| Abstract: | The influence of melt-extrusion on the degradation behavior of poly(3-hydroxybutyrate-co-7% 3-hydroxyvalerate) in a small-scale compost and in salt media with Aspergillus fumigatus has been studied. The degradation has been monitored by Size Exclusion Chromatography (SEC), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and X-ray analysis. During the first 9 weeks of composting the degradation proceeds through surface erosion without any significant change in molecular weight or weight crystallinity. After 10 months the weight average molecular weight, Mw, has decreased by approximately 15–50%. It is suggested that degradation mechanism is converted from enzymatic to chemical hydrolysis as the porosity of the samples increases which facilitates water penetration. In addition, the acidic degradation products would accelerate the chemical hydrolysis inside the sample due to lowering of the pH. During degradation in media containing A. fumigatus the sample processed at low temperature exhibited extensive surface degradation and a 12% reduction of the Mw. In contrast the sample processed at high temperature showed an homogeneous surface degradation and no reduction in molecular weight. The differences in degradation are attributed to variations in the initial morphology of the samples caused by the processing conditions. Further investigations are, however, required to separate effects attributed to local differences in the compost environment and the structure of the samples. |
