NaC1 presence and purification affect the properties of mixed culture PHAs

The mechanical properties of bacterial polyhydroxyalkanoates (PHAs) can be tailored by changing the type of substrate in the accumulation stage. Hence different comonomer distributions can be produced with significant variations in their physico-chemical properties. In the present study, the biopolymer produced by a mixed microbial community enriched in PHA accumulators fed with different substrate composition was characterised. The accumulation experiments were: single acetic (A1) and propionic acids (A2); an equivolumetric mixture of acetic and propionic acids (A3); VFA mixture (A4); and this VFA mixture and a concentration of 21.6 g NaCl/L in the reactor (B1). The objective was to investigate the impact of different circumstances on biopolymer composition and properties. The obtained copolymers were constituted by units of hydroxybutyrate (FIB) and hydroxyvalerate (HV) with HB:HV ratios between 96:4 and 34:66 (wt%). Thermal properties showed a clear dependence on the HB:HV ratio although no apparent connection with the decomposition temperature was found. Salinity affected both biopolymer composition and properties. The physico-chemical properties of purified and no purified polymer were also determined. Purification was found not to affect the molecular weight, while crystallinity augmented more than 70% and the thermal properties also increased. This study shows that, besides the substrate composition, also salts present in the media and the purification stage affect the properties of the produced biopolymer. (C) 2016 Elsevier Ltd. All rights reserved.