Isolation and purification of medium chain length poly(3-hydroxyalkanoates) (mcl-PHA) for medical applications using nonchlorinated solvents.

A novel process was developed to isolate poly([R]-3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHO) and poly([R]-3-hydroxy-ω-undecenoate-co-3-hydroxy-ω-nonenoate-co-3-hydroxy-ω-heptenoate) (PHUE) from Pseudomonas putida species. Methyl tert-butyl ether (MTBE), ethyl acetate, acetone, and methylene chloride efficiently extracted PHO from freeze-dried biomass. The ratio of solvent to biomass was 15:1 (vol/wt). The nonchlorinated solvents required 18 h of extraction to achieve methylene chloride's yield of 15 wt % within 60 min. In the case of PHUE, the yield was 15-17 wt % after 60 min of extraction at room temperature, independently of the solvent used. MTBE performed best in life cycle assessment (LCA) if contamination of the environment is avoided. Filtration of the extract containing 8 wt % of raw polyhydroxyalkanoate (PHA) through activated charcoal revealed colorless polymers with less than one endotoxin unit/g. The ratio (v/v) of the solution to activated charcoal was 2:1. The loss (impurities and polymers) amounted up to 50 wt %.