Optimization of melt processing parameters to produce polyhydroxyalkanoate biopolymers for packaging applications

Abstract

Driven by increasing environmental awareness and depletion of fossil fuels, the packaging industry is more strongly focusing on the production of sustainable plastics. Innovative biopolymers such as polyhydroxyalkanoates (PHAs) are among the main drivers of growth in the field of biobased and biodegradable plastics, with production capacities estimated to increase tenfold in the next five years. Poly(3-hydroxybutyrate) (PHB) is a stiff and brittle material with a narrow processing window, but copolymers like poly(3- hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) are considered promising food packaging materials as they show increased flexibility with a medium oxygen permeability. However, further optimization regarding thermal and mechanical properties is necessary, which can be obtained through a strict control over its processing conditions. To increase the potential of PHBHHx as packaging material, melt processing parameters such as extrusion and mold temperature, screw speed and cooling time were varied to study the influence on the mechanical performance of injection molded test samples. This study particularly shows that the stretchability of PHBHHx can be increased extensively by selecting appropriate processing conditions during injection molding. Optimal mechanical properties are obtained by processing at lower temperatures (145°C) and molding at elevated temperatures (80°C). On the contrary, processing at higher temperatures (160°C) and molding at lowered temperatures (40°C) results in material embrittlement with decreased stretchability. To understand these findings, the processed induced crystallinity of the biopolymer was investigated. This study shows the importance of optimal processing conditions with improved mechanical properties of PHBHHx, making these biopolymers highly suitable for a wide range of flexible packaging applications.