Xiaoqing Zhang

Interfacial Microstructure and Properties of Carbon Fiber Composites Modified with Graphene Oxide

The performance of carbon fiber-reinforced composites is dependent to a great extent on the properties of fiber-matrix interface. To improve the interfacial properties in carbon fiber/epoxy composites, we directly introduced graphene oxide (GO) sheets dispersed in the fiber sizing onto the surface of individual carbon fibers. The applied graphite oxide, which could be exfoliated to single-layer GO sheets, was verified by atomic force microscope (AFM). The surface topography of modified carbon fibers and the distribution of GO sheets in the interfacial region of carbon fibers were detected by scanning electron microscopy (SEM). The interfacial properties between carbon fiber and matrix were investigated by microbond test and three-point short beam shear test. The tensile properties of unidirectional (UD) composites were investigated in accordance with ASTM standards. The results of the tests reveal an improved interfacial and tensile properties in GO-modified carbon fiber composites. Furthermore, significant enhancement of interfacial shear strength (IFSS), interlaminar shear strength (ILSS), and tensile properties was achieved in the composites when only 5 wt % of GO sheets introduced in the fiber sizing. This means that an alternative method for improving the interfacial and tensile properties of carbon fiber composites by controlling the fiber-matrix interface was developed. Such multiscale reinforced composites show great potential with their improved mechanical performance to be likely applied in the aerospace and automotive industries.

Facile preparation route for graphene oxide reinforced polyamide 6 composites via in situ anionic ring-opening polymerization

In this study, a new and facile route has been developed to prepare graphene oxide (GO) reinforced polyamide 6 (PA6) composites and synthesize simultaneously PA6 grafted GO hybrid materials: e-caprolactam (CL) was firstly fixed onto the GO sheets coupling by 4,4′-methylenebis(phenyl isocyanate), and then PA6 was grafted from the GO surface by in situ anionic ring-opening polymerization. The polymerization processing was effectively carried out at relatively low reaction temperature (150 °C) and in a short reaction time (20 to 40 min) by using a caprolactam magnesium bromide (C1) initiator in combination with a difunctional hexamethylene-1,6-dicarbamoylcaprolactam (C20) activator. The PA6 grafted graphene oxide (g-GO) was verified by 1H NMR, FTIR, TGA, XPS and AFM. The PA6 grafted GO sheets (g-GO) contain about 74 wt% polymers, which make the GO sheets homogenously dispersed in matrix and gain good interfacial adhesion. The tensile results show that the tensile strength and Youngs modulus of the nanocomposites can be obviously improved by incorporation of g-GO at low contents. Furthermore, the crystallization temperature and degree of crystallinity of PA6-GO nanocomposites both increased in the non-isothermal crystallization process, especially for the composites with GO loading less than 0.2 wt%. This simple and effective approach is believed to offer possibilities for broadening the graphene applications with the development of PA6-graphene nanocomposites.

Grafting of amine-capped cross-linked polyphosphazenes onto carbon fiber surfaces: a novel coupling agent for fiber reinforced composites

The performance of carbon fiber reinforced composites is to a great extent dictated by the interfacial adhesion strength between the fibers and matrix. In order to improve the interfacial properties of carbon fiber/polypropylene (PP) composites, a new surface treatment has been developed to graft the amine-capped cross-linked polyphosphazenes (ACP) onto carbon fibers as a novel coupling agent through in situ polycondensation between hexachlorocyclotriphosphazene (HCCP) and 4,4′-diaminodiphenyl ether (DDE) under mild reaction conditions, and maleic anhydride grafted PP (M-PP) was used as the matrix. The chemical composition of the modified carbon fibers was verified by Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectra (XPS). The surface morphologies of the modified carbon fibers were detected by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The interfacial shear strength (IFSS) between carbon fibers and the matrix was investigated by a microbond test. The grafted ACP with a quantity of amine groups uniformly covered the carbon fiber surfaces, which results in strong interfacial adhesion between the modified carbon fibers and M-PP. The results of the test reveal a significant improvement of IFSS in the ACP grafted carbon fiber composites with an increase of 223.0% compared to the unmodified carbon fiber composites. In this work, we propose a facile and effective method for improving the interfacial properties of carbon fiber composites by grafting a novel coupling agent.