Highly-efficient isolation of microcrystalline cellulose and nanocellulose from sunflower seed waste via environmentally benign method

The main focus of the study was to create natural microcrystalline cellulose obtained from a raw material source, the residue of sunflower seeds following oil extraction. For this purpose, organosolvent oxidation was chosen instead of the conventional method, whereby microcrystalline cellulose (MCC) was extracted from sunflower seed husks (SFHs), after which the refining of cellulose nanocrystals (CNCs) was carefully conducted. The organosolvent method of obtaining MCC involves the use of peroxyacetic acid (PAA), which provides a high yield of cellulose and eliminates the need to use chlorine-containing compounds in the process of bleaching. The environmentally benign method of obtaining MCC using the organosolvent method consisted of halving the concentration of acetic acid and hydrogen peroxide, to 58% and 15%, respectively, so as to obtain PAA, which yields an MCC of 47.8%. Physico-chemical characterization of particle sizes, optical properties, chemical and crystal structure, surface morphology, and thermal stability of MCC and CNCs was performed. FTIR analysis revealed the structural similarity of all the materialsof the extracted cellulose. Surface morphology was observed using SEM, showing that the surface of MCC fibers appeared rough, whereas that of CNCs was smooth with overlapping rod-like structures. The surface of CNC film was found to be colorless and composed of nanofibrils. XRD analysis and determination of average particle size revealed that the MCC had a crystallinity index (CI) of 72.9 ± 4%, a coherent scattering length (CSL) of 2.9 ± 0.1 nm, and an average particle length of 1971 ± 100 nm and width of 266 ± 35 nm. Acid hydrolysis resulted in the reduction of the length of CNCs by 4 times and the width by around 5 times, accompanied by an increase in the CI value. Cellulose was found to break down in the temperature range of 200–358 °C. Overall, SFHs are considered to be an effective potential source for CNCs, while the method employed herein for the extraction of cellulose from agricultural biomass waste is both cost-effective and environmentally benign. Graphical abstract