Extraction and Characterization of Cellulose and Cellulose Nanowhiskers from Almond Shell Biomass, Metal Removal and Toxicity Analysis

Abstract

Almond shell is a major agro-industry waste. Cellulose is the major crystalline component of naturally porous almond shell biomass. In this study, cellulose (ASC) was isolated from almond shell (AS) by the dewaxing-alkali treatment-bleaching method, and nanocrystalline cellulose (ASN) was obtained by sulphuric acid hydrolysis of the obtained ASC. Separation efficiency was confirmed by X-ray diffraction and IR absorption studies. ASC exhibited predominantly microporous monolithic structures under a scanning electron microscope. Its porosity resulted in significant absorption of Cu(II) and Pb(II) ions when applied as an absorbent in their solutions. Transmission electron microscopy and atomic force microscopy revealed the formation of ASN nanowhiskers with an average length and diameter of 170 nm and 20 nm, respectively. Zeta potential of -32.4 mV suggested good colloidal dispersibility of the nanowhiskers. No hemolytic toxicity to erythrocyte cells was recorded, which suggested the potential applicability of the obtained nanomaterial in foods and pharmaceuticals. Remarkably high crystallinity and thermal resistance observed from calorimetry and thermogravimetry studies indicated enhanced density of the crystalline moiety during synthesis. ASC and ASN can be developed as effective metal absorption substrates and reinforcement agents in heat-resistant composite materials.