Investigation into the dyeing of pre‐mordanted & cationised woven cotton fabric with cochineal

Abstract

Dyeing cotton with natural dyes typically requires the pre‐application of a mordant, which enables better dye exhaustion from solution and ‘fixes’ the colorant in the fibre. The most common application system for cellulosic fibres is a combination of plant‐derived tannins and aluminium salts, such as aluminium sulphate. However, a recognised commercial deficiency of this mordanting process is the relatively poor exhaustion of the aluminium from the mordanting bath into the fibre leading to a discharge of metal salts into the environment, and in addition, the subsequent exhaustion of the dye into the metal mordanted cotton is similarly incomplete. This study reports for the first time on an improved commercial and craft process based on the pre‐application of the novel ECOFAST™ Pure cationic fixing agent to cotton to impart better natural colorant dyeing characteristics and minimise environmental impact. The pre‐modification of the cotton with ECOFAST™ Pure, at 5%–10% on weight of fabric, increased the cochineal dye exhaustion up to ~99%, a significant increase from the ~62% dye exhaustion observed with the tannic acid/alum pre‐mordanted cotton fabric. Lower temperature dyeing of the ECOFAST™ Pure modified cotton at 60°C also resulted in improved dye exhaustion and colour strength relative to the traditional tannic acid/alum mordanted cotton. The incorporation of a levelling agent, Matexil DA‐AC, into the dyebath formulation improved the dye levelness, decreased the dye exhaustion, but also unexpectedly increased the colour strength of the dyed fabrics at the 2% on weight of fabric (o.w.f.) levelling agent application level.