Nordic Pulp & Paper Research Journal 2018; aop Bleaching Sandeep Kumar Tripathi*, Nishi Kant Bhardwaj and Himadri Roy Ghatak Additives to decrease cellulose chain scission during ozone bleaching of wheat straw pulp https://doi.org/10.1515/npprj-2018-3048 Received March 6, 2018; accepted June 4, 2018 Abstract: The efcacy of diferent chemical additives like acetic acid, ammonium molybdate, diethylene triamine pentaacetic acid (DTPA), mannitol, methanol, per acetic acid (PAA), sodium hypochlorite (NaOCl) and sulfamic acid as carbohydrate protector during ozone bleaching of wheat straw pulp was studied. DTPA was found the most efective additive for ozone bleaching followed by the methanol. Using DTPA during ozone treatment im- proved the delignifcation efciency by 13.8 %, bleaching efciency by 19.8%, selectivity of ozone by 124 % and re- duced the chain scission number of glycosidic linkages in cellulose by 55.3 % compared to that of control. Ozone treatment along with DTPA reduced the Fe, Cu and Mn con- tent in the pulp by 52 %, 27 % and 70 %, respectively. Use of methanol improved the delignifcation efciency by 9.0 %, bleaching efciency by 12.2 %, selectivity by 32.4 % and reduced the chain scission number by 22.2 % compared to that of control. The NaOCl was found to be the most efective for improving the delignifcation efciency fol- lowed by PAA, they improved the delignifcation efciency by 29.3% and 27.3%, respectively. The PAA improved the bleaching efciency to a maximum of 39.9% followed by 30.2 % with NaOCl. Keywords: additives for ozone bleaching; bleaching ef- ciency; chain scission number; delignifcation efciency; selectivity. *Corresponding author: Sandeep Kumar Tripathi, Avantha Centre for Industrial Research & Development, Paper Mill Campus, Yamuna Nagar – 135 001, Haryana, India, e-mail: skt1973@redifmail.com Nishi Kant Bhardwaj, Avantha Centre for Industrial Research & Development, Paper Mill Campus, Yamuna Nagar – 135 001, Haryana, India, e-mail: bhardwaj@avantharesearch.org Himadri Roy Ghatak, Department of Chemical Engineering, Sant Longowal Institute of Engineering and Technology, Longowal-148106, Sangrur, Punjab, India, e-mail: hrghatak@sliet.ac.in Ozone bleaching of pulp is considered as one of the best available technologies from environmental point of view. Ozone is a strong oxidating agent and it reacts with al- most all the organic materials, including lignocellulosic materials used for papermaking. Presently about 24 mills worldwide are producing about 8 million tons of ozone bleached pulp and 4 companies have recently purchased new ozone bleaching stages (Metais 2017). During reac- tion of ozone with lignocellulosic raw materials, the ozone reactions are more selective toward lignin compared to carbohydrates but formation of intermediate radicals dur- ing ozone bleaching has detrimental efect on carbohy- dtes (Medwick et al. 1992, Zhang et al. 2000). Formation of radicals during ozone bleaching of pulps promotes the unwanted attack on carbohydrates and decomposition of ozone in water. Reaction of ozone with the carbohydrate fraction of pulp reduces the pulp viscosity thereby the un- desirable decline in strength properties of paper (Ragnar et al. 1999). The pulp viscosity refects the degree of poly- merisation of the cellulose chain. Reaction of ozone with lignin generates highly reactive radicals that can lead to cellulose depolymerisation. Ozone also oxidizes cellulose, possibly subjecting it to subsequent depolymerisation un- der alkaline conditions (Ragnar et al. 1999 and Pouyet et al. 2013). Ozone is also decomposed by the catalytic ac- tion of transition metal ions present in pulp and forms hy- droxyl, hydroperoxyl and superoxide anion radical inter- mediates which may be detrimental to the carbohydrates (Brolin et al. 1993). Ozone bleaching of pulps having low physical strength properties, such as agro residue based raw material pulps, is supposed to be more critical. Higher degradation of carbohydrates during ozone bleaching of agro residue pulps may further deteriorate the physical strength properties and make the pulp unusable for paper- making. The detrimental efects of ozone can be avoided by using diferent chemicals that work as carbohydrate protectors. Substantial research has been carried out for discov- ering suitable carbohydrate protector for ozone bleach- ing of pulps, mostly on hardwood and softwood pulps. A lot of chemicals have been reported to improve selec- tivity of ozone for diferent pulps. Based on the cellu- Brought to you by | Uppsala University Library Authenticated Download Date | 8/3/18 6:41 AM