DEVELOPMENT OF CHLORINE FREE NOVEL BLEACHING PROCESS FOR WHEAT STRAW PULP TO REDUCE THE TOXICITY LEVEL OF EFFLUENTS

Abstract

Wheat straw is a non-wood agricultural residue which serves as an excellent fibrous source for pulp and paper industry. In the present work, TCF bleaching sequences were developed for indigenous variety of AS/AQ wheat straw pulp. Different chemicals such as acid, oxygen, oxone, dithionite, alkali and hydrogen peroxide were optimized in different stages and sequences at varying doses of bleaching agents and reaction conditions. Multistage TCF bleach sequences i.e., AOOxPP*, AOOxEP, AOOxYP, AO′Ox′P′ are resulted from various optimization trials during the study. It was very promising to find out that cellulose remained protected whereas most of the residual lignin was removed during the process. Most of the hemicelluloses were washed away during bleaching. However, it is quite evident from the pulps’ sugar analysis that only a small fraction of hemicelluloses remained intact in the bleached pulp which is important in fiber preparation and its bonding during papermaking process. Similarly, hexenuronic acid was also removed during successive stages of bleaching that may be the causes of reduction in fiber strength, brightness and brightness stability. The results also revealed that the developed bleaching sequences are effective and selective to fully bleach the pulp with brightness gain greater than 80% ISO without deteriorating its fibre characteristics such as kappa number, viscosity, strength and brightness stability etc. A considerable reduction in effluent load with reduced toxicity and zero AOX level shows the advantage of process over chlorinated bleaching processes. Thus the study provides enough evidence to fill the gap between producing quality products and requirements for a healthy environment using TCF bleaching sequences.