W. Xu, R. Verma, S. Jambhulkar, R. Franklin, K. Song
Arizona State University,
Keywords: graphene, polymer, composites, exfoliation, orientation, mechanics
Summary:Polymeric fibers have broad applications in automobile, aerospace, wearable textiles, batteries, biomedical implants, and 3-D printing. However, most polymer fibers display weak and compliant nature. Graphene, a single layer of graphite showing intrinsic modulus of ~1 TPa and strength of ~130 GPa, is one of the promising reinforcement for the polymer fiber. Currently, graphene nanoplatelets (GNPs) have been intensively investigated with the generally used techniques of simple purifying, sonication, mixing, drying, and molding. The inefficiency of controlling graphene morphologies, dimensions, and orientations led to a low-stress transfer from graphene to polymers, especially in highly loaded composites. Our study utilized an in-house designed and assembled apparatus to spin polymer/graphene composite fibers with unique microstructures. Pure polymer (1-phase), graphene core-polymer shell (2-phase), and polymer-graphene-polymer coaxial (3-phase) fibers have been fabricated. The examination of the fiber dimensions and microstructures showed that the 3-phase samples showed the most efficient mechanical enhancement due to the polymer constraining on graphene and their assistance in exfoliations and orientations. Upon mechanically drawing at three different temperature stages, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) suggest that the stiffening and strengthening of polymers are results of the improved crystallinity of polymers, the exfoliation and orientation graphene, and, the elimination of defects. Raman scattering exhibited improved graphene orientations along the fiber direction, especially in 3-phase fibers, which resulted in a 132% increase in tensile stress and 293% increase in Young’s modulus as compared to 1-phase pure polymer fibers.