Effect of temperature on synthesis of cellulose nanoparticles via ionic liquid hydrolysis process

This paper elucidated the properties of cellulose nanoparticles (CNPs) extracted from microcrystalline cellulose by hydrolysis reaction by using 1-butyl-3-methylimidazolium acetate (BmimOAc) as a catalyst and solvent at various temperatures (i.e. 70, 80, 90, 100 and 110 °C). X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) were used to characterise the samples and the relevant analysis was presented in detail. It was found that the initial peak from microcrystalline cellulose at the preferential orientation of (200) split into two broad peaks, with the preferential orientations found to be (110) and (020) as per XRD analysis. This showed that native cellulose experienced a structural transformation from its initial cellulose type I to the terminated phase of cellulose type II in CNPs, with a remarkable reduction in crystallinity after the hydrolysis reaction in BmimOAc. The reaction temperature was found to refine the individual cellulosic fibres with a smooth, homogenous, and defined width, which was obtained at an optimum temperature of 80 °C. The application of BmimOAc as both catalyst and solvent thus introduces a green chemistry approach as it does not produce any hazardous waste products. Additionally, it is an economical process as the recovery of the ionic liquid is high, reaching up to 86%.