Ultrasound enhancement of cellulose processing in ionic liquids: from dissolution towards functionalization

Abstract

The ionic liquids 1-allyl-3-methylimidazoliumchloride[Amim][Cl] and 1-butyl-3-methylimidazoliumchloride[Bmim][Cl] were utilized in the dissolution of different natural cellulose biopolymers. The biopolymers subject to this investigation were microcrystalline cellulose, cotton linters as well as Kraft cellulose cut to 0.35 mm fibres. High-intensity acoustic irradiation by means of an ultrasonic horn was applied to enhance the dissolution process. The ionic liquids investigated were able to dissolve cellulose at elevated temperatures, in high concentrations, although significant differences were observed, depending on the type of cellulose and ionic liquid. Moreover, the dissolution process under conventional heating was rather slow, typically extending for a period of several hours. Upon use of high-power ultrasound, the dissolution process was dramatically intensified and complete dissolution was achieved in a matter of few minutes only. Various approaches to cellulose functionalization were proposed and investigated. The effect of external parameters, such as the reaction temperature, the cellulose–derivatising agent molar ratio and the batch time of experiment were studied. Various physico-chemical methods, such as acid methanolysis, TGA, DSC, SEM as well as NMR on ¹H and ¹³C nuclei were applied to investigate the structure and morphology of both the cellulose samples and ionic liquids before and after processing.