Swelling properties of pulp treated with deep eutectic solvents

The reaction of cellulose with water produces swelling and structural changes of the fibres, both effects being of crucial importance for the understanding of paper formation. It was investigated how the treatment of pulp with deep eutectic solvents affects the swelling kinetics of the fibres. Unbleached kraft pulp was treated with three deep eutectic solvents containing choline chloride (ChCl) – ChCl:lactic acid (1:9), ChCl:oxalic acid (1:1) and ChCl:malic acid (1:1) – and with the system alanine:lactic acid (1:9). The rate and maximum swelling of the pulp in water were determined using a modified monitoring unit for measuring swelling ability. Since paper swells extremely rapidly in water even at 23°C, this apparatus made it possible for the first time to obtain accurate rate data on the swelling of DES-delignified pulp in water.