EFFECT OF ALKALINE SULFITE AND SULFITE-SULFIDE PULPING ON THE CHEMICAL-REACTIVITY OF VISCOSE PULPS FROM WHEAT STRAW

The stabilizing effect of alkaline sulphite pulping on the short-chain celluloses and hemicelluloses lowered the alpha-cellulose content. This drawback was overcome by increasing the acid concentration in prehydrolysis, in order to hydrolyse a greater amount of the short-chain carbohydrates. Alkaline sulphite pulping raised the yield, lowered the permanganate number, improved the degree of whiteness and lowered bleachability. The best chemical reactivity was attained when the amount of sodium used as sulphite was 40\%. In the case of sulphide-sulphite pulping, 10\% of the total sodium as sulphide and 10\% as sulphite improved the yield, enhanced delignification, lowered the bleach requirement and improved the chemical characteristics. The reactivity was improved when 20\% of the total sodium were as sulphide and 20\% as sulphite. Under mild prehydrolysis conditions, sulphate pulping improved the reactivity. Further improvements were achieved with alkaline sulphite pulping. However, sulphide-sulphite pulping decreased the reactivity. Under stronger prehydrolysis conditions, 20\% sulphidity impaired the reactivity, while 40\% sulphidity improved it. With alkaline sulphite pulping, the reactivity was improved when 10\% of the total sodium were used as sulphite. Sulphide-sulphite pulping improved the reactivity when 20\% of the total sodium were as sulphide and 20\% as sulphite.