Optimal Hypochlorite Bleaching Duration for Sesbania grandiflora Pulp

Abstract Sesbania grandiflora is a fast growing species with 3 to 4 years of harvest rotation. Meanwhile, high cellulose content of the plant has made it a potential commercial pulpwood in Malaysia however the information is limited. Bleaching is an important process in pulp and paper manufacturing. Sodium hypochlorite was commonly used as the bleaching agent due to its strong oxidising bleaching in brightening the pulp. To reveal potential of Sesbania grandiflora as pulpwood, this research was carried out to determine the optimal duration by bleaching the Sesbania grandiflora with sodium hypochlorite. Sesbania pulp was treated with 5.00wt% of sodium hypochlorite solution in the water bath under the temperatures of 50°C. Three bleaching durations were taken: 20mins, 40mins and 60mins. The procedures of laboratory handsheets making and testing were conducted according to modified TAPPI standard. The results proved that 60mins was the optimal bleaching duration which showed the highest brightness percentage and the least lignin content. The reduction of lignin content also the kappa number had contributed to the brightness of the pulp. However, the overall strength properties of the Sesbania handsheets such as bursting test, tearing test and folding endurance test were decreased due to the fibre degradation when bleaching. The optical properties and strength properties of bleached handsheets showed significantly difference as compared to the unbleached handsheets and the differences become obvious as the bleaching duration increase.