Rheological analysis of heat labile poly(3-hydroxybutyrate-co-3-hydroxyvalerate):poly(ethylene glycol) blends

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-HV) has shown great promise as a sustainable and biodegradable packaging material, however, progressive embrittlement, caused by secondary crystallisation, and a poor thermal stability has limited widespread use. The addition of low molecular weight poly(ethylene glycol) (PEG) has previously been shown to reduce the rate of secondary crystallisation resulting in a more viable material. This paper aims to analyse the melt miscibility of these two polymers and to assess the effect of PEG on the thermal stability. As a result of the poor thermal stability of PHB-co-HV a modified rheological procedure is implemented to create Han plots and enable assessment of the miscibility. This approach showed PHB-co-HV and PEG to be miscible within the concentrations and molecular weights studied lending itself to the fine tuning of the properties of PHB-co-HV in order to produce the most suitable and stable packaging material. The presence of PEG was observed to increase the degradation rate of PHB-co-HV at 185 °C, however, the incorporation of PEG also enabled processing at lower temperatures significantly reducing the degradation rate and widening the narrow processing window commonly found with this polymer.