| The aging effects of atmospheric plasma treated fiber surfaces were important for storage and processing of the fibers. One of the high performance fibers, ultrahigh modulus polyethylene (UHMPE) fiber was chosen as a model system to investigate the aging process of atmospheric pressure plasma jet (APPJ) treated fibers surfaces in terms of surface chemical composition, surface wettability, interfacial shear strength (IFSS) with epoxy, and fiber tensile strength measured at time intervals of 0, 7, 15 and 30 days after initial plasma treatment. The fiber was first plasma treated and then stored at temperatures varying from -80℃to 80℃on the same 0% relative humidity (RH) and on RH varying at 0%, 65%, and 100% at the same temperature of 20℃. Immediately after the plasma treatment, scanning electron microscope (SEM) showed that the fiber surface was roughened; X-ray photoelectron spectroscopy analysis showed surface chemical composition was changed; contact angle measurement showed an increase of surface wettability, microbond test showed an increase in IFSS; tensile strength test showed a decrease in fiber tensile strength. During 30 days of the aging process, the results indicated that temperature and humidity both significantly affected the aging effect of plasma treated UHMPE fibers. With the increase of relative humidity or decrease of temperature, the IFSS value decreased more slowly, and the contact angle increased more slowly. But after 30days, the IFSS value and contact angle reached a similar level for all groups. Moisture shows no effect on the single fiber tensile strength during aging. Decreasing temperature or increasing relative humidity hindered the surface rearrangement of polymer chain after plasma treatment.
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