Cold Pad-Batch dyeing method for cotton fabric dyeing with reactive dyes using ultrasonic energy

Abstract

Reactive dyes are vastly used in dyeing and printing of cotton fibre. These dyes have a distinctive reactive nature due to active groups which form covalent bonds with –OH groups of cotton through substitution and/or addition mechanism. Among many methods used for dyeing cotton with reactive dyes, the Cold Pad Batch (CPB) method is relatively more environment friendly due to high dye fixation and non requirement of thermal energy. The dyed fabric production rate is low due to requirement of at least twelve hours batching time for dye fixation. The proposed CPB method for dyeing cotton involves ultrasonic energy resulting into a one third decrease in batching time. The dyeing of cotton fibre was carried out with CI reactive red 195 and CI reactive black 5 by conventional and ultrasonic (US) method. The study showed that the use of ultrasonic energy not only shortens the batching time but the alkalis concentrations can considerably be reduced. In this case, the colour strength (K/S) and dye fixation (%F) also enhances without any adverse effect on colour fastness of the dyed fabric. The appearance of dyed fibre surface using scanning electron microscope (SEM) showed relative straightening of fibre convolutions and significant swelling of the fibre upon ultrasonic application. The total colour difference values ΔE (CMC) for the proposed method, were found within close proximity to the conventionally dyed sample.

Introduction

Ultrasonic energy can clean or homogenize materials, accelerate both physical and chemical reactions [1], these qualities can be utilized for improvement of textile processing methods. Environmental concern has remained focused on textile processing methods for quite some time. The use of ultrasonic energy is widely studied in terms of improvement of washing fastness [2], [3]. The textile dyeing industry is always struggling to cope with high energy costs, rapid technological changes and the faster delivery time requirement. The effective management of ultrasonic energy can reduce energy cost and improve productivity [4]. Ultrasonic energy improves the productivity of dyes as well as the fastness properties [5], the individual and combined effects of ultrasonic cavitation and heat on dyeing cotton fabric with a direct dye are discussed [6]; dyeing wool fibre under ultrasonic energy is also studied [7].

In dyeing process, the object is to transport or diffuse dyes and chemicals into the fibre. Various novel processes, including ultrasound, are being introduced and studied as more environmentally-friendly alternatives [8], [9], [10], [11], [12]. Encouraging results have been reported for the use of ultrasound energy in dyeing processes which include direct dyeing of cotton fabric [13], here, the dyeing time, temperature of dyeing bath, the amount of dye required and the required concentration of electrolyte considerably reduces. The dyeing of polyester fiber [8] under ultrasonic energy results into increased dye uptake and enhanced dyeing rate. The dyeing of PA fabric with disperse and acid dyes studied for ultrasonic application at various temperatures showed accelerated dyeing rate and an overall increase in the depth of shade [9]. There is no influence attributed to ultrasound on dye uptake and dyeing rate on less crystalline fibres [14]. Dyeing PAC fibres [15] and dyeing of cationized cotton under ultrasonic energy for colour removal [16].

Cold Pad Batch (CPB) dyeing offers the most economical and convenient method of dyeing cotton with reactive dyes. The energy and water consumptions are at the lowest and salt addition is eliminated, thus rendering it more eco friendly [17] and the dye fixation is also high [18]. The CPB procedure is simple since the only step involved is the passage of fabric through the dye bath and squeezing through the dyeing padder with subsequent batching for twelve hours. The long batching time makes CPB procedure less attractive to many dyers seeking high production rates. This creates a serious need of reduced batching time. The proposed method involves the use of ultrasonic energy at room temperature during batching stage with aim to reduce the batching time and dyeing auxiliary concentrations. The reduced dyeing auxiliary concentration leads to minimize the waste effluent [17], [19]. The alternative dyeing methods to CPB like Pad-dry-cure, Pad-steam and Batchwise are expensive due to the requirement of thermal energy for dye fixation [20]. This work presents the CPB dyeing method of cotton fabric with reactive dyes by using ultrasonic energy and its comparison with the conventional method.