The influence of woven fabric structures on the continuous dyeing of Lyocell fabrics with reactive dyes
Tencel, a regenerated cellulosic fibre is synthesised by an environmental friendly process. It can be dyed by the same dye types as recommended for other cellulosic fibres. The behaviour of reactive dyes on Tencel woven fabric varies with the type and the density of woven fabric. The highly crystalline Tencel fibre is less easy to dye uniformly by the continuous dyeing methods because of the short time of contact between the dye and fibre. The purpose of this work is to investigate the influences of weave structure on dyeing of standard Tencel fabric using reactive dyes applied by continuous dyeing methods. Programmes are developed using Matlab software to measure the fabric porosity and uniformity of fibre coloration (UFC) in the yarns of the woven fabric. UFC is also measured subjectively. Firstly, fabrics of four different weave structures (plain, 2/1, 3/1, 5/1 twill fabric) are studied. The visual depth and UFC standard deviation values is highest for the 2/1 twill fabric, gradually reducing towards the 5/1 twill fabric. Secondly, nine plain weave fabrics of different fabric densities are dyed using different padding procedures - a liquor temperature of 40⁰C with a 1 min dwell time and with a 5 min dwell time, and liquor at room temperature without any dwell time. The padded fabrics are then fixed by pad-steam, pad-dry-steam, pad-batch and pad-dry-thermosol continuous dyeing processes. To improve colour depth the plain weave fabrics are given a caustic pre-treatment and their dyeing characteristics are compared with untreated fabrics. The causticised fabrics are dyed using the same padding procedures, for comparison. The optimum dyeing procedure is found to be padding with a dwell time of 1 min in liquor at 40⁰C after caustic pre-treatment to achieve the highest visual depth, dye uptake, and uniformity of fibre coloration. The fibrillation tendency of the Tencel plain weave fabrics is also reduced using this procedure. Numerical relationships are established to enable the prediction of dyeing properties such as colour strength, UFC for fabrics of different weave structures, applied by the various continuous dyeing processes.