The effect of transcrystallinity on the transverse mechanical properties of single‐polymer polyethylene composites

The microstructure of polyethylene (PE)/PE composites, consisting of the high‐density PE (HDPE) matrix and ultrahigh molecular‐weight PE (UHMWPE) fibers, was investigated. Single‐fiber composites were prepared and analyzed in a hot‐stage crystallization unit attached to a polarizing microscope, aiming to find out how the conditions of crystallization affected the transcrystallinity ( tc ) growth at the fiber‐matrix interface. Thermal treatments leading to two extreme microstructures, of either maximum or minimum thickness of the transcrystalline zone, were sought. It was found that a uniform transcrystalline layer was developed on the UHMWPE fiber from the HDPE melt under isothermal conditions, whereas rapid cooling from the melt prevented the generation of tc . The mechanical properties of unidirectional composite laminae either with or without the transcrystalline zone were measured. A comparison of the transverse strength predicted by theoretical models with the experimental values revealed good interfacial adhesion in the PE/PE system. It was shown that the tc growth had a negligible effect on the composite mechanical properties in the longitudinal direction, whereas it resulted in a 50% decrease of the transverse tensile strength and strain to failure. Scanning electron microscopy attributed that observation to premature brittle failure at tc / tc contact regions. © 1995 John Wiley & Sons, Inc.