Stress Relaxation Behaviors of Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

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.