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Pretreatment of softwood dissolving pulp with ionic liquids

Li, Dongfang, Sevastyanova, Olena, Ek, Monica
Holzforschung 2012 v.66 no.8 pp. 935-943
X-ray diffraction, acetates, cellulose, chlorides, crystal structure, dissolving pulp, ethanol, gel chromatography, hardwood, ionic liquids, molecular weight, nuclear magnetic resonance spectroscopy, polymerization, scanning electron microscopy, softwood, temperature, textile fibers, thermal stability, thermogravimetry, viscosity
Few Scandinavian pulp mills produce dissolving pulps; however, the demand on textile fibers is increasing. This study investigates the chemical interaction of dissolving pulp with ionic liquids (ILs), where softwood and hardwood industrial dissolving pulps were pretreated with ILs 1-butyl-3-methy-limidazolium acetate ([C₄mim⁺]CH₃COO⁻) and 1-butyl-3-methyl-imdazolium chloride ([C₄mim⁺]Cl⁻). Time and temperature dependence of the dissolution process as well as the impact of the pretreatment on the molecular weight properties, thermal stability, morphology, and crystallinity of the cellulose were evaluated by means of size exclusion chromatography (SEC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR). It was shown that the dissolution of cellulosic material in ILs is a temperature-dependent process; however, the viscosity of ILs affected the efficiency of dissolution at a given temperature. Molecular weight properties were affected negatively by increased dissolution temperature, while the type of antisolvent for the regeneration had no major impact on the degree of polymerization of cellulose. Water was more efficient than ethanol for the regeneration of cellulose when performed at an elevated temperature. The pretreatment decreased the crystallinity of cellulosic material. This might lead to the increased accessibility and reactivity of cellulose.