RAPID BLEACHING OF LINEN FABRICS

Loomstate (Grey) linen fabric tvas scoured in the presence of nonionic wetting agent at 90 degrees for 30 minutes using aqueous solutions of NaOH (16 g/L) or CaCO3 (40 g/L) or NaOH (16 g/L) plus Na2S (2 g/L) pl us Na2SO3 (2 g/L) or tap water. A material-to-liquor ratio of 1 : 30 w as employed. The scouring effect, expressed as percent loss in fabric weight, was offset by sodium carbonate. Scoured fabric brought about b y making use of the alkaline mixture was employed for bleaching. Bleac hing of grey anti scoured linen fabrics was carried out using a new ox idizing combination, viz. NaClO2/KMnO4, under different permanganate c oncentration, pH's and duration. Results obtained indicated that the b leaching effect - expressed as whiteness index and loss in fabric weig ht - of sodium chlorite is much greater in the case bf scoured than gr ey fabric. Presence of KMnO4 in the bleaching formulation not only imp roves the bleaching effect but also reduces the differences in whitene ss between the scoured and grey fabrics. A bleaching formulation consi sting of NaClO2 (5 g/L), KMnO4 (0.4 g/L), and nonionic wetting agent ( 1 g/L) is adequate for bleaching grey and scoured linen fabric, provid ed that bleaching is carried out at pH 6 and 90 degrees, for 90 minute s using a material-to-liquor ratio of 1 : 30. Comparable or even bette r results are obtained at pH 4 but pH 6 is preferred because evolution of chlorine dioxine is minimized. Consumption of NaClO2/KMnO4 cooxida nt during the bleaching treatment of grey and scoured linen fabrics wa s also examined. Furthermore, a free radical mechanism was reported to account for the effeciency and ease of application of tile NaClO2/KMn O4. bleaching system.