Interfacial engineering of polypropylene/graphene nanocomposites: improvement of graphene dispersion by using tryptophan as a stabilizer

In this work, graphene nanosheets functionalized with polypropylene (PP) chains through non-covalent π–π interactions, PP-f-graphene, were prepared and their reinforcing effect on PP was investigated. With the aid of tryptophan, graphene can stably disperse in water due to the non-covalent π–π interactions between graphene and tryptophan. By mixing the aqueous dispersion of tryptophan-functionalized graphene and the xylene solution of polypropylene-graft-maleic anhydride (MAPP), a binary phase system was obtained. The graphene nanosheets continuously transferred from water phase into xylene phase as the reaction between MAPP and tryptophan at the water/oil interface proceeded. The structure of the resultant PP-f-graphene nanosheets was carefully characterized by spectroscopy and microscopy methods. The results confirmed that MAPP chains have been successfully bonded onto graphene surfaces. PP/PP-f-graphene nanocomposites were fabricated by melt blending. A well-dispersed PP-f-graphene in PP matrix was realized due to the strong adsorption between graphene and functionalized PP. The addition of only 0.6 wt% of PP-f-graphene increased the tensile strength and flexural modulus of PP by 20.8% and 44.6%, respectively. The crystallization temperature and rate of PP were also elevated by the incorporation of PP-f-graphene. Making use of the interaction between graphene and functionalized PP is a facile method to improve the dispersion of graphene in the PP matrix.