Effect of polyamic acids on interfacial shear strength in carbon fiber/aromatic thermoplastics

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Abstract
Carbon fiber surfaces were coated in various thickness with polyamic acids (PAA) prepared from (1) benzophenone tetracarboxylic dianhydride (BTDA) and 4,4'‐diaminodiphenyl ether (ODA), (2) BTDA and 4,4'‐diaminodiphenyl sulfone (DAS), and (3) BTDA and ODA modified with bisaminopropyldisilane, designated as PAA‐1, PAA‐2 and PAA‐3 respectively. The treated carbon fiber, with or without imidization, was embedded in thermoplastic polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone (PSF), and polyphenylsulfide (PPS) by the microbond method, and the interfacial shear strength was measured by pulling out the fiber from the embedded resin. Maximum increments in interfacial bonding strength from 24% to 35% were obtained from PAA‐1 in PEEK in PEI, PAA‐2 in PEEK, PEI, PSF, and PPS, and PAA‐3 in PEEK and PES. Imidization of PAA‐1 and PAA‐2 before resin application reduced their bonding capability. A linear relationship between the length of the embedded fiber and debonding load was found in the case of PEEK, PEI, and PSF; scattered results were obtained in the case of PES and PPS. Inadequate specimen annealing was believed to be the cause for PES, Brittle fracture appeared to occur in the case of PPS.

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