Electrically conductive resins can be made by adding electrically conductive fillers to typically insulating polymers. Resins with an electrical resistivity of approximately 10(6) Omega cm or less can be used for electromagnetic and radio frequency interference shielding applications. This research focused on performing compounding runs followed by injection molding and shielding effectiveness (SE) testing of carbon filled nylon 6,6- and polycarbonate-based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch-based carbon fiber. For each polymer, conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2(3) factorial design and a complete replicate in each polymer. The objective of this study was to determine the effects and interactions of each filler on the SE properties of the conductive resins. Carbon black caused the largest increase in SE. Also, each single filler and each two filler interaction caused a statistically significant increase in SE. (C) 2003 Wiley Periodicals, Inc.
In this work, heat-shrinkable characteristics of a polyethylene compound were obtained by blending mixtures of low-density polyethylene with varying amount of peroxide. These were then extruded and molded to the required shape and then cross-linked by chemical means, followed by heating and stretching and then cooled to "freeze-in" the oriented polymer structure (elastic memory). A decrease in the melting point and heat of fusion (DeltaH(f)), as determined from the DSC melting enthalpies, was observed with an increase in the dicumyl peroxide (DCP) concentration. Tests on the heat shrinkablity of the samples showed that the stretching temperature has a large effect on the shrinkage temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. The elongation at break decreased with an increase in the DCP concentration. Increasing the temperature in lightly cross-linked samples (low percent DCP) resulted in a reduction in the elongation at break. Increasing the cross-linking density (DCP content) gave an opposite effect. (C) 2003 Wiley Periodicals, Inc.
Blends of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalene dicarboxylate) (PET/PEN) have exhibited properties that are of commercial interest to the packaging industry. Melt processing of PET with PEN results in transesterification reactions. The blend properties are controlled by the kinetics of these reactions. The chemical kinetics equations have been modified to predict theoretical processing temperatures required for different blend compositions to achieve critical levels of transesterification. These values are found to be in close agreement with the experimentally observed values obtained for blends processed in a twin-screw extruder. The critical transesterification temperature is dependent on the equilibrium melting point of the miscible blend and the nature of the PET and PEN resins used for preparing the blend. (C) 2003 Wiley Periodicals, Inc.
Viscoelastic effects on mixing flows obtained with kneading paddles in a single-screw, continuous mixer were explored using 2-D finite element method numerical simulations. The single-mode Phan-Thien Tanner nonlinear, viscoelastic fluid model was used with parameters for a dough-like material. The viscoelastic limits of the simulations were found using elastic viscous stress splitting, 4 x 4 sub-elements for stress, streamline upwind, and streamline upwind Petrov-Galerkin (SUPG). Mesh refinement and comparison between methods was also done. The single-screw mixer was modeled by taking the kneading paddle as the point of reference, fixing the mesh in time, Rigid rotation and no slip boundary conditions at the walls were used with inertia taken into account. Results include velocity, pressure, and stress profiles. The addition of viscoelasticity caused the shear and normal stresses to vary greatly from the viscous results, with a resulting loss of symmetry in the velocity and pressure profiles in the flow region. (C) 2003 Wiley Periodicals, Inc.
In rotational molding, polymer powders are subjected to heating, melting, cooling, and subsequent solidification in biaxially rotating molds. Heat transfer phenomena during rotational molding are significantly affected by the presence of endothermic and exothermic transitions. In this paper instead of using the traditional moving interface method, a new approach is presented which is applicable to semicrystalline materials like linear low-density polyethylene. Melting is described by a statistical model and crystallization by a kinetic model. The model parameters are determined from differential scanning calorimetry measurements. The one-dimensional unsteady heat conduction equation is solved by a finite difference method. The numerical predictions are in good agreement with experimental data. The overall heat transfer model can be used for process optimization purposes. (C) 2003 Wiley Periodicals, Inc.
Polypropylene (PP) has not been used extensively in rotational foam molding because it has been traditionally considered as nonfavorable for foaming applications because of its relatively weak melt strength and melt elasticity at elevated temperatures. However, because of the unique end-use properties of PP, PP foams have recently grown in importance. An experimental study was conducted to identify feasible processing strategies for producing PP foams with satisfactory morphologies in dry-blending-based rotational foam molding. The obtained results revealed that cell coalescence plays a key role in the production of PP foams in rotational foam molding. If it is efficiently suppressed, the cell morphology of the PP foams improves dramatically. To suppress cell coalescence, it would be necessary to preserve the melt strength of PP during processing. One way of doing this is maintaining the temperature of the PP melt as low as possible. This can be accomplished by either lowering the decomposition temperature of the chemical blowing agent by using an activator such as zinc oxide and/or reducing the temperature of the oven. (C) 2003 Wiley Periodicals, Inc.
In this study the morphology of LDPE/TPS blends prepared by a one-step extrusion process is compared to that obtained by reprocessing of the original blends. The influence of composition and melt drawing is examined. A novel methodology based on the form factor of the dispersed particle was used to estimate the equivalent spherical particle size of dispersed thermoplastic starch (TPS). This approach allows for the quantitative comparison of average dispersed phase particles regardless of their shape. Blends prepared in the one-step extrusion process show increased levels of anisotropy as a consequence of a combination of coalescence and particle deformation during melt drawing. Reprocessed materials demonstrate morphologies that are highly stable to a wide range of hot stretch ratio conditions. The TPS particles of reprocessed blends show no coalescence and a low degree of deformation. This phenomenon is explained by plasticizer evaporation resulting from the second processing step. The TPS is transformed from a highly deformable phase to one resembling a partially cross-linked material. These data indicate that the one-step processing of LDPE/TPS blends can be used to generate a wide range of highly elongated morphological structures. A two-step approach, analogous to typical compounding and shaping operations and involving controlled glycerol removal in the second step can be used to prepare a wide range of highly stable, more isotropic, dispersed particle morphologies. (C) 2003 Wiley Periodicals, Inc.
The purpose of this study was to investigate in detail the adsorption performance of poly(2-hydroxyethylmethacrylate-methacryloylamidophenylalanine) [p(HEMA-MAPA)] beads. The metal-complexing comonomer MAPA was synthesized by reacting methacryloyl chloride with phenylalanine. Spherical beads with an average size of 150-200 mum were obtained by radical suspension polymerization of HEMA and MAPA, conducted in an aqueous dispersion medium. The beads had a specific surface area of 19.1 m(2)/g, and were characterized by means of swelling studies, FTIR, and elemental analysis. Beads with a swelling ratio of 68% and containing 3.2 mmol MAPA/g were used for the removal of heavy metal ions. Adsorption experiments were conducted with the MAPA-functionalized beads involving the heavy metal ions cadmium, arsenic, chromium, mercury, and lead. Metal adsorption was found to be dependent on the characteristics of the solution (i.e., medium pH and metal concentration) and the type of metals to be adsorbed. We have obtained adsorption capacities equal to 669.4 mg/g for Hg(II), 584.4 mg/g for Pb(II), 268.4 mg/g for Cd(II), 204.1 mg/g for As(III), and 115.2 mg/g for Cr(III). The adsorption capacities on molar basis were in the order of Hg(II) > Pb(II) > Cd(II) > As(III) > Cr(Ill). Adsorption of heavy metal ions from synthetic wastewater was also studied. The adsorption capacities were 24.5 mg/g for Cd(II), 16.9 mg/g for Cr(III), 144.4 mg/g for Hg(II), 90.9 mg/g for Pb(II), and 8.0 mg/g for As(III) at 0.5 mmol/l initial metal concentration. Naturally, depending on the desired goals, the beads containing metal could be regenerated for appropriate disposal. Our results suggest that p(HEMA-MAPA) beads are good metal adsorbers and have a great potential for environmental protection. (C) 2003 Wiley Periodicals, Inc.
A fire retardant phosphorous-containing bisphenol compound, bis(3-diethyl phosphono-4-hydroxyphenyl)-sulfide (DPHS), has been inserted in an epoxy network. In particular, a chain extension procedure has been used to incorporate DPHS into a standard bisphenol epoxy resin. Different amine catalysts have been tested to promote the reaction of DPHS with the epoxy oligomer. The cure kinetics of this chain-extended oligomer, using an aliphatic amine (triethylene-tetraamine, TETA) as hardener, has been studied with the aid of differential scanning calorimetry and compared with that of the standard stoichiometric epoxy/TETA formulation. For each formulation the activation energy of the curing reactions has been evaluated by the Kissinger method. The results of thermogravimetric and flammability tests indicate that DPHS promoted the formation of a char, leading to an improved fire resistance. Finally, a comparison of the thermal and mechanical properties of the standard stoichiometric formulation relative to those of the epoxy modified with DPHS, and cured with TETA, showed only marginal changes in the physical and mechanical properties. (C) 2003 Wiley Periodicals, Inc.
Blends and copolyesters of poly(ethylene terephthalate)/poly(ethylene 2,6- naphthalene dicarboxylate), PET/PEN, have shown promise in high performance container applications. In the first part of this series on the processing characteristics of PET/PEN blends, we investigated the applicability of reaction kinetics to predict the critical transesterification temperature during processing and the influence of the equilibrium melting point of the miscible blends on the critical transesterification temperature. In the present work, we have studied both the rheology and degradation kinetics of the blends as a function of material composition. Melt viscosity loss was measured as a function of time and temperature. Activation energies for degradation were calculated from experimental data. Results show that blends containing a minimum of 10% PEN by weight are as stable as PEN in terms of thermal and thermal-oxidative degradation. Addition of low amounts of PEN to PET causes a depression in melt viscosity. A critical composition of 10% PEN by weight is required before an increase in blend viscosity is observed. (C) 2003 Wiley Periodicals, Inc.
Reactive molding process of thermosetting materials is an area where advanced computer simulations can provide useful information to detect molding problems prior to the mold making. Examples of such problems are premature gelation, undesired weld-line locations, and air traps, However there is a lack of suitable software that would allow the modeling in a fully three-dimensional (3-D) space for such reactive systems. A new approach for the 3-D simulation of reactive molding process is presented in the paper. In the filling stage fluid dynamics and heat transfer are modeled within a system of resin and a mold, combined with appropriate viscosity and curing reaction models. During the curing phase only heat transfer and curing kinetics are taken into account. The presented approach was verified by comparing computational results for a cylindrical test to experimental measurements and was successfully applied on a real industrial process in manufacturing of a medium voltage combi sensor. The selected results of such simulations are also presented in the paper. (C) 2003 Wiley Periodicals, Inc.
Plastic energy dissipation (PED) of polymer particulates is, essentially, the energy dissipated during large and repeated plastic deformations of compacted polymer particulates while still in the solid state. PED is higher or much higher than VED, the viscous energy dissipation source of polymeric melts, because the stresses necessary to plastically deform viscoelastic polymer solids are orders of magnitude higher than the stresses needed to support viscous flow. In the last few years our group has demonstrated experimentally the dominant role which PED plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin-screw extruders and counterrotating continuous mixers/melters, in which the deformation of solid polymers is mandatory We have also developed simple empirical methods of predicting the total axial distance needed for melting a given polymer in specific processing/compounding machines and processing conditions, as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores the more complex issue of how the PED behavior of single-component polymers may affect the PED (and the heating/melting) behavior of multi-component polymer blends. (C) 2003 Wiley Periodicals, Inc.
Potato starch was chemically modified in an APV self-wiping twin screw extruder to produce hydroxypropylated starch. The product obtained had a molar degree of substitution (MS) between 0.06 and 0.26. The selectivity of the hydroxypropylation reaction varied between 50 and 95%, yields varied between 15 and 95%, and conversions between 30 and 91%. Using viscosity data of native and hydroxypropylated starch, together with extruder parameters like temperatures, residence time distribution, and shear rates, a model was set up to predict the MS values, conversions, and selectivities. With this model, interactions between temperature, reaction, and viscosity can be understood and predicted. (C) 2003 Wiley Periodicals, Inc.
Free-radical retrograde precipitation polymerization process in the past has shown excellent control characteristics over reaction rate, molecular weight, and in the entrapment of live radicals for the generation of block copolymers. The same principle has now been extended to study the reaction confinement to a nanoscale region. Nanosized polymer particles have been reported to form from block copolymers, conventional precipitation polymerization methods, or through emulsion polymerization approaches. In this work, we present a new method of generating nanosized polymer particles by polymerizing the monomer in an environment that precipitates the polymer above the lower critical solution temperature. The nanoparticles have been characterized by both tapping-mode atomic force microscopy observations and in situ synchrotron time resolved small-angle X-ray scattering analysis. The results from both the techniques showed the formation of nanoparticles in the size range of 15-30 nm, directly from the polymerization process. (C) 2003 Wiley Periodicals, Inc.
Full-shot gas-assisted injection-molding has the advantage of eliminating the switchover mark that usually occurs on the surface of short-shot gas-assisted molded parts. The purpose of this report was to study the effects of processing parameters on the moldability of the full-shot gas-assisted injection-molding process. Experiments were carried out on an 80-ton injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. The materials used were general-purpose polystyrene and polypropylene. A plate cavity with a gas channel of various geometries (trapezoid, semicircle, and rectangle) across the center was used to mold the parts. After molding, the lengths of gas penetration were determined. The hollowed core ratio by the gas was also determined. A numerical analysis was carried out to find out the temperature distribution of the polymer melt inside the gas channel. It was found that the sink mark of molded parts decreases with the length of gas penetration. Molded parts using trapezoidal gas channel had the longest gas penetration length. In addition, a thermal contraction model was proposed to predict the gas penetration volume inside the parts. Good agreement was reached between the experimental data and the calculated result. (C) 2003 Wiley Periodicals, Inc.
Precision injection molding of thin-wall parts has become an important concern in 3C (computer, communication, and consumer electronics) plastics industry. Previous studies in precision injection molding control focused on the injection screw, the hydraulic system control and the associated operations. In the present study, the influence of relevant parameters, including injection speed, melt temperature, mold temperature, filling-packing switchover, and packing pressure, on the mold plate separation under different clamping pressures was investigated as part of precision molding control. A two-cavity tensile test specimen mold equipped with four linear variable displacement transducers (LVDTs) on mold exteriors and across the parting surface was used for experiments. A PC-based monitoring system was also built to detect the mold separation signals. Mold separation can also be identified from part weight variation and exhibits relevant correspondence with part weight. It was found that because of the high injection speed required for thin-wall molding, mold separation is not negligible. In all situations, mold separation decreases with increasing clamping pressure. As melt temperature and mold temperature increase, mold separation increases, resulting in an increase of part weight. Similarly, when packing pressure and injection speed increase, mold separation also increases. Earlier switchover from filling to packing can decrease mold separation as well as part weight. Among all parameters, packing pressure exhibits the greatest influence on mold separation and the associated part weight change. Variation of melt temperature and mold temperature also changes the gate freezing time and the associated packing pressure distribution and mold separation. The influence also becomes larger when molding thin-wall parts as compared with conventional injection molded parts because of the larger injection pressure required for molding. Simulations also show good correspondence with experimental measurements. (C) 2003 Wiley Periodicals, Inc.