The degradation behavior of plasma-treated poly(L-lactic acid) (PLLA) was studied. The plasma treatment was carried out in air environment and sample surfaces were analyzed by electron spectroscopy for chemical analysis (ESCA) and water contact angle measurement. For determining the degradation rates of samples the mass loss was determined from the dry weights before and after degradation. The glass transition temperature (T_g) and crystallinity of the specimens were measured using a differential scanning calorimeter (DSC). The surface morphology of specimens was examined with a scanning electron microscope (SEM). The oxygen content of the PLLA surface was increased by the air-plasma treatment and its water contact angle decreased accordingly. However, after degraded for 4 weeks, the water contact angles of the plasma-treated PLLA became to be almost the same as those of the normal PLLA presumably due to the degradation of the hydrophilic surface formed by the air-plasma treatment The degradation rates of the plasma-treated samples were faster than those of the normal samples in initial periods presumably because of the hydrophilic surface of the plasma-treated PLLA. However, the weight losses of the normal and plasma-treated samples became to be similar after 6 weeks degradation, which may be due to the 1oss of the hydrophilic surface of the plasma-treated PLLA by hydrolysis. The T_g and crystallinity of the normal and plasma-treated samples increased in initial degradation periods. The increasing rates of T_g and crystallinity of the plasma-treated samples were faster than those of the normal samples.

본 연구에서는 플라즈마 처리한 poly(L-lactic acid) (PLLA)의 가수분해 거동을 조사하였다. 플라즈마 처리는 공기 분위기 하에서 행하였고 시료의 표면성질 변화는 전자분광법 (ESCA), 물 접촉각 등으로 분석하였다. PLLA의 분해속도는 시간의 경과에 따른 시료의 무게 손실로부터 구하였다. 시료의 유리전이온도 및 결정화도 변화는 시차주사 열량분석기 (DSC)를 이용하여 측정하였고, 표면형태 변화는 주사전자 현미경 (SEM)으로 관찰하였다. 플라즈마 처리한 PLLA의 표면은 플라즈마 처리를 하지않은 PLLA에 비해 산소량이 증가하였고, 이로 인하여 친수성이 증가하였다. 플라즈마 처리한 PLLA의 분해속도가 초기에는 플라즈마 처리를 하지않은 PLLA에 비해 빨랐으나 그 후에는 친수성 표면의 소실에 의하여 분해속도가 큰 차이를 나타내지 않았다. 플라즈마 처리 및 미처리 PLLA의 유리전이온도 및 결정화도는 분해 초기 (약 4주간)에 증가하였고, 증가속도는 미처리 시료에 비해 플라즈마 처리한 시료가 빨랐다.

Keywords: poly(L-lactic acid); degradation; gydrolysis; air plasma