The objective of this article is to review the use of conductive plastics in the shielding of electromagnetic interference (EMI). The theory of EMI shielding and evaluation methods of EMI materials are discussed. Different approaches in achieving high conductivity of plastics are reviewed. Emphasis is placed on filled plastics which are a promising way for shielding and do not require a secondary process. Literature on properties and processing of several common conducting plastics is reviewed. Design and processing requirements of such filled plastics are also given. (C) 1995 John Wiley and Sons, Inc.
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. (C) 1995 John Wiley and Sons, Inc.
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. (C) 1995 John Wiley gr Sons, Inc.
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. (C) 1995 John Wiley & Sons, Inc.
The use of newly developed polymer processing technologies to enable the microstructure control of nonreactive and reactive polymer systems, which up to now have been manufactured with conventional chemical polymerization processes, has been rapidly becoming popular, particularly in the field of polymer alloy systems. In this article the mechanisms of morphological development and its control for polymer alloys used mostly in a twin-screw extruder have been reviewed mainly from our studies. And furthermore, on-line monitoring and handling techniques developed at The Japan Steel Works are described in relation to the evolution of microstructure of polymer systems in a twin-screw extruder. (C) 1995 John Wiley & Sons, Inc.
The effects of compatibilizing agents on the morphology and properties of high density polyethylene (HDPE) and polyamide-6 blends were investigated. The ternary blends were studied with the objective of understanding and optimizing the compatibilization of HDPE and polyamide-6. The blends were prepared by melt mixing the individual components in a twin-screw extruder. Mechanical property, theological property, differential scanning calorimetry, and scanning electron microscopy results are discussed. The addition of compatibilizing agents results in a greatly reduced dispersed phase particle size. The properties of the blends level out after a compatibilizer level of 3 wt% has been reached. The theological, mechanical, and thermal property results indicate the presence of the compatibilizing agent along the interfacial boundary regions between the other two phases. (C) 1995 John Wiley and Sons, Inc.
Process developments in reactive extrusion or reactive compounding are largely carried out in closely intermeshing corotating twin-screw extruders. The aim of this article is to present an analytical process model for this reactor type in order to facilitate the design of screw geometry and the settings of process parameters. Taking simultaneously into account aspects of flow behavior, heat transfer, thermodynamics, physics, and chemistry, a powerful mathematical model has been developed which was compared with practical results (e.g., residence time, pressure buildup, drive energy, bulk temperature, and conversion) on lab and production scale machines. The experiments were mostly carried out for the anionic bulk polymerizations of nylon 6 and polystyrene. Furthermore the reactive bending of nylon 6 and polyethyleneterephthalate was examined. Based on these chemical systems the practical use of computer-aided process design will be discussed. (C) 1995 John Wiley & Sons, Inc.
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 degrees to 110 degrees. 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. (C) 1995 John Wiley and Sons, Inc.
A model dissolution/reprecipitation process is studied for the recycling of high-density polyethylene (HDPE). The process proposed basically comprises dissolution of the plastic in an appropriate solvent, reprecipitation by using a nonsolvent, thorough washing of the material obtained, and drying. The solvent mixtures involved are separated by distillation for further reuse. Toluene/acetone was tried as a potential solvent/nonsolvent pair and proved to be very satisfactory, similarly to the case of recycling low-density polyethylene. Further investigation was focused on the effect of sample history through successive recycling cycles. The recycled grades were evaluated in terms of the following properties: melt flow index (MFI), molecular weight, crystallinity, mechanical performance in tensile mode, and grain size analysis. In all cases the recycled polymer exhibited excellent retention of its properties. (C) 1995 John Wiley and Sons, Inc.
The quality of thermoplastic injection molded parts is mainly determined during the post-filling process. To enhance the control capacity over the pose-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. (C) 1995 John Wiley and Sons, Inc.
Gas-assisted injection molding (GAIM) has proven itself to be a breakthrough in molding technology. However, the process involves additional gas-related parameters to control the molding process. The interaction between melt and gas makes the gas-assisted process complicated. To make satisfactory parts, the material, the mold, and process parameters determine the ''moldability'' of a specific system. The concept of ''molding areas'' on the critical plane can be extended from thermoplastic injection molding to GAIM. This research is devoted to the development of a proper moldability diagram for GAIM. The first part of this study employs gas-related parameters to define the molding area. The second parr is devoted to identifying the relative importance of process parameters. The results show that melt temperature and short shot are the two factors which most significantly affect the GAIM process. The third part of this study defines the moldability based on critical parameters. The application of the moldability concept is demonstrated in selecting the optimum rib geometry. These moldability studies are intended to give first guidelines for system optimization. (C) 1995 John Wiley and Sons, Inc.
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. (C) 1995 John Wiley and Sons, Inc.
Polymer blends containing nylon-6 of different molecular weights (MW) and polypropylene (PP) were prepared by using a twin screw extrudes in order to examine the effects of molecular weights of nylon and the influences of different types of compatibilizing agents on the phase morphology and the properties. The morphology of the resulting blends was characterized by using both scanning electron microscope (SEM) and optical microscope and the properties measured included Izod impact strength, melt flow index (MI), flexural modulus, and heat distortion temperature (HDT). It was found that the molecular weights of the nylon matrix had a significant effect on the phase morphology. The fracture surface of the low MW nylon blend demonstrated a uniformed phase morphology with the dispersed PP particles of dimensions in the range of 1 mu m in diameter embedded in the nylon matrix, suggesting an improved compatibility as compared with the high MW nylon system, even though these two constituents were incompatible in nature. Three different types of compatibilizers, including maleic anhydride modified PP (MA-g-PP), acrylic acid modified PP (AA-g-PP), and ethylene glycidyl methacrylate copolymer (EGMA), were used to examine their effects. It seemed that blends compatibilized with MA-g-PP exhibited the most homogeneous phase morphology and superior mechanical properties among the three. In the blends containing low MW nylon as the matrix phase, the Izod impact strength was shown to have increased by about 40% as compared with the noncompatibilized blend, while a 20% increase of the impact strength was measured in the high MW nylon system. The effects of nylon's molecular weights and the compatibilizers were also studied in systems of PP/nylon blends reinforced with silane-treated glass fibers. It was shown that the properties of the composites relied on the phase morphology which, in turn, was affected by both the molecular weight of nylon and the compatibilizing agents. (C) 1995 John Wiley and Sons, Inc.
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. (C) 1995 John Wiley and Sons, Inc.
Five, ten, and twenty percent by weight blends of polysulfone in polycarbonate and polyetherimide in polycarbonate were produced by melt blending. The materials were injection molded into plaques. Mechanical analysis consisting of tensile, pendulum impact, and ballistic impact testing was conducted using the plaques or samples machined from the plaques. The average impact strength and percentage of ductile failures decreased with increasing composition of polysulfone and polyetherimide. The tensile test results indicate that a relationship exists between the percent composition and the yield strength for the blends with the blends showing an improvement in tensile strength. The ballistic testing results show that a possibly linear relationship exists between the percent composition and the critical velocity for complete penetration. Differential scanning calorimetry was conducted to measure the glass transition temperatures of the materials. The presence of two glass transition temperatures and lack of transparency have indicated that the blends are immiscible. (C) 1995 John Wiley and Sons, Inc.
In recent years, the notion of the expert system (ES) has become very popular, and its enormous potential to industry and ways in which it could improve decision-making have been recognized. This article presents the research work of an expert system (ESIMCOST) the authors developed to assist the manufacturers in the injection mold cost estimation at the early product design stage. The system domain is concerned with the concurrent decision-making of the plastic part design, injection mold design, and mold-making process planning during the cost estimation process. Numerous interrelated variables and technical data for estimating the injection mold cost are well organized. With the inputs of the features of a plastic part, the ESIMCOST will generate an estimated cost of the injection mold required to produce the part. Some of the projected benefits from the system implementation are addressed in the article. (C) 1995 John Wiley & Sons, Inc.
On-line/in-line measurement technologies are increasingly finding uses for controlling the quality of polymeric materials during all phases of production and for minimizing waste in the form of off-spec materials. In addition to commercial/developmental sensors for theological or spectroscopic monitoring of extrusion processes, prototype instruments have been recently developed for in-line optical monitoring of multiphase polymer melts. In this article, examples of developments in in-line/on-line Fourier Transform Infrared (FTIR) and Near Infrared (NIR) spectroscopy and optical microscopy and their applications to extrusion processes will be presented. (C) 1995 John Wiley and Sons, Inc.