© Color. Technol., 121 (2005) 41 Web ref: 20050109 Coloration Technology Society of Dyers and Colourists Effect of metal ion binding of chitosan on the printability of pretreated wool fabric A Abou-Okeil* and O A Hakeim Textile Research Division, National Research Center, Dokki, Cairo, Egypt Email: aokeil2004@yahoo.com Received: 4 August 2004; Accepted: 2 December 2004 In this study, chitosan was used as a pretreatment agent for wool fabric to increase the metal binding during the mordanting process with copper sulphate. The copper( II ) binding was measured by measuring volumetrically the concentration of metal ions that remained in the solution after mordanting. The pretreated mordanted wool samples were then subjected to printing with a natural dye, 2-hydroxy- 1,4-naphthoquinone (lawsone). The results indicate that color strength and wash fastness of the pretreated printed wool samples were enhanced compared to the untreated samples. This enhancement depends mainly on the molecular weight and concentration of chitosan. Introduction Chitin, the second-most abundant biopolymer in nature next to cellulose, is a high molecular weight linear polymer of 2-acetamido-2-deoxy– D-glucopyranose units linked together by 1,4-glucosidic bonds [1,2]. Chitin is obtained in large quantities from crustacean shells, which are waste products of seafood processing industries. Chitosan is the N-deacetylated product of chitin and is obtained by means of treating chitin in hot concentrated alkaline solution. Chitosan has many important characteristics, such as hydrophilicity, biocompatibility, biodegradability and antibacterial properties. It is also used as a sorbent for heavy metal ions because the amino and/or hydroxy groups on chitosan chains act as coordination sites [3–6]. It is reported that chitosan has the highest chelating ability in comparison to other natural polymers obtained from seafood wastes [3]. In comparison to chitin, the ability of chitosan to adsorb metals is superior due to its higher content of amino functional groups [3,7]. The sorption of heavy metals including Cu 2+ , Ni 2+ ,Zn 2+ , Cd 2+ , Hs 2+ , Pb 2+ , Cr 3+ , Va 2+ and Mo 2+ by raw and chemically-modified chitosan has been extensively studied [3,4,8–15]. Wool, as a protein fibre, has polar and ionisable groups on the side chain of amino acid residues which are able to bind charged species such as metal ions. The rate and the extent of uptake have been reported to depend on various factors such as the kind of metal and its valence state, the solution concentration, pH, time, temperature, etc. [16]. The treatment of wool with metals may induce useful changes in fibre properties [16]. Zirconium and titanium salts can be used to impart flame resistance to wool. Mercury salts confer improved wrinkle recovery, abrasion and shrinkage resistance on wool, although their use has never been industrially exploited because of toxicity and low durability. On the contrary, the reaction of chromium salts with wool has been successfully used for chrome dyeing [17]. Mordant dyeing is a special process used in the dyeing of wool and silk where the fibre is first treated with a metal and the metal-exchanged fibre (mordanted fibre) is contacted with a solution containing mordant dye to form a metal–dye complex on the surface of the fabric which is stable. Depending on the metal and the dye used, different colours are obtained. Most natural dyes are applied by mordanting with metal salts. Wool is highly reactive toward natural dyes and mordants, when it is treated with metallic salts it hydrolyses them into an acidic and a basic component. The basic component is adsorbed at carboxylic acid sites and the acid component is removed in the course of washing. The metal uptake of wool fibres can be enhanced by chemical modification of the fibres using chelating agents which are able to coordinate metal ions [18,19], such as tannic acid and ethylenediaminetetraacetic acid (EDTA). The aim of the present work was to investigate the effect of pretreating wool with different molecular weights of chitosan on the printability of wool with a natural dye, 2- hydroxy-1,4-naphthoquinone (lawsone). In this study, the chitosan acted as a chelating agent able to coordinate the metal ions of the mordant, copper sulphate. The impact of this pretreatment on colour strength, fastness properties, yellowness and the residual metal ions in the mordanting bath, for ecological consideration, was also studied. Experimental Materials Wool fabric, supplied by Vestia Co., was scoured according to the method reported by Nation et al. [20]. Chitosan (deacetylation level, 85%) and lawsone (2-hydroxy-1,4- naphthoquinone; 1) were supplied by Sigma and were used without further purification. Carboxymethylcellulose (CMC) was supplied by Hoechst under the commercial name Tylose C600. Acetic acid, sodium nitrite, sodium