Wettability of carbon nanotube-grafted carbon fibers and their interfacial properties in polypropylene thermoplastic composite

The interfacial properties of carbon fiber (CF) reinforced thermoplastic composites depend strongly on the wettability and surface characteristics of the reinforcing fibers, and their compatibility with a chosen matrix. The interface between conventional fibers and thermoplastic matrices is generally weak, due to a lack of specific chemical interaction, especially in the case of polyolefins. Carbon nanotube-grafted-carbon fibers (CNT-g-CF) are considered to be potential reinforcements as they provide additional mechanical interlocking. Commercial CFs were successfully grafted with nanotubes using a continuous, and hence scalable, CVD method. X-ray photoelectron spectroscopy, Wilhelmy wetting measurements, and scanning electron microscopy confirmed the successful grafting and resulting hydrophobic surface chemistry, dominated by van der Waals interactions. The grafted CNTs, with diameters and lengths around 10 nm and 140 nm respectively, were well suited to improve the overall wettability and interfacial shear strength (+53.4 %) of the CNT-g-CF in a polypropylene matrix when compared to as-received unsized CFs.