Dimethyl formamide (DMF), with a high selectivity to delignification, was used as a solvent for pulping. Many lignocellulosic materials, such as bagasse [144, 173], wheat straw [143], rich straw [174] and canola stalks [175], have been subjected to pulping in this context and the main operation parameters (time, temperature concentration, liquid to wood ratio, etc.) were optimized.

DMF pulping has many advantages such as obtained pulp with more hemi — celluloses, less cellulose degradation, high yield, low residual lignin content, high brightness and good strength. The pulp produced was easy to be bleached and the yield after bleaching was higher than the yield of kraft pulp [173]. For example, pulps with high mechanical properties comparable to kraft pulp were produced under such conditions, i. e., at 210°C for 150 min with 50% DMF [143].

The relatively high selectivity of acetone fractionation process is ascribed to the unique chemical mechanism. In most organosolv fractionation processes, protic solvents (such as alcohols with the addition of acids or bases) result in the main delignification and degradation of carbohydrate under certain conditions. However, in an aprotic DMF solvent, the main and only reaction during frac­tionation process is delignification. The reaction results in the cleavage of car­bohydrate-lignin ether linkage and hydrolysis of fi-O-4 and a-O-4 bonds of lignin to form small fragments of lignin. In addition, DMF plays an important role in protecting carbohydrates [173, 176].

It should be noted that other than the organic solvents mentioned above, phenols, esters, ammonia, amines, formamide, dioxane, etc., have also been used to fractionation of a variety of lignocellulosic materials, but these processes are mainly investigated to production of pulps in a laboratory scale presently [2, 4, 13].