The influence of processing induced differences in molecular structure on the biological and non-biological degradation of poly (3-hydroxybutyrate-co-3-hydroxyvalerate), P(3-HB-co-3-HV)

Abstract

The influence of processing conditions on the degradation rate of melt-extruded poly(3-hydroxybutyrate-co-7%3-hydroxyvalerate) in pure fungal cultures ( Phanerochaete chrysosporium, Penicillium simplicissimum and Aspergillus fumigatus) and by chemical hydrolysis (pH 10.5, 60°C) was investigated. The degradation was monitored by gravimetry, size exclusion chromatography (SEC), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray scattering, infrared spectroscopy (FTIR) and tensile testing. The rate of erosion, measured as weight loss, was highest for the samples processed at high temperature, and lowest for the samples processed at the lowest temperature. The erosion rate during microbial degradation was not controlled by molecular weight or by the lamellar distribution. An increase in the degree of crystallinity reduced the rate of erosion. A correlation was found between the rate of erosion and the intensities of the sharp X-ray reflections (020) and (110). The rate of weight loss increased with increasing peak ratio I (020)/I (110) indicating that the positioning of the oxygen atoms affected the recognition capability of the extra-cellular enzymes. The reproducibility in weight loss of the samples between the different experiments was good. The erosion proceeded without any decrease in molecular weight. The molecular weight of the samples subjected to chemical hydrolysis exhibited a 50% drop within 40 days. Microtomed samples showed higher rates of chain scission in the center than at the surface. The degree of crystallinity increased by 35% as measured by DSC. The initial appearance of the melting endotherm, governed by the processing conditions, was maintained at 60°C until the molecular weight dropped below 50% of the initial value. The embrittlement of the samples measured as the elongation at break (ε b) was controlled by the decrease in molecular weight.