High density polyethylene (HDPE)/themally expandable microcapsule (EMC) and HDPE/EMC/Kenaf composites were fabricated by a twin screw extruder. Based on the foaming behavior of HDPE/EMC composites with screw rpm, content of EMC and die temperature, the optimum foaming conditions were selected 40 rpm, 5 wt%, and 160 oC.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. PE-g-maleic anhydride (MAH) was also used to increase compatibility between HDPE and Kenaf as a compatibilizer. Thermal properties of HDPE/EMC and HDPE/Kenaf/EMC composites were investigated by DSC and TGA, and there was no district change in thermal properties. It was checked that the applicable EMC content was below 20 wt% from the results of mechanical properties, specific gravity, and water uptake of HDPE/Kenaf/EMC composites. The effect of the compatibilizer on foaming behavior was confirmed 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 Kenaf contents and the effect was obvious in case of the composites with the compatibilizer.

이축압출기(twin screw extruder)를 이용하여 고밀도 폴리에틸렌(high density polyethylene, HDPE)/열팽창성 마이크로캡슐(thermally expandable microcapsule, EMC) 복합체와 HDPE/EMC/Kenaf 복합체를 제조하였다. 이축압출기의 스크류 속도(rpm), EMC 함량, 그리고 압출기 다이 온도에 따른 HDPE/EMC 복합체의 발포거동을 분석하여, 40 rpm, 5 wt% 그리고 160 oC를 최적 발포조건으로 선정하였다. 선정된 발포 조건에서 HDPE/EMC/Kenaf 복합체의 발포거동 및 물성을 평가하였으며, 복합체 제조에 이용된 Kenaf 섬유의 길이는 1, 3, 5 mm로 조절하였다. 또한 HDPE와 Kenaf의 혼화성에 따른 발포체의 물성을 비교하기 위해 혼화제로 PE-g-MAH를 사용하였다. 복합체의 열적특성은 시차주사열용량분석기(DSC)와 열중량분석기(TGA)를 이용하였고, 복합체의 열적특성에는 큰 변화를 나타내지 않았다. 복합체의 기계적 물성, 비중, 함수율 측정 결과 Kenaf 섬유의 함량은 20 wt% 미만 함량이 적절함을 확인하였고, 비중과 SEM을 이용한 발포셀의 구조 확인 결과 상용화제 적용 여부에 따라 발포거동에 큰 차이를 보이는 것을 확인하였다. 복합체의 유변학적 특성은 동적유변측정기를 이용하여 측정하였고, 복합체의 복소 점도와 전단박하 현상은 증가하였고, 상용화제 적용시 그 효과가 더욱 뚜렷해지는 것을 확인하였다.

Keywords: HDPE; Kenaf; thermal expendable microcapsule; composites; foaming