Chemically modified poly(lactic acid): structural approach employing two distinct monomers

Abstract

The chemical modification of poly(lactic acid) with different monomers has been investigated, since comparative studies of the use of two monomers are scarce in literature. The present study aims to determine the number of acid groups available after modification as well as their final molar mass. Therefore, maleic anhydride (MA) and glycidyl methacrylate (GMA) were grafted separately onto PLA in the presence of peroxide according to a 22 factorial design, where monomer and peroxide concentrations were varied. All reactions were carried out in the melt in a Haake rheometer. The acidity percentage and molar mass of the polymer were determined by means of acid group titration and size-exclusion chromatography, respectively. The thermal properties of the modified PLA were assessed using DSC. The results showed that the two different monomers modified PLA properties differently. Whereas GMA increased the molar mass and decreased the acidity percentage of PLA, the presence of MA had an opposite result. This finding has important implications on subsequent reactions. The independent variable peroxide concentration was which most affected acidity percentage when MA was used. On the other hand, when GMA was used the variable which most affected acidity percentage was the monomer concentration.