Improved interfacial shear strength and durability of single carbon fiber reinforced isotactic polypropylene composites using water-dispersible graft copolymer as a coupling agent

A synthesized water-dispersible graft copolymer (WDGP) was evaluated as a coupling agent in carbon fiber/isotactic polypropylene composites. Measurements of the interfacial shear strength (IFSS) were made using single fiber composite (SFC) specimens. A graft copolymer of isotactic polypropylene backbone grafted with polyacrylamide (PAAm) was synthesized for testing as a coupling agent. Optimal conditions for the coupling agent treatment and SFC specimens preparation were established. Improvement in the IFSS was 18% at room temperature, whereas improvement was >60% under wet conditions, after 1 h in boiling water. This improvement is due to chemical bonding in the interphase between functional groups in carbon fiber and PAAm in WDGP coupling agent, and interdiffusion in the interphase between IPP in WDGP coupling agent and matrix IPP. The hydrophobic nature of the interfacial region and crosslinking between amide groups in grafted PAAm chains based on inter- and intramolecular interactions may be the reason for the high improvement of the IFSS under wet conditions. In addition, the spherulite size and transcrystallinity seem to correlate with the IFSS of SFC specimens.