bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling crosslink density of coreactive polymers in an extruder reactor
Authors: Curry John , Andersen Paul
Published: April 2003

A common technique for the manufacture of polymer alloys is melt blending of polymers with specific chemical interactions. For instance, an amido ester crosslink forms when oxazoline‐grafted PS is mixed with acid‐grafted PE. The crosslink builds melt viscosity and stabilizes product morphology. Reaction control is critical since overreacted alloys from gels and underreacted alloys have gross composition gradients and/or tend to phase coalesce so that product properties are variable. Polymer reactions in plasticating compounders are particularly difficult control problems since several unit operations involving plastication, heat exchange, mixing, and separating of by‐products must be sequenced properly to control a reaction. Reactive polystyrene (OPS) and reactive polyethylene (APE) with oxazoline and carboxylic acid functionality, respectively, were melt blended in a ZSK compounding extruder under a variety of conditions. The extent of crosslink was monitored by the strong shear viscosity increase of the reacted product, the infrared absorption by the crosslink, and reactant depletion in the melt. The phase morphology was characterized by optical phase contrast microscopy. A response surface of product shear viscosity vs. the primary operational parameters of extrusion rate and extruder RPM is interpreted in terms of characteristic reaction time and development of reactive interfaces during the mixing process. Response surfaces result from storing coordinates and responses while exercising a new feedback loop control system.
Distributive mixing in the nonintermeshing twin‐screw extruder with a newtonian fluid
Authors: Bigio David , Baim William
Published: April 2003

Visual studies have been performed on the partially filled, nonintermeshing twin‐screw extruder (NITSE) to determine its distributive mixing abilities. Four parameters were studied: percent screw stagger, percent channel fill, screw speed, and fluid viscosity. It was found that screw speed and viscosity had no statistically significant effect on mixing, while percent channel fill and percent screw stagger were factors affecting mixing that were intimately related by the type of screw‐to‐screw fluid transfer. The two types of transfer were fluid‐to‐fluid, which occurred when the percent fill was greater than the percent stagger, and deposition, which occurred when the percent fill was less than the percent stagger.
Tensor failure criteria for composites: Properties and comparison of the ellipsoid failure surfaces with experiments
Authors: Theocaris Pericles S.
Published: April 2003

A realistic criterion was introduced in the 3D principal stress space for describing failure of transversely isotropic bodies taking also into account the strength differential effect. This criterion is represented by an elliptic paraboloid failure surface (EPFS). The criterion stipulates that in the compression–compression–compression octant these materials may sustain very high loadings. To remedy this ambiguous definition of failure in this zone, an improved version of the EPFS was also introduced as a complement of the EPFS criterion. Based on the same principles as the EPFS, a symmetric ellipsoid failure surface is defined whose symmetry axis is parallel to the hydrostatic axis, which is also passing though the three pairs of failure strengths in tension and compression along each of the principal stress axes. Both criteria are completely defined by stipulating that their symmetry axes are parallel to the hydrostatic axis and that the fourth rank tensors H defining failure should have a zero eigenvalue associated with the spherical tensor 1. Extensive experimental evidence with different orthotropic materials has shown that their failure results corroborate both criteria, depending on the form of their structure.
Compression molding using a generalized eulerian–lagrangian formulation with automatic remeshing
Authors: Ahmed Alauddin , Alexandrou Andreas N.
Published: April 2003

A generalized Eulerian‐Lagrangian approach is used to study the compression molding of viscoelastic polymers. The complete, unsteady, two‐dimensional equations of motion are used in the analysis. The White–Metzner model is used to describe the constitutive behavior of the material. The solution is obtained using a mixed Galerkin finite element method. An automatic remeshing scheme is introduced to reduce the mesh distortion during the solution procedure. Results for the pressure and force required in mold closing are presented for the isothermal filling of a rectangular cavity. © 1992 John Wiley & Sons, Inc.
An overview of additives and modifiers for polymer blends: Facts, deductions, and uncertainties
Authors: Mascia L. , Xanthos M.
Published: April 2003

Polymer blends with enhanced properties and processability for specific applications are modified through the incorporation of a variety of additives. The performance of these additives is often difficult to predict from considerations of their known behavior in the separate blend constituents. This overview article discusses additives and modifiers in terms of types and specific functions (e.g., impact modifiers, compatibilizers, flame retardants, stabilizers) and provides an analysis of the possible effects of their repartition in the constituent phases and at the interface. © 1992 John Wiley & Sons, Inc.
Free‐radical retrograde‐precipitation polymerization process
Authors: Caneba Gerard T.
Published: April 2003

In this article, we present a newly discovered polymerization process, called the freeradical retrograde‐precipitation polymerization (FRRPP) process, that is shown to have certain desirable features not normally found in free‐radical polymerization processes. Here, free radical polymerization occurs with an unusual but widely applicable polymer precipitation phenomenon. Local heating is observed in the vicinity of the radical sites, which results in the controlled rate of propagation with a decrease in the rate of radical–radical termination reactions. In the case experiments, the existence of hot spots in the reactor fluid is shown to occur. There is also evidence of slowdown of the growth of polymer radicals after initiator decomposition. The polymer radicals, shown to have a relatively narrow molecular weight distribution, continue to grow at a controlled rate long after all the initiator molecules have decomposed. The addition of a second monomer results in the formation of a thermoplastic elastomer triblock copolymer. © 1992 John Wiley & Sons, Inc.
Practical aspects of reactive compounding in a continuous kneader
Authors: Jakopin Stan
Published: April 2003

Reactive compounding is continuously emerging as a novel processing technique to modify existing polymer systems and improve performance/properties. The essential elements of control over the internal pressure and temperature combined with understanding of the chemistry and process equipment brings optimal results. Today's role of contract manufacturer is not only to provide the facilities and hardware but also the understanding of process technology to help develop new products in the most economic and timely fashion. © 1992 John Wiley & Sons, Inc.
Alternative procedures for the recycling of sheet molding compounds
Authors: Patel S. H. , Gonsalves K. E. , Stivala S. S. , Reich L. , Trivedi D. H.
Published: April 2003

To establish the parameters for converting sheet molding compounds (SMCs) to useful products, various technical approaches, viz., solvent extraction, hydrolysis, and pyrolysis, have been explored. Thermogravimetric analysis of an SMC sample indicated that it contains about 25% by weight organics and 75% inorganics, mainly glass fibers and CaCO3 as filler. Solvent extraction of ground SMC with acetone, methylene chloride, chloroform, or chloroform : benzene (1 : 1 vol) yielded low quantities of a gummy, viscous extract. Hydrolysis of the extracted SMC sample under strong alkaline conditions was also studied. A unit structure was postulated for the hydrolysate based upon elemental and molecular weight analysis. Pyrolysis of both extracted and unextracted SMCs in nitrogen at 500°C and in air at 400°C yielded organic oils. These oils were characterized for their calorific values. The products of pyrolysis consisted of mainly aromatics along with some oligomers. The extract and the oil from pyrolysis appear to be compatible with epoxy systems. Their use as an extender for epoxy systems, while that of the inorganic residue (glass fibers and CaCO3) as a filler for epoxy system, have been explored. © 1993 John Wiley & Sons, Inc.
Encapsulation process for electronic devices using injection molding method
Authors: Sakai Tadamoto
Published: April 2003

In this article, a new encapsulation injection molding method for electronic devices such as integrated circuits (ICs) is described as a superior technology to the conventional transfer molding process widely used in the electronics industries. The quantitative analysis has been carried out utilizing a computer simulation program covering cavity‐filling behavior to analyze the relationship between the deformation of gold wires that are bonded with mounted IC chips and mold geometries, operational conditions, and physical properties of a thermoplastic encapsulant, i.e., polyphenylene sulfide. As a result, a new technology to encapsulate ICs has been established, preventing no practical gold wire deformation or break‐up damage. © 1993 John Wiley & Sons, Inc.
Assessing polymer crystallizability from nonisothermal crystallization behavior
Authors: Nadkarni V. M. , Bulakh N. N. , Jog J. P.
Published: April 2003

Crystallization of polymers plays an important role in polymer processing because the structure developed during crystallization influences the mechanical and physical properties of the polymer product. The crystallization of polymers takes place under nonisothermal crystallization is essential for optimizing the processing conditions to obtain a product with desired properties. A simple approach based upon analysis of the nonisothermal crystallization behavior of a polymer to characterize the inherent crystallizability of the polymer and its sensitivity to processing conditions is reported. The polymers used in the present investigation include various grades of polyethylenes and polypropylenes. It is shown that a simple graphical analysis of the nonisothermal crystallization parameters can be used to quantify the inherent crystallizability of polymers and sensitivity of its structure development to changes in the cooling rates. © 1993 John Wiley & Sons, Inc.
Viscoelastic simulations of extrudate swell for an HDPE melt through slit and capillary dies
Authors: Kiriakidis D. G. , Mitsoulis E.
Published: April 2003

Extrudate swell studies of a high‐density polyethylene (HDPE) melt have been undertaken in flows through slit and capillary dies with the purpose of finding out the effect of die‐length/diameter (gap) (L/D or L/2H) ratio on the viscoelastic behavior. Numerical solutions have been obtained by using the finite element method (FEM) and an integral constitutive equation of the K‐BKZ type with a spectrum of relaxation times. The material parameters have been obtained by fitting experimental viscosity and normal stress data for the melt as measured in shear, and elongational viscosity data available in the literature. Different L/D (L/2H) ratios have been considered ranging from very short to infinitely long dies. The numerical simulations reveal that as the flow rate increases, viscoelastic effects exhibited by the HDPE melt become important and manifest themselves in an enhanced swelling behavior after the die exit, while small, Newtonian‐like vortices exist in the contraction before entry to the die. Elastic recovery is also captured in an enhanced extrudate swell, which is always higher at the same apparent shear rate for the capillary than the slit dies and decreases drastically as the L/D (L/2H) ratio increases, reaching asymptotic values for very long dies. Such behavior is in agreement with experimental findings from flows through slit and capillary dies and in sharp contrast with purely viscous simulations which cannot predict such strong viscoelastic phenomena associated with the memory of the polymer melt. © 1993 John Wiley & Sons, Inc.
Biaxial orientation of poly (ethylene terephthalate). Part II: The strain–hardening parameter
Authors: Chandran Prashant , Jabarin Saleh
Published: April 2003

Results of a study of the orientation characteristics of extruded poly(ethylene terephthalate) (PET) (Homopolymer) sheets are discussed with respect to stretching condition. PET exhibits strain‐induced crystallization upon being stretched to large extension ratios. This may lead to strain‐hardening, which is accompanied by an upswing in the stress–strain curve recorded during the process of extension. A parameter pertaining to the extension ratio, at which the onset of strain‐hardening occurs during stretching of the specimen, is defined. This is called the strain‐hardening parameter (SHP). The dependence of the SHP on the mode of stretching, the temperature of stretching, the strain rate, and the limiting extension ratio in the first stretch direction, are studied. It is seen that the SHP in both simultaneous and sequential modes decreases with increasing strain rate and the limiting extension ratio in the first stretch direction, while it increases with increasing temperature of stretching. For specimens stretched in the simultaneous mode at 90°C, SHP versus extension rate shows a minimum. This could be due to viscous dissipation at high rates of extension. Also studied is the relationship of strain‐hardening and the SHP with strain‐induced crystallization. It is seen that for specimens stretched in the uniaxial constrained mode, the rapid increase in properties with extension occurs much before the upswing in the stress–strain curve. The upswing occurs at the extension ratio at which the increase in properties once again becomes gradual. This means that the upswing in the stress–strain curve indicates significant completion of strain‐induced crystallization and the establishment of structural order within the specimen. © 1993 John Wiley & Sons, Inc.
Current trends in cae: Simulations of latest innovations in injection molding
Authors: Himasekhar K. , Turng L. S. , Wang V. W. , Chiang H. H. , Wang K. K.
Published: April 2003

The advent of CAE (computer‐aided engineering) technology for injection molding and related processes is having a rapidly growing impact on the molding industry. Proper use of this technology has enhanced engineers' capability in handling all aspects of the molding process and has been proven to benefit both productivity and product quality. However, while CAE can serve as a powerful tool to help engineers make rational engineering decisions, it is by no means a panacea for solving all molding problems. The viability of CAE packages depends heavily not only on the scientific principles and numerical methods used for developing the software, but also on the reliability of the input data such as material properties and process conditions. This article discusses the state‐of‐the‐art of the technology with an emphasis on simulations of latest innovations in injection molding. A three‐layer approach that systematically integrates and efficiently utilizes various CAE tools to solve design problems at different levels of sophistication is also presented. © 1993 by John Wiley & Sons, Inc.
Failure prediction of fiber reinforced laminates under hygrothermal and mechanical in‐plane loads
Authors: Philippidis T. P. , Theocaris Pericles S.
Published: April 2003

A theoretical investigation using the failure tensor polynomial criterion was carried out to study the effect of off‐diagonal failure tensor components on the limit behavior of symmetric fiber reinforced laminates under both mechanical and hygrothermal loading. In spite of obvious similarities in the mathematical expression of numerous failure criteria based on the tensor polynomial theory, their predictions may be substantially different depending on loading conditions and on the choice of stress‐interaction terms. Although these predictions for unidirectional fiber reinforced laminae under biaxial loading do not exhibit remarkable differences, this is not the case for multidirectional laminates. Comparison of theoretical predictions with experimental data from in‐plane loaded cross‐ply Graphite/Epoxy laminates proved the reliability of the so‐called generalized elliptic paraboloid failure surface criterion, assuming the existence of a safe triaxial loading path which may depend on the anisotropy of the medium and its suitability for use in structural design applications. © 1993 John Wiley & Sons, Inc.
Numerical analysis of the resin transfer molding process by the finite element method
Authors: Trochu F. , Gauvin R. , Gao D.‐M.
Published: April 2003

As large components of fiber reinforced composite materials are being more frequently produced by Resin Transfer Molding (RTM), a computer simulation of the injection process can help the mold designer to accomplish three important tasks: (1) to ensure a complete filling of the mold through adequate positioning of the injection ports and of the air vents; (2) to verify the integrity of the mold during the filling process through knowledge of the pressure distribution; and (3) to optimize the production cycle using information about the filling time. The resin impregnation is usually modeled as a flow through a porous medium. It is governed by Darcy's law, which states that the flow rate is proportional to the pressure gradient. In our model, Darcy equation is solved at each time step inside the saturated part of the mold using nonconforming finite elements. This method was chosen because the approximated flow rates, contrary to conforming finite elements, satisfy locally the important physical condition of resin conservation across inter‐element boundaries. This permits simplification of the numerical procedure. It is no longer necessary to resort to a control volume approach to move the flow front forward. The resin pressure distribution and the resin front positions are obtained by the computer simulation and calculated results for selected mold geometries are compared with experimental observations. Molds with inserts, multiple injection ports, and the case of anisotropic preforms can be analyzed by the computer program. © 1993 by John Wiley & Sons, Inc.
Theoretical modeling of dispersive melting mechanism of polymers in an extruder
Authors: Huang Han‐Xiong , Peng Yu‐Cheng
Published: April 2003

Studies on the melting in a single‐screw extruder have mainly concentrated on the Maddock melting mechanism. The dispersive melting mechanism, named by us, is of great practical utility. A six‐block physical model is first proposed for the dispersive melting mechanism in the present study. Then nonisothermal non‐Newtonian mathematical models for the dispersive and Maddock melting mechanisms are developed. It has been demonstrated that the dispersive melting model has a number of advantages over the Maddock melting model: the mechanical power consumption can be decreased; the polymer temperature profile is more uniform and its average temperature is lower. Furthermore, melting can be accelerated and hence the total melting length shortened. © 1993 by John Wiley & Sons, Inc.
Development of an expert system for injection molding operations
Authors: Kameoka Seiji , Haramoto Nobuhiro , Sakai Tadamoto
Published: April 2003

To provide a computer assisted system in finding optimum conditions for injection molding operations, an Expert System based on Artificial Intelligence (AI) technique and knowledge or “know‐how” from many skilled injection molding operators has been developed. For the construction of this Expert System, we have originally applied a new method of “Multi‐dimensional Matrix” that represents the relationship between the parameters of each molding condition and expert's knowledge. In this article we describe an outline of the system and the process of converting expert knowledge into AI rules, and demonstrate some molded samples obtained using this Expert System. © 1993 by John Wiley & Sons, Inc.
Plassex: An expert system for plastics selection
Authors: Agrawal Deepak , Vasudevan P. T.
Published: April 2003

PLASSEX is a forward‐chaining rule‐based expert system for plastic selection written in CParaOPS5. This system prompts the user for desired properties, and lists all plastics suitable for a particular application. At present, PLASSEX has 393 plastics in the data base and considers up to 39 polymer properties in order to select the right plastic. More properties can be added to the system with some understanding of the code. This system also provides the user with a help facility. PLASSEX has a number of other features; for instance it gives the user an opportunity to modify any property in case the system fails to come up with a suitable plastic the first time. © 1993 by John Wiley & Sons, Inc.
Graft copolymers and ionomeric associations from mixtures of phenoxy with acid functionalized polyolefins—Part I: Reactants, compositions, and morphology
Authors: Mascia L. , Bellahdeb F.
Published: April 2003

Mixtures of phenoxy, (a polyhydroxyether of bisphenol A) with respectively ethylene–propylene copolymer containing grafted anhydride groups along the chains (EP‐g‐MA), terpolymers of ethylene, t‐butyl acrylate and acrylic acid (EAA), and the sodium ionomer of a terpolymer of ethylene alkyl acrylate and methacrylic acid (I), were produced on a 25 cc torque rheometer. Small amounts of different organic sodium compounds, exhibiting varying levels of base strength, were also used to catalyze the reaction between the functional groups of the two polymers in the mixture. It was found that whereas EP‐g‐MA reacted with phenoxy to produce both graft copolymers and cross‐linked products in varying amounts, the terpolymers containing carboxylic acid groups in the backbone of the polymer chains would never give rise to the formation of cross‐linked products even when large amount of a strong base, such as sodium ethoxide, was used to catalyze the reactions. The latter mixtures exhibited the characteristics of ionomers, involving also alkoxide anions from the phenoxy component to an extent which depended on the base strength of the sodium compound used. The ionomeric mixtures displayed morphological features varying from finely dispersed particles to cocontinuous phases. © 1994 John Wiley & Sons, Inc.
Melt viscosity of polycarbonate–polyolefin blends
Authors: Huang Jan‐Chan , Shen Hsiao‐Fu , Chu Ying‐Ti
Published: April 2003

The flow behavior of polycarbonate (PC) blended with three kinds of polyolefins (LDPE, HDPE, PP) was studied at 260°C using an Instron Capillary Rheometer. Flow behavior of the blends was found to be very different from that of the individual components, and significant viscosity reductions were observed for blends consisting of 5% and 15% polyolefins. In particular, the viscosity of PC/HDPE was found to be much lower than that of the parent viscosity at a shear rate below 100 1/s. For pure components, a crossover of PC viscosity was observed at high shear rate for HDPE and PP. Interfacial slippage in the blends has been suggested as the flow mechanism by which a substantial reduction in the melt viscosities of either component takes place upon the addition of a small amount of the other. A new method was proposed to evaluate the relationship between the characteristic slip factor of the blend and the viscosity of the mixture. A single master curve was obtained, i.e., σm/αAB = a · p±b, where σm is the shear stress at the matrix, αAB the slip factor, p the viscosity ratio, and a, b the constants. © 1994 John Wiley & Sons, Inc.
Blends of thermotropic liquid crystalline and thermoplastic polymers: A short review
Authors: Roetting Oliver , Hinrichsen Georg
Published: April 2003

In this short review, some important phenomena often observed in blends of thermotropic liquid crystalline and thermoplastic polymers are described. Their outstanding physical properties will probably lead to applications as in situ composites. LCP of low concentration in the thermoplastic matrix can be used as a processing agent. The relations between rheology, morphology, and mechanical properties of the blends are explained. Flexible elements in the LCP‐molecules can lead to partial miscibility and improved adhesion between the components. A review of recent literature is given. © 1994 John Wiley & Sons, Inc.
Polystyrene–polyethylene interpenetrating‐like networks: Influence of the vinyl network cross‐linking agent on IPN properties
Authors: Greco Roberto , Astarita Maria Francesca , Fiedlerovà Agnesa , Borsig Eberhard
Published: April 2003

The influence of a cross‐linking agent (divinyl benzene) on new polystyrene–polyethylene, IPN‐like networks was investigated by means of thermal, mechanical tests and a few microscopy observations. It was found that with increased concentration of cross‐linking agent, i.e., with PS cross‐linking density, Young's and storage moduli, measured in the molten rubbery state, increased linearly. Also the elongation and the stress at break were very sensitive to the content of cross‐linking agent, mainly in the low concentration region (0 to 2%). PE and PS domains of about 1 μm circular cross sections were observed on a smoothed surface of a PE/PS blend. Smaller and uniformly dispersed domains were observed for all the IPN‐like systems. The crystallinity, measured by DSC and WAXS, and the IPN morphological features, appeared to be independent of the styrene cross‐linking content, viz., the content of DVB. The overall behavior seemed to resemble that of classical simultaneous IPNs. © 1994 John Wiley & Sons, Inc.
On the measurements of the radial temperature distribution in an extruder channel
Authors: Esseghir Mohamed , Sernas Valentinas
Published: April 2003

In single‐screw extrusion it is not unusual to encounter large temperature variations within the screw channel, especially at high pumping rates. These temperature variations result in nonhomogeneities that affect the quality of the final product. Although there have been numerous efforts aiming at the simulation of the flow in the channel of a single‐screw extruder, and the prediction of important flow quantities, there is hardly any published work in which the temperature distribution in the screw channel was actually measured. Such measurements, if available, would provide data by which computer simulations could be validated. In the present study, a fast‐response, cam‐driven thermocouple system was developed and used to measure the radial temperature distribution in the screw channel. The measurements are carried out on a well‐controlled, custom‐built, single‐screw extruder. Temperature profiles in the centerline of the screw channel were obtained for various operating conditions of the machine. The data obtained revealed interesting features of the flow as well as the dominant heat transfer mechanisms. The system as developed here can be improved to accommodate larger industrial applications. © 1994 John Wiley & Sons, Inc.
Recovery of poly(methyl methacrylate) by the dissolution/reprecipitation process: A model study
Authors: Papaspyrides C. D. , Gouli S. , Poulakis J. G.
Published: April 2003

Approaches to plastics recycling mainly include direct recovery keeping the polymer structure intact, depolymerization and then reuse of monomers, and methods involving reduction of polymer to gases and low molecular weight oils. The model process presented here belongs to the first category: It is proposed dissolution of the starting material, reprecipitation, thorough washing of the polymer obtained, and drying. With regard to the solvent mixtures involved, these are separated by distillation for further reuse. The technique is applied to poly(methyl methacrylate) (PMMA) molding compound, recycled as model starting material. The following criteria are considered: (a) precipitation of the polymer in an acceptable form; (b) maximum “waste” concentration; (c) maximum solution/nonsolvent volume ratio; and (d) maximum extent of poly(methyl methacrylate), solvent, and nonsolvent recovery. On the basis of these criteria, toluene/n‐hexane proved to be the most satisfactory solvent/nonsolvent system. © 1994 John Wiley & Sons, Inc.
Polycarbonate/ABS blends: Processability, thermal properties, and mechanical and impact behavior
Authors: Greco Roberto , Astarita Maria Francesca , Dong Lisong , Sorrentino A.
Published: April 2003

PC/ABS blends, encompassing the whole composition range between PC and ABS, were prepared by a Brabender‐like apparatus and compression molded in sheets. The analysis of processability, confirming the improved PC processability by ABS additions, was accomplished by the same apparatus used for the blend preparation. A DSC investigation confirmed the inward Tg shift found by other authors. Two very different mechanical tests were performed: (a) tensile stress–strain on unnotched specimens at a very low deformation rate, showing a decreased PC ductility in blends with ABS additions; and (b) flexural impact tests (Charpy mode) on sharply notched specimens at a very high deformation rate, where a strong synergistic effect was detected in a restricted composition range (20–30% ABS). A comparison of the experimental data of the Young's modulus versus blend composition with the Kerner's model predictions confirmed the good adhesion existing between PC and ABS domains. The results were interpreted on the hypothesis of interlayer zones existing at the PC/ABS boundary. © 1994 John Wiley & Sons, Inc.
Injection molding of medical plastics: A review
Authors: Amellal Karim , Tzoganakis Costas , Penlidis Alexander , Rempel Garry L.
Published: April 2003

Given the tight competition in the area of plastics for medical applications, the requirements for consistent quality, standardized, safe, and low‐cost medical components have become a big challenge for molders. The survival of injection molding companies for medical applications depends strongly on the success of design, manufacturing, and marketing strategies that different companies have established to meet these requirements. Very often, the design and manufacturing operations to produce medical plastics for the health‐care market have to be adjusted on a daily basis in order to satisfy increasingly strict, government‐regulated, biomedical requirements in addition to all the other pressures expected in this market. As a result, molders of medical plastics are always seeking more systematic ways to improve product quality and produce more at a minimum cost. This brings an advantage to those processors that can combine high‐tech molding with low‐cost production. In this article, based on the open literature, we present a review of the latest activities (last decade) in the field of injection molding of medical plastics together with some comments on modern injection molding processes that can be used. © 1994 John Wiley & Sons, Inc.
Development and application of CAE technology for the gas‐assisted injection molding process
Authors: Turng L. S.
Published: April 2003

Gas‐assisted injection molding is an innovative process that can provide tremendous flexibility in design and manufacturing of plastics parts once it is fully understood and matured. The research effort presented in this article is aimed at development of Computer‐Aided Engineering (CAE) technology for gas‐assisted injection molding. To achieve the goal, efforts have been made in developing a numerical analysis for predicting the filling and post‐filling behavior and verifying the predictions through collaboration with the industry and universities. This article firstly describes the physics of this process, which leads to the various advantages and the inherent difficulties associated with the design and processing. Secondly, it discusses the methodology of numerically modeling and simulating gas‐assisted injection molding filling dynamics together with experimental comparison. At the end of this article, it presents the various advantages of applying the CAE technology for the gas‐assisted injection molding process, such as evaluating the various gas‐assisted injection molding processes and establishing preliminary design guidelines. © 1995 John Wiley & Sons, Inc.
Experimental study on the effects of adding compression to injection molding process
Authors: Yang S. Y. , Ke M. Z.
Published: April 2003

The quality of thermoplastic injection molded parts is mainly determined during the post‐filling process. To enhance the control capacity over the post‐filling process, adding compression to the conventional injection molding process opens a flexible channel for pressure control. This study experimentally investigated the effects of adding compression on the thermal‐mechanical history and on the quality of molded parts. An instrumented molding machine with a compression mechanism was used. Molds for rectangular plate and circular disk were equipped with a movable cavity wall and shut‐off mechanism. The thermomechanical history during the injection compression molding was identified with the aid of a PC‐based data acquisition system. The quality of parts was evaluated by flatness, deviation from mold dimensions, and birefringence. It has been found that the thermomechanical history of the melt under injection compression molding follows a quadrilateral‐shaped path over the p‐v‐T diagram. The control capacity over post‐filling is enhanced. It thus can produce parts with better dimensional control with less frozen‐in orientation than those from conventional injection molding. © 1995 John Wiley & Sons, Inc.
Improvement of weldline strength of fiber reinforced polycarbonate injection molded articles using simultaneous composite injection molding
Authors: Tomari Kiyotaka , Takashima Hiroki , Hamada Hiroyuki
Published: April 2003

Fiber reinforced thermoplastics (FRTP) injection molded articles have many advantages. However, moldings with a complex geometry often encounter weldline problems. Mechanical properties of the injection moldings are often reduced by weldlines, because the fibers at weldline regions orient perpendicularly to the flow directions. We have reported that weldline strength is improved by “back‐flow” during the holding stage. In this article, we have attempted to adapt the SCI (Simultaneous Composite Injection) molding method to improve weld strength of FRTP injection moldings. The back‐flow is expected to occur when there is a difference of holding pressure between two cylinders of the SCI molding machine. The effect of pressure difference between two injection cylinders on the back‐flow phenomena is discussed for fiber reinforced polycarbonate. It is clear that the strength reduction by the weldline can be suppressed down to negligibly small levels in SCI molding. © 1995 John Wiley & Sons, Inc.
Volatile emissions during thermoplastics processing—a review
Authors: Patel S. H. , Xanthos M.
Published: April 2003

Types and amounts of volatiles emitted during thermoplastics processing depend upon the chemical structure of the material and the choice of processing conditions. The identification of volatiles and the development of analytical techniques for measuring their concentration in the workplace are of paramount importance to establish or revise threshold limit values that would minimize exposure to hazardous chemical substances and lead to corrective action. In this review, information related to the types of volatiles emanating from injection molding machines and extruders as well as analytical methods for their measurement was collected, analyzed, and tabulated. Emphasis was placed on the four major commodity plastics, viz., polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS). Although the main emphasis is on emissions during processing, related literature under simulated conditions is also mentioned. © 1995 John Wiley & Sons, Inc.
Modeling the reactive modification of HDPE in a nonintermeshing twin screw extruder
Authors: Thompson M. R. , Hrymak A. N. , Hamielec A. E.
Published: April 2003

The chemical modification of high density polyethylene (HDPE) in a counter‐rotating nonintermeshing twin screw extruder is modeled using a simultaneous random scission and cross‐linking integro‐differential equation. The roles of mixing and kinetics in the free‐radical reaction are investigated. The modification experiments use a masterbatch feed of HDPE with various concentrations of 2,5‐dimethyl‐2,5‐(t‐butylperoxy)‐3‐hexyne. The extruder operating parameters studied were barrel temperature, screw speed, and the degree of screw flight stagger. The reaction model is fit using the molecular weight averages and the gel content measured experimentally. The reaction time for HDPE is determined by use of the residence time distribution of the extruder with a segregation (macromixing) assumption. The segregation model is compared against the plug flow assumption, where the mean residence time of the measured distribution is used for the length of reaction of all polymer species within the extruder. The calculated molecular weight distributions are insensitive to the mixing model used. © 1995 John Wiley & Sons, Inc.
A process for coupling wood to thermoplastic using graft copolymers
Authors: Chen Meng‐Jiu , Meister John J. , Gunnells David W. , Gardner Douglas J.
Published: April 2003

A chemical modification method has been developed to convert lignin into lignin–styrene graft copolymers. The graft products are macromolecular surface active agents because, within each molecule, a hydrocarbon sidechain has been grown off of a natural oxyphenylpropyl backbone. Surface activity of the graft copolymers was indicated by their capacity to form stable emulsions between incompatible fluid phases and to adhesively bond to wood surfaces. Dynamic contact angle measurement using the Wilhelmy plate technique showed that the graft copolymers changed the contact angle of water on wood from 50° to 110°. Coating birch wood (Betula papyrifera) with lignin–styrene graft copolymerization product increases the water contact angle and the binding strength of polystyrene on the wood. Lap shear strengths increased 56%, from 1826 to 2840 kPa, when the wood was coated with a graft copolymer containing 51.7% lignin. Binding was tested by coating the birch with a solution of graft copolymer, drying the wood, injection molding polystyrene onto the surface of the wood, and pulling the polystyrene off the wood surface in a lap shear brace. These properties of the copolymers were used to design a process for forming wood‐thermoplastic composites. © 1995 John Wiley & Sons, Inc.
Weldlines in injection‐molded parts: A review
Authors: Fellahi S. , Meddad A. , Fisa B. , Favis B. D.
Published: April 2003

It is a well‐known fact that weldlines are unavoidable in most injection‐molded products of even moderate complexity. While there are many situations where they are barely perceptible, weldlines represent a potential source of weakness in molded parts. In injection molding weldlines are generated when two separate melt streams join either in multigated molds or as a consequence of flow around obstacles. The development of many interesting materials has been hampered by poor weldline strength. Among such materials are plastics reinforced with fibers or platelets, liquid crystal polymers, and a number of multiphase polymer blends. Weldlines have ever been called the “Achilles' heel” of these multiphase materials. This article is a review of the literature published on weldlines in injected parts. It deals primarily with the aspects related to the mechanical behavior of weldline‐containing parts. It begins with a brief description of the phenomena important for the part formation in the mold, including those leading to weldlines, in addition to the techniques used to characterize weldline‐containing parts. The following three sections consider the structure and properties of weldlines in neat amorphous and semicrystalline polymers, filled and reinforced plastics, and finally in polymer blends and alloys. In the last section methods developed for increasing the weldline strength are discussed. © 1994 John Wiley & Sons, Inc.
Applications of on‐line rheometry in reactive compounding
Authors: Xanthos M.
Published: April 2003

On‐line rheological measurements are usually employed to monitor the reactive modification of single polymers during extrusion. This article provides data on the use of an on‐line rheometer to monitor the reactive compatibilization of polyamide/polyolefin blends in a corotating twin‐screw extruder. The type of functionalized compatibilizer and the choice of compounding conditions are among the variables examined. On‐line and off‐line rheological data are correlated with the morphologies of the extrudates and the mechanical properties of injection‐molded samples in attempts to establish general relationships between on‐line rheology, microstructure, and properties of polymer blends. © 1995 John Wiley & Sons, Inc.
A new approach to reclaimed PET utilization—blends of recycled pet suitable for extrusion blow‐molding technology
Authors: Tsiourvas D. , Tsartolia E. , Stassinopoulos A. , Barrell M. , Bontemps J.
Published: April 2003

Polymer blending of reclaimed PET with various types of polyethylene was utilized for the production of materials suitable for the manufacturing of containers using conventional extrusion blow‐molding equipment. Several marketed polymers bearing functional groups that are potentially reactive to PET end groups were used as compatibilizers. A number of blends were produced and found to possess melt properties suitable for the production of extrusion blow‐molded containers having acceptable mechanical characteristics. Containers were tested for compatibility with different chemicals and permeability of commonly used organic solvents. © 1995 John Wiley & Sons, Inc.
Technology for the improvement of polymer properties
Authors: Kestelman V. N.
Published: April 2003

A new physical method of modification of polymers is discussed. The method is developed to improve strength and other properties of molded polymers and to shorten the post‐treatment time. © 1995 John Wiley & Sons, Inc.
Chemical recycling of mixed plastics of pyrolysis
Authors: Kaminsky W.
Published: April 2003

Most plastics are produced from oil and have a high potential as hydrocarbon sources for the chemical industry. Pyrolysis is a practicable way to pyrolyze mixed plastics. The fluidized bed pyrolysis has turned out to be particularly advantageous. Twenty‐five to 45% of product gas with a high heating value and 30–50% of an oil rich in aromatics could be recovered. The oil is comparable to that of a mixture of light benzene and bituminous coal tar. Up to 60% of ethene and propene are produced by using mixed polyolefins as feedstock. Under appropriate conditions the pyrolysis could be successful on the market. © 1995 John Wiley & Sons, Inc.
The relationship between economic value added and stock market performance: A theoretical analysis
Authors: Keef Stephen P. , Roush Melvin L.
Published: April 2003

Recently in this journal, Turvey et al. (2000, p. 415) report that “… there is absolutely no relationship between EVA and stock market performance” with their sample of Canadian agribusiness firms. We examine the implied relation by invoking a set of perfect market assumptions that are not radically out of kilter with a semistrong form efficient market. We use a simple project as the focus of the analysis. We initially explore the way that the market value of the project evolves over time. We then effect a similar analysis on the project's economic profit. The latter is the theoretical construct underlying EVA. A comparison of these two time series argues that Turvey et al.'s (2000) result is not unexpected from a theoretical perspective. Notwithstanding, we offer brief suggestions as to why executives adopt EVA as a measure of financial performance. [EconLit citations: D81, G30, M41.] © 2003 Wiley Periodicals, Inc. Agribusiness 19: 245–253, 2003.
The role of consumer ethnocentrism in food product evaluation
Authors: Orth Ulrich R. , Firbasová Zuzana
Published: April 2003

Despite the abundance of literature on country‐of‐origin (COO) effects there is a need for additional empirical research into antecedents of the COO effect. This study examines to what extent consumer ethnocentrism (as measured by the CETSCALE) can singularly, as well as in concert with other variables, predict consumers' evaluation of a domestic versus foreign food product. A conjoint experiment was utilized in an exploratory analysis to ascertain the value consumers in Czech Republic place on yogurt being from their own or other countries. The resulting utilities were related to a consumer's level of ethnocentrism. The findings suggest that consumer ethnocentrism is a strong and significant predictor of consumer product evaluations. Adding the ethnocentrism variable to a set of demographic and psychographic variables significantly improves the predictive ability of the set. Potential applications at the practitioners' level include the identification of market segments that react more favorably to domestic produce. [EconLit citations: M310, Q130, C120.] © 2003 Wiley Periodicals, Inc. Agribusiness 19: 137–153, 2003.
Evidence of neuronal migration disorders in Knobloch syndrome: Clinical and molecular analysis of two novel families
Authors: Kliemann Susana E. , Waetge Ricardo T.L. , Suzuki Oscar T. , Passos‐Bueno M. Rita , Rosemberg Sérgio
Published: April 2003

Knobloch syndrome is an autosomal recessive disease characterized by the early onset of severe myopia, vitreoretinal degeneration with retinal detachment, macular abnormalities, and midline encephalocele, mainly in the occipital region. Intra and interfamilial variability is present since the encephalocele is not found in all patients, and the degree of myopia is variable. Analysis of the associated malformations suggests alterations during early neuroectodermal morphogenesis. Only 24 cases have been reported. Recently, the gene responsible for the syndrome, mapped to 21q22.3, was identified. The present study reports on four new cases, revealing the existence of neuronal migratory defects associated with the disorder for the first time. © 2003 Wiley‐Liss, Inc.
Initial droplet size distribution in miniemulsion polymerization
Authors: Sood A. , Awasthi S. K.
Published: April 2003

The initial droplet size distribution of miniemulsions has not yet been measured. It is deduced from previous experimental results that the distribution is broad. Furthermore, the small fraction of the distribution, depending on the nonideality of the cosurfactant–monomer system, may not be stable. This may lead to a rearrangement of the distribution leading to a bimodal distribution. The stability criterion is based on the phenomenon of molecular diffusion or Ostwald ripening. Experimental proof in support of the conclusion regarding the bimodal distribution is cited. The practical significance of the conclusion for making emulsion polymers with high solid contents is given. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3058–3065, 2003