In-situ polymerization of different molecular weight polyethylene glycol and maleic acid onto carbon fiber for reinforcing polyamide 66

The interfacial adhesion character highly depends on the molecular interactions on the interface, including bond combination and molecular entanglement, and mobility for sharing load. In situ polymerization of different molecular weight polyethylene glycol (PEG) and maleic acid (MA) is used to form a hyperbranched polyester (HBPE) layer on an electrochemically oxidized carbon fiber (OCF) surface. It is found that more terminal hydroxyl groups are formed under the reaction at 280°C than that at other temperature. The branch extent and molecule chain length on the HBPE sizing reach balance by choice of 2000 molecular weight PEG monomer. HBPE as a film has uniform coverage on the OCF surface. The interlaminar shear strength of polyamide 66 composite reinforced with the sized OCF by in situ polymerization of 2000 molecular weight PEG and MA at 280°C is the optimal, which is enhanced to 90.5 MPa by 169% compared to unoxidized fiber and by 70% compared to OCF. The significant interfacial property improvement is attributed to the abundant terminal hydroxyl groups and appropriate chain length of the formed HBPE sizing, which enhanced optimally the interaction of fiber/sizing and sizing/matrix by balancing the contribution of molecular entanglement, deformation and covalent interconnection to interface.