| The improvement of the toughness of carbon fiber reinforced polymer matrix composites has been the hot research topic in recent years. Introducing flexible layer into the interface can uniformly disperse the stress at interface, decrease the stress concentration, relax the residual stress and improve the toughness of the composites, but there still exists disadvantages that the flexible layer could not be easy to form good adhesion with the matrix, resulting in the decreased strength and modulus. In this work, a diblock copolymer Hydroxyl-Terminated poly(n-butylacrylate)-b-poly(glycidyl methacrylate)(OH-PnBA-b-PGMA) was synthesized by atom transfer radical polymerization(ATRP), and then introduced into the interface between carbon fiber(CF) and epoxy resin. The micro-phase separation at the interface induced the grafted blocks PnBA collapse on fiber surface to relax the thermal residual stress and improve the toughness, and the other blocks PGMA stretched into the resin matrix to favor the interfacial adhesion. Micro-Raman spectroscopy results indicated that, longer PnBA block could undergo greater deformation at the interface, which released more stresses and so resulted in the decreased interfacial residual stress. When the polymerization degree of PnBA was180, the thermal residual stress decreased to451.9±37.7MPa, even lower than that in washed carbon fiber(CF0) composite(546.9±31.8MPa). Dynamic mechanical analysis(DMA) and impact performance test results revealed that, the maximum area of tanδ peak corresponding to the P-relaxation mode was14.28, and the optimal value of notched impact strength was9.21±1.42KJ/m2. Microbond test results showed that, when the polymerization degree of PnBA was180and that of PGMA was70, the interfacial adhesion achieved optimal, and the interfacial shear strength(IFSS) value reached up to52.3MPa±1.45MPa, increasing by75.17%compared with that of CFO/epoxy resin composite.In order to improve the strength and modulus of the flexible chains, copolymer poly(n-butylacrylate)-co-poly(hydroxyethyl acrylate)(PnBA-co-PHEA) was synthesized by ATRP, and thus the photo-crosslinkable polymers poly(methacryloyloxyethyl acrylate)(PMEA) could be introduced into the flexible chains. The monomer reactivity ratios were estimated to be rHEA=1.505and rnBA=0.894by KT method, implying that PnBA-co-PHEA was random copolymer. DMA determined that the glass transition temperature could be increased with increasing ultraviolet radiation time, accompanying with the increased strength of the interfacial layer. In this system, through changing the PMEA units in the copolymers and/or ultraviolet irradiation time, we could effectively control the cohesive strength and deformation ability of the flexible layer, and thus regulate the strength and toughness of CF/epoxy resin composites. Microbond test results showed that, when nBA/MEA ratio was160:60and the irradiation time was30min, the IFSS value reached up to53.30±1.44MPa. DMA and impact performance test results revealed that, the maximum area of tanδ peak corresponding to the P-relaxation mode was13.81, and the optimal value of the notched impact strength was16.41±0.64KJ/m2.The environmental resistance properties of carbon fiber, with various surface modifications, reinforcing epoxy resin composites have been studied by a microbond test. As for CF-PnBA-b-PGMA/epoxy resin composites, on one hand, the interfacial thermal stress, induced by the different volume changes between carbon fiber and epoxy resin, could be partially relieved by deformation of the flexible PnBA blocks; on the other hand, the assembly morphology due to the micro-phase separation of diblock copolymer OH-PnBA-b-PGMA at the interface could partly modify the CF surface defects forming in the oxidation treatment, which decreased the water uptake at the interface. Thus, the introduction of OH-PnBA-b-PGMA into the interface effectively decreased the interfacial degradation rate during both the cooling-heating cycling (between-40℃and95℃) and the hygrothermal treatment (30℃and95℃). After50cooling-heating cycles, the IFSS value was still as high as32.69±2.13MPa; after immersion in the hot water for1h, the IFSS decreased by23.27%, still as high as23.79±1.87MPa after being immersed in the hot water for48h.The polymeric self-consistent field theory was used to investigate the microstructures and the interfacial properties of grafted diblock copolymers and/or grafted binary homopolymers in homopolymer melt, which could provide more detailed information for the interface structure design of the fiber/polymer composite materials. The simulations showed that, with varying grafting density and/or chain length, the grafted polymers assembled into various micro-structures, such as semispherical, wormlike, semicylinder-like, and sandwich-like lamellar morphologies. The calculations indicated that, the interfacial properties strongly depended on the physicochemical parameters of the system, including the chemical incompatibility between different components, the composition of the grafted polymers, the chain-length, and the chain-grafting density. In addition, our theoretical results not only reproduced the general feature of experimental observations, but also elucidated the internal structural information and complement the findings in the region of high grafting densities of diblock copolymers. |
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