Polypropylene/poly(methyl methacrylate)/graphene composites with high electrical resistivity anisotropy via sequential biaxial stretching

An efficient strategy is developed for the fabrication of graphene-filled polypropylene (PP) nanocomposites with graphene nanosheets orderly oriented in the in-plane direction. The nanocomposites with an anisotropic coefficient as high as 35 000 in electrical resistivity were fabricated by a sequential biaxial stretching process. Polymethylmethacrylate (PMMA) was employed to bridge graphene to the non-polar PP matrix, which facilitates the homogeneous dispersion and the orientation of the chemically converted graphene nanosheets. A PMMA/graphene masterbatch was firstly prepared and blended into the PP matrix. During the biaxial stretching, the PMMA/graphene phase was transformed from beads to sheets, which induced the in-plane orientation of the graphene nanosheets. As a consequence, the storage modulus and the conductivity of the nanocomposites were improved in the in-plane direction. The effects of graphene content and draw ratio on the anisotropy of the PP/PMMA/graphene nanocomposites were discussed in detail. This strategy of orientation-effectiveness and cost-effectiveness can be potentially integrated with commercialized biaxial stretching processes to produce high-quality anisotropic polyolefin/graphene composite films.