The physical and chemical properties of plasma treated ultra-high-molecular-weight polyethylene fibers

A uniform and smooth transfer of stresses across the polymer matrix/fiber interface is enhanced when adhesion between the matrix and fiber surface is optimized. In the absence of covalent bonds matching the Hansen solubility (cohesion) parameters (HSP) of the fiber surface with the HSP of a matrix polymer assures maximum physical adhesion to transfer loads uniformly. Plasma treatment of ultra-high-molecular-weight polyethylene (UHMWPE) fibers is shown to significantly increase the amount of oxygen in the surface. There are two distinct types of surfaces in both the plasma treated and the untreated UHMWPE fibers. One type is typical of polyethylene (PE) polymers while the other is characteristic of the oxygenated surface at much higher values of HSP. The oxygenated surface of the plasma treated fibers has the HSP δD, δP, and δH equal to 16.5, 15.3, and 8.2, compared to the pure PE surface with HSP at 18.0, 1.2, and 1.4, all in MPa½. The dispersion parameter has been lowered somewhat by the plasma treatment, while the polar and hydrogen bonding parameters are much higher. The HSP methodology predicts enhanced adhesion is possible by skillful use of anhydride and nitrile functional groups in matrix or tie polymers to promote compatibility in the system.