Reduction of cycle time by addition of silicon carbide filler to syndiotactic polystyrene/glass fiber composites

Abstract

Reducing cycle time in injection molding process is important because it can save operational cost and increase product yield. Cycle time can be categorized by six criteria, which are metering time, time for closing a mold, packing time, holding time, cooling time, and the time needed to open a mold and to eject the molded product. It was found that the metering time is crucial to predict the cycle time of glass fiber reinforced syndiotactic polystyrene (sPS/GF, 60/40 by weight). In many cases, however, cycle time could be reduced by saving cooling time. This study is motivated by the demand to reduce the cycle time of sPS/GF composite. Since the increase of thermal conductivity leads to the reduction of cooling time, silicon carbide (SiC) is employed to evaluate if it can increase the thermal conductivity of sPS/GF composite. When SiC is added to replace entire GF in sPS/GF composite, the mechanical property of the resulting sPS/SiC (60/40 by weight) composite was not satisfied even though its thermal conductivity was enhanced to about 62 %. Within tolerable ranges in mechanical properties, SiC was added to replace a half amount of existing GF filler. sPS/GF/SiC (60/20/20 by weight) composite achieved the enhancement of thermal conductivity from 0.230 to 0.308 W/m K (34 %) which resulted in the effective reduction of both cooling time and cycle time from 16 to 10 s and from 47 to 38 s, respectively. It should be noted that additional time saving was obtained by 3 s between 6 s in cooling and 9 s in overall cycle time. It can be interpreted by the fact that the increase of thermal conductivity also accelerated the heating rate of sPS/GF/SiC composite.