The design of plastic injection mold requires precision and efficiency of the injection. Therefore mold design engineers need to determine the size location and number of the gates to fit the length of the plastic flow in the work piece so that when the injection mold is built they’ll get the complete and specified specimen. This research was conducted to study the influence of injection flow channel thickness affects the flow index. Poly ethylene high density High density polyethylene HDPE was used in the experiments. The flow of plastic was Spiral Test according to ASTM: D 3123-94 with rectangular cross-sectional area of 6 mm. wide 6 mm. pitch. It was found that the thickness of the flow channel at 0.51.01.5 and 2.0 mm. which has the best flow rates at the best injection speed at 25% the injection pressure at 30% and the flow distance of 52 116 238 and 299 mm respectively with the plastic melting temperature between 190 C and 220 C.

This research was concentrated on characterized mechanical properties and adjusted compatibility of poly (lactic acid) (PLA) with thermoplastic starch (TPS) as biodegradable polymers composites. PLA was blended with TPS at the proportion of 10 20 30 50 and 70 wt% as well as 2 phr chain extender by an internal mixer at 200°C. The blended materials were then injection molded at 230°C. Tensile testing showed that as the amount of TPS increase the elongation at break tended to increase but the tensile strength and modulus tended to decrease. The morphology was investigated by scanning electron microscope. It was found that distinct phase between PLA and TPS was observed. Yet adding the chain extender clearly improved the compatibility between PLA and TPS. The blended materials were also analyzed by differential scanning calorimetry method to study thermal properties. It was found that as the amount of TPS increased the glass transition temperature (Tg) melting temperature (Tm) and cold crystallization temperature (Tcc) deceased. Additionally chain extenders did not affect thermal properties. The thermal stability of the composites decreased when increasing the amount of TPS because of the degradation of TPS in PLA. However when heated at 100ºC for 1 hr the PLA sample bent while TPS did not bend. When PLA was mixed with TPS the composite was bent according to adding TPS.