Water-assisted injection-molding technology has received extensive attention in recent years, due to the lightweight of plastic parts, relatively low-resin cost per part, faster cycle time, and flexibility in the design and manufacture. However, there are still some unsolved problems that confound the overall success of this technology. One of these is the water "fingering" phenomenon, in which the water bubbles penetrate outside designed water channels and form finger-shape branches. This study has investigated the effects of various processing parameters on the formation of fingering in water-assisted injection-molded thermoplastic parts. Both amorphous and semicrystalline polymers were used to mold the parts. The influence of water channel geometry, including aspect ratio and fillet geometry, on the fingering was also investigated. It was found that water-assisted injection-molded amorphous materials gave less fingering, while molded semicrystalline parts gave more fingering when compared to those molded by gas-assisted injection molding. For the water channels used in this study, the channels with a rib on the top produced parts with the least water fingering. Water fingering in molded parts decreases with the height-to-thickness ratio of the channels. The water pressure, water injection delay time and short-shot size were found to be the principal parameters affecting the formation of water fingering. In addition, a numerical simulation based on the transient heat conduction model was also carried out to help better explain the mechanism for the formation of fingering in water-assisted injection-molded thermoplastics. (c) 2006 Wiley Periodicals, Inc.
Uniform melt front velocity is recommended for injection mold filling to minimize the part nonuniformity. A method of profiling the injection velocity for such a uniform mold filling is presented in this paper. Based on a neural network model developed for estimating the melt flow length from online measurable variables, the profiling problem is transformed into an optimization to minimize the difference between the predicted melt flow length and a given ramp. The rate of the ramp determines the rate of the melt front velocity traveling in the cavity during filling. Experiments with different molds show that the proposed method is effective in profiling the screw injection velocity to achieve a uniform mold filling. (C) 2006 Wiley Periodicals, Inc.
Sulfonated polysulfone (sPSU) was considered as an alternative material for low-temperature proton exchange membrane fuel cell. The possibility of manufacturing sPSU films by a continuous extrusion process is examined. The use of a plasticizer (polyethyleneglycol, PEG) is essential to decrease the glass transition temperature of the material in order to make it processable in the melt state. However, the acidic character of sPSU induces significant degradation of the sPSU/PEG mixtures even at low temperatures (120 degrees C), necessitating the use of high amounts of PEG to perform the extrusion of sPSU film. In these experiments, 30-40% of plasticizer had to be used to successfully produce a film, but a high level of porosity was produced in the membrane after removing the PEG. Although porosity significantly improves the proton conductivity of the membranes, in a fuel cell, the fuel crossover also increases as a result. (c) 2006 Wiley Periodicals, Inc.
The possibility of manufacturing sulfonated polysulfone (sPSU) membranes by an extrusion process is explored for low-temperature proton exchange membrane fuel cell applications. Because the acid form of sPSU is not suitable for melt-phase processing, the use of the salt form of the polymer was considered, as sulfonate groups are much less reactive than sulfonic acid groups. This form of sPSU makes it possible to use an extrusion process with the help of a suitable plasticizer, such as poly(ethyleneglycol) (PEG). The residual porosity of the film, induced by removing the soluble PEG with water, was found to improve the proton conductivity of the membrane. The membrane fabrication process has a prominent effect on the final properties of the film. For the same composition, a solvent-casting procedure can produce membranes with proton conductivity twice as high as that attainable with a melt-phase process. However, extruded membranes exhibit a greater longevity than do cast membranes. At the same time, the proton conductivity of extruded membranes is less dependent on the ion-exchange capacity of the polymer.
Domain size of 10% dispersed polystyrene in polyethylene was followed in a 34-mm intermeshing counter-rotating twin screw extruder. Variables studied included the effects of barrel temperature, screw speed, viscosity ratio of dispersed-to-continuous phase, and parallel melt versus preblended solids feeds. After steady state was achieved, die samples were quenched for later photomicrographing. The extruder was then stopped and quenched, with subsequent pulling of the screws. From 7 to 12 additional samples were taken along the 18/1 L/D extruder for determination of the mechanism of dispersion and dispersed phase domain size by optical microscopy. At low temperatures, the polystyrene tended to fracture with sharp edges. The fine particles formed in the initial breakup underwent no further size reduction. At higher temperatures, fractured segments had rounder edges, but the size of the small domains remained constant throughout the axial length. There was some evidence of flocculation and coalescence prior to exit through the die. (c) 2006 Wiley Periodicals, Inc.
A new approach for controlling part cooling in plastic injection molding is developed using a PI controller and coolant flow rate as the manipulated variable. The method uses an average part surface temperature within the mold as the setpoint parameter. A mechatronic control system was developed for providing variable coolant flow rates. The control strategy was simulated using plant models, implemented and tested on a 50-tonne plastic injection-molding machine with good closed loop responses. (C) 2006 Wiley Periodicals, Inc.
A three-dimensional flow of a low-density polyethylene in a spiral-mandrel die for a blown-film extrusion is simulated. The effect of elongational viscosity on the flow in the spiral-mandrel die is analyzed. Elongational viscosity is found to have only a minor effect on the velocity distribution, but a significant effect on the pressure and temperature distributions in the die. (c) 2006 Wiley Periodicals, Inc.
Polymerization of an acrylate derivative of bisphenol-A by ionizing radiation in the presence of an organically modified montmorillonite was carried out in order to produce a flame-retardant composite. The measurement of the thermal effect during irradiation indicates that radiation curing of pure resin and resin-clay mixtures occurred in both cases. Moreover, differential scanning calorimetry and dynamic mechanical thermal analysis showed that a curing completion can be obtained by thermal curing after irradiation with a significant increase of the glass transition temperature. The morphology was investigated by X-ray diffraction and transmission electron microscopy. These have indicated that gamma irradiation leads to the formation of a microcomposite structure after radiation curing. The flame resistant characteristics were studied by means of thermal gravimetric analysis under nitrogen and air and by cone calorimeter tests. In particular, thermal gravimetric analysis in air showed that the presence of the dispersed clay in the polymer matrix increases the oxidation temperature. This is attributed to the formation of a more stable char, due to a protective skin of clay aggregates that builds up on the surface of the volatilizing polymer matrix during thermal degradation which protects the charred polymer from reactions with oxygen. Finally, the cone calorimeter tests show a reduction of heat release of the clay-polymer composite with respect to the neat resin. The contribution of the clay in reducing the rate of heat release is attributed to the dispersion of the filler that allows build-up of an inorganic surface layer at a rate which is sufficient for effectively compete with the feeding of the flame with combustible pyrolysis products. (c) 2006 Wiley Periodicals, Inc.
The functional monomer, N-phenyl methacrylamide (PMA), was synthesized by reacting methacryloyl chloride with aniline. Free-radical solution copolymerization of PMA and acrylamide (AA) in various feed ratios was synthesized by using benzoyl peroxide initiator in N,N-dimethylformamide at 70 degrees C. Copolymer structure was elucidated by infrared and proton nuclear magnetic resonance spectroscopy. The copolymer composition was determined from the corresponding H-1 NMR spectra of the copolymers. Finemann-Ross and Kelen-Tudos methods were used to determine the reactivity ratios of the monomers. Thermal characterization of the copolymers was carried out using differential scanning calorimetry and thermogravimetric analysis. Thermal stability of the copolymers increases with the increase of PMA content in the copolymer. (C) 2006 Wiley Periodicals, Inc.