Effect of ionic groups on the surface and the interfacial adhesion propertiesof poly( p-phenylene benzoxazole) ( PBO) f iber

The modified poly (p2phenylene benzoxazole) ( PBO) containing ionic groups in polymer chains (sulfonatedpoly p - phenylene benzoxazole , SPBO) was obtained by copolymerization from 1 , 3 - diamino -4 , 6 -dihydroxybenzenedihydrochloride (DAR) and terephthalic acid ( TPA) , with addition of certain amount s of 52sulfoisophthalicacid monosodium salt in replace of TPA , in polyphosphoric acid. The SPBO fiber was obtained for the first timethrough a dry-jet wet-spinning technique. After incorporation of ionic groups into PBO macromolecular chains , thewetting properties of PBO fiber are improved. The contact angles of water and ethanol on PBO fiber surface decreasef rom 71. 4°and 37. 2°to 66. 3°and 30. 6°respectively. And the surface f ree energy of SPBO fiber increases tO₃8. 9 mJ·m- 2 , which is 9. 6 % higher than that of PBO fiber. XPS analysis shows that the surface nit rogen-to-carbon ratio is increased f rom 0. 0157 to 0. 0471 and oxygen2tO₂carbon ratio is increased f rom 0. 2331 to 0. 3070 , andthe ionization energy (or binding energy) of C1s and O1s decreases. The interfacial shear st rength ( IFSS) was determined by the microbond pull out test . The int roduction of ionic group s leads to a 23 % increase in IFSS f rom8. 2 MPa for PBO/ epoxy to 10. 1 MPa for SPBO/ epoxy. In addition , the surface morphology of the pull-outed PBOand SPBO fibers was observed by scanning elect ron microscopy. It is found that the failure mode changed f romfiber/ mat rix interface adhesive failure to partly cohesive failure mode.