Influence of twist and filament location in a yarn on effectiveness of atmospheric pressure plasma jet treatment of filament yarns

A twist free polyethylene terephthalate (PET) filament tow and ultrahigh modulus polyethylene (UHMPE) filament tows with 0, 1, 2, and 3 twist/cm are used as model systems to investigate the penetration of atmospheric pressure plasma jet modification effects through a single yarn. The change in surface wettability is determined using static contact angle measurements. Morphological and chemical changes on the fiber surface are characterized by scanning electron microscopy and X-ray photoelectron microscopy. The adhesion improvement is analyzed by micro-bond pullout test. For the PET filament tow, the fibers from the middle layer tend to have poorer treatment effect than those from the top and the bottom layers in terms of surface roughness, wettability and surface chemical composition change. For the UHMPE yarns, as the twist level increases, the plasma treatment is less effective in improving the fiber surface chemical composition, wettability and interfacial shear strength to epoxy due to the tightened yarn structure.