Effect of 3-Hydroxyvalerate Content on Thermal, Mechanical, and Rheological Properties of...

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with various 3-hydroxyvalerate (3HV) contents biosynthesized by mixed microbial consortia (MMC) fed fermented dairy manure at the large-scale level was assessed over a 3-month period. The thermal, mechanical, and rheological behavior and the chemical structure of the extracted PHBV biopolymers were studied. The recovery of crude PHBV extracted in a large Soxhlet extractor with CHCl₃ for 24 h ranged between 20.6% to 31.8% and purified to yield between 8.9% to 26.9% all based on original biomass. ¹³C-NMR spectroscopy revealed that the extracted PHBVs have a random distribution of 3HV and 3-hydroxybutyrate (3HB) units and with 3HV content between 16% and 24%. The glass transition temperature (T) of the extracted PHBVs varied between -0.7 and -7.4 °C. Some of the extracted PHBVs showed two melting temperatures (T) which the lower T₁ ranged between 126.1 °C and 159.7 °C and the higher T₂ varied between 152.1 °C and 170.1 °C. The weight average molar mass of extracted PHBVs was wide ranging from 6.49 × 10⁵ g·mol^-1 to 28.0 × 10⁵ g·mol^-1. The flexural and tensile properties were also determined. The extracted polymers showed a reverse relationship between the 3HV content and Young's modulus, tensile strength, flexural modulus, and flexural strength properties.