bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental analysis of plastic sheet extrusion
Authors: Marinelli J. M. , Lee L. James
Published: April 2003

Analysis of a plastic sheet extrusion line was carried out using a 2.5‐in. extruder in conjunction with a three‐roll stack system for processing of both poly(methyl methacrylate) (PMMA) and high‐impact polystyrene (HIPS). Tests conducted include dynamic responses, sheet cooling behavior, velocity and thickness profiles, and frozen‐in strain measurements. Experiments with PMMA were also performed on an extrusion‐air cooling line to provide a basis for comparison with the extrusion‐roll stack system. The results showed that the size and stability of the bank in the extrusion‐roll stack system affected the thickness variations and the frozen‐in strains. Operating the roll stack system was found to allow for fairly rapid rearrangements from parabolic to plug velocity profiles. Line comparisons between the roll stack and air cooling showed that the roll stack minimized thickness variations, frozen‐in strains, and surface flaws.
Practical techniques for the use of pet—glass fiber reinforcements in composites
Authors: Cordova D. S. , Coffin D. R. , Rowan H. H.
Published: April 2003

The need for composite materials with improved properties tailored to the requirements of specific end uses has led to the development of hybrids reinforcement systems in which two or more reinforcing fibers are combined in a thermosetting matrix. Polyester fibers (PET) are currently being used in combination with other fibers, particularly fiberglass, for impact strength and surface quality improvement. The use of polyester fiber in combination with glass fiber as a reinforcement for composite materials has resulted in the development of novel types of hybrid composites. This study discusses our work to achieve an optimum balance of composite properties through changes in matrix formulation, composite compounding, and processing steps. A number of these parameters are shown to have a significant effect on the performance of the composite. This work includes an analysis of thermoset polyester and epoxy resin formulations, in addition to the effect of other additives for typical BMC, SMC, and injection‐molding operations. The fiber loading, PET–glass fiber ratio, and fiber length are briefly discussed, as these are factors in determining the composite properties. These characteristics are discussed in combination with the compounding techniques. The combination of both factors were observed to have a major effect on the mechanical and surface appearance of the composite. The coherency and dispersibility of the specific PET fiber used had additional effects on resin compounding and final composite characteristics.
From the layout to the scientifically engineered molded part—the computer opens up new horizons
Authors: Schmitz J. , Haack W. , Lutterbeck K. , Rest H. , Schmachtenberg E. , Wölfel U.
Published: April 2003

Plastic components can only be competitive if they make use of the material and thereby emerge technically and economically superior to conventional materials. This places, high requirements on designers and presupposes extensive experience. A situation where the optimal version can only be established in expensive prototype molds is unacceptable. Above all, though, the time that this takes is preventing substitution by plastic parts from gaining an increasing market in the industrial component sector. The tasks which companies have to tackle today include increasing performance and making freely available experience that is currently confined to individuals. The establishment of specified work sequences helps to avoid errors. The chief tasks involved in design are compilation of specifications, material selection, and shaping and dimensioning. The designer's work can be broken down into acquisition of information, calculation, decision making, and drawing. The use of computers can help towards rationalization in the design field as well. This rationalization ought not only to give shorter transit times but improved components as well. The following program packages are available: a data bank program for managing design data, a search program with corresponding data file for material selection, a 3D graphic system for compiling drawings, a FE program for dimensioning, and an expert program to aid the designer in decision making. Apart from the conventional free design it is also possible to define individual functional elements or assemblies, such as snap fastenings or ribs, by way of design macros. These macros are designed and calculated in principle and then simply aligned auttomatically when incorporated in a specific part. Computersided dimensioning makes it possible to establish all the factors influencing quality in a specific application and to recognize weak points in simulated tests right at the design stage. The conventional concept of dimensioning (applying a sum of reducing coefficients to make allowance for loading) has thus been dispensed with, and a route is shown which permits precise allowance to be made for all the influences in a particular loading case. This therefore ensures optimum material utilization.
Microscopy techniques used in polymer research
Authors: Bartosiewicz L. , Kelly C. J.
Published: April 2003

Microstructural analyses with optical and scanning electron microscopy can identify processing variables that lead to less than optimum mechanical properties of molded and friction welded polymer components. Delineation of the major phase arrangements in blends of polycarbonate (PC) and poly(butylene terephthalate) (PBT) was key to identifying stress concentrations and internal defects. Phase separations, crystalline arrangement, structure refinements, and shear stresses introduced during molding or friction welding were evident and help to explain the unpredictable impact fracture mode and strength. The techniques help identify when the brittle ribbonlike PC phase extends to the surface without being encapsulated or surrounded by the PBT phase.
Intensification of the calendering process with the help of wedge‐shaped parts
Authors: Kohlert C. , Reher E. O. , Bothmer D.
Published: April 2003

Increased quality demands on products of the elastomer processing industry induced special investigations on additional intensifying components in processing machines. Thus, in collaboration with Soviet colleagues, a special wedge to be fitted into calenders for cord coating has been developed and tested. Elongation of the deformation zone results in improved homogenization, in higher degassing effect, in improved thread guidance and hence in an improvement in the quality of the coated cord. This paper presents the modelling of the flow between the wedge and the roll, up to the level of a parameter study of the dependence of the integral process parameters on geometrical, technological, and rheological factors. The construction of the wedge is explained, and the results obtained in the experimental investigation of the effect of the wedge technology on qualitative and quantitative parameters of the cord are discussed. The utilization of such wedgeshaped components as a continuously operating process viscometer, particularly for rolling and calendering processes, is presented, and further potential applications of the wedge technology in the production of high‐grade finished products are discussed.
Nylon 66 fundamentals and its processes
Authors: Ku Ping L.
Published: April 2003

The objective of this paper is to search for and critically examine the pertinent details of the current bulk continuous nylon 66 processes (described in the patents), which are practiced or followed by most nylon producing industries. The two monomers for making nylon 66 and their homologues including dibasic and monobasic acids, diamines, and primary amines show very interesting melting point behavior. On the other hand, compounds containing even numbers of carbon atoms show consistently higher melting points than the neighboring odd number compounds of higher molecular weights. However, the boiling points of all four series follow the usual rule: The higher the molecular weight, the higher the boiling point. It has been proven that the quality of nylon 66 has been greatly improved by lowering the residence time during the polymerization. For instance, the spinning rate employed was at a level of 7000 m/min, and the tensile strength of the spun yarn was much improved, which was attributed to the overall quality of the polymer.
Orientation development and crystallization in melt spinning of fibers
Authors: White James L. , Cakmak Mukerrem
Published: April 2003

A critical review is presented of the development of orientation and crystallization in melt spinning. Methods of characterizing fiber structure are described. The development of molecular orientation in flow and approaches to the representation of crystallization in melt spinning processes are considered. Detailed critiques of the literature are given for the melt spinning of polystyrene, polyethylene, polypropylene, poly(vinylidene fluoride), poly(ethylene terephthalate), nylon‐6, and nylon‐66. Emphasis is given to the problems of spinline crystallization, polymorphism, orientation development, and crystalline morphology. The important role of spinline stress in determining structure development is emphasized. The influence of high speeds on melt spun fiber structure is described.
Process optimization in stretch blow molding
Authors: Menges G. , Esser K. , Hüsgen U. , Kunze B.
Published: April 2003

In stretch below molding the stretching temperature has the most significant influence on the article performance besides the stretching ratio. Therefore, a very sophisticated control system was developed for a laboratory stretch below molding plant on which PP bottles are produced. The processing window for the stretching of the used polypropylene homopolymer is within a temperature range of 145–153°C. For that reason a very precisely operating temperature control system had to be developed and integrated into the microprocessor, which runs the complete process beginning with the heating of the preform and ending with demolding the finished bottle. For the heating infrared heaters are used, which are able to heat up the preform (6 mm wall thickness) in times of about 60 s. During the so‐called transient time shortly before the preform is moved into the mold, its surface temperature is read at four different spots simultaneously. That is done by a device developed especially for this task, which consists mainly of four pyrometers. The temperature signals are fed into the microprocessor which then in the case of deviation from the set points adjusts the power of the IR heaters. The closed‐loop temperature control is done by a special algorithm, which takes into account that the controlled system is a coupled multivariable system, which is modeled by a system of linear equations. Tests have proved that the control system is able to react fast and precisely to set point changes and to keep the preform temperature and its distribution constant throughout the production within a range of approximately 2°C.
Rheological observation of gelation and fusion process of poly(vinyl chloride) plastisol
Authors: Nakajima N. , Harrell E. R.
Published: April 2003

This paper begins with a brief description of the history of development of PVC plastisol. It, then, presents technical background on the nature of PVC plastisol, covering subjects of particle size distribution and nature of agglomerates, viscosity aging and deagglomeration, rheology of suspension, gelation and fusion, and thermodynamic interaction between polymer and plasticizer. The main part of the paper concerns rheological observation of the gelation and fusion process of PVC plastisol, as the title of the paper indicates. This is a summary of recent work by the authors plus their new work on the effect of plasticizer type. The first half is the investigation of gelation and fusion mechanisms with use of a model plastisol system. Viscoelastic measurements, thermal analyses on the behavior of glass transition, and the scanning electron microscopic examination of the particulate structure were used to support the investigation. The last half considers the effect of the material variables on the gelation and fusion behavior; molecular weight, extractable additives (emulsifiers), agglomerates and fine particles, size of primary particles and plasticizer type are covered. Among these material variables, the plasticizer type has by far the largest influence on the gelation behavior. The observed solvent power is not necessarily in agreement with the thermodynamic interaction parameters found in the literature. It is indicated that a further systematic investigation is necessary to elucidate the nature of the plasticizer–polymer interaction.
Fluid flow and heat transfer in wire coating: A review
Authors: Mitsoulis Evan
Published: April 2003

Progress in the analysis of the wire‐coating process is reviewed. In particular, the melt flow analysis inside high‐speed, pressure‐type, wire‐coating dies is presented. Early analytical efforts have been based on the lubrication approximation theory under isothermal conditions. Recent advances include full nonisothermal flow analysis using numerical finite element methods. Wire‐coating coextrusion is also reviewed. A need for more experimental data and inclusion of viscoelastic effects in the constitutive models used in the analysis are of primary importance for future work.
Phase separation effects in processing of glass‐bead‐ and glass‐fiber‐filled thermoplastics by injection molding
Authors: Hegler Ralph P. , Mennig Günter , Schmauch Claus
Published: April 2003

Dumbbell specimens, tubular specimens, spirals, and rectangular boxes were used to study phase separation effects occurring in injection molding of glass‐bead‐ and glass‐fiber‐filled thermoplastics. The weight specific separation effects were more pronounced with beads than with fibers, and they increase with increasing bead diameter. The weight distribution is further influenced by mold geometry, filler concentration, matrix material, and processing conditions. If the use of fillers, which promote inhomogeneity, is unavoidable, it is possible to improve the distribution of the rigid phase by a favorable choice of injection speed and melt temperature. Analysis which was made with dumbbell specimens and spirals showed no significant measurable size specific separation effects. With the theories available at present a qualitative interpretation of the origin of the observed separation phenomena is feasible.
Temperature dependence of the melt viscosity of epoxy resins
Authors: Utracki L. A. , Ghijsels A.
Published: April 2003

The zero‐shear viscosity η0 of five epoxy resins were analyzed on the basis of the free volume concept. The experimental data, spanning at least six decades in viscosity, were linearized by means of a viscosity–temperature relation η0 = η0(T), derived by Utracki a few years earlier. The linearization enables the following conclusions to be drawn: (1) There is no liquid–liquid transition within the investigated temperature range: T/Tg = 1.05–1.38 (Tg is the glass transition temperature); (2) the derived equation can be used to calculate η0 vs. T dependence; and (3) the equation can be generalized to permit prediction of the η0 = η0(T) dependence of any epoxy resins (of the type studied here) on the basis of a single point determination of viscosity and Tg of the sample.
Infrared radiation in the processing of plastics: Precise adjustment–the key to productivity
Authors: Esser K. , Haberstroh E. , Hüsgen U. , Weinand D.
Published: April 2003

Infrared radiation plays a large role in many areas of plastics processing, whether in the heating of thermoplastics for purposes of subsequent forming or in noncontact temperature measurement. This paper sets out to deepen our understanding of the plastics‐specific problem associated with infrared radiation. First of all, a brief outline is given of the necessary fundamental physical principles, before going to to discuss measurement results in terms of the radiation‐related properties of plastics. The influence of pigmentation and crystalline structures is investigated, together with the temperature dependence of absorption behavior. Linking up the radiator characteristics and absorption properties of plastics, a physical model is then presented which can be used to calculate energy efficiency and temperature homogeneity in the heating of plates. The results are presented in diagrams. In addition, the special problems of infrared heating in stretch blow molding are examined. Here, we attempt to attain a high level of penetration into the thick‐walled parisons by means of short‐wave radiation and thereby guarantee uniform and rapid heating. A program for establishing the intensity distribution of radiation on a semifinished product has been developed for geometerical configurations generally found in thermoforming machines and this will run on a personal computer. It will allow the optimization of uniform or deliberately nonuniform temperature distributions over the surface. If the stretching process is to be selectively influenced, it is essential to have knowledge not only of the temperature distribution in the semifinished part but also of the stretching behavior of the material. A highly informative testing procedure was developed to this end, which reveals the suitability of the material in question for a stretching process. A further section covers the infrared temperature measurement frequently applied in plastics processing for process analysis, monitoring, and control. The different types of measuring devices and their advantuges and drawbacks are discussed here. An analysis is also conducted of disturbance variables and possible means of correction are indicated.
Damage accumulation and friction of fibrous composites
Authors: Lhymn C. , Park I. K.
Published: April 2003

A theory of friction has been constructed from the bond reputed concept incorporating the physics of damage accumulation and adhesion. The theory specifically emphasizes the role of crack propagation as a mechanism of energy dissipation. The model thus constructed can explain the effect of roughness, fiber orientation on friction. The model has been further extended to consider the effect of normal load on friction as well as the sliding velocity on friction. The experimental data appear to support the proposed equations.
An improved theory of metering in an intermeshing corotating twin‐screw extruder
Authors: Szydlowski Witold , White James L.
Published: April 2003

An improved analysis of flow in the screw elements of an intermeshing corotating twin screw extruder is presented. The new theory based on an isothermal Newtonian fluid model allows explicit consideration of the geometry of the intermeshing region. Flow rates are computed as a function of the pressure gradients and screw speeds. Both left‐handed and right‐handed screws are considered.
Nonisothermal pressurization of variable viscosity newtonian fluids between two parallel plates
Authors: Sun Tzu‐Hsiung
Published: April 2003

Nonisothermal flow of a variable‐viscosity Newtonian fluid between parallel plates is analyzed to study the effect of heat transfer and viscosity effect on the pumping capacity of the device. Results indicate that the pumping capacity is greatly reduced in the entrance regions of a pumping device such as a single screw extruder or calender. This reduction in pumping capacity can cause sever surging effects in the device, for the pumping capacity is enhanced by the thermal effect in the exit region.
Twin screw extruders; development of technology and analysis of flow
Authors: White James L. , Szydlowski Witold , Min Kyonsuku , Kim Myung‐Hwan
Published: April 2003

A critical evaluation of the technological development and studies of mechanisms of flow in twin screw extruders is presented. We include (i) intermeshing counter‐rotating twin screw machines, (ii) tangential counter‐rotating twin screw extruders, and (iii) intermeshing corotating twin screw machines.
Effect of recycle on properties and profits: Algorithms
Authors: Throne James L.
Published: April 2003

In many plastics processes, nonvirgin materials make up relatively small percentages of materials added to the main processing stream. In thermoforming, however, as much as half the material that passes through the extrusion and thermoforming process chain is “nonproduct” web. Economics usually dictate that this material must be reprocessed. Materials that experience high levels of shear and/or temperature usually exhibit measurable and significant property loss. This means that the mixture of materials fed to the process has properties some‐what less than those of the virgin resin. This paper presents algorithms for determining final product properties, given single‐pass property loss and fraction of recycle in the resin mixture going to the process. The following cases are considered:

Linear, where the single‐pass property loss is directly proportional to the mixture property prior to processing. This was first worked out by Smoluk for tensile strengths

Power‐law, where the single‐pass property loss is proportional to the mixture property to a power. Impact strength is an example

Offset, where the single‐pass property is equal to the mixture property minus a fixed amount. Fire retardancy seems to be an example of this

Logarithmic, where the law of mixtures is logarithmic. Viscosity and intrinsic viscosity (molecular weight) are examples here

For cases 1, 2, and 4, the algorithm yields a closed solution for steady‐state processes. The offset case yields a nested series that converges in about 20 steps. In addition, if a value can be placed on material property loss (either through higher product reject rates or higher virgin material costs), a “profit” algorithm can be created to determine the actual processing costs. From this, scenarios for reuse of regrind and/or off‐spec materials can be created. An example of such an algorithm is given.
Variable‐viscosity flow in heated and cooled channels with internal viscous dissipation
Authors: Sun Tzu‐Hsiung
Published: April 2003

A similarity solution is given to a very viscous Newtonian fluidflowing in a channel which is suddenly heated or cooled. The viscosity is assumed purely an exponential function of temperature and heat generation is very large. The asymtoptic approximation is that the downstream viscosity at the channel wall differs by an order of magnitude from that in the upstream flow. This solution can be used to check results of numerical simulation in the injection of either a thermoplastic or a thermoset resin into a cooled or heated mold, respectively.
Pressure buildup in the feed zone of a single screw extruder—the effect of density compressibility
Authors: Sun Tzu‐Hsiung
Published: April 2003

The effect of density compressibility of granular polymeric solids on the pressure development inside the feed zone of a single screw extruder was calculated. Results indicate that, for a given flow rate, density compressibility enhances pressure rise inside the extruder, remedying the under estimation of previous theory. A substantial rise in pressure buildup may result for compressibility above a certain level. This may explain observed surging during the processing of low bulk density materials.
Production, properties, and application of polyurethane RRIM
Authors: Braun H.‐J. , Eyerer P. , Frank U. , Hüttner M. , Ludwig H.‐J. , Wurster T.
Published: April 2003

The production of automotive exterior body panels in the PUR–RRIM process is a comparatively new technology that provides a great potential for further improvements and makes it possible to produce plastic components for the automotive industry that, at relatively thin wall thicknesses, meet maximum requirements in regard to

part geometry

dimensional stability

the high industrial standards valid in the automotive industry

surface quality (avoidance of sink marks, pores, etc.)

durable fastening

For a better acceptance of RRIM moldings, cost reductions in the production process are necessary which, in turn, require noticeable progress in the material and process development. Due to the improvements made in the field of both raw materials and production units, the PUR–RRIM process has, in the last few years, become interesting also for high‐volume production. A handicap in this connection is that the development of the RRIM process is, to a large extent, based on the practical experience of a few experts. For its use in high‐volume production it is, however, inevitable to have at hand through scientific data on material, design, process and resulting correlations. It is the objective of the Institute for Polymer Testing and Polymer Science in Stuttgart to help establish these data and, through close contacts to the industry, make them usable in practice.
A 3‐D finite eiement model for polymer melt flow
Authors: Tanguy Philippe A. , Fortin André , Bertrand François
Published: April 2003

A finite element investigation of 3‐dimensional polymer melt flows in a sudden contraction is presented. In continuity with the 2‐dimensional work of the authors,2 the present study uses the augmented Lagrangian method to cope with the nonlinear rheological behavior of melts. Two kinds of situation are considered: the flow of a nonisothermal melt obeying the Carreau A model of viscosity; the isothermal flow of a Bingham fluid. In the first situation, our interest is focused on the influence of the shear‐thinning nature of the melt onto the 3‐dimensional temperature pattern inside the contraction. In particular, the mechanism of creation of hot spots is shown in the small channel. In the second situation, the influence of the yield stress on the flow pattern is studied. It is shown in particular that a slow motion secondary flow (quasistagnant region) is created before the contraction for large values of the yield stress.
Polystyrene and styrene copolymers. I. Their manufacture and application
Authors: Ku Ping L.
Published: April 2003

The manufacturing processes for polystyrene (PS) and its copolymers, including styrene–acrylonitrile (SAN), high impact polystyrene (HIPS), acrylonitrile–butadiene–styrene (ABS), styrene–butadiene latex (SBR for coating), styrene–butadiene block copolymers (SBS), and styrene–acrylate copolymers (SMMA), are discussed and illustrated. The synthetic methods for such products are bulk, emulsion, suspension, and free radical polymerization techniques, all either in batch or in continuous operations. By comparison, it was found that continuous bulk is the most economical process among the above‐mentioned polymerization methods. However, the suspension method is still the only way to make expandable polystyrene beads (EPS). Some ionic polymerization techniques for making homo‐ and copolymers are also discussed. Types of styrene‐containing polymers, like all other resins, are classified according to their property distribution. Some are uniquely outstanding and others have a balance of properties, which, in turn, are functions of the molecular weight and molecular weight distribution (MWD), the nature of the components, and the methods and conditions of polymerization. Therefore, each product can be produced in many grades, for a variety of applications.
Multilayer sheet coextrusion: Analysis and design
Authors: Mitsoulis Evan
Published: April 2003

A numerical simulation of multilayer coextrusion flows has been undertaken for polymer melts used in producing multilayered plastic sheets. Viscosity data and other material properties are used for typical melts and adhesives applied in coextrusion. Industrial designs have been employed for feedblock geometry and multimanifold vane flat dies. The analysis is based on the lubrication approximation theory (LAT), which treats the flow locally as fully developed. A Newton‐Raphson iterative scheme is employed to solve the equations for a pressure‐driven flow of N number of layers (N ⩽ 11). For a given total flow rate and flow rate ratios (or correspondingly total sheet thickness and individual layer thicknesses), the solution provides the interface locations and individual pressure drops that each extruder has to supply. The shear stresses at the channel walls are checked as a criterion for proper design. The die design or melt combinations are altered to produce smooth shear stresses with no humps or discontinuities at the points of confluence. A Adiabatic temperature rises are also computed based on the pressure drops in the system. Such an analysis provides a quick qualitative as well as quantitative insight into the proper design and melt combinations for multilayer sheet coextrusion.
Tribological properties of silicone‐impregnated polymer composites—two‐body abrasion
Authors: Lhymn Yoon , Lhymn C.
Published: April 2003

The friction and wear behavior of silicone‐impregnated fiber‐reinforced thermoplastics has been investigated as a function of normal load in air, water, and oil lubricants using a two‐body abrasion tester. The measured tribological data have been phenomenologically explained by a wear/friction equation derived from the concepts of crack propagation and wear failure mode.
Viscoelastic properties of structural silicone rubber sealants
Authors: Tock Richard W. , Dinivahi M. V. R. N. , Chew Choon Hoi
Published: April 2003

The behavior of silicone rubber materials subjected to uniaxial stress fields cannot be predicted by classical mechanical theory which is based on linear stress–strain relationships. Nor do theories based on “ideal elastomer” concepts work well when extensions exceed 30%. For these reasons, there are few design specifications related to the use of silicone rubber sealants for structural applications. This paper presents a theoretical approach used to predict the behavior of silicone rubber under uniaxial stress fields. The model is based on the concept of the classical Maxwell treatment of viscoelasticity and stress relaxation behavior. However, the Hookean spring component of the Maxwell element is replaced with an ideal elastomer component. With this substitution, the new model permits the crosslink density of the silicone elastomer to be estimated from test data and allows a stress level to be predicted as a complex function of extension, crosslink density, absolute temperature, and relaxation time. Simple uniaxial tensile tests were performed on two commercial silicone rubber sealants. Their experimental behavior was compared to the predicted performance based on the new viscoelastic model. Agreement was found to be quite good. It is hoped that the model, therefore, will help in the basic understanding of structural sealant behavior and perhaps lead to better design specifications for structural glazing.
Wide angle X‐ray diffraction investigations of orientation of chopped fibers in fabricated thermoplastic parts
Authors: Lim Soonho , Kikutani Takeshi , White James L. , Kyu Thein
Published: April 2003

A method of determining fiber orientation in composites using wide angle X‐ray diffraction (WAXD) is described. This approach is based upon examining the alignment of the highly oriented crystalline fibers. X‐ray studies were carried out using Kevlar [poly(p‐phenylene terephthalamide) (PPTA)] fibers suspended at a 0.31 volume fraction loading in a polycarbonate matrix. A pole figure device was used to determine the orientation distribution and average orientation factor of the PPTA crystallographic chain axes relative to reference axes located in the test specimen. We prepared ideally oriented uniaxial and bioaxial composites as reference specimens using a compression molding machine. The fiber orientations in capillary extrudates, slit die extrudates, cold rolled sheets, and injection‐molded specimens were examined by WAXD. The capillary extrudates showed uniaxial orientation but the slit die extrudates and cold rolled sheets exhibited biaxial orientation. Injection‐molded specimens contained complex states of fiber orientation.
Dynamic and steady shear rheological properties of a polydisperse polystyrene
Authors: Huang Jan‐Chan , Dharia Amitkumar N.
Published: April 2003

Non‐Newtonian viscosity, storage, and loss moduli of a polydisperse polystyrene are measured. Molecular weight distribution of the polystyrene is measured by gel permeation chromatography. The rheological model of Carreau is modified with molecular‐weight‐dependent relaxation times to obtain rheological functions of the polydisperse polystyrene. It is found that five parameters in the model can satisfactorily describe the rheological functions measured.
Unsteady flow of rubber compounds at injection molding conditions
Authors: Isayev A. I. , Huang Yeong‐Hua
Published: April 2003

An automated rheometer is developed for an evaluation of the processability of rubber compounds at injection molding conditions. The rheometer utilizes a screw injection molding machine in order to push rubber compounds through a thermostated slit die at controlled flow rates. Three pressure transducers are flush‐mounted along the die length and a displacement transducer is installed to measure the screw motion. Signals generated by the pressure and displacement transducers and thermocouple are supplied to an A/D converted and the IBM PC/AT computer. Unsteady character of flow of rubber compounds is observed. The obtained data are compared with predictions from modeling of flow, using the viscoelastic plastic constitutive equation.
Characterization of rotational molding grade polyethylene powders
Authors: Throne J. L. , Sohn M.‐S.
Published: April 2003

Rotational molding grade polyethylene powders are classified according to sieve size, to typically–35 mesh, and by flowability, usually determined by pouring freeflowing powder from a funnel onto a fixed base cone. In the latter case, the static angle of repose is then measured. This study concentrates on general methods of characterizing powders and relating these methods of flowability of five selected commercial rotational molding grade polyethylene powders. The techniques described in this study include methods for measuring particle size distribution, particle shape characteristics, static and dynamic angles of repose, powder shear strength, and angle of internal friction. All powders examined had similar particle size distribution profiles, with distributions skewed to the coarser, −35 mesh size particles. The static and dynamic angles of repose were quite similar and the latter were essentially independent of the volume fraction of powder in the rotating cylinder and of the speed of rotation of the cylinder. All powders had shape parameters–elongational ratio, chunkiness, circularity, and roundness–that were essentially similar and independent of particle size, and the compressibilities of the bulk powders were not strongly dependent on powder bed height.
Structure–property considerations for rotationally molded polyethylenes
Authors: Throne J. L. , Sohn M.‐S.
Published: April 2003

In a companion study,1 it was found that five commercially available rotational molding grade polyethylenes had similar particle size distribution profiles and dynamic angles of repose. There were measurable differences in their general particle shapes. These powders were rotationally molded in an axisymmetric cylinder mold using time–temperature molding cycles recommended for these materials. Wall sections were then cut from the molded cylinders and tensile strengths, Young's moduli, elongations at break, and Izod impact strengths were measured. The resins were then injection molded and similar mechanical tests were performed. The rotationally molded samples exhibited porosity, the level of which depended strongly on the residence time in the isothermal oven. The rotationally molded samples showed greater strengths and moduli, but lower elongations at break and impact strengths. The rotationally molded samples also showed higher crystallinity levels and substantially larger spherulite dimensions. These observations support the mechanical property data.
Peroxide crosslinking of LLDPE during reactive extrusion
Authors: Tang Y. , Tzoganakis C. , Hamielec A. E. , Vlachopoulos J.
Published: April 2003

An experimental study of the free‐radical‐induced crosslinking of linear‐low‐density polyethylene (LLDPE) in the melt phase has been carried out. Experiments have been performed both in a single‐screw plasticating extruder and in an extrusion plastometer using a peroxide as the free‐radical source. Concentration of the peroxide was in the range of 0.005–0.08 wt % for rheological investigation and was extended to 5 wt % for gel content examination. Results in the form of melt flow index (MFI) values, viscosity curves, extrudate swell, and gel content of the produced resins are presented here.
The characterization of uniaxial graphite fiber/epoxy composites by mechanical testing and scanning electron microscopy
Authors: Cha Cheol Y. , Fellers John F. , Mathews Archie
Published: April 2003

The effect of the constituent material on the mechanical properties and on the overall crack propagation behavior of uniaxial graphite/epoxy composites was studied using two different types of graphite fibers, i.e., PAN precursor and pitch precursor fibers in combination with an epoxy known for its toughness. The tensile properties and interlaminar shear strength (ILSS) of composites with various fiber volume fraction were studied using an Instron Universal Testing Machine. The fracture surface of composites was studied using scanning electron microscopy (SEM). The surprising result from the tensile tests is that the percent elongation of AS4/epoxy composites was much higher than that of individual components, i.e., the epoxy and the fiber. The stress–strain curves of AS4 fiber/epoxy composites show yielding. The yielding is interpreted to result from shear stress concentration due to the fiber breakage. Two causes of failure mode were observed in this study: (1) ductile plastic deformation by the PAN‐based AS4/epoxy composites; (ii) brittle catastrophic failure shown by the pitch‐based VSB‐16/epoxy composites. The tensile strengths and moduli of the composites increased as the volume fraction of fibers increased. The principal fracture features of AS4/epoxy composites under tension were fiber pullout (bundles and single fibers) and very rough fracture surface due to the pullout of fiber bundles with epoxy, whereas VSB‐16/epoxy composites under tensile and bending loads showed only tensile (or compressive) failure. The composites of epoxy/PAN (polyacrylonitrile)‐based fibers (AS4) showed greater ILSS than those of the pitch‐based fiber (VSB‐16)/epoxy. The most characteristic features of the interlaminar shear failure surface of AS4/epoxy composites are delamination and formation of hackles.
Effect of pressure on the impregnation of thermoplastic resin into a unidirectional fiber bundle
Authors: Kim T. W. , Jun E. J. , Um M. K. , Lee W. I.
Published: April 2003

Impregnation of molten thermoplastic resin into continuous unidirectional fiber tows was investigated. The degree of impregnation is defined as the ratio between the number of impregnated fibers and the total number of fibers of a tow. The degree of impregnation was modeled as a function of time, impregnation pressure, impregnation temperature, and tow size, assuming that the radial inward flow of resin through the fiber tow is governed by Darcy's law. The effect of the impregnation pressure on the permeability was studied. Experiments were performed to evaluate the validity of the model. Toray T300 graphite fiber bundles and Polyetheretherketone (PEEK) resin were used. Pressure and temperature were applied to fiber tows surrounded with resin powder in a mold. After a predetermined time, the sample was taken out and the degree of impregnation was measured from the microphotographs of the cross sections of samples. Experiments were performed for different impregnation conditions such as impregnation time, pressure, temperature, and tow size. Good agreement was found between the model and the experimental data.
An improved analytical melting theory
Authors: Rauwendaal Chris
Published: April 2003

The first quantitative description of melting in single screw extruders was given by Z. Tadmor around 1965. A simple analytical theory was developed for Newtonian fluids, assuming the fluid viscosity to be unaffected by changes in temperature. Also, an approximate analytical theory was developed for a power‐law fluid, assuming the power‐law constants to be independent of temperature and viscous dissipation to be negligible. Later workers extended the theory, however, most of these extensions did not allow closed‐form analytical solutions, thus requiring numerical techniques to obtain solutions. One of the most crucial assumptions in the analytical melting theory is the assumption that the viscosity of the polymer melt in the melt film is not affected by temperature differences in the melt film. This assumption has been eliminated in the improved melting theory by deriving an exact solution of the temperature and velocity profile in pure drag flow of a temperature dependent power‐law fluid between two parallel plates. It will be shown that the inclusion of the temperature dependence of the viscosity dramatically affects the predictions of the melting rate. It will further be shown how the new theory can be used to predict the optimum barrel temperature for melting.
Sheet molding compound—basic considerations
Authors: Stillhard Bruno
Published: April 2003

The SMC process has reached a new level of quality with the recent generation of compression presses. SMC ply preheating has allowed shorter cycle times and improved flow properties. Cycle times of less than 1 min are now possible. Surface quality is improved with accurate press‐velocity control and accurate parallelism control of the movable platen. When mold vacuum is used, the surface quality can approach the auto‐maker's Class A finish standards without the use of time‐consuming in‐mold coating. The parallelism control allows tighter tolerances on the shear edge of the mold. If this is combined with accurately controlled press‐force profile, a substantial reduction in flash can be achieved. The never presses are equipped with microprocessor controls. On‐line quality control is possible, since all relevant parameters can be stored or closed‐loop controlled. Statistical process control (SPC) can therefore be achieved without the need for additional hardware.
Biodegradable plastics: A review
Authors: Huang Jan‐Chan , Shetty Aditya S. , Wang Ming‐Song
Published: April 2003

In this paper, the approach of biodegradation to reduce the environmental impact of plastic wastes is reviewed. The mechanism of biodegradation and the processing and applications of these materials are also discussed in relation to the structural characters of their molecules. The synthetic biodegradable materials such as starch based biodegradable materials are compared with naturally occurring biodegradable materials such as poly(hydroxy butyrate) (PHB) in terms of their applications, processing difficulty, and degradation mechanism. The future trends of these materials are anticipated.
Effect of oscillations during extrusion on rheology and mechanical properties of polymers
Authors: Isayev A. I. , Wong C. M. , Zeng X.
Published: April 2003

An experimental study associated with the applications of sound and ultrasonic waves to extrusion is conducted. Two laboratory setups are developed for these purposes incorporating orthogonal and parallel superposition of oscillations on pressure flow during extrusion. The orthogonal superposition of sound oscillations is imposed in an annular die. The parallel superposition of ultrasound oscillations is imposed in a circular die. Several materials including unfilled and filled thermoplastics, thermoplastic elastomer, and elastomer are tested. Die characteristics, power consumption, and die swell are determined during extrusion. The rheological properties, molecular weight, tensile properties, and impact strength of materials with and without sound and ultrasound treatment are investigated, indicating permanent changes in these properties. The observed effects are found to depend on melt temperature, flow rate, nature of polymer system, and oscillating parameters such as frequency and deformation amplitude.
An investigation of the shrinkage behavior of oriented PVC in a hot air tunnel
Authors: Bigg D. M.
Published: April 2003

The behavior of PVC shrink films in a hot‐air tunnel oven was analyzed. The films were found to undergo two modes of shrinkage. Primary shrinkage, which corresponded to macroscopic dimensional changes to conform to the container surface, occurred rapidly once the film was heated above its relaxation temperature. Secondary shrinkage, which corresponded to the elimination of wrinkles and bubbles in the shrunk film, was a much slower process that occurred only when the film was heated above 70°C. The film temperature could be reasonably estimated from a Nusselt analysis of heat transfer between turbulent air and a cylinder.
Blends of polyolefins: Characteristic melting and crystallization data
Authors: Haghighat Siavash , Birley Arthur W.
Published: April 2003

A range of polyolefins have been studied by differential scanning calorimetry (DSC). In addition to the pure polymers, many binary blends and one ternary system have been investigated. Data are reported for HDPE, LDPE, LLDPE, PP, and PB and for many of these binary blends and for the HDPE–LDPE–LLDPE system.
Thermomechanical load and property changes in processing of polymeric materials
Authors: Meissner Konrad , Poltersdorf Bernd
Published: April 2003

We introduce a quantification method for mechanical and thermal loads during processing. In the case of polymers, mechanochemical reactions as well as thermal and thermo‐oxidizing processes are relevant, and rheokinetic analysis is used to understand the property changes in polymeric materials. A formal kinetic equation is established which takes into consideration structurization and destruction phenomena and the nonisothermal of the process. Parameter identification shows that the kinetic equation provides a good description of the change in viscosity over time as a function of mechanical and thermal loads using the example of HDPE in the kneading chamber of a laboratory kneader. Applications in process modeling and optimization are noted, and a so‐called damage diagram is set up.
Application of an enhanced flash‐tank devolatilization system to a degassing extruder
Authors: Craig T. O.
Published: April 2003

The design and operation of a foam‐enhanced flash‐tank devolatilization system applied to a conventional degassing extruder are described. The extruder degenerates to a melt feed device and devolatilization takes place in a static mixer in which foaming is induced. The flash‐tank provides vapor disengagement space. Improved residual volatile levels and throughput rates are achieved, as well as the elimination of downgraded polymer that is caused by vent port flooding in degassing extruders.