© Color. Technol., 121 (2005) 325 Web ref: 20050607 Coloration Technology Society of Dyers and Colourists Dyeing of cationised cotton using nanoscale pigment dispersions Kuanjun Fang,* Chaoxia Wang, Xia Zhang and Yi Xu College of Textiles and Clothing, Southern Yangtze University, 1800 Lihu Road, Wuxi 214122, China Email: fangkuanjun@vip.sina.com Received: 19 May 2005; Accepted: 20 September 2005 Cotton modified with a cationic reagent has been dyed by an exhaustion process using nanoscale pigment dispersions. Pigment uptake, colour yield and fastness properties on cotton were measured. Uptake of pigment was found to be closely related to the concentration of cationic reagent, pH of the pretreatment bath, pretreatment temperature and time of cationisation. These factors also influenced the fastness properties of the fabric. Nanoscale pigment dispersions gave a much higher colour yield than conventional pigment dispersions on cotton. Fastness properties were acceptable for wash-down effects. It is clear that exhaust dyeing using nanoscale pigment dispersions offers a number of advantages in terms of pigment requirement, improved handle and appearance, and also in environmental protection. Introduction The dyeing of cotton fabrics with anionic dyes such as direct and reactive dyes requires the presence of large quantities of electrolyte to increase dye uptake, resulting in serious environmental problems when disposing of the dyebath effluent. One method of avoiding this problem is to cationise the cotton fibre by chemical means. This has the effect of increasing the substantivity of anionic dyes such as the types mentioned, due to the presence of the positive charges imparted to the fibre [1–5]. Pigments have been used for a long time for printing and pad-dyeing of textiles. Since pigments are insoluble they have no substantivity for cotton, and a binder is required to fix the pigment particles on the fibre surface in order to give colour fastness. It has however been reported that it is possible to dye cotton with pigments using an exhaust process, provided the fibre has been pretreated with a cationic auxiliary to provide the necessary affinity [6,7]. This technique has been widely used for the dyeing of T-shirts, sportswear, jackets and trousers on fibres such as cotton, rayon, acrylic, polyester, nylon and protein fibres. In general, pigment dyeing can achieve Grade 3 for dry rub fastness at medium depths of colour [8]. On the other hand, conventional pigment dyeing has drawbacks in terms of wet rub fastness and coarse handle. These problems can be alleviated by pretreating the fabric with cationic reagents and by increasing the dispersion of the pigment [9,10]. By modifying the pigment surface, the average diameter of the pigment particles can be reduced to 100–200 nm, giving the pigment dispersion greater stability and colour strength approaching that of dyestuffs [11]. The present study was conducted to explore the exhaust dyeing properties on cationised cotton of a nanoscale pigment dispersion prepared using a microfluidiser. The effect of pretreatment variables, such as the amount of cationic reagent, pH, treatment temperature and time, on colour yield and fastness properties was investigated. In addition, the difference in the performance of a nanoscale and a conventionally dispersed pigment has been studied. Experimental Materials The fabric was plain knitted 100% cotton, scoured and bleached (32 tex and 120 g/m 2 ). The cationic reagent KZ-76K, a solution of a polymeric quaternary ammonium salt containing reactive groups, was obtained from Daxiang Chemical Co. Ltd, Shanghai, China. This company also supplied the binder. Other chemicals, such as sodium hydroxide and sodium carbonate, were laboratory grade. Preparation of nanoscale pigment dispersion A conventional pigment, CI Pigment Red 22 (1), was used in this study. This was stirred with an aqueous solution of an anionic polymeric dispersant XG-1 (3% on weight of pigment) on an IKA high-speed mixer for 30 min at 10 000 rpm. The resulting conventional pigment dispersion had an average particle diameter of around 1500 nm. This dispersion was converted to a nanoscale dispersion on an M-110EHI microfluidiser (Microfluidics Int., USA), processing at a pressure of 22 000 Pa for 2.5 h, which resulted in an average particle diameter of 128 nm and the final pigment dispersion had 40% solid content [12]. N O 2 N H N CH 3 O N O H 1