High density polyethylene HDPE/Themal expandable micro capsule (EMC) and HDPE/EMC/Kenaf composites were fabricated by twin screw extruder. Based on the foaming behavior of HDPE/EMC composites, the optimum foaming conditions were selected at 40 rpm, 5 wt%, and 160 ℃. Foaming behavior and physical properties of HDPE/Kenaf/EMC composites were evaluated at the selected foaming conditions and the length of Kenaf fiber was controlled at 1, 3, and 5 mm. Thermal properties of HDPE/EMC and HDPE/KF/EMC composites were investigated by DSC and TGA, and there was no district change in thermal properties. The effect of the compatibilizer on foaming behavior was observed by cell structure measured by SEM. The rheological properties of the composites were investigated by dynamic Rheometer. The complex viscosity and shear thinning effect of the composites increased with KF contents and the effect was obvious in case of the composites with the compatibilizer.
In order to select an optimum fabrication condition of HDPE/KF composites with high content of KF, PE-g-MAH with different MAH content and two kinds of KF with different length were applied manufacturing the composites and measuring thephysical properties. The chemical structure and grafting degree of PE-g-MAH were confirmed by the existence of carbonyl group streching peak at 1700 cm-1 and a back titration, respectively. Based on the physical properties and SEM pictures for fractured surface, MAH3 was the best as the compatibilizer. The non-isothermal crystallization behavior of the HDPE/KF/EMC composites was made by Ozawa analysis which is the extension of Avrami model. The values of n were 2.3, 1.5 and 2.3 for the pure HDPE, HDPE/KF composites and HDPE/KF/EMC extrudates, respectively. The fact that the crystal geometry of HDPE changed from disk to rod shaped was confirmed by Ozawa analysis, when KF added to HDPE matrix. On the other hand, the crystal geometry returned to the pure HDPE.