Isolation and characterization of nanocellulose from selected hardwoods, viz., Eucalyptus tereticornis Sm. and Casuarina equisetifolia L., by steam explosion method

Extraction of nanocellulose is challenging, especially from hardwoods due to its complex chemical structure as well as structural hierarchy. In this study, nanocellulose was isolated from wood pulp of two hardwood species, namely Eucalyptus tereticornis Sm. and Casuarina equisetifolia L. by steam explosion process. Pure cellulose wood pulp was obtained through Kraft pulping process followed by alkaline and bleaching pre-treatments. Isolated nanocellulose was characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Fourier Transformed Infrared (FTIR) Spectra, Thermogravimetric Analysis (TGA), and X-ray diffraction (XRD) studies. Nanocellulose obtained from both species showed non-significant difference with average diameter of 27.801 nm for eucalyptus and 28.690 nm for casuarina, which was confirmed from TEM and AFM images. FTIR spectra of nanocellulose showed prominent peaks corresponding to cellulose and absence of peaks corresponding to lignin. The elemental purity of nanocellulose was confirmed with EDAX detector. XRD analysis showed the enrichment of crystalline cellulose in nanocellulose, and also confirmed the significant conversion of cellulose I to cellulose II. During TG analysis the untreated fibres started to degrade earlier than the nanocellulose which indicated the higher thermal stability of nanocellulose. Highly entangled network like structure along with high aspect ratio make the nanofibres a versatile material for reinforcing the composites. This successful method can be replicated for industrial level production of cellulose nanofibres.