Plasma treatment of wool

The effects of a plasma treatment on wool such as anti-felting effect, degreasing, improved dyestuff absorption and increase in wetting properties have been documented in numerous publications [42-46]. Other changes in wool properties are summerised below  

Plasma treatment of wool followed by polymer application has also been studied [36]. Almost all polymers used currently on pre-chlorinated wool cannot be used on plasma-treated top. Silicone resins applied to plasma-treated wool increase the shrinkage over that for untreated wool. However, the combined plasma/ PMS/Hercosett treatment encompassing the top treatment gives excellent shrink resistance [53]. The polymer after-treatment reduces both relaxation and felting shrinkage almost independently of plasma treatment time. 

There is more even and quicker penetration of dyestuffs and chemicals on plasma- 

Plasma treatment increases the hydrophillic groups in the wool fibre and the cystine present in the surface layer is converted to cysteic acid [55, 56]. The 

Woollen sliver and yam have been treated in low temperature plasma in a vacuum chamber for times from 20 to 30 min [61], There is a significant increase in the strength which lead to better stability of the material during subsequent processing. Fabrics made from treated wool do not felt and also the shrinkage is reduced e.g. from 37% to 3-5%. 

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W. Rakowski, Plasma Treatment of Wool, PhD. dissertation, PoUsh Textile Institute, Lodz, 1991 idem, Pr. Inst. Wlok. 36—37, 184—201 (1987) K. M. Byrne, Finishing of Wool using Plasma Technology, IWS Technical Information Bulletin CPB 109, International Wool Secretariat, Tikley, U.K., (1991). 

The oxidative plasma treatment of wool, at low temperature and pressure, modifies to a large extent the cuti-... 

The field of industrial plasma engineering has grown in recent years. The uses are motivated by plasma s ability to accomplish industrially relevent results more efficiently and cheaply than competing processes. The research program concerning plasma treatment of textile materials was launched at the Polish Textile Institute in 1973 to improve the soil release properties of double jersey fabrics from textunsed polyester yams. The first experiments with wool date back to 1980 to replace the chlorination in fabric preparation for printing. Tliree machines for continuous plasma treatment of wool top have been developed as follows ... 

Figure 14-6. Apparatus for low pressure plasma treatment of wool [9].

The most recent machine for continuous plasma treatment of wool top developed at the Textile Institute in Lodz consists of (Fig. 14-10) a vacuum generation... 

Figure 14-10. Prototype machine for continuous plasma treatment of wool top [36].

Rakowski, W., 1997. Plasma treatment of wool today, part I Fibre properties, spinning and shrinkproofing. J. Soc. Dyers Colour. 113, 250-255. 

Thomas, H., Hocker, H., 1995. Plasma treatment of wool—special regard to the dyeing properties. In Proceedings of the 9th International Wool Textile Research Conference IV, pp. 351-358. 

A GD generator was used by Kan (2001) to study the oxygen plasma treatment of wool fibres of differing diameter. The power, pressure and time of treatment were 80 W, 10 Pa and 5 min, respectively. After the treatment, it... 

Plasma treatment of wool fibre (a) sample 1 untreated and (b) sample 2 argon plasma treated for 7 min. Source Courtesy of Masukuni and Norihiro, 2006.)... 

W. Rakowski, Plasma, Treatment of Wool, Biella Wool Textile Award (1992). 

An average size of continuous treatment plant for antifelt treatment of wool releases approximately 140 g/hour AOX. As an optimization of the process is possible only within certain limits, alternative processes for an antifelt treatment have to be chosen to substitute the chlorination process, for example, enzymatic processes, oxidative processes (KMn04, persulfate), or corona or plasma treatment. In many cases combinations with resin treatments are proposed. 

Physical, as well as chemical, pretreatment processes have been combined with the enzyme treatment of wool. A low-temperature plasma is applied to the fibres prior to treatment with polymeric shrinkproofing agent [122]. Combined protease and heat treatment with a saturated steam [123] and the use of high frequency radiation on enzyme treated materials are reported. 

Plasma Treatment of Textile Fibers Treatment of Wool... 

Plasma technologies have been investigated for quite some time with the aim of improving wettability and thus the adhesion of coatings. However, a much broader range of applications is feasible with plasma (Buyle, 2009) these apphcations include the improvement of printability and dyeability (Rahman and Nur, 2014), and antishrink treatment of wool, the scouring of wool (Rahman and Nur, 2014), sterilization, and the desizing of cotton. 

Research on plasma treatment on wool fiber as a pretreatment was started in 1956 (Rakowski, 1997). Plasma-treated wool fiber displays improved antifelting property, dye-ability, and surface wettability. The plasma treatment can alter the surface morphology and chemical composition, but the effect depends greatly on the plasma gas used, system pressure, discharge power, and also treatment lime. Plasma treatment on wool fiber is a dry process in which fiber alteralion is concentrated on the fiber surface and less damage is caused to the bulk fiber. This is a major advantage of plasma treatment on wool fiber. 

Analyses of comparative costs of conventional chlorination and plasma processing of wool (Lewis, 1977 Rakowski, 1989) have demonstrated that energy costs for chlorination are 7 kWh/kg wool whereas for low-pressure plasma treatment it is only 0.3-0.6 kWh/kg wool. The application of low-pressure plasma for modification of 120t/year of wool can save 27,000m of water, 441 of sodium hypochlorite, 161 of sodium bisulfite, 111 of bisulfuric acid, and 685 MWh of electrical energy (Rakowski, 1989 Tsai et al., 1997). 

To quantify the effectiveness of atmospheric pressure plasma on textile dyeing, dyne bath coloration is evaluated to obtain exhaustion curves which identify the kinetic behavior of dyes during dyeing processes as a function of process operating parameters. There are a number of such documenting curves for plasma treatments to wool, for example as presented by the research of Holme [21]. 

Mention has already been made of the effectiveness of corona or plasma treatment in increasing the influence of subsequent or concurrent polymer treatment. As examples of polymers used in this way, mention can be made of reactive cationic polysiloxane [294] and polymerisation on the fibre of tetrafluoroethylene or hexafluoropropylene [299]. Water repellency was also improved by the fluorinated polymers. Tetrafluoroethylene gave superior shrink resistance this polymer covered the scale edges of the wool, whereas this did not occur with poly(hexafluoropropylene). 

Oxidation of the surface of wool fibers is known to reduce felting shrinkage as well as improve other properties of wool fibers (37) Oxidation may be proformed or effected in a number of ways including gas phase plasma treatment (38). 

A useful side effect of the radiation and especially the plasma treatments is the cleaning of the fibre surface. Fibre lubricants, sizing agents, soil and other residuals are burned off This provides, combined with the creation of reactive radicals on the fibre surface, better wetting properties and a higher adhesion of coatings and laminations. Anti-felting finishes for wool are also achievable with plasma treatments. 

Figure 14-13. Fibre cross-section of the wool following plasma treatment (enlargement 30 OOOX).

Plasma treated wool may exhibit more or less firm or harsh handle because of surface roughening. This property is very important for hand-knitting yams or yams for underwear fabrics. Softeners generally deteriorate the shrink resistance imparted by plasma treatment or plasma plus polymer after-treatment quite heavily [36]. The enzyme treatment is capable of improving the handle of plasma treated wool as well as plasma treated and polymer after-treated hand-knitting yams without imparting their shrink resistance [62]. 

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