Characterization of vulcanized polyhydroxyalkanoate composites filled with calcium carbonate

Polyhydroxyalkanoates (PHAs) are bio-based plastics produced by bacterial fermentation from renewable resources. PHAs with unsaturated bonds can undergo post-biosynthetic chemical modification or crosslinking to improve material properties. Previous studies have demonstrated that sulfur-vulcanized PHAs exhibited rubber-like properties and increased toughness. On the other hand, it is also important to add inexpensive fillers, such as calcium carbonate (CaCO 3 ), to reduce the amount of expensive resins required. This study investigated​ vulcanized PHA with​ varying CaCO 3 loadings (0, 10, 30, and 50 per hundred resin, phr) in a sulfur vulcanization system consisting of zinc oxide, stearic acid, 2-mercaptobenzothiazole, and sulfur. ​First, ​poly(3-hydroxybutyrate- co -3-hydroxy-5-hexenoate) [P(3HB- co -3H5HE)] ​​was biosynthesized using recombinant Escherichia coli , yielding a copolymer with a 3H5HE fraction of 47 mol%. The effects of CaCO 3 content on the physical properties of the vulcanized PHA copolymers were evaluated. The results indicate that 10 phr loading of CaCO 3 slightly increased tensile strength and toughness, whereas 50 phr CaCO 3 loading maximized elongation at break and Young’s modulus. Also, the tensile set of vulcanized PHA copolymers slightly increased from 8% to 10% after 200% elongation with the incorporation of CaCO 3 , suggesting reduced elastic recovery.