Experimental analysis of temperature and crystallinity profiles of wood sawdust/polypropylene composites during cooling

The temperature profiles of wood sawdust/polypropylene (PP) composite melts during cooling were experimentally investigated with a cooling jacket apparatus connected to the end of an injection-molding machine. Real-time melting temperature was measured with an unsheathed thermocouple array coupled with a high-speed data-acquisition unit. The crystallinity level of the solidified composites was evaluated with an X-ray diffractometer. Before the crystallization temperature (T-c) was reached, the cooling rate of the melt layer near the wall was greater than that near the center. After T-c was reached, the opposite behavior was observed. Wood sawdust content did not affect the general temperature and crystallinity profiles across the duct diameter but led to more nonuniform temperature profiles across the duct diameter. The sawdust particles could act as a nucleating agent during the nucleation stage to increase T, of the PP and as an interfering agent during the crystal growth stage to decrease the overall crystallinity level of the PP. The temperature and crystallinity profiles were not affected by the coolant flow rate. The normalized induction time changed with reduced radius (r/R, where r is the distance between the central duct to any point along the cross-section of the duct and R is the duct radius) positions and coolant flow rate, especially for neat PP and PP composites with a low sawdust content (10 wt %). (c) 2006 Wiley Periodicals, Inc.