Constructing of Dyes Suitable for Eco-friendly Dyeing Wool Fibers in Supercritical Carbon Dioxide

Abstract

Compared with traditional water dyeing, supercritical carbon dioxide (scCO2) dyeing is more environmentally benign. scCO2 is widely used as a green solvent in dyeing synthetic fibers. However, studies involving dyeing natural fibers in scCO2 are scarce. The commonly used methods result in corrosion of the dyeing equipment. Thus, the development of new special dyes suitable for scCO2 dyeing is necessary; in addition, insight into the dyeing mechanism is important in promoting the design and synthesis of dyes for wool fibers in scCO2. On the basis of our previous work, a possible dyeing mechanism in which the dyes exhibit hydrophobic interaction with keratins is proposed. The NN bond twisting in azo dyes promotes the dyes embedding into the spaces of the alpha helices in proteins. According to the proposed mechanism, two new azo disperse dyes (azo thiazole-N­(CH3)2 and azo thiazole-OCH3 ) were synthesized; these dyes enable the dyeing of wool fibers in scCO2. Meanwhile, the introduction of a succinimidyl ester group results in the fixation rate of the new reactive disperse dyes azo thiazole-NHS and azo-NHS reaching 100%. The byproduct of azo thiazole-NHS and azo-NHS reacting with the amino group of wool keratin is not corrosive to the dyeing equipment, thus enabling an eco-friendly dyeing process for wool fibers. Our strategy of introducing a succinimidyl ester reactive group will promote the development of new functional disperse dyes suitable for dyeing wool fibers in scCO2.

Recent advances in supercritical fluid dyeing

“…The choice of modifying disperse dyes with appropriate reactive groups able to bind with the textiles functionalities seems to be the winning strategy, which has allowed F values of up to 98%-100% to be obtained. 65,67,70 However, the intensity of coloration is still much lower with respect to PET and other synthetic polymers. Future investigations could probably be directed at deepening the chemistry of coloration in the supercritical environment.…”

“…Coloration efficiency is generally quantified by means of the K/S and the fixation efficiency (F). 57,[63][64][65][66][67][68][69][70] Two K/S values are generally evaluated: the first one on the "just-dyed" samples, the second after treating the textiles with an appropriate high temperature solvent extraction to remove the unfixed dye. The data reported in Table 4 refer to the after-extraction K/S.…”

“…It can easily react both with the amino and hydroxyl groups of proteinaceous and cellulosic fibres (Figure 2), even though the production of hydrochloric acid as a by-product is considered a disadvantage due to corrosive concerns. 70 The data in Table 4 show that different considerations affect the azo-structured and anthraquinone-structured chlorotriazine dyes. As far as the azo-structured chlorotriazine dyes are concerned, the best results were obtained on cotton by Gao et al, 63 who succeeded in dyeing this fibre without the use of any carrier or co-solvent: K/S values of up to 13 and fixation of up to 92% with good fastness performance were obtained.…”

“…70 In a preliminary work, SFD of wool with conventional disperse dyes was investigated, and showed that CI Disperse Red 153 and CI Disperse Blue 148 resulted in the highest K/S values (up to 2) and 80% F. 74 Subsequently, the new disperse dyes were synthesised 70 ; they had structures similar to the above-cited conventional disperse dyes but were provided with specific functional groups: thiazole-OH, thiazole-N(CH 3 ) 2 , tiazole-OCH 2 , succinimidyl ester (NHS) and thiazole-NHS. Among all the investigated groups, the NHS and the thiazole-NHS ones enabled a 100% F to be obtained, 70 even though the K/S values were approximately halved with respect to those obtained with CI Disperse Red 153 and CI Disperse Blue 148. 74 The authors also proposed a possible mechanism of reaction between the NHS reactive group and wool keratin, which is illustrated in Figure 5.…”

“…According to Table 4, the chlorotriazine reactive group has been the most investigated in recent years. It can easily react both with the amino and hydroxyl groups of proteinaceous and cellulosic fibres (Figure 2), even though the production of hydrochloric acid as a by‐product is considered a disadvantage due to corrosive concerns 70 . The data in Table 4 show that different considerations affect the azo‐structured and anthraquinone‐structured chlorotriazine dyes.…”