Abstract
The molecular weight of self-emulsifying amphiphilic epoxy sizing emulsions has a big effect on the carbon fibres and interfacial properties of their composites. Novel amphiphilic epoxy sizing emulsions with four different molecular weights (7500, 11,000, 15,000 and 17,000) were successfully prepared by a self-emulsifying method and applied to improve interfacial bonding between carbon fibres (CFs) and an epoxy resin (EP). The effect of molecular weight on the quality of emulsions, the sized CFs and the interfacial properties of the CF/EP composite system were studied. The results reveal that these novel sizing emulsions exhibited strong emulsifying ability and high processability. The most favourable wettability and adequate CF surface free energy were obtained by the emulsion with a molecular weight of 7500. Compared with unsized CFs, the monofilament fibre tensile performance was remarkably improved when increasing the shape parameter from 5.08 to 7.20. The interfacial sheer strength (IFSS) of the CF/EP composite was greatly increased by 96% with the emulsion of 7500. The enhanced interfacial adhesion benefits were attributed mainly from the enhanced charge interaction between CFs and the sizing layer as well as the compatibility and the mechanical interlock between the sizing layer and the epoxy matrix.
Highlights
Carbon fibre reinforced plastic composites (CFRPs) are widely used in industry due to the many advantages they offer, including high specific mechanical properties, adequate protection from corrosion and fatigue resistance
The performance of CFRPs, which are composed of different materials, are affected by their components, the mechanical properties of which are dominated by carbon fibres (CFs)
The molecular weights of four sizing emulsions were found to be in the range of 7500–18,000 g/mol, confirming that PEA and ODA chains were grafted on the epoxy backbone
Summary
Carbon fibre reinforced plastic composites (CFRPs) are widely used in industry due to the many advantages they offer, including high specific mechanical properties, adequate protection from corrosion and fatigue resistance. Polymers 2020, 12, 2439 resulting in an improvement of the chemical compatibility with the resin matrix This is necessary for producing high-performance CFs in industry. In a study by Chen et al, a waterborne epoxy sizing agent for CFs was prepared by polyfunctional group novolac epoxy resin (F-51) and diethanolamine (DEOA) via a self-emulsifying technique. Amino-terminated polyoxypropylene (PEA) has many ether groups and terminated amino groups in its molecular chain, which implies outstanding hydrophilicity with desirable compatibility and reactivity with an epoxy It was considered an appropriate epoxy to modify for the purpose of this study. Amphiphilic epoxy sizing emulsions with four different molecular weights were prepared by modifying an epoxy with PEA and ODA via a self-emulsifying method. The influence of molecular weight on the emulsions, the CFs and the interfacial adhesion in the CF/EP system was investigated
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