Improvement in bleachability of pulps from non-wood raw materials using acid followed by alkaline peroxide treatment

Oxygen delignification technology is driven mainly by environmental, economical and energy related issues had played a major role in terms of unbleached pulp Kappa reduction. In India, agro residues contribute a major raw material in furnish. The adoption of oxygen treatment technology for the size of the Indian mills is matter of economic viability. Due to its high capital cost, most of the small paper mills based on agro residue raw materials are unable to adopt oxygen treatment for reducing the Kappa number. An alternate cost effective route for unbleached pulp Kappa number reduction may be of great interest for such mills. In present study, a combination of acid followed by alkali and peroxide treatment on unbleached pulps from wheat straw, bagasse and bamboo was carried out. It was observed that, when oxygen treatment was carried out on unbleached pulps from these raw materials, the drop in Kappa number was as high as 45%similar to 55%. However, there was considerable loss in pulp strength, which varied between 10%similar to 20%. Such a loss in strength from agro residue pulps before the subsequent bleaching stages is not desirable. In contrast, when these pulps were treated with acid followed by alkali and peroxide, it was observed that the drop in Kappa number of pulps was quite appreciable (30%similar to 42%). This was accompanied by simultaneous gain in brightness of up to 10 units. When compared with the oxygen treated pulps, the drop in the pulp strength was negligible. It was further observed that the bleaching response of such pulps was better than the oxygen treated pulps and it was possible to achieve higher end brightness. The above studies clearly indicated that the acid followed by alkali and peroxide treatment of pulps from wheat straw, bagasse and bamboo could be a viable route for reducing unbleached Kappa number for small mills using these raw materials and achieving high end brightness and can be seen as substitute for oxygen delignification step.