DOI 10.1515/hf-2012-0197 Holzforschung 2013; 67(8): 863–870 Phumla Faith Vena*, Michel Brienzo, María del Prado García-Aparicio, Johann F. Görgens* and Tim Rypstra Hemicelluloses extraction from giant bamboo (Bambusa balcooa Roxburgh) prior to kraft or soda-AQ pulping and its effect on pulp physical properties Abstract: The alkaline and acid preextraction of giant bamboo (Bambusa balcooa Roxburgh), grown in South Africa, before kraft and soda-anthraquinone (AQ) pulp- ing was in focus and the effects of NaOH concentration, temperature, and time on hemicelluloses extraction were studied by means of a statistical experimental design. The NaOH concentration exerted the strongest influence, solubilizing up to 20.4% of the available xylan with 2.0 M NaOH at 90°C for 240 min. The optimal extraction condi- tion was achieved with 1 M NaOH at 90°C for 240 min, in the course of which 13.6% of the xylan was removed; the screened pulp yield was 50.4% without viscosity reduc- tion, whereas the burst index of the handsheets was even improved. In the case of dilute acid preextraction before soda-AQ pulping, 11.3% xylan could be removed without affecting the pulp quality. The viscosity of the pulp was even better than that of pulps from nonextracted bamboo. The biorefinery approach, alkaline preextraction in com- bination with kraft pulping, is superior to the approach, acid prehydrolysis/soda-AQ pulping. Keywords: alkali and acid preextraction, biorefinery, giant bamboo, handsheet strengths, hemicelluloses, kraft pulping, prehydrolysis, pulp quality, soda-AQ pulping *Corresponding authors: Phumla Faith Vena and Johann F. Görgens, Department of Process Engineering, University of Stellenbosch, Private Bag Matieland X1, 7602 Stellenbosch, South Africa, e-mail: michelbrienzo@yahoo.com.br; jgorgens@sun.ac.za Michel Brienzo and María del Prado García-Aparicio: Department of Process Engineering, University of Stellenbosch, Private Bag Matieland X1, 7602 Stellenbosch, South Africa Tim Rypstra: Department of Forest and Wood Science, University of Stellenbosch, Private Bag Matieland X1, 7602 Stellenbosch, South Africa Introduction Hemicelluloses (HC) solubilized during pulping and as a part of the black liquor are usually incinerated in the recov- ery furnace together with dissolved lignin (Ragauskas et al. 2006). The scientific efforts, subsumed as biore- finery, would like to change this situation. Biorefinery is an analogous notion to the petroleum refinery, where multiple value-added products and fuels are produced in an optimized way. Based on the principles of biorefin- ery, HC could be preextracted before pulping and used as value-added products (van Heiningen 2006; Walton et al. 2010). This approach has many advantages for kraft and soda-anthraquinone (AQ) processes: lowering the alkali requirements for cooking, increment of delignification rate, elevated production capacity, and possible reduc- tion of the bleaching chemicals consumption (De Lopez et al. 1996; Al-Dajani and Tschirner 2008; Sixta and Schild 2009; Huang et al. 2010). Bamboo, a naturally fast-growing and low-cost ligno- cellulosic material, is most frequently used for the produc- tion of paper and as a reinforcing fiber (He et al. 2008). Kraft pulping is the best choice for the delignification of bamboo because of the favorable yields and high viscosi- ties (Vu et al. 2004). The main chemical constituents of bamboo are not too different to those of woody materi- als, but the fiber length is longer. The glucan content of bamboo is 40–53%, whereas the cellulose content of soft- woods and hardwoods is from approximately 40–52% and from 38% to 56%, respectively (Vena et al. 2010). The main HC in bamboo are 4-O-acetyl-4-O-methylglucuron- oxylans, which account for approximately 25% of the cell wall material. Bamboo xylan contains 6–7% acetyl groups (8–17% acetyl groups in hardwood xylan). Bamboo lignins have a higher content of phenolic hydroxyl groups and are partly esterified resulting in a higher susceptibility to alkaline hydrolysis and reactivity to pulping chemicals (Salmela et al. 2008). However, residual kraft lignin in Brought to you by | University of Stellenbosch Authenticated | 146.232.26.187 Download Date | 2/18/14 4:09 PM