Spherulitic Growth Rate of Blends of Polyhydroxybutyrate (PHB) with Oligomeric Atactic PHB-diol

Abstract

Spherulitic growth rates of blends of polyhydroxybutyrate (PHB) with oligomers of atactic R,S-PHB-OH (Mn = 610, 910, and 2670 g/mol), as well as atactic R,S-PHB (Mn = 30 000 g/mol), were investigated by polarized light optical microscopy in the range from 50°C to 110°C. The temperature of maximum growth rate of PHB spherulites was affected by the molecular weight of the second amorphous component of atactic R,S-PHB-OH and the content of R,S-PHB-OH, Mn = 910 in PHB blends. It shifted from 90°C to 65°C with the presence of 75 wt% R,S-PHB-OH, Mn = 910. In order to apply the Boon and Azcue theory to experimental spherulitic growth rate data, the activation energy, U* ∼ 13.8 kJ/mol, which accounts for the molecular mobility, was calculated by using dielectric spectroscopy measurements. The equilibrium melting temperature,To m , was used as a fitting parameter for applying the Boon and Azcue theory to experimental growth rate data. From the fitting results, the value of the parameter Kg of the PHB blends virtually did not change with addition of the second component, i.e., R,S-PHB-diol or R,S-PHB; the crystallization of pure PHB and PHB blends was in regime III.