Transcrystalline Interphase in Advanced Polymer Composites

Abstract

Surface induced transcrystallization in fibers has been reported in some advanced polymer composites. It is believed that the transcrystalline interphase may affect stress transfer efficiency between the reinforcing fiber and the matrix in addition to exhibiting different mechanical properties from the neat matrix. In this work, attempts were made to examine the effects of transcrystallinity on composite performance, particularly on fiber/matrix interfacial bond strength, and to investigate possible attributes of transcrystallization. Three polymer resins were investigated: polyetherketoneketone (PEEK), polyetheretherketone (PEEK) and polyphenylene-sulfide (PPS); four types of fiber were used: PAN-based AU-4 carbon, pitch-based carbon, PPDT aramid and E-glass. It is found that PPDT aramid and pitch-based carbon fibers induce a transcrystalline interphase in all three polymers, due to an epitaxial effect. Under certain conditions, transcrystallization has also been observed in the PAN-based carbon and E-glass fibers, which may be partially attributed to the thermal conductivity mismatch between the fiber and the matrix. Plasma treatment on the fiber surface showed a negligible effect on inducing transcrystallization, whereas solution coating of PPDT aramid creating an epitaxially-favored environment on the fiber surface showed a positive effect. Mechanical test results, including microdebonding, flexural mechanical and short beam shear tests, of the PEKK composites showed increases of 5–25% in the composite properties with the transcrystallinity. However, the effect of transcrystallinity on the interfacial bond strength decreases as the fiber content increases in the composites.