On novel bio-hybrid system based on PLA and POSS

In this work, a novel strategy for the preparation of bio-hybrid systems based on polylactic acid (PLA) and polyhedral oligomeric silsesquioxane (POSS) was developed. Indeed, the new method consists in a preliminary functionalization of the polymer matrix and a subsequent reaction of silsesquioxane molecules, characterized by amino or hydroxyl functionalities, potentially capable of reacting with maleic anhydride groups created onto PLA by a free radical process. The method adopted to create maleic anhydride-grafted polylactic acid (PLA-g-MA) allowed to graft 0.7 wt% of MA onto the polymer backbone, avoiding a dramatic reduction of PLA molecular mass. ¹H-NMR measurements demonstrated a different reactivity of the two used POSS, namely trans-cyclohexanediolisobutyl POSS (POSS-OH) and aminopropyl heptaisobutyl POSS (POSS-NH₂). Indeed, the amino group of POSS-NH₂ was found to react with the maleic anhydride group of PLA-g-MA allowing to obtain a hybrid system, carrying silsesquioxane molecules along the polymer backbone while the reactivity of POSS-OH turned out to be much lower. Thermal properties of the synthesized hybrid systems were assessed by means of DSC measurements. Indeed, the presence of POSS grafted onto the macromolecular chain was found to improve PLA crystallinity, by affecting the crystal nucleation density. Moreover, a decrease of surface water wettability was observed in the films made of PLA-g-MA/POSS-NH₂.