OZONE BLEACHING OF CELLULOSIC FIBRES. EXPERIENCE WITH TOWELS

Abstract

The bleaching method with hydrogen peroxide is expensive due to the high consumption of products, water and energy, while with ozone it is very advantageous. The objective of this study was to evaluate the use of ozone in the bleaching of towel samples, made of terry fiber fabric, 100 % cotton. Raw and pretreated samples (desizing-scouring) were used, at pH 5, with water content of 30 %. The experiments were carried out at room temperature, with exposure times: 5 to 30 min; gas flows: 10 and 20 L h-1; concentrations of ozone in the gas: 40 to 80 mg L-1. The degree of whiteness (GB) and degree of polymerization (GP) were measured, comparing them with bleaching with hydrogen peroxide for dyeing. The pretreatment of the fabric indicated a favorable effect, but the increase in gas flow did not. Ozone bleaching was improved by increasing the time and the concentration of ozone in the gas. However, short times are recommended to avoid damage to the fabric. The efficiency of the process improved by increasing the humidity of the reactor inlet gas. Under the experimental conditions evaluated, no effect on hydrophilicity was observed. The GB of the pretreated and ozonated samples up to 10 min, applying dry gas, was similar to the conventional process for dyeing pastel tones, but with some degradation. While, applying the wet gas, the ozonized raw fabric (10 min) reached a GB to dye medium to dark tones without affecting the required GP. Bleaching of raw fabrics was.