Optimization of Atmospheric Plasma Treatment Parameters for Hydrophilic Surface Functionalization of Non-Woven Fabrics Through Design of Experiment

The use of hydrophilic polymers is a promising technology in various application fields such as filters and oil-water separation membranes, but it is difficult to directly utilize them due to problems such as a very small number and low mechanical properties. Accordingly, various attempts have been made to modify the surface of the non-hydrophilic material to be hydrophilic. The plasma treatment method in which activated ions collide with the surface to be modified by supplying energy to the gas has the advantage of being able to modify the surface easily and simply without major damage to the surface of the polymer. Among them, atmospheric pressure plasma is attracting attention in that it can perform surface modification with only a plasma source and a substrate without a special device such as a vacuum system or solvent treatment. It is well known that the surface of the non-hydrophilic polymer is modified to be hydrophilic when plasma treatment is performed using a specific gas on the polymer surface, but the effect of each process variable and the optimized conditions are not discussed in detail.<br/>Although the nonwoven fabric treated with atmospheric pressure plasma parameters as described above has many advantages, it has a problem, named the aging effect, in that the hydrophilic effect rapidly decreases over time. The aging effect is a phenomenon that occurs due to the characteristic that the reactors formed by plasma treatment return to their original state over time. Many studies have introduced various physicochemical methods in the plasma treatment process to solve this problem, when optimizing for improved conditions, a large problem arises in that a lot of time is additionally required because the effect over time for each condition must be reflected. Therefore, we propose a post-treatment method that uses the "design of experiment" to find the factor that has the greatest influence on the aging effect and reduces the decrease in the hydrophilic performance of the nonwoven fabric while maintaining the first optimized condition.<br/>Design of Experiments (DoE) is a statistical technique for quickly optimizing the performance of experimental results using input process variables. By analyzing the results of the DoE experiment, it is possible to find out which factors have a statistically significant effect on the results, how and which factors are interdependent, and finally, the experimental conditions can be optimized for the purpose of the experiment. A process capability index is a tool for determining whether the results of a set of process results meet a specific quality. Experimental results conducted with optimized process variables can be statistically verified by confirming process consistency and process yield through process capability analysis.<br/>In this study, a chain of experimental procedures based on various parameter combinations was performed using the DoE method, and the main factors that had the largest influence were found by quantifying the effect of each process variable of plasma treatment. In addition, based on the results, multiple regression analysis was used to optimize the experimental parameters under the conditions of maximizing the hydrophilicity of the polymer surface, and the excellence of the optimized conditions was shown statistically and physicochemically through process capability analysis and surface analysis. Finally, to evaluate the effect of reducing the effect over time, the estimation of hydrophilicity ability over time was also conducted. A series of experiments and analysis procedures were characterized by Minitab 20 software, X-ray photoelectron spectroscopy (XPS), Atomic Force Microscope (AFM), and contact angle analyzer.