Fung and hardcastle 2001 nahed and el shishtawy 2010

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; Fung and Hardcastle 2001 ; Nahed and El-Shishtawy 2010 ). Also, ultrasound has a signi fi cant effect on the reduction of particle size of the disperse dye (Saligram et al. 1993 ; Ahmed and Loman 1996 ). On the other hand, the fi gure shows that thermo fi xation has a negative in fl uence on the K / S values of the prints. These results show that thermo fi xation in the absence of a carrier fi xes only 50 70 % dye, while in the steaming process steam condenses on the cold fabric, raising its temperature to 100 °C and swelling the thickener fi lm. The condensed water is largely evaporated again during the exposure to steam, but the thickener is not bound into the fabric as in dry fi xation, subsequently handle of the fabric becomes softer. The absorption capacity (build-up) increases in proportion to the steam pressure and corresponding temperature. The depth of colour achieved at high pressures is not possible by using longer durations at lower pressures. The steaming is the best technique for dye fi xation and has thus been selected to be applied. 8.5 pH of Printing Paste As disperse dyes are sensitive to alkalis, polyester is normally dyed under acidic condition (Ahmed and Loman 1996 ). Sodium dihydrogen phosphate is recom- mended because, unlike some organic acids, it has no corrosive effect on nickel screens and is compatible with natural thickeners. Figure 19 illustrates the effect of printing paste pH using the nanotreated dye with ultrasound exposure for 8 h on the K / S of polyester fabrics. The printing process is carried out using two stock dye solutions having 1 and 3 % disperse dye concentrations printed on polyester fabric and followed by steaming at 130 °C for 30 min. The best values of colour strength are achieved in the case of both stock dye solutions at pH 6, which implies that the use of a nanoparticle disperse dye helps in dye penetration into the fi bres more easily at more neutral pH value. Fig. 19 In fl uence of pH of printing paste on the colour strength of polyester prints (Osman and Khairy 2013 ) Advances in Nanotextile Finishes An Approach Towards Sustainability 27
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8.6 Steaming Conditions The fi xation is incomplete even though using saturated steam at 100 °C, if carrier is not used. In addition, the colour depth achieved at high pressures is not possible with longer durations at lower pressures (Lee and Kim 2001 ). Fibres of the most common polyester are quite crystalline, very hydrophobic, and have no ionic groups. Hot water does not swell them, and large dye molecules (that have lower diffusion coef fi cients) do not easily penetrate into the fi bre interior. For the samples used in this study, the effect of steaming temperature and time on the K / S of polyester fabrics printed with disperse dye nanoparticles of the two different concentrations is investigated and the data is plotted in Fig. 20 .
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  • Fall '19
  • N. Gokarneshan

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