Effect of 3-Hydroxyvalerate Content on Thermal, Mechanical, and Rheological Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Biopolymers Produced from Fermented Dairy Manure
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 (Tg) of the extracted PHBVs varied between &minus;0.7 and &minus;7.4 &deg;C. Some of the extracted PHBVs showed two melting temperatures (Tm) which the lower Tm1 ranged between 126.1 &deg;C and 159.7 &deg;C and the higher Tm2 varied between 152.1 &deg;C and 170.1 &deg;C. The weight average molar mass of extracted PHBVs was wide ranging from 6.49 &times; 105 g&middot;mol&minus;1 to 28.0 &times; 105 g&middot;mol&minus;1. The flexural and tensile properties were also determined. The extracted polymers showed a reverse relationship between the 3HV content and Young&rsquo;s modulus, tensile strength, flexural modulus, and flexural strength properties.