Processing and Thermomechanical Properties of PHA

Abstract

The biodegradability and biocompatibility of polyhydroxyalkanoates (PHA) make them a class of materials with a wide range of applications, raising interest from scientists and industries. PHA 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 PHA’s melt behavior and rheology of PHA blends can strongly support the processing of this challenging class of polymers. In this review, particular attention has been devoted to reviewing the limited number of studies on PHA’s rheological properties, since these are of primary importance to understanding and handling the melt properties of PHA. 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 aging. The high fragility of most PHA based materials and the possible variations 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, fibers, and polymeric blends is of fundamental importance to achieve PHA materials with relevant thermal and mechanical properties and with limited effect on PHA-based materials performance due to aging. The selection of any additive in PHA-based materials must consider the importance of maintaining the sustainability and biodegradability in several environments for this class of polymers, since this is one of the main properties able to justify the higher cost of PHA versus other bio-based polymers. Then additives, fillers, etc., should be selected, giving preference to those of bio-based origin and being biodegradable/biocompatible depending on the targeted final application.

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