Uniformity And Penetration Of Surface Modification Of Atmospheric Pressure Plasma Jet Treatment Into Textile Materials

Textile industry is the one whose foreign trade surplus has become the largest. It is one of the industries which severely pollute our environment and largely consume energy and water. The status shows that about 900 millions tons of waste water is exhausted every year in textile industry. For wastewate in dyeing and printing, it has some characteristics of difficulty to decoloring and containing organic matter with high concentration. Therefore, the sustainable development of textile industry heavily depends on whether the wastewater problem can be solved. In order to deal with the problems, the processing route of dyeing, pringting and finishing needs to be improved.Plasma treatment is a gaseous technology in which physical method is combined with chemical method. Compared with traditional physical and chemical treatments, it has some advantages of low pollution, low energy consumption, without involving water and chemicals. Especially in low temperature plasma, the electrons with high energy and other excited or ionized particles initiate physical and chemical reaction only on the suface of substrate with the thickness of several nanometers. However, the lower gas temperature has no effect on the bulk property. Therefore, the low temperature plasma treatment can be used to modify polymer surface. With the increasing ecologic and economic limits to textile industry, as an environmental friendly surface modification technology, plasma treatment has been widely used in polymer surface modification, which is effective and applicable.Previously most plasma treatments were done at low pressure, which can not realize on-line process due to expensive vacuum system. However, the recently developed non-equilibrium low temperature surface treatment at atmospheric pressure can be directly added into process line. For porous textiles, the plasma treatment effects not only limit on outer surface of substrate but also the active species in plasma can penetrate through pores in materials to modify other inner surface. There is difference in interaction of plasma and textiles between low and atmospheric pressure because of special structure and processing speciality of textiles. At low pressure or vacumm, plasma can be generated in two parallel polar plates or loops and is full of the whole veseel. All the surfaces of treated substrates are directly contacted with plasma and treated. However, at atmospheric pressure, especially for atmospheric pressure plasma jet, plasma is generated in noddle and then ejects to form plasma jet. Only some surfaces of the treated substrate are directly contacted with plasma jet and modified. Whether the inner surfaces can be treated depends on the permeability of active species in plasma jet through pores and interaction with the inner surface of textiles.Based on research current situation of above-metioned important problem, in order to uniformily treat all surfaces of textiles, it is necessary to investigate uniformity and penetration of atmospheric pressure plasma jet treatment into textile structure and develop new theory to explain interaction between active and non-active speices and the treated substrated, which directs its treating porous textiles. Therefore, the objective of this study is to investigate the uniformity and penetration of surface modification into textile materials including fiber, yarn and fabric treated by atmospheric pressure plasma jet (APPJ). Exposure to helium/oxygen plasma at atmospheric pressure makes improvement in the wettability, dyeability, adhesion of single fiber, yarn and woven fabric. Morphological and chemical changes on the fiber or fabric surface are characterized by Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), Fourier Transform Infrared Spectrometer (FTIR) and X-ray Photoelectron Spectra (XPS), respectively. Change in surface wettability is determined using static and dynamic contact angle, water-absorption time, and capillary flow height. The effect of plasma treatments on dyeability is evaluated by K/S value and dye diffusion in fiber cross-section using optical microscope, fluorescence microscope, and Laser Confocal Scanning Microscope (LCSM). The adhesion improvement is analyzed by micro-bond pullout test.Firstly, the uniformity of surface modification APPJ treatment into the whole surface of a single fiber was investigted. After the nylon 6 fibers were treated for different, the wettability using DCA315 static contact angle tester and dyeability using optical, fluorescence and laser confocal scanning microscope were measured. The plasma treatments result in an average of 10～20°decrease in the advancing contact angle and 20～30°decrease in the receding contact angle. An increased and uniform dye diffusion rate of nylon 6 fibers in the whole .cross-section is observed using LCSM. These effects are attributed to the surface physical and chemical change caused by the plasma treatments. SEM confirms that the fiber surfaces are roughened and XPS shows that there are more polar groups on the fiber surface after the plasma treatments. With the increase of plasma treatment time, a greater degree of etching is achieved and more polar groups such as hydroxyl and carboxyl groups are produced on the surface of the nylon 6 fibers, leading to better wettability and thus better dyeability of the fiber. It was concluded that atmospheric pressure plasma jet could modify the whole surface of a single fiber and the uniformity of fiber surface modification was increased with the increament of treatment time.Secondly, the APPJ effect on the each single fiber in the different position of filament tow was investigated. The polyester filaments without twisting are used as the model system. The cross-section of polyester filament is regarded as roundness and divided into six layers. Each layer has ten single filaments. The contact angle of each filamnet was measured. It was found that the contact angle of each treated filament was much smaller than that of control and there was difference in the wettability improvement between each filament. Therefore it was concluded that APPJ could treat each filamernt homogenously in pararrel filament tow. Meanwhile, the penetration of surface modification of APPJ into filament tow with twists was investigated. After he UHMPE filaments with different number of twists were treated by APPJ, the satic contact angle and Interface Shear Strength (IFSS) were measured. The results indicated that with the increasing number of twisting, the modification effect was decreased, which was confirmed by the increasing averge and standard divation of contact angle and the decreasing IFSS values. It was indicated that the increasing number of twist could weaken the permeability of APPJ treatment into yarns.After investigating the characteriss of APPJ treating single fiber and yarn, the penetration and penetration depth of surface modification into fabric was studied. The woven wool fabric was used as model to investigate the influence of technological parameter on penetration of surface modification into fabric. The fabrics were treated under various treatment conditions such as different output power, different nozzle to substrate distance, different substrate moving speed, different gas temperature and different treatment time to see how these technological parameters influenced the penetration of plasma through the fabric. It was found that the effectiveness of the plasma treatment as well as plasma penetration through the fabric were positively associated to the plasma output power and the treatment time but had no relation with the substrate moving speed. When the nozzle-to-substrate was too small (<1mm) or too large (>6mm) the effect of the plasma treatment diminishes, while optimal results were obtained when the nozzle-to-substrate distance was set at 2～3mm. Therefore, in order to achieve reasonable treatment effect on both sides of a fabric, plasma treatment condition had to be carefully chosen.The permeability of plasma into fabric is greatly related to pore size and its distribution. In order to investigate the influence of pore size of fabric on penetration of surface modification of APPJ into fabric, four kinds of polyester woven fabrics with different pore size and polyester fibers tightly pasted on two sides of fabrics were used as the model porous medium, which was treated using optimal technological parameter obtained by the above experiment. The static contact angle of control and the treated fibers were measured and the relation between penetration and pore size was obtained. Complete penetration was realized in fabric with pore size bigger than 200μm and nearly no penetration was found in fabric with the pore size smaller than 10 urn. This was attributed to the more number of active species in plasma jet diffusing through the bigger pores in fabric. Those species could get to the inner surface without losing their modifying ability during the movement process. Therefore the pore size seemed to be a more important factor affecting penetration of active species in plasma jet.When the thicker fabric or several layers of fabrics are treated by APPJ, it is necessary to know the pentration depth of APPJ surface modification into fabric with different pore size. The several-layer fabrics were stacked together to simulate the fabric with certain thickness. After treatment, the wettability of two sides was evaluated by water absorption time and capillary height. It was found that the modification depth was increased with the increasing pore size of fabric treated for certain time and the modification effect could be pentrated 2 mm into fabric with the pore size of 200μm.In order to determine the relation between treatment time and penetration depth of surface modification into fabric, four-layer stack of polyester woven fabrics was the model porous medium exposed to helium/oxygen atmospheric pressure plasma jet for different treatment time. The water absorption time of two sides decreased from 200 s to almost 0 s. The capillary height of every fabric layer was linearly increased with the increasing treatment time and but was linearly decreased with the increasing layer. Based on the relation between treatment time and the number of layer, the empirical model between pentration depth and treatment time was established to predict the penetration depth of surface modification effect into fabric.In summary, the results show that such a plasma jet is possible and effective in penetration of surface modification into textile structure. It can treat the whole surfaces of a single fiber and each filament in the treated parallel filament tow uniformly. The number of twisting affects the APPJ surface modification of filaments. For porous fabrics, rapid and efficient treatment on both sides of the treated samples is found to be ensured. And the degree and depth of penetration depends on the penetration of active species in plasma jet, which is affected by plasma parameters and materials structure. The former includes treatment time, power, gas temperature, jet-to-substrate distance. The latter includes number of twisting and pore size.Thereby, the APPJ system regime used offers the attractive prospect of controlling the surface modification of non-compact materials of various texture, porosity, etc. The pore size seems to have a more severe influence than the plasma parameters. In addition, the pentration mechanism of atmospheric pressure plasma jet into textile structure was preliminary explored. The relation between penetration depth of surface modification effect and treatment time was establish. These findings will have important effects on industrialization of textiles treated by atmospheric pressure plasma jet.