Study On Atmospheric Pressure Plasma Assisted Green Sizing Technology Of Cotton Yarn

A lot of polyvinyl alcohol (PVA) has been discharged to the natural environment due to the high cost of recycling, which has caused great pollution because of its poor biodegradability in natural conditions. The biodegradability of polyacrylic acid sizes depends on their macromolecule structures and varies a lot. Although the BOD5/CODcr values of most polyacrylic acid sizes are less than0.25which is lower than that of PVA, polyacrylic acid sizes are difficult to degrade in natural environment. So, PVA and other sizes which could lead to environment contamination have been facing prohibition in recent years. The annual symposium for size and sizing technology in China has advocated usage of green sizes, energy saving and application of eco-friendly sizing technology for five years in a row.Starch size and its modifications are one of the most promising green sizes and they are biodegradable and abundantly available. They are often used in combination with PVA because of their poor fluidity and unstable viscosity. Some problems, such as brittleness and stiffness of size films and poor sizing properties will be encountered if starch size and its modifications are used alone, which severely affected the subsequent weaving process. Raw cotton fiber is hydrophobic due to the existence of its surface cuticle layer mainly composed of pectin and waxes, which brings a lot of difficulties for the wetting process of cotton yarn and the permeability of size to the yarn. Furthermore, the sizing time in the size box is greatly reduced to1-2sec with the development of high-speed sizing technology, which challenges the permeability and coverage effect of the size to the yarn.He/O2atmospheric pressure plasma (APP) assisted eco-friendly sizing technology (EFST) of cotton yarn has been developed in this study to consume the disadvantages of starch sizes, raw cotton fiber and the high-speed sizing technology aiming to size raw cotton yarn, especially high count yarn, with starch sizes. The EFST employs APP pretreatment of the yarn in combination with green size recipes including components of glycerol and phosphate modified starch (PM-Starch) during sizing. The yarn’s wettability, the sizing adhesion strength of cotton yarn (SAS) as well as the influence of moisture regain (MR) on them under APP treatment has been studied in this paper. The EFST and its effect on desizing, scouring, bleaching and dyeing properties of knitted cotton fabric were studied as well.Firstly, how He/O2APP pretreatment influences the wettability of raw cotton fiber was studied. He/O2APP pretreatment can dramatically improve the hydrophilicity of cotton fiber by physical bombardment and chemical etching of its hydrophobic surface. And therefore, chemical reactions triggered by radicals introduce large quantities of functional groups including C-OH, COOH and C=O to the fiber surface, which makes the surface free energy fundamentally promoted leading to a drop of Water Contact Angle (WCA) from140°to0°and Water Adsorption Time (WAT) from a few hours to only0.8sec or much less. The surface roughness and wettability of the fiber vary with APP treatment conditions including treatment duration, the O2flux and Jet to the Substrate Distance (JTSD). The surface roughness grows increasingly with the decrease of JTSD from2to0.5mm. WAT of the fiber goes down with the rise of treatment duration and O2flux, while it goes up with the increase of JTSD. There is no apparent aging effect for the wettability of cotton fiber after APP treatment because the cuticle layer of the fiber has been severely spoiled due to plasma etching, oxidation and introduction of functional groups.Secondly, the influence of He/O2APP pretreatment on SAS between cotton yarn and PM-Starch and the breaking strength of the sized yarn was investigated in this study. Results show that the surface roughness and wettability play important roles on SAS and breaking strength of sized cotton yarn, namely, they rise with the raising of surface roughness and wettability. One of the probable reasons is the "mechanical interlocking effect" induced by roughness modification which increases the cohesion force of size to fiber and van der waals’ force between them. The other is that the introduction of functional groups such as C-OH、C=O and O-C=O to the fiber surface not only facilitate the permeating of the size into the yarn but also form some intermolecular hydrogen bonds between the fiber and the size. Both of them contribute to the improvement of SAS between the fiber and the size due to increased contact area and hydrogen bond forces between the fiber and the size. The surface roughness increases first and then decreases with the prolongation of treatment duration and rise of O2flux, while improves as JTSD goes down. The wettability of the fiber rises increasingly with the rise of treatment time. SAS and breaking strength of the sized yarn increase first and then decrease with the prolongation of treatment duration and rise of O2flux, and improve with the decrease of JTSD showing the same regularity with the change of surface roughness. With the optimized APP treatment conditions, SAS and breaking strength of the sized yarn could be greatly improved by59%and36%, respectively. In conclusion, He/O2APP pretreatment of the yarn can effectively roughen fiber surface and improve the wettability, size permeability, SAS and breaking strength of the sized yarn.Emphasis has also been laid on the influence of MR of cotton fiber on its wettability and sizing adhesion in this paper. Results demonstrated that the etching effect of APP on fiber surface is better when MR is lower, such as0.5%, and a large number of nearly round-shaped particles with diameters of around0.5to1μm appeared on the fiber surface after the plasma treatment. A moderate etching effect was found on the fiber surface of Sample with a higher MR of9.3%. It can be concluded that cotton fibers with lower MRs can be more efficiently etched than those with higher MRs. X-ray photoelectron spectroscopy (XPS) result showed that more functional groups including C-OH、O-C-O/C=O and O-C=O have been introduced to the fiber surface resulting in better wettability, size permeability and SAS of the yarn, and a more uniform size permeation into the yarn from yam surface was obtained at the same time. When MR is higher, such as9.3%and26.4%, a lot of water will exist on the fiber surface and consume large quantities of plasma energy, which weakens the APP treatment effect leading to poor wettability, size permeability and SAS of the yarn. Besides, the size permeation prefers to the APP treated side of the yarn showing a poor uniformity.On the basis of above research, the EFST has been proposed and put into practice. APP pretreatment of the yarn was conducted first and then the green size with PM-Starch and glycerol ingredients was used to size the yam. Results show that EFST can impart the yarn better sizing properties, such as improved size-pick-up, breaking strength, breaking elongation, abrasion resistance time and more effective reduction of yarn hairs, compared with TST. In comparison with typical TST using the sizing recipe with30%PVA1799and70%PM-Starch, the optimized EFST can impart the yarn an increase of19.4%,5.3%,3.4%and169.2%for the size-pick-up, breaking strength, breaking elongation and the abrasion resistance time, respectively, and a reduction of59.3%for the yarn hairiness index value at level1. The sizing properties can be obviously improved by the atmospheric pressure plasma treatment which can roughen the fiber surface, etch away the hydrophobic cuticle layer and introduce polar groups. The glycerol in the green sizing recipes can effectively reduce the yarn hairiness and increase size-pick-up and abrasion resistance. The eco-friendly sizing technology has no observable negative influence on desizing of cotton fabrics. Furthermore, a better water diffusion in the fabric can be achieved because of the improved hydrophilicity by the plasma treatment.In the end, the influence of APP treatment before sizing on pretreatment and dyeing properties of knitted cotton fabric has been ascertained through green and traditional pretreatment technologies. INVAZYME(?) ADC enzyme desizing, KDN301enzyme scouring and H2O2bleaching were employed in the green pretreatment technology, while NaOH desizing, scouring agent204for scouring, H2O2bleaching were adopted in the traditional pretreatment technology. Results illustrate that Size, pectins, cotton waxes and other natural contaminations can be more efficiently removed from APP pretreated fabrics than not APP treated ones, and consequently higher weight loss, wettability, whiteness, dying rate, final dye up-take and K/S value will be obtained. APP pretreated fabrics have better desizing, scouring, bleaching and dyeing performances than not APP treated ones, and dyeing properties such as color levelness and dry rubbing fastness of dyed fabric are not apparently affected by APP. The color difference shows almost the same regularity with the changing of K/S values and relative unlevelness index (RUI) values are between0.2and0.49showing good levelling property, which means APP treatment has no apparent effect on dyeing properties. The possible reasons for APP pretreated fabrics getting better pretreatment and dyeing performances are as follows:one is the removal of hydrophobic cuticle layer, the other is the increase of functional groups by APP oxidation. Both contribute to the improvement of hydrophilicity of sized fabric leading to quick removal of size, residual cotton waxes and pectins under the action of pretreatment reagents, which improves desizing, scouring and bleaching effect.APP pretreated fabrics can obtain almost the same pretreatment and dyeing performances by using the traditional technology with scouring process excluded. When the green pretreatment technology with the use of INVAZYME(?) ADC starch enzyme and scouring enzyme is applied to the APP pretreated fabrics, almost the same pretreatment and dyeing performances with that of the traditional technology can be attained. It can be concluded that both green and traditional pretreatment technology can provide the sized fabric with a good pretreatment effect and APP pretreatment can substantially improve pretreatment effects, dyeing performances and dyeing properties. With the application of APP treatment and optimized pretreatment technology, the scouring process can be omitted to save energy and reagents, not affecting the pretreatment effects, dyeing performances and dyeing properties.