Thermal degradation of polylactic acid (PLA)/polyhydroxybutyrate (PHB) blends: A systematic review

Polylactic acid (PLA) and polyhydroxybutyrate (PHB) are two biopolyesters obtained from renewable resources like corn or sugar under bacterial fermentation. PLA is the most widely used biopolymer in diverse applications. Addition of PHB to PLA can improves the crystallinity of PLA, and thereby its mechanical strength. However, both PLA and PHB suffer from poor thermal stability, which limits their potential industrial application. The purpose of this review is to explain thermal decomposition behavior and mechanism of these polymers and systematically categorize available reports on thermal degradation of the neat PLA and PHB, and also as-processed PLA/PHB blends along with PLA/PHB blends modified/reinforced with plasticizers, additives or crosslinkers. The characteristic temperatures (Tonset, and peak temperature or Tmax) of PLA and PHB are taken as the key parameters governing thermal degradation behavior of PLA/PHB blends and composites with variable composition. From this survey we can conclude that the thermal stability of PLA in PLA/PHB blend is lower than the neat PLA, contrary to the PHB with higher thermal stability in PLA/PHB blend. Therefore, thermal degradation mechanism of PLA/PHB blends must be taken as a complex physico-chemical phenomenon. Moreover, the selection of additive severely affects the thermal stability of PLA/PHB blends. Processing method and localization of additive in different phases or at the interface of the phases are factors determining the ultimate thermal stability of blend.