Abstract:

Pre-treatment (preparation) of cotton fabrics constructed from different grade cotton fibres with variable physicochemical properties using a single recipe to yield single results was investigated. The differences in fabric whiteness index and the reactive colour strength arising from these different grade cotton fibres were also examined. Thus, five cotton substrates with different characteristic properties were individually subjected to various pre-treatments processes followed by H2O2 bleaching. These pre-treatments include conventional scouring, reductive scouring (using D-glucose in a scouring bath), oxidative scouring, acidic pectinase scouring, alkaline pectinase scouring, and acidic demineralisation after scouring, or in combination with desizing (using D-gluconic acid) and grey mercerisation. For the other set of samples, mercerisation and cationisation were carried out after peroxide bleaching. The latter was conducted using the pad-steam technique. The fabrics were monitored for W.I after bleaching, K/S after dyeing, the degree of polymerisation, Eisenhute’s tendering factor, the residual wax content as well as the tensile strength and elongation at break. The results obtained show that the most effective pre-treatment processes which reduce the differences in both the whiteness index and the depth of colour (upon reactive dyeing) among bleached and dyed cotton are the following: reductive scouring of cotton fabric using D-glucose along with sodium hydroxide, acidic demineralisation with D-gluconic acid and acidic pectinase scouring. It was also found that pre-treating the cotton fabrics with reductive scouring largely reduces the oxidation of cotton cellulose when boiling off the alkalis.