Mechanical Properties of Uniaxially Cold‐Drawn Films of Poly[(R)‐3‐hydroxybutyrate] and Its Copolymers

Abstract

AbstractUniaxially oriented films of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) and two kind of copolymers, poly[(R)‐3‐hydroxybutyrate‐co‐8%‐[R]‐3‐hydroxyvalerate] (P(3HB‐co‐8%‐3HV)), and poly[(R)‐3‐hydroxybutyrate‐co‐[R]‐5%‐3‐hydroxyhexanoate] (P(3HB‐co‐5%‐3HH)), were prepared by cold‐drawing from amorphous preforms 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%∼1800%, and subsequent annealing under tension led to improvement of the tensile strength and Young's modulus. Two‐step drawing resulted in further improvement of the mechanical properties. The mechanical properties remained unchanged after storing for 6 months at room temperature, suggesting that high orientation and crystallinity suppress the secondary crystallization.