Comparison of kraft and ternary deep eutectic solvent pulping of scots pine

Abstract

Kraft method, the most widely used method in pulp production, causes to various environmental problems. Therefore, environmentally friendly pulp production methods have been investigated. In recent years, environmentally friendly deep eutectic solvents (DESs) as cooking liquor have been investigated. In this study, the possibilities of using a ternary DES (TDES) in pulp production from Scots pine (Pinus sylvestris L.) chips were investigated. TDES constituents were choline chloride (ChCl), lactic acid (LA), and glycerol (G). The effects of cooking temperature (145 °C and 155 °C) and cooking time (3 h, 3.5 h, and 4 h) on pulp and paper properties in TDES pulping were investigated. For comparison, kraft pulp from Scots pine was produced with conditions of 18% active alkali, 25% sulfidity, 155 °C cooking temperature, and 3.5 h cooking time. The highest lignin removal was obtained from TDES3 pulping conditions (155 °C and 4 h) with 76.0%. Lignin removal in the kraft pulp was 67.8%. TDES pulps were more quickly beaten to the target freeness level of 25°SR (the times for TDES3 and kraft pulps were 90 sec and 1350 sec, respectively.). Crystallinity index (CrI) values of kraft pulp and TDES3 pulp were 70.7% and 68.0%, respectively. TDES6 pulp had the highest pulp strength. But, the strength properties of all TDES pulps had lower than kraft pulp. TDES pulping can be a greener alternative to kraft pulping.