Influence of moisture on wettability and sizing properties of raw cotton yarns treated with He/O2 atmospheric pressure plasma jet

The He/O2 atmospheric pressure plasma treatment can effectively improve the wettability and sizing properties of raw cotton yarns. However, the treatment effects may be greatly influenced by the moisture regain (MR) of the cotton yarn. In this study, raw cotton fibers, yarns and rovings with three different MRs (0.5%, 9.3% and 26.4%) are treated by atmospheric pressure plasma jet (APPJ) in He/O2 at a ratio of 30:0.3 L/min to study how MRs affect their wettability and sizing properties. SEM and XPS analyses show that cotton fibers with lower MRs are more efficiently etched and more polar bonds, such as COH/COC, OCO/CO and OCO, are imparted by the APPJ treatment. Consequently, the cotton yarn obtains higher wicking heights and smaller contact angles at lower MRs. The size adhesion analysis proves that the adhesion between the roving and the size becomes weaker as the MR increases. Observation of the cross sections shows that the roving with the lowest MR has a more uniform layer of size permeation than that for higher MR samples, while the side facing the plasma jet has a thicker size impregnation than the other side. The MR has negative effects on the surface etching, the improvement of hydrophilicity, sizing adhesion and size permeation uniformity of raw cotton yarns by APPJ.