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In this research, a resin film of the MAM/EP blend curing system containing the triblock copolymer polymethyl methacrylate- b -poly-n-butyl acrylate- b -polymethyl methacrylate (MAM) was prepared. Such resin film was inserted into the interlaminar of rapid-curing composites to simultaneously improve both mode I, mode II fracture toughness and impact resistance. Both the Mode I and Mode II interlaminar fracture toughness of the composites were carefully investigated as a function of MAM content of the MAM/EP resin film (0, 20 and 40 phr@50 μm). A maximum improvement up to 109% and 70.2% on Mode I and Mode II fracture toughness, respectively was obtained with the introduction of the 40 phr@50 μm compared to the laminates with the introduction of the 0 phr@50 μm. Analysis of the fracture surfaces of the laminates elucidated that the distinctive improvement of the interlaminar fracture toughness could be attributed to the characteristic interlaminar structures of MAM in epoxy resin by self-assembly. The interleaved laminates also displayed an increase of 26.7% for the compression after impact (CAI) properties, and showed excellent impact resistance. The interlaminar shear strength (ILSS) of the composite was thereafter explored, which indicated slight enhancements to the strengths. [ABSTRACT FROM AUTHOR]

In this work, a dicyclopentadiene monomer/Grubbs 2 catalyst was added to a mixture of epoxy oligomers and methyl nadic anhydride to obtain a poly‐dicyclopentadiene (DCPD) modified epoxy cross‐linked network via sequential curing. The hybrid resin was used as a matrix for preparing carbon fiber composites. The results indicated that the addition of DCPD monomers significantly reduced the viscosity of the epoxy resin. The toughness and heat resistance of the co‐cured resin was improved without significant loss of strength, which was attributed to the high compatibility between epoxy and the modifier polymer. Regarding the composites, the flexural strength of the hybrid resin‐derived composite first increased and then diminished slightly. Meanwhile, the mode‐I interlaminar fracture toughness continued to increase with the increase of PDCPD content compared to the non‐modified composites. Generally, the change trend of the above properties in the composites was consistent with the change trend of the strength and toughness exhibited in the bulk resin with increasing PDCPD contents, while the change extent was inconsistent due to factors such as fiber volume content and interfacial bonding. Highlights: The epoxy/PDCPD hybrid resin system was obtained via sequential curing.The PDCPD as modifier can reduce the viscosity of the epoxy curing system.The toughness and heat resistance of the PDCPD modified epoxy resin was improved.The loss in flexural strength of the hybrid resin system was insignificant.The GIC of the epoxy composites modified with PDCPD improved appreciably. [ABSTRACT FROM AUTHOR]

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 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]