# Characterization of vulcanized polyhydroxyalkanoate composites filled with calcium carbonate

“Characterization of vulcanized polyhydroxyalkanoate composites filled with calcium carbonate” (2026), by Phimthong Khamjapo et al. Materials Science research paper. Original abstract below, unchanged. A free PDF is available.

- Authors: Phimthong Khamjapo, Yuki Miyahara, Takeharu Tsuge
- Published: October 31, 2026
- Field: Materials Science
- DOI: https://doi.org/10.1007/s44347-026-00075-3
- Free PDF: https://link.springer.com/content/pdf/10.1007/s44347-026-00075-3.pdf

## Abstract

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.

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