Influence of ethanol pretreatment on effectiveness of atmospheric pressure plasma treatment of polyethylene fibers

Unlike low pressure plasmas, atmospheric pressure plasmas can treat materials with adsorbed liquids such as organic solvents used as cleaning agents in preparation of material surfaces for plasma treatments. These solvents may interact with the plasmas to influence the treatment results. This paper studies the influence of ethanol pretreatment on atmospheric pressure plasma jet (APPJ) treatment of ultrahigh molecular weight polyethylene (UHMWPE) fibers when a mixture of helium and 1% of oxygen is used as the treatment gas. The fibers had 0.82% and 0.86% weight gain after soaking in ethanol for 12 and 24 h, respectively. Scanning electron microscopy shows that the surface of fibers soaked in ethanol for 12 h or longer before the plasma treatment does not show any morphological change. X-ray photoelectron spectroscopy shows oxygen content doubled for the plasma treated fibers compared with control but a rather small increase in oxygen content on the surface of the ethanol pretreated UHMWPE fibers compared with the plasma treated fibers without pretreatment. Water contact angle of the ethanol pretreated fibers did not change after the plasma treatment compared with the control fiber. Microbond test shows that the interfacial shear strength values (IFSS) of the fibers to epoxy do not change for the ethanol pretreated fibers while that of the plasma directly treated fibers increases significantly. It is likely that ethanol absorbed into the fiber reacts with the plasma, forming a weakly bonded layer of polymers that reduced plasma etching and IFSS.