PHA obtained from mixed microbial cultures fed with food industry by-products : thermorheological characteristics and benchmarking with commercial PHA

Abstract

Polyhydroxyalkanoates (PHA) have two major assets which make them promising polymers for future packaging application to reduce the ecological footprint of plastics: they are fully biodegradable and bio-based. However, PHA are not yet used in plastic bags, pouches or flat thin films because they are still 10 times more expensive than conventional plastics used for such application, and most of all, because they show a very narrow processing window. PHA are very difficult to transform in films or extruded sheets, and thus the film blowing of commercial PHA has only been recently successfully achieved by our group. We report on the thermorheological characterization of new PHA obtained from mixed microbial cultures (MMC) fed with food industry by-products, namely cheese whey and olive mills wastewaters produced at lab scale and also from the up-scaling of the bioengineering process. These MMC PHA possess a high degree of HV copolymerization (HV molar fraction between 8 and 20 % with respect to HB). The melting temperatures measured from DSC and temperature sweeps in SAOS are consistent with data reported in the literature for PHA obtained from pure culture, and are nearly 20 C below the melting point of commercial PHA possessing few amounts of HV. The thermal degradation of the MMC PHA assessed rheologically and with TGA analysis occurs at lower temperatures than those reported in the literature. This is related to the large content of impurity remaining after the recovery of the PHA from the MMC, as shown by data obtained after a purification process. The effects of such impurities on the crystalline structure obtained from WAXD and on the crystallization kinetics measured with SAOS will be discussed. Mechanical spectra and flow curves of the melts will be benchmarked with the ones measured with commercial products in order to assess the processability of these new bioplastics. Finally, the use of MMC PHA as processing aids for commercial PHA will be discussed.