Deep Eutectic Solvent (DES) treatment in nanofibrillation of secondary cellulose raw materials

More environmental friendly and inexpensive chemicals are desired in the production of nanocelluloses. Deep Eutectic Solvents (DES) are a new class of solvent, which has been investigated as a green media in biomass processing. These solvents are easy to synthesize, based on readily available bulk chemicals, and they have low toxicity and are mainly biodegradable, which make DES one of the most promising solvents for sustainable material production. The utilization of secondary raw materials, such as waste paper and board, in preparation of micro- and nanocelluloses would further improve the sustainability of production, since those materials have a high cellulose content even though they may have shortened fiber lengths and decreased mechanical strength in the macro-scale.
DES prepared by mixing choline chloride and urea was used as chemical pretreatment in a nanofibrillation of different secondary fiber sources using Masuko grinder without any other chemical treatments. The characteristics of the nanofibrils obtained from the DES pre-treated materials, such as waste board (B), fluting (F), and waste milk container board (MCB) were compared with the nanofibrils obtained directly from virgin bleached chemical birch pulp (BCP), NaOH swelled waste board (NaOH-B), and bleached chemical birch pulp (NaOH-BCP). In addition, the prepared nanocelluloses were used as strengthen additives in board.
DES treated board pulps were nanofibrillated more easily than NaOH swollen pulps. The nanofibril suspensions obtained from the DES pretreatment had viscous gel-like appearances, with shear thinning behavior without changes in their initial crystalline structure. Strength properties in board increased highly with the addition of nanofibrillated waste boards, but the best results according to strength properties and dewaterability obtained with the addition of less fibrillated microfibrils. Consequently, DES chemical pretreatment with a disk grinder appears to be a promising route to obtain cellulose micro-and nanofibrils from waste board and paper that can be used as strengthening additives in board.