Non-Isothermal Glass and Melt Crystallization of Poly(3-hydroxybutyrate) Biopolymer: Kinetics and Mechanisms

Abstract

Biopolymers are the materials familiar for their promising potential of superseding the conventional petrochemical-based polymers. Polyhydroxyalkanotes (PHAs), a sub-class of biopolymers, comprise a group of natural biodegradable polyesters which have found invaluable applications in biomedical science and environmental remediation. This paper reports a detailed kinetic investigation on the non-isothermal glass and melt crystallization of poly(3-hydroxybutyrate) (P3HB) (a key representative of PHAs) by utilizing an advanced kinetic approach to polymer crystallization mechanisms. The kinetic study revealed that both the glass and melt crystallization processes of P3HB pursue single-step nucleation and diffusion phenomena. Moreover, the diffusion activation energies of the aforementioned processes are similar to each other and are in agreement with the universal activation energy value of segmental jumps during diffusion processes in polymers. However, P3HB glass crystallization goes to completion by following a different process mechanism in comparison with its melt crystallization. The P3HB glass crystallization more likely follows interface-controlled two-dimensional (2D) growth of spherulites. The P3HB melt crystallization, on the other hand, pursues diffusion-controlled one-dimensional (1D) growth of spherulites. Thermodynamics points out that the transition state is structurally more oriented in the case of P3HB melt crystallization rather than P3HB glass crystallization. The obtained kinetic and thermodynamic parameters are interpreted in terms of their rational physical meanings and the practical worth of the present study is discussed.