Pulping and Bleaching of Acacia auriculiformis (Akashmoni) Planted in Bangladesh for Paper Production

Abstract

Acacias were established and found that the Acacia auriculiformis Acacia mangium and Acacia hybrid were promising species in respect to survival and growth performance in Bangladesh. Therefore, these three species were introduced in the social forestry program in Bangladesh. Variation of anatomical, morphological and chemical characteristics with annual growth ring from first and second generation Acacia auriculiformis were investigated. The fiber length and wall thickness increased and proportion of ray cells decreased with increasing annual growth ring. First generation Acacia auriculiformis had higher proportion of fibre, longer fiber length than second generation Acacia auriculiformis. The average percentage of fibres, vessels and rays were 77.56%, 15.14% and 7.31% for first generation Acacia auriculiformis and 77.19%, 15.64% and 7.16%, for second generation Acacia auriculiformis, respectively. The holocellolose, α-cellulose and pentosan content increased and lignin and extractives content decreased with increasing annual growth ring. Hollocellolose, α-cellulose, pentosan and lignin content in first generation Acacia auriculiformis were higher than second generation Acacia auriculiformis. The physical, chemical and fibre characteristics of 6, 8 and 10 years old Acacia auriculiformis wood from second generation seed and their suitability for pulping were assessed and compared with the wood of 10 years old from first generation seed. Acacia auriculiformis of 8 years old had the highest α-cellulose and lower lignin than 6 and 10 years old, which are similar to first generation wood. This study also evaluated the effect of cooking time, temperature and active alkali on Kraft pulping. The most influence factors for pulp yield and kappa number were active alkali charge and time. The highest screened rejects were observed for young tree. Delignification degree of first generation was faster than second generation Acacia auriculiformis. In this study, the chemical, physical and morphological characteristics of plantation Acacia hybrid and Acacia mangium wood grown in Bangladesh were assessed for their suitability in papermaking. The α-cellulose content in Acacia hybrid was 45.5%, which was 1.3% lower than Acacia mangium and 2.1% higher than Acacia auriculiformis. Kraft pulping of AcaciaAbstract III Department of Applied Chemistry and Chemical Engineering, University of Dhaka and BCSIR, Dhaka hybrid was carried out with varying active alkali charge and cooking time. Acacia hybrid required drastic chemical charge to cook properly. At the cooking conditions of 18% active alkali charge in 120 min of cooking, kappa number reached to 27.6 with pulp yield of 45.9% and no reject. But pulp yield was quite high as compared to Acacia auriculiformis and Acacia mangium. Both Acacia hybrid and Acacia auriculiformis pulps showed almost similar papermaking properties. But the maximum tear index of Acacia hybrid was at a tensile index of 76.3 N.m/g while it for 61.9 N.m/g for Acacia auriculiformis and 57.2 N.m/g for Acacia mangium. At these peak levels tear index values are almost similar (10 mN.m2/g) for Acacia auriculiformis and Acacia hybrid. In respect to pulp yield and papermaking properties, Acacia auriculiformis produced the better pulpwood than Acacia mangium. Laboratory and semi-pilot scale pulping of A. auriculiformis were also assessed and compared with Acacia hybrid and A. mangium grown in the same forest. Higher pulp yield and lower kappa number than the laboratory scale cooked were showed by 8 years Acacia auriculiformis and A. mangium and pulp yield and kappa number lower for Acacia hybrid. Kraft pulps from Acacia hybrid, Acacia mangium of 8 years old and Acacia auriculiformis of 6, 8 and 10 years old were pre-treated with oxygen, peroxyformic acid and acid treatment prior to bleaching. The kappa number reduction was 52-63% by oxygen delignification, 31- 35% by peroxyformic acid (PFA) pre-treatment and 11-13% by acid pre-treatment. Oxygen delignified pulp required less chlorine dioxide charge to reach target brightness. At the consumption of 30 kg ClO2/ton of pulp, the pulp brightness reached to 65-71% for the untreated pulp, 81-85% for the oxygen delignified pulp, 81-82% for the PFA treatment and 79- 80% for acid pre-treated pulp. COD load in bleached effluent was much lower in oxygen delignified pulp. Cold alkali extraction of unbleached and oxygen delignified pulps was also carried out with varying alkali charge to remove hexenuronic acid (HexA) from the pulp. Xylan removal from the pulp was insignificant and resulted in no removal of HexA. Acid pretreatment removed 55.7% to 17.8% HexA from Acacia hybrid, 57.5% to 16.3% from Acacia auriculiformis of 10 years and 58.6% to 20.1% from Acacia auriculiformis of 6 years old, resulting in improved final pulp brightness.