Extraction of Nanocrystals from Millet (Eleusine Coracana) Husk Waste : Optimization using Box Behnken Design Method in Response Surface Methodology (Rsm)

Abstract

Cellulose nanocrystals (CNCs) have unique and diverse applications in the various fields of developing nanomaterials. In this work, cellulose nanocrystals were extracted from millet husk residue waste using a homogenized acid hydrolysis method. The effects of the process variables namely; homogenization speed, acid concentration and acid to cellulose ratio on the yield and swelling capacity were investigated and optimized using the Box Behnken design method in response surface methodology. The cellulose and nano-cellulose obtained were characterized using transform infrared microscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The numerical optimization analysis results showed that the maximum yield of CNCs from cellulose was 93.12 % and obtained at homogenization speed, acid concentration, and acid to cellulose ratio of 7464.0 rpm, 63.40 wt %, and 18.83 wt % respectively. The maximum swelling capacity of 2.81 % was obtained at homogenization speed, acid concentration, and acid to cellulose ratio of 8000 rpm, 62.5 wt %, and 25 wt % respectively. A mathematical model was obtained to predict the yield and the swelling capacity of cellulose nanocrystals with R2 of the value of 98.9 % and 97.9% respectively. The TGA showed that the thermal stability of cellulose was higher than that of CNCs, FTIR results showed functional groups of CNCs and cellulose were similar, SEM image of CNCs is porous and displayed narrow particle size and needle-like morphology as compared to cellulose and XRD pattern presented an increase in the intensity of CNCs.