An innovative and sustainable process for producing poly(3-hydroxybutyrate-co-3-hydroxyvalerate): simulating volatile fatty acid role and biodegradability

Renewable resources, such as biogas and volatile fatty acids from organic substrate digestion, are used to generate the poly(3-hydroxybutyrate-co-3-hydroxyvalerate), a biopolymer with mechanical and thermal characteristics comparable with fossil fuel-based plastic. A double-stage fermentation was simulated for generating poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and analysing the role of odd fatty carbon acids on 3-hydroxyvalerate building block inclusion. Valeric acid was then supplied at various concentrations of 100–2000 ppm since it was responsible for the highest 3-HV molar fraction accumulated. The recovery of granules of biopolymer through non-halogenated extraction was also simulated: methyl ethyl ketone was employed for solubilising the granules, and a mixture of methanol and water (7:3) was applied during the precipitation stage. The recovery yields ranged from 78% to 96%, basing on the amount of polymer entering the extraction line, i.e. 0.5 and 2.5 kg, with a 3-hydroxyvalerate content of 40%mol and 20%mol, respectively. The biopolymer with the lowest and highest 3-hydroxyvalerate content were finally used for the theoretical assessment of biodegradability: a maximum weight loss of 90% was obtained for the polymer containing the highest 3-hydroxyvalerate fraction, thus confirming the dependence of the biodegradability on the biopolymer molecular structure.