Mechanical properties and enzymatic degradation of poly([ R]-3-hydroxybutyrate- co-[ R]-3-hydroxyhexanoate) uniaxially cold-drawn films

Abstract

Uniaxially oriented films of poly([ R]-3-hydroxybutyrate- co-[ R]-3-hydroxyhexanoate) (P(3HB- co-3HH)) with 5 and 12 mol% 3HH comonomer were prepared by cold-drawing from an amorphous preform at temperatures near to the respective glass transition temperatures. Melt-quenched films in a rubber state could be stretched reproducibly to a draw ratio of 500%. Subsequent annealing under tension led to improvement of the tensile strength and Young's modulus. Two step drawing of P(3HB- co-5%-3HH) films resulted in further improvement of the mechanical properties. The X-ray fiber diagrams showed increasing orientation and crystallinity of the films with draw ratio. The mechanical properties remained unchanged after storing for several months at room temperature, suggesting that high orientation and crystallinity suppress the secondary crystallization. Cold-drawn P(3HB- co-3HH) films were enzymatically degraded with an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The enzymatic degradation was investigated by means of weight-loss profiles and scanning electron microscopy.