Interphase formation and structure in phenolic composites containing ultra-high modulus polyethylene fibre

The acid-catalysed cure reaction of a phenolic resin at 80degreesC results in the trapping of water as micron-sized spherical domains within the resin. When untreated commercial ultra-high modulus polyethylene (UHMPE) fibre is used as reinforcement with this resin, the water is trapped at the interface due to the poor wet-out of the fibre by the resin. This produces low interfacial shear strengths. A short radio frequency plasma treatment of the fibre in oxygen or water increases the shear strength by more than a factor of 2. The water liberated on resin cure is not trapped at the interface of the plasma-treated fibres, due to the enhanced wet-out of the fibre by the phenolic resin prior to cure. The plasma-treated UHMPE shows surface restructuring by XPS over a period of a week, but there is no loss of interfacial shear strength when the phenolic composite is fabricated, consistent with rapid reorientation of the carbonyl and carboxyl functionality in the presence of the resin.