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Abstract
A technique for grafting acrylic polymers on the surface of ultra-high molecular weight polyethylene (UHMWPE) fibers utilizing 60Co gamma radiation at low dose rates and low total dose has been developed. Unlike some of the more prevalent surface modification schemes, this technique achieves surface grafting with complete retention of the exceptional UHMWPE fiber mechanical properties. In particular, poly(butyl acrylate) and poly(cyclohexyl methacrylate) were successfully grafted onto UHMWPE fibers with no loss in tensile properties. The surface and tensile properties of the fibers were evaluated using Fourier transform infrared/photoacoustic spectroscopy (FTIR/PAS), X-ray photoelectron spectroscopy (XPS), and tensile tests. The reinforcement efficiency of untreated, polymer-grafted, and plasma-treated UHMWPE fibers in polystyrene and a poly(styrene-co-butyl acrylate-co-cyclohexyl methacrylate) statistical terpolymer was characterized using mechanical tensile tests. The thermoplastic matrix composites were prepared with 4 wt% discontinuous (10 mm), randomly distributed UHMWPE fibers. An approximate 30% increase in composite strength and modulus was observed for poly(cyclohexyl methacrylate)-grafted fibers in the terpolymer and polystyrene matrices. A comparable improvement was realized with the plasma-treated fibers. On the other hand, poly(butyl acrylate) grafts induced void formation, i.e. energy dissipation through plastic deformation and volume expansion at the fiber/matrix interface in terpolymer composites. The latter resulted in a 75% increase in the elongation to failure. The effect of polymer grafts on fiber/matrix adhesion is discussed in terms of the graft and matrix chain interactions and solubility, graft chain mobility, and fracture surface characteristics as determined by scanning electron microscopy (SEM).