Controlled eco-friendly shrink-resist finishing of wool using bromelain

Abstract

Shrink-resist finishing is imperative to introduce dimensional stability and characteristic handle for wider acceptance of woolen garments. Conventionally used oxidative anti-felting treatments using sodium hypochlorite, gaseous chlorine, dichloroisocyanuric acid etc. release chlorine leading to high concentration of absorbable organic halides in waste water; application of resin results in stiffer handle because of spot welding effect. In contrast, enzymatic processing using protease is a sustainable alternative to substitute eco-hazardous conventional processes though diffusion of protease deep inside the wool in alkaline pH is the major concern for substantial weight as well as tensile loss thus limiting its application on wool. Treatment with bromelain even at very mild alkaline pH around 7.5 in absence of salt results in considerable damage in wool structure with consequence of higher weight and tensile loss due to partial/complete removal of cuticles on the surface. In this work, bromelain, a type of proteolytic enzyme, was used along with salt in acidic pH for controlled superficial hydrolysis of wool. A two-step acidic bromelain treatment was opted first using Box–Behnken design keeping in view minimum area shrinkage succeeded by optimization of the treatment parameters to achieve least area-shrinkage, weight loss, strength loss along with improved subjective softness. Controlled adsorption of bromelain at the outer surface of wool in presence of salt at pH ∼6 was observed yielding desirable anti-felting behaviour with minimum weight and strength loss. In contrast to conventional chlorine based technologies, acidic bromelain may be used in presence of sodium chloride to yield machine washable wool possessing minimum loss in weight and tensile strength both at industrial level.