Effect of 4-Hydroxybutyrate Content on Physical Properties of Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

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.