The thermal stability of polycarbonate resin (PC) composites filled with silica particles surface-treated with polyphenol reagents has been investigated. The composites were prepared by mixing the surface-treated silica particle with PC using a plastometer at 280°C. For the composites containing 15vol% non-treated silica particles, the number-average molecular weight (M_n) of PC in the composites, measured by gel permeation chromatography, decreased from 24300 to 18100 at a mixing time of 60min, while unfilled PC resin control decreased to 21700. The magnitude of the storage modulus (E′) and the glass transition temperature (T_g) of the composites were evaluated by dynamic viscoelastometry. Both decreased with decreasing molecular weight of PC. These results suggest that the PC molecule depolymerized during the mixing process due to the thermal energy and stress. On the other hand, we found that the surface treatment of silica particles with tannic acid reduced the decrease in PC M_n to 22400 and also reduced the decrease in E′ and T_g. In addition, we studied the effects of surface treatment of silica particles using polyphenol groups with different numbers of hydroxy groups. Reagents with many hydroxy groups resulted in higher M_n retention than those containing reagents with fewer hydroxy groups. These findings suggest that the addition of surface-treated particles in PC improved the stability of PC composites. This implies that surface treatment may be an effective method in recycle of PC resin composites.

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Bagasse is obtained by squeezing sugar cane. In Okinawa, Japan, about 2.3 hundred thousand tons of bagasse is produced every year and used mainly as boiler fuel in factories. This research, embracing the new point of view that bagasse is invaluable for use other than fuel, aims to demonstrate its utility as a composite material. The first example is Bulk Molding Compound (BMC) composed of high density polyethylene (HDPE) mixed with powdered glass and powdered bagasse and processed by injection molding. When the bagasse content is increased, there is little improvement in tensile strength due to the existence of holes caused by trapped gas arising from high viscosity. The addition of bagasse however contributes to reduced shrinkage of the product. Another example is linear low density polyethylene (LLDPE) combined with chopped strand glass fiber and short bagasse fiber. With an increase in bagasse content, the tensile strength increases because glass fibers become fixed when they pierce into the bagasse fibers. Shrinkage is also reduced. Under the optimum conditions determined through SN ratio analysis based on design of experiment, the tensile strength of the product showed an efficient high strength which is in accord with the predicted strength within the 95% confidence limit range.

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The material recyclability of cut wastes of polypropylene and rayon fabrics generated during the manufacture of non-woven fabrics was investigated by using an injection molding method. In this system, the cut waste of rayon fiber was fed directly into the injection molding machine together with the cut waste of polypropylene. The polypropylene and rayon act as matrix and fiber reinforcement, respectively. The volume fraction of the reinforcing fibers was varied by adjusting the supply amount (number of bundles) of rayon and polypropylene waste fabrics. The molding temperature was determined by the melting point of polypropylene. The tensile modulus and strength of the molded composites increased with increasing content of rayon fiber. The composites were characterized by SEM observations of fracture surfaces. The results suggest that the injection molding method described herein shows promise in contributing toward the material recycle of cut wastes of rayon non-woven fabric as a reinforcement for thermoplastic composites.

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