Synthesis and investigation of sustainable long-chain branched poly(lactic acid-r-malic acid) copolymer as toughening agent for PLA blends

Poly(lactic acid) (PLA) is the most promising candidate for biobased and biodegradable plastic which combines biocompatibility, renewability as well as excellent processability. However, toughening is still needed for PLA as to obtain materials suitable for broader applications. In this work, long-chain branched random copolymers poly(lactic acid-r-malic acid) (PMLA) were synthesized based on bio-resourced lactic acid (LA) and malic acid (MA) through polycondensation as toughening agent for PLA. The chemical structures of PMLA were characterized by 1H NMR and 1H–13C HSQC analysis. In the PLA and PMLA blends, PMLA has apparent effect on the crystallinity of PLA and the blends show a great increase of elongation at break to over 300 % even at low PMLA content of 2%wt. Furthermore, the thermal properties of the blend are characterized through DSC and the micro-structure investigated through Positron annihilation lifetime spectroscopic (PALS) technique. PMLA with long-chain branched topology shows an excellent capability in the toughening of PLA and maintains the total biodegradability of the resultant blend at the same time, that is critical for environment-friendly materials.