Enhanced interfacial characteristics in PLA/graphene composites through numerically-designed interface treatment

Despite the various biomedical applications of Polylactic acid (PLA), its usage has been limited due to the inherent poor mechanical properties of this biodegradable polymer. Accordingly, the reinforcement of PLA with nanoscale fillers such as graphene sheets is a promising research area that is just beginning to be explored. Considering the significant role of interfacial characteristics on the mechanical properties of polymer-based nanocomposites, a main challenge is how to strengthen the interface region. In this regard, a set of pull-out tests, using molecular dynamics simulations, are conducted to deeply analyze the effect of graphene surface treatment on the interfacial features of PLA composites embedded with this two-dimensional nanofiller. Our results reveal that small functional groups such as -OH, -COOH, -NH2, and -CH3 molecules along with the PLA grafted chains can significantly improve the interfacial interactions and consequently, shear strength and fracture toughness of these nanocomposites. This particular outcome maximizes by increasing the size and amount of small groups and raising the grafting density of the PLA chains to an optimal concentration. We further demonstrate that compared to the small functional groups, covalently bonded PLA chains have a more pronounced effect on the interface behavior.