COUPLING CARBON-FIBERS TO EPOXY MATRICES WITH GRAFTED SIDE-CHAIN LIQUID-CRYSTAL POLYMERS

This work investigated the interfacial adhesion between carbon fibers grafted with liquid-crystalline compounds and an epoxy matrix using th e ''single-fiber tensile test''. The liquid-crystalline monomer and it s side-chain liquid-crystalline polymer contain phenolic groups and ca n therefore bond covalently to both carbon fibers and epoxy matrices. Their mesogenic nature also offers the possibility of forming highly o rdered interfacial structures. Epoxy specimens containing a single car bon fiber embedded along their length were loaded in tension and obser ved in transmission by polarized light microscopy. Both stress birefri ngence due to plastic shear deformation of the epoxy and the fiber's c ritical fragmentation length, l(c), were measured. Relative to specime ns with ungrafted fibers or monomer-grafted fibers, those containing f ibers grafted with the self-ordering polymer revealed the greatest pla stic deformation in the matrix possibly caused by strong interfacial a dhesion. Measurements of critical fragmentation lengths suggest the gr afted liquid-crystal polymer causes toughening of the carbon fiber/epo xy interface.