The effect of 4-hydroxybutyrate (4HB) content in bio-synthesized poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB)) copolymer on the physical properties of P(3HB-co-4HB) was investigated. It was found that the molecular weight of P(3HB-co-4HB) increased with increasing 4HB content. Contrary to expectation, the melt viscosity decreased with increasing 4HB chain relatively flexible compared with the 3HB chain. This resulted in the lowering of melt processability due to the loss tangent drops in P(3HB-co-4HB). An increase in the 4HB content of 16% or more increased chain randomness of the copolymer, as a result, the crystallization was prohibited and resulted in amorphous P(3HB-co-4HB) copolymer having a high glass transition temperature. Crystalline P(3HB-co-4HB) shows brittle behavior with high mechanical strength. Increasing flexible 4HB content in copolymer leads to the high elongation at break with the lowering of strength of crystalline P(3HB-co-4HB). It may result in the improvement of drawing characteristics in melt processing.

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB)) 공중합체의 4-hydroxybutyrate(4HB) 함량이 물성에 미치는 영향을 살펴보았다. 박테리아에 의하여 만들어진 P(3HB-co-4HB)는 4HB 함량 증가에 따라 분자량이 증가됨을 알 수 있었다. 하지만 유연한 4HB 사슬에 의하여 융융 점도의 감소를 초래하여 loss tangent 증가로 인한 용융 가공성은 감소됨을 확인하였다. 16% 이상의 4HB 함량 증가는 공중합체의 randomness를 증가시켜 유리전이온도는 증가되며 사슬 결정화를 방해하여 비결정성 P(3HB-co-4HB)가 얻어짐을 알 수 있었다. Brittle하고 높은 강도를 갖는 결정성 P(3HB-co-4HB)는 상대적으로 유연한 4HB 사슬 함량 증가에 따라 강도는 감소하나 신율이 증가되어 고분자 가공에서 연신 특성이 개선될 것으로 판단된다.

Keywords: biopolymer, poly(3-hyroxybutyrate-co-4-hyroxybutyrate), thermal property, rheological property, mechanical property.