Two Step Extrusion Process: From Thermal Recycling of PHB to Plasticized PLA by Reactive Extrusion Grafting of PHB Degradation Products onto PLA Chains

A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.