Stress relaxation behavior of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) copolymer in melt processing was studied. The effect of 4HB content in copolymer on stress relaxation was mainly investigated and it was understood by generalized Maxwell viscoelastic model. As the 4HB content increased, the stress relaxation occurred quickly due to the flexibility of 4HB chain compare to 3HB chain. It was also found that the lowering of randomness in copolymer chain sequence prohibited the stress relaxation due to the increase of crystallinity in copolymer. Stress relaxation can be controlled by the blending of P(3HB-co-4HB) having different 4HB content. The relaxation time of P(3HB-co-4HB) was evaluated by generalized Maxwell viscoelastic model. It was found that the relaxation time was more closely related to the 4HB content than crystallinity of copolymer.

생분해성 poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB))의 용융가공 시 발생하는 응력이완 거동에 대하여 살펴보았다. P(3HB-co-4HB)의 4-hydroxybutyrate(4HB) 함량 변화가 응력 이완에 미치는 영향을 중점적으로 확인하여 이를 generalized Maxwell 점탄성 모델을 이용하여 해석하였다. 3-hydroxybutyrate(3HB) 사슬과 비교하여 상대적으로 유연한 4HB사슬 함량이 공중합체에 증가됨에 따라 응력이완이 빨리 일어남을 알 수 있었다. 공중합체 사슬 랜덤화 차이는 P(3HB-co-4HB)의 결정화 거동을 변화시켜 결정화에 의해 응력이완이 방해 받음을 확인하였다. 아울러 4HB 함량이 서로 다른 P(3HB-co-4HB)의 용융 블렌딩에 의하여 4HB 함량과 결정화도를 변화시켜 P(3HB-co-4HB)의 응력이완 현상 조절이 가능함을 확인하였다. Generalized Maxwell 모델을 적용하여 relaxation time을 계산한 결과, relaxation time은 결정화도 보다 공중합체의 4HB 함량과 더 밀접한 관계가 있음을 알 수 있었다.

Keywords: biodegradable polymer, poly(3-hydroxybutyrate-co-4-hydroxybutyrate), stress relaxation, generalized Maxwell model, relaxation time.