Influence of reprocessing on monopolymer blends of polyhydroxybutyrate (PHB)

This work addresses the mechanical recycling of the biobased and biodegradable polymer Polyhydroxybutyrate (PHB) by investigating different properties at each stage from once extruded (E) PHB blended with virgin (V) material in two ratios (E20V80 and E80V20) and further extruded five times (E5). For both series, thermal analyses revealed a stable melting and decomposition temperature even after five reprocessing cycles and a marginally decreased crystallinity. The tensile strength remained almost constant for the series E80V20 with a drop observed only from E3. Strain at break decreased from E80V20 to E5, which was corroborated by Charpy Notched Impact results showing a progressive sample brittleness. E20V80 showed similar trends to the E80V20 series, but with higher values in the impact strength and only differed in the tensile strength in which an increase was observed from E20V80 to E1 and a drop observed only at E4. Rheology studies showed an indistinct trend for the E80V20 series, but in E20V80, the viscosity dropped with each processing cycle. Hence, on a practical basis adding lesser quantities of virgin material to the reprocessed material is feasible with attention need only be given to the processing parameters (as viscosity is low). • Mechanical recycling of PHB blended with virgin material in 2 ratios (80/20 and 20/80) • Thermal stability maintained after five cycles; slight decrease in crystallinity • Tensile strength stable with 20 % virgin material • With 80% virgin material higher impact strength, but reduced viscosity • Lesser virgin material feasible, but difficult processing due to low viscosity