World Journal of Textile Engineering and Technology, 2019, 5, 97-104 97 E-ISSN: 2415-5489/19 © 2019 Scientific Array Kinetics of Dyeing in Continuous Circulation with Direct Dyes: Tencel Case M.J. Lis 1,* , Fabricio Maesta Bezerra 2 , Xu Meng 3 , Hongfei Qian 3 and A.P.S. Immich 4 1 INTEXTER-UPC, Colon, 15. 08222. Terrassa, Barcelona, Spain 2 Universidade Tecnológica de Paraná, Brazil 3 Shaoxing University, China 4 Universidade Federal de Santa Catarina, Engineering, Brazil Abstract: Due to the special characteristics of Tencel fibres, it is important to gather new data and information in order to improve our knowledge of their performance during dyeing. Kinetic equations are used to describe the behaviour of the heterogeneous dye-fibre system under isothermal conditions in order to determine the evolution of dye exhaustion versus dyeing time. Direct dyes are particularly suitable because they are physically absorbed and because they exhibit outstanding substantivity to cellulose. In addition, some of these dyes have a linear structure which ensures good correlation with structural differences in the fibres. The aim of this study is to quantify the kinetic behaviour of the Tencel-C.I. Direct Blue 1 system (one of the most common dyes in dyeing studies) by using three bi-parametric empirical dyeing-rate equations and a continuous-flow dyeing cell to obtain experimental data at six different temperatures: 30, 40, 50, 60, 70 and 80ºC. In order to check the level of adjustment of the equations we record the at three exhaustion levels: 50%, 80%, and final exhaustion. Keywords: Tencel, kinetics, direct dyes, activation energy. 1. INTRODUCTION Cellulosic fiber, mainly cotton, is the main raw material for the textile industry. However, the difficulty of planting led to a reduction in cotton production, which resulted in increased demand for wood-based cellulose fibers. These fibers are high performance and find applications in industrial textiles, home textiles, clothing, etc. [1]. The size of cellulosic fiber market exceeded USD 17.5 billion in 2015 and an increase of more than 9.0% is estimated by the CAGR (Compound Annual Growth Rate). The global apparel market has been estimated at more than USD 1 trillion in 2015 and demand is expected to increase in the period of 2016- 2024 [2]. Fibers of cellulosic origin can be divided into three main groups, such as, natural, artificial (man-made) and nanofibers. The most widely used example of man- made cellulosic fiber in the industry is viscose, but due to the non-ecological nature of its production, the valorization of Tencel fibers is increasing [3]. Tencel® fibers can be obtained by dry jetwet spinning the Lyocell®/NMMO/water by coagulating (in water or NMMO aqueous solution), washing, drying and post-treatment. This process is considered to be environmentally friendly because the solvent NMNO *Address correspondence to this author at the INTEXTER-UPC, Colon, 15. 08222. Terrassa, Barcelona, Spain; Tel: +34937398277; Fax: +34937398272; E-mail: manuel-jose.lis@upc.edu (N-Methylomorpholine-N-Oxide) is recovered, purified and recycled [4]. Another advantage of Tencel® spinning process is the possibility of modifying the cellulosic fibers by introducing the desired modifier into the spinning solution. Thus, fibers with superior properties such as antibacterial, luminescent, magnetic, thermochromic can be produced [3,5]. Tencel® also has high potential as technical textiles, in addition to traditional textiles, such as functional coating materials, technical fabrics, fibrous powder for plastics as a reinforcement, a special textile fiber for seat covers, etc. [6]. One of the resources to increase the value added and to extend an application of Lyocell® fibers is coloring [7]. The colorants used for Lyocell® dyeing are the same as those used for cotton dyeing [8]. However, Babar and coworkers report that Lyocell® fibers subjected to reactive dyes show better color yield when compared to cotton fibers with the same amount of colorant studied [8,9]. Environmental issues related to waste disposal, as well as high consumption of water and energy have long been taken very seriously by textile industries, especially those with dyeing stages. Therefore, a higher color intensity for the same amount of dye for lyocell fibers may lead to a more economical and ecological dyeing process [8,10]. Post-dyeing lyocell fibers with the reactive dyes, direct dyes or vat dyes is still the dominant dyeing method [7].