Effect of hydroxyl polar groups on the surface and the interfacial adhesion properties of PBO fiber

The modified poly(p-phenylene benzoxazole) (PBO) containing polar hydroxyl groups in macromolecular chains was obtained by copolymerization from 1，3-diamino-4，6-dihydroxybenzenedihydroch1oride (DAR) and terephthalic acid (TPA) in poly (phosphoric acid) (PPA) solvent，with addition of certain amounts of 2，5-dihydroxyterephthalic acid (DHTA) to replace TPA. The obtained DHPBO-PPA dope was directly spun into fibers via a dry-jet wet-spinning process. The resultant polymers were characterized mainly by means of FTIR，dynamic contact angle analysis，etc. The interfacial shear strength (IFSS) was determined by the microbond pull-out test . The surface morphologies of the pull-out PBO and DHPBO fibers were observed by scanning elect ron microscopy. With the incorporation of 50 mol% hydroxyl polar groups，the contact angle on PBO fiber for water decreases from 71.4° to 50.7°，and the contact angle for ethanol decreases from 37.2° to 27.4°. The surface free-energy of DHPBO (20 % mol content of DHTA) fiber increases to 43.96 mJ/m²，which is 23.83% higher than that of PBO fiber. The IFSS between DHPBO (10% mol content of DHTA) fibers and epoxy resin is 18.87 MPa，which is 92.55% higher than that of PBO fibers.