A Method for Evaluating the Film-Blowing Processability of Biodegradable Materials

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), an emergent biodegradable polymer, exhibits excellent biodegradability in nature, particularly in seawater. However, the challenge in film-blowing of PHBHHx limits its wide-scale application. More generally, the suitability of biodegradable polymers (such as PHBHHx) for blown film processing has been rarely reported, and the commonly used extensional viscosity test methods are not applicable due to the low melt viscosity of most biodegradable polymers. To overcome these challenges, in this work, a laboratory test method for evaluating the film-blowing processability of biodegradable materials using a small amount of raw materials was established. The key indicators for film-blowing processability were proposed, including the entrance pressure drop in capillary rheology and the tensile stress and strain at break of melt in the DMA test. The generalizability of the key indicators was verified using various commercially available blown film materials, including biodegradable and nonbiodegradable polymers. Based on the key indicators, the optimal formulation of PHBHHx for film-blowing was designed and successfully validated in pilot equipment. Finally, a quantitative relation between material formulation, key indicators, and film-blowing processability was developed to guide the blown film processing and formulation design. Not limited to biodegradable polymers, the method can also be applied to evaluate film-blowing processability of other polymer materials.