Without the incorporation of a carrier in the

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without the incorporation of a carrier in the printing paste and only pH is adjusted at 6. Very good fastness properties are seen in the dye fi xation of the prints by steaming at 130 °C for 30 min, and no differences are seen from prints of untreated dye with ultrasound. The in fl uence of grinding on size of dye particle is shown in SEM measurement. 8.2 Related Aspects Disperse dyes are those which are water insoluble have af fi nity towards certain hydrophobic fi bres (Schindler and Hauser 2004 ). They conform to the non-ionic class of dyes, and are the generally used dyes in the textile industry for dyeing synthetic fi bres like polyester, acrylic, and acetate (Gao and Cranston 2008 ; Du et al. 2009 ). The water solubility of disperse dyes is very low and hence should be 24 N. Gokarneshan et al.
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milled to a very low particle size and dispersed in water using a surfactant (dis- persing agent) or a carrier must be added during textile colouration (Chattopadhyay and Patel 2009 ). The actual mechanism by which a carrier used in dyeing accel- erates textile colouration has been widely debated. Polyester fi bres absorb the carrier and swell. This swelling can impede liquor fl ow in packaging causing unlevelness. The overall effect leads to lowering of the polymer glass transition temperature ( T g ), thus promoting polymer chain movements and creating free volume. This speeds up diffusion of the dye into the fi bres. Alternatively, the carrier may form a liquid fi lm around the surface of the fi bre in which the dye is very soluble, thus increasing the rate of transfer into the fi bre (Harrocks and Anand 2000 ). Power ultrasound (US) can enhance a wide variety of chemical and physical processes, mainly due to the phenomenon known as cavitations in a liquid medium that is the growth and explosive collapse of microscopic bubbles. Sudden and explosive collapse of these bubbles can generate hot spots (Lachapelle and Maibach 2009 ), i.e. localized high temperature, high pressure, shock waves, and severe shear forces capable of breaking chemical bonds. Many efforts have been made explore this technique in the textile colouration as it is a major wet process, which con- sumes much energy and water and releases large ef fl uent to the environment. The phenomenon of cavitations lead to improvements in ultrasound-assisted colouration processes, and hence other mechanical and chemical effects are as follows: Dispersion (breaking up of aggregates with high relative molecular mass); Degassing (explosion of dissolved or entrapped air from fi bre capillaries); Diffusion (accelerating the rate of diffusion of dye inside the fi bre); Intense agitation of the liquid; Destruction of the diffusion layer at dye/ fi bre interfaces; Generation of free radicals; and Dilation of polymeric amorphous regions.
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  • Fall '19
  • N. Gokarneshan

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