Process optimization and characterization of nanocellulose from chestnut shell

Abstract

Nanocellulose, a unique and promising natural substance extracted from cellulose-based materials, has gained tremendous attention for its use in various applications. Latest studies hypothesized that green extraction techniques reveal high-yield cellulose nanoparticles with lower environmental hazard and also highlighted that selectivity and characteristics of final products are highly dependent upon process parameters. This study aimed to produce nanocellulose powders from the chestnut shell –an agroindustrial waste without pertinent reuse– by acid hydrolysis (conventional), microwave-assisted acid hydrolysis, hydrotropic solvent, and deep eutectic solvent extraction techniques. The effectiveness of process parameters was investigated, and optimum conditions were determined by targeting the highest yields for each method. Additionally, the physico-chemical and microstructural properties of nanocellulose powders produced by each method were analyzed to investigate the product characteristics. The highest yield was obtained by deep eutectic solvent extraction (99.2%) followed by hydrotropic solvent (89.6%), conventional (64.5%), and microwave-assisted (34.1%) extractions. The methods bearing strong acid solvents resulted in a higher crystallinity index (up to 81%). The highest viscosity and absolute zeta potential values were obtained in deep eutectic solvent extraction as 843.6 cp and −23.7 mV, respectively. For all nanocellulose suspensions, the storage modulus (G′) was greater than the loss modulus (G″), indicating a more gel-like behavior. Nanocellulose powders produced by different methods had characteristic Fourier transform Infrared (FTIR) spectrum. The results of X-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) evidenced that nanofibrils could be produced via hydrotropic and deep eutectic solvent extraction systems while acid hydrolysis, i.e., conventional and microwave-assisted extraction generate nanocrystals. Obtained results indicated that green solvent systems could be utilized in the production of nanocellulose with many advantages, including efficiency, sustainability, reduced environmental harm, and low cost.