Fractionation of lignocellulosic materials with ionic liquids. 1. Effect of mechanical treatment

The selective precipitation of wood dissolved in 1-allyl-3- methylimidazolium chloride ([amim]Cl) with a nonsolvent is a straightforward method for fractionating lignocellulosic components. In this study we have solvated and precipitated fractions of pulverized Norway spruce (Picea abies) and Eucalyptus grandis wood. This was achieved by agitating and heating the lignocellulosic materials in [amim]Cl followed by precipitation using nonsolvents, such as acetonitrile (MeCN) and water. Water was also used to extract material, which was determined to be high molecular weight galactoglucomannan. Products were analyzed by benzoylation followed by size-exclusion chromatography (SEC) and IR. It was found that the selectivity of precipitation was not significantly dependent upon the chemical composition of the precipitating components. The efficiency of precipitation was found to be dependent upon molecular weight, with the dissolved higher molecular weight and partially soluble wood components precipitating first. Moreover, when coarse sawdust samples were fractionated, the selective dissolution of cellulose from the fiber was observed, which allowed for the regeneration of a fraction of delignified and bleachable cellulose. Additionally, finely milled softwood samples, with demonstrated narrowly distributed low molecular weights, did not efficiently fractionate most likely due to the presence of an extensive lignin-carbohydrate complex (LCC) network.