Processing and thermomechanical properties of PHA

The biodegradability and biocompatibility of PHAs make them a class of materials with wide range of applications, raising interest of scientist and industries. PHAs applications are limited by a narrow processing window, easy degradation during melt processing, variable crystallization rate and high crystallinity of commercial PHA grades. Knowledge of PHAs melt behavior can strongly support in the processing of this challenging class of polymers. In PHA based materials, the presence of a rigid amorphous fraction, which produces a stiffening of the amorphous segments at the crystal/amorphous interface, can contribute to the progressive change of the mechanical properties with ageing. The high fragility of most PHA based materials and the possible variation in mechanical properties with time, are very relevant limitations for the exploitation of these polymers. The selection of proper processing conditions and of proper additives such as plasticizers, nucleating agents, fillers, nanofiller, fibres, polymeric blends is of fundamental importance to achieve PHA materials with relevant thermal and mechanical properties and with limited effect on PHAs based materials performance due to ageing. The selection of any additive in PHA based materials must consider the importance to maintain the sustainability and biodegradability in several environment for this class of polymers, since this is one of the main properties able to justify the higher cost of PHAs versus other biobased polymers. Then additives, fillers etc should be selected giving preference to those of biobased origin and being biodegradable/biocompatible depending from the target final application.