본 연구는 poly-lactic acid(이하 PLA)와 목분을 이용한 bio-composites 제조에 있어 첨가제로 사용된 편백나무 수피 (CYP-B)와 피마자왁스(HCO)가 강도 및 치수안정성에 미치는 영향을 조사하기 위하여 수행하였다. 충전제로 radiata pine 목분(RDP)을 사용하여 제조한 composites의 인장강도는 CYP-B의 영향을 받지 않았다. 반면 활엽수 잡목 목분 (MIX)에 CYP-B를 composites의 전체 중량 대비 2.5 wt% 첨가하여 제조한 시편의 인장강도는 증가하였으나, 5 wt%의 CYP-B를 첨가하여 제조한 시편에서는 감소하여 첨가제없이 제조한 시편과 차이가 없었다. 충격강도는 무첨가제로 제 조한 시편과 비교하여 100 mesh 표준망체를 통과한 RDP(< 0.150 mm) 및 60 mesh 표준망체 통과 HCO(< 0.250 mm)로 제조한 시편에서 높았으며, 첨가량의 증가에 따른 영향은 없었다. PLA와 RDP에 CYP-B를 첨가제로 사용하여 제조한 시편을 70℃ 온수 및 80℃ oven에 노출한 이후 측정한 중량증가율은 첨가제없이 제조한 시편과 차이가 없었으며, PLA/ MIX에서는 첨가제의 적용 및 첨가량 증가에 따른 영향도 없었다. 온수 및 고온에 노출시킨 PLA/RDP의 부피팽윤율은 무첨가제 시편과 비교하여 CYP-B를 첨가제로 사용한 시편에서 차이가 없었으나, 적은 입도의 HCO 사용은 부정적인 영향을 미쳤다. PLA/MIX의 경우, 온수-침지 시편에서는 적은 입도의 CYP-B 그리고 고온-노출 시편에서는 CYP-B와 적은 입도의 HCO를 적용한 시편에서 무첨가제로 제조한 시편과 비교하여 부피팽윤율이 낮았다. PLA에 목분의 혼합은 composites의 열안정성에 부정적인 영향을 미치나, HCO의 적용으로 기존 목재-플라스틱 복합재에서 물성 개선을 위하여 사용되는 화석연료-기반 첨가제보다 열안정성을 크게 개선시키는 것으로 조사되었다. 결과를 종합하면, PLA에 목분의 혼합으로 인하여 저하된 충격강도의 증가를 위하여 첨가제의 사용이 필요하며, PLA/RDP에 첨가제로 큰 입도의 CYPB 또는 적은 입도의 HCO 사용이 최적의 composites 제조 조건으로 생각한다. 이렇게 제조한 composites가 국립산림 과학원에서 고시한 목재-플라스틱 복합재의 충격강도(>3.0 KJ/m2) 및 수분흡수율(<8.0%) 기준을 만족하여 다양한 용 도의 생분해성 플라스틱 소재로 적용이 가능할 것으로 판단된다.

 This study was conducted to investigate the effect of CYP-B and HCO used as an additive on the

 mechanical strength and dimensional stability of bio-composites fabricated with PLA and wood powder. Tensile strength of the PLA-based composites fabricated with RDP (PLA/RDP), which was used as a filler, was not affected by the addition of CYP-B. On the other hand, tensile strength of the PLA-based composites made with MIX (PLA/MIX) increased with the addition of 2.5 wt% CYP-B based on the total weight of the composites. When the content of the CYP-B increased to 5 wt%, the tensile strength did not differ from one of the PLA/MIX fabricated without any additives. Impact strengths of the PLA/RDP made with the RDP of < 0.150 mm and the HCO of < 0.250 mm were higher than those

 without any additives, but the increases of the RDP and HCO contents did not have an effect on the impact strength. No significant differences between the water absorption rate(WAR) of the PLA/RDP added with CYP-B as an additive (PLA/RDP/CYP-B) and PLA/RDP were found after immersed in 70℃ water for 2h and exposed in 80℃ over for 48h.

 The WAR of PLA/MIX was not influenced by the application and content of the additives. The total volumetric swelling rate (TVS) of the hot water-immersed and high temperature-exposed PLA/RDP was not affected by the addition of CYP-B, but showed a negative effect in the TVS of the PLA/RDP made with the HCO of < 0.250 mm. For PLA/MIX, TVSs of the hot water-immersed specimens made with the CYP-B of < 0.150 mm as well as the high temperature-exposed specimens made with the CYP-B and the HCO of < 0.250 mm were lower than those of the specimens fabricated without any additives. The addition of wood powder in PLA had a negative effect on the thermal stability of the composites, but the stability was increased with the application of HCO as a additive compared to that of petroleum-based additives used in conventional wood-plastic composites for the improvement of various properties. In conclusion, the application of additives in the fabrication of PLA-wood-based composites is required to compensate the impact strength decreased with the use of wood powder. It is determined that the applications of CYP-B of > 0.150 mm and HCO of < 0.250 mm in the mixture of PLA and RDP is an optimal condition. The composites fabricated with the conditions satisfied the minimum requirements of impact strength (>3.0 KJ/m2) and water absorption rate (<8.0%) designated by the National Institute of Forest Science. It is thought that the composites have a potential as a raw material for the production of bio-degradable plastics.

Bio-composites, Poly(lactic acid), Wood flour, Additive, Strengths, Dimensional stability

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