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.

聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（PHB-co-HV）作为一种可持续和可生物降解的包装材料已显示出巨大的潜力，但是，由于二次结晶引起的逐渐脆化和较差的热稳定性限制了其广泛应用. 先前已显示添加低分子量聚（乙二醇）（PEG）可降低二次结晶的速率，从而产生更可行的材料。本文旨在分析这两种聚合物的熔体混溶性，并评估 PEG 对热稳定性的影响。由于 PHB-co-HV 的热稳定性较差，因此实施了改进的流变程序以创建 Han 图并能够评估混溶性。这种方法表明 PHB-co-HV 和 PEG 在所研究的浓度和分子量范围内是可混溶的，这有助于微调 PHB-co-HV 的特性，以生产最合适和最稳定的包装材料。观察到 PEG 的存在会增加 PHB-co-HV 在 185 °C 的降解速率，然而，PEG 的掺入还能够在较低温度下进行加工，显着降低降解速率并扩大该聚合物常见的狭窄加工窗口.