Reactive functionalization of poly(lactic acid), PLA: Effects of the reactive modifier, initiator and processing conditions on the final grafted maleic anhydride content and molecular weight of PLA

A response surface methodology (RSM) design was used to analyze the effects of maleic anhydride (MA) and 2,5-bis(tert-butylperoxy)-2,5-dimethyl hexane (Luperox or L101) content, and TSE screw speed on the degree of grafted MA (MAg) and number average molecular weight (Mn) of maleated PLA (PLA-g-MA), which can be used as a reactive compatibilizer in production of PLA blends with various components. PLA-g-MA's FTIR peaks indicated that MA was grafted onto the PLA backbone and oligomeric MA was also present. A maximum of 0.52 wt% MAg determined by titration was achieved at the expense of a 50% reduction of Mn and an increase in the polydispersity index to around 2.0. Generally, increasing L101 increased the degree of grafting and decreased Mn. L101 and MAg had a large effect on the stability of PLA-g-MA's Mn during storage. Nominally, amounts of MA equal to 4.5 wt%, L101 between 0.45 and 0.65 wt%, and screw speed of 20 rpm provided the optimal conditions for grafting MA onto PLA.