Thermal and rheological properties of poly-(3- hydroxybutyrate-co-3- hydroxyvalerate) and poly (lactic acid) blends for food packaging applications

Poly (L-lactic acid) (PLA) and Poly (3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) are bio-derived semi-crystalline polymers of interest to the food packaging industry looking for alternatives to the petroleum based materials. The PHBV polymer is too brittle and temperature sensitive to be used for film. Therefore, the blends of PHBV with PLA were explored as an alternative way of achieving desired properties. The objective of this study was to characterize the thermal and rheological properties of PHBV (Tianan 5%) blended with PLA (6202D) resin at 20, 30, 40, and 50% PLA and relate these findings to potential food packaging applications. The thermal analysis showed increasing concentration of PHBV resulted in lower thermal stability of PLA. Several melting transitions for the blends were observed representative of phase separated polymers. The viscosity of all the blends remained unchanged during the one hour time sweep at 170°C, but the complex viscosity was lower than Tianan 5%. The frequency sweep showed no improvement in the complex viscosity of the blends compared to Tianan 5%. These blends were processed in a lab scale extruder at 175°C. The brittleness and low melt strength made it difficult to extrude blown films, as the various blends started to fracture mmediately exiting the blown film die.