastics
Authors: Gust H. , Hengl R. , Eyerer P. 
Published: April 2003

AbstractMechanical tests of prestressed and nonprestressed specimens show that prior stressing often significantly changes the stress–strain curve of amorphous and partly crystalline thermoplastics.1–3 Specimens subjected to a prior mechanical stress show a flatter stress–strain curve (even with a “kink”) than those not previously stressed. The original properties of prestressed specimens can be restored by tempering (at least in the range of small elongations). Specimens made of ABS react differently: After certain longterm prior stresses, followed by short‐term tensile tests, brittle fracture occurs.
Model formulation for material feeding in counter‐rotating twin‐screw extruders
Authors: Poltersdorf Bernd , Fiedler Lothar 
Published: April 2003

AbstractAssuming that the solid moves in consequence of wall friction and friction of the material, transport equations have been established by means of a force and momentum balance on the volume element. These equations serve as a basis for describing the material feeding. That is, transition of the polymer from the feed hopper, or the feeding device, into the filling region of screws and the transport and compression of the solid polymer, i.e., the movement of the feed towards the plasticating zone, with simultaneous decrease of porosity. Depending on the geometry of the screws and on technological and material parameters, the model gives information on degree of filling, compression, pressure buildup, throughput of solids transport zone, and power consumption. The process model is suited for the design of the solids transport zone.
Extrusion of polymers in the plastic state through pure‐shear convergent—divergent dies
Authors: Mascia L. , Zhao J. 
Published: April 2003

AbstractExtrusion experiments have been carried out by forcing the polymer at temperatures below the melting point through a variety of convergent–divergent dies in which the cross section area at entry and exit was the same, giving a state of pure‐shear deformations, with the aim of producing extrudates exhibiting biaxial orientation. PTFE has been used to model the process for the analysis of extrusion forces as it is well characterized with respect to both frictional behavior and yield characteristics. UHMWPE, on the other hand, was used to determine the extent of orientation and mechanical properties in function of the die geometry and extrusion temperature. Dies with low converging angles were found to develop extrusion forces three to four times higher than corresponding dies with larger converging angles and to produce a highly unbalanced orientation with a bias in the transverse direction. A special die design feature producing a crossply orientation pattern was also examined.
Introduction to compatibilization of polymer blends
Authors: Markham Richard L. 
Published: April 2003

AbstractThe key to preparation of commercially useful blends based on immiscible polymer pairs is compatibilization. Advances over the past ten years have considerably enhanced the understanding of this phenomenon. The selection of an appropriate compatibilizer and the processing technique to enhance the compatibilization is quite complex. The selection of the compatibilizer is aided by the application of the principles of miscibility and of organic interactions. It may be advantageous to prepare the compatibilizer in situ. Chemical modification of the base components to enhance interactions between the components is an important option. Processing and rheological effects must also be taken into account. The combination of the compatibilizer and the processing conditions must yield a morphology that will preserve the desired properties of each component while minimizing the undesirable properties. This morphology must be reproducible and stable in the ultimate product and through subsequent recycling processes.
Computer simulation and experiments of flow distribution in flat sheet dies
Authors: Vlcek J. , Mailvaganam G. N. , Vlachopoulos J. , Perdikoulias J. 
Published: April 2003

AbstractThe Control Volume Method is used in a two‐dimensional computer software package to simulate three‐dimensional nonisothermal flows of polymer melts through flat sheet dies. The results of the simulation are compared to experiments performed with different materials on an experimental die, and to a three‐dimensional simulation using the Finite Element Method. This comparison shows that for the case of negligible extensional effects, the two‐dimensional package performs reasonably well.
Extrusion of self‐reinforced polyethylene
Authors: Pornnimit Benjamin , Ehrenstein Gottfried W. 
Published: April 2003

AbstractIn recent years, efforts aimed at producing high‐strength polymers have intensified noticeably. In addition to additive‐based reinforcement, self‐reinforcement without additives represents a way to increase material strength. In this study, the effects of self‐reinforced polyethylene during extrusion with a conventional single‐screw extruder are investigated. High extrusion pressure and controlled flow conditions at a low stock temperature, in conjunction with a longitudinal flow gradient in the die, permit the production of high‐strength, extremely rigid profiles from high‐density polyethylene (HDPE). The reinforcement is due to the shish‐kebab structure, which is responsible for the improvement of thermal and mechanical properties. The growth of shish‐kebab structures with an extended chain crystal axis and the radially lamellar structure, originated by flow‐induced crystallization, depends on the orientation of the macromolecules in the melt. Compared to a conventional extruded profile, the high‐strength profile exhibits molecular chain orientation largely parallel to the direction of extrusion, homogeneous transparency, and an approximately tenfold increase in Young's modulus, as well as improved thermal properties and good dimensional stability.
A knowledge‐based design approach for injection molding of plastic balls
Authors: Tseng A. A. , Arinze B. , Kaplan J. D. 
Published: April 2003

AbstractMany firms have begun to recognize the promise and potential offered by knowledge‐based systems (KBSs) to their design and manufacturing processes. KBSs incorporate the problem solving heuristics of human experts to solve difficult problems in various problem domains. A knowledge‐based approach is proposed here for the computer‐aided design of injection molded parts. The proposed KBS contains acquired knowledge of mold design alternatives and the assessment criteria for these designs. It employs this knowledge and user‐entered problem characteristics to assist in the selection of a mold design for specific requirements. The rule‐based KBS was developed using the 1st Class KBS development shell. In addition, the associated computer‐aided design system is described in some detail, along with areas for future research.