Preparation of cellulose nanocrystals using highly recyclable organic acid treated softwood pulp

Cellulose nanocrystals (CNC) were successfully obtained from softwood pulp by p-toluenesulfonic acid (p-TsOH) hydrolysis under the treatment of p-TsOH mass concentration of 60%, temperature of 70 °C, reaction time of 4 h, and pulp to solution ratio of 1:20 (g / mL). Zeta potential and dynamic light scattering (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) were used to characterize the physical-chemical properties of the CNC. Under these conditions, the CNC exhibited good thermal stability in the suspension with a high crystallinity index of 90.1%. The CNC had an average diameter of 4.87 nm and average length 175.5 nm with no undesired elemental contamination. The degradation temperature of the CNC was relatively high at 310 °C. Moreover, p-TsOH was recovered by crystallization technology, and the recovery rate was over 70%, providing an environmentally friendly way for the development of biomass materials.