Influence of dimethyl formamide pulping of wheat straw on cellulose degradation and comparison with Kraft process Y. Ziaie-Shirkolaee, J. Mohammadi-Rovshandeh * , P. Rezayati-Charani, M.B. Khajeheian Department of Chemical Engineering, Faculty of Engineering, Tehran University, P.O. Box, 11365/4563 Tehran, Iran Received 4 February 2007; received in revised form 5 June 2007; accepted 27 July 2007 Available online 29 September 2007 Abstract The pulping of wheat straw with dimethyl formamide was studied in order to investigate the effects of the cooking variables (temper- ature (190 °C, 200 °C, and 210 °C) and time (120 min, 150 min, and 180 min) and organic solvent ratio (30%, 50%, and 70%) dimethyl formamide (DMF + water) value) on the degradation of cellulose and degree of polymerization (DP) of organosolv pulp. The SCAN viscosity was applied to estimating the extent of cellulose degradation produced by cooking condition and then, it was compared with Kraft pulp at equal Kappa number. Response of pulp and handsheets properties to the process variables were analyzed using statistical software (MINITAB 14). The process variables (cooking temperature and cooking time) must be set at low variables with high DMF ratio in order to ensure a high yield and high SCAN viscosity. Also, pulps with high mechanical properties can be acceptably obtained at 210 °C for 150 min with 50% DMF. Generally, the cooking temperature was a significant factor while the cooking time and DMF ratio had a smaller role. By the comparison of Kraft and organosolv pulp, it can be resulted that DMF basically had improvement role on reducing of cellulose degra- dation by reason of high SCAN viscosity of organosolv pulp than Kraft pulp under equal kappa number and, scanning electron micros- copy (SEM) of obtained pulp. Consequently, the protective action of organic solvent on non-cellulosic polysaccharides of wheat straw against degradation under Kraft pulping conditions was pointed as a main reason of the fairly high yield of organosolv pulps. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Cellulose degradation; Lignin; Organosolv pulping; Dimethyl formamide; Wheat straw 1. Introduction In the recent decade, a great attention of the world agri- cultural research was focused on non-wood materials with perspective for environmental industrial utilization. Wheat straw, bagasse, reed, rice straw as a one of the important non-wood fibers sources for pulping and paper making, has been studied (Jime ´nez et al., 1997, 2000; Shatalov and Pereira, 2002, 2005, 2007; Rezayati-Charani et al., 2006). The process, by which raw materials are pulped, produces large amounts of highly polluting waste water, especially in sulfite and sulfate based processes. These rea- sons have raised the need for new processes that reduce unpleasant effects such as organosolv processes (Ziaie- Shirkolaee et al., 2007). In conventional cooking and organosolv cooking, the lignin structure must be broken into smaller parts before it will dissolve in the cooking liquor. No solvent or combi- nation of solvents has yet been found that will dissolve lig- nin directly from the wood matrix. Without chemical reactions, lignin will not dissolve. One reason is that it forms chemical bonds with wood polysaccharides. Process variables such as cooking time and temperature also influ- ence the reactions in the same way as in conventional cook- ing. The cleavage of ether bonds in the lignin structure is a key delignification reaction (McDonough, 1992). The reactions taking place during alkaline organosolv cooking are similar to those in the corresponding conven- tional processes (Kraft, soda, and alkaline sulfite). At 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.07.066 * Corresponding author. Tel.: +98 182465 2601; fax: +98 182465 2600. E-mail address: roshandeh@ut.ac.ir (J. Mohammadi-Rovshandeh). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 3568–3578