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In this study, a series of GO with different oxidation levels were prepared via a modified Hummers' method, in which the oxidant/graphite ratio and oxidation time were varied. The change of GO structure as a function of oxidation level was investigated by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction measurements. The prepared GO were used for reinforcing epoxy resins, and the surfaces of GO were functionalized by the amine hardener during the dispersion process. Microscopic observations show that the oxidation level has a significant impact on the dispersion state of GO in the epoxy matrix. Both GO with the low and high oxidation levels tend to have low degree of dispersion, even aggregate. The influences of oxidation level on the performances of epoxy/GO composites, including curing behaviors, rheological, thermal and mechanical properties, were investigated in detail. Notably, the GO with optimum level of oxidation (denominated as GO-4) shows superior toughening effects on the epoxy matrix, compared to the reported epoxy/GO composites. The incorporation of merely 0.2 wt% GO-4 would yield 56 and 128% enhancement in the critical stress intensity factor ( K IC ) and the critical strain energy release rate ( G IC ), respectively. [ABSTRACT FROM AUTHOR]

In this work, the tackified PDCPD (PDCPD-T) specialized for vacuum assistant resin infusion process (VARI) was developed. The epoxy resin and methyl nadic anhydride (NMA) was subsequently added to the PDCPD-T to improve the interfacial bonding with the carbon fibres. The results showed that the introduction of NMA-cured epoxy undermined the mechanical properties of the PDCPD-T owing to the agglomeration of the tackifier particles. Nonetheless, the mechanical properties of the CFRCs based on the co-cured blends of the PDCPD-T and the NMA-cured epoxy were comprehensively improved compared to the composites based on the PDCPD-T. The improvement was that a part of NMA-cured epoxy in the co-cured blends would phase separate on the surface of the carbon fibre, which formed the "bridge" connecting the matrix and the carbon fibre. In addition, the degree of the tackifier agglomeration would also decrease due to the decrease in the surrounding epoxy concentration. [Display omitted] • The continuous carbon fiber reinforced polydicyclopentadiene (PDCPD) composites based on the vacuum-assisted resin infusion process are realized by tackifying the dicyclopentadiene (DCPD) monomer. • The further addition of anhydride-cured epoxy resin to the tackified DCPD monomer solves the problem of poor interfacial bonding between the PDCPD resin and the carbon fiber. • The carbon fiber composites based on the modified PDCPD matrix are proved to be far superior in interlaminar fracture toughness and impact resistance than the epoxy-based composites. [ABSTRACT FROM AUTHOR]

In this study, a phase inversion approach was employed to fabricate four different thicknesses (20 μm to 100 μm) of polyethersulfone (PES) porous films with visible holes (1 hole/cm2) on the surface, applied as interleaves to improve the interlaminar fracture toughness of carbon fiber/epoxy composite laminates prepared by vacuum assistant resin infusion process (VARI). The film could dissolve into the epoxy resin which as clearly evident by the optical microscopy under a controlled condition. It was noted that the thickness of the resin-rich layer and the distribution of PES microspheres in the interlaminar layer depended on the thickness of the PES porous film. Also, mode I and mode II fracture toughness, interlaminar shear strength (ILSS), flexural properties as well as tensile properties of the CF/EP composites had all been characterized and analyzed in detail and in order. The results demonstrated that mode I and mode II fracture energies at the optimal interleaved laminates for the toughened system were increased by 61.5% and 55.1% compared to the composites without interleaves, respectively. Besides, PES porous film interleaved laminates displayed an increase of 32% for the interlaminar shear strength and no significant changes in the flexural and tensile properties. It was observed that the films induced toughening via two mechanisms: i) cohesive failure in a thicker resin region and ii) crack deflection and microcrack caused by PES microspheres, illustrated in the microstructure analysis of the failure surfaces and the observations of the crack propagation path. [ABSTRACT FROM AUTHOR]