New insights into the beta-form crystal toughening mechanism in pre-oriented PHBV films

Tensile deformation behaviors of pre-oriented poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films annealed at different temperatures with or without β-form structures were investigated using the in-situ small and wide-angle X-ray scattering techniques, as well as DSC and SEM. The sample with β-form structure showed better ductility. It is convinced that the system can be viewed as a highly stretched and entangled network embedded in highly oriented fibrils being composed of shish-kebabs. Compared with sample without β structure, a tentative deformation mechanism for the sample with β structure was proposed in this paper, which we believe would shed light on the relationship between β structure and mechanical property of PHBV film. The important role of β-form played in the stretching process of pre-oriented film was also proposed for the first time, in which we stress the role of β-form structure in stabilizing the ordered microstructures and thereby improving the mechanical properties of the material.