Composites of polyethylene reinforced with chopped polyethylene fibers: Effect of transcrystalline interphase

In composites consisting of polyethylene reinforced with randomly oriented chopped polyethylene fibers, a highly uniform transcrystalline interphase was found to develop on the fiber surfaces under isothermal conditions. The interphase was also observed to develop, to an equal extent, on the fiber ends. A significant increase in both the tensile strength and the Young's modulus occurred with increasing fiber volume fraction. Following thermal treatment, a substantial increase in the Young's modulus was observed. This increase, expressed by the modulus ratio (isothermal/quenched), was very similar to that in the pure matrix, indicating that the increase in modulus was due to bulk crystallization in the matrix only rather than to the expected effect of transcrystallinity. No significant change in tensile strength occurred following the thermal treatment. Thermal analysis performed on the different composites and pure matrices showed evidence of the presence of the transcrystalline interphase. SEM pictures revealed significant amounts of matrix debris on the fiber surfaces in the isothermally treated composites, which reflects the increased interfacial bonding in these materials.