Structural changes of waste biomass induced by alkaline treatment: the effect on crystallinity and thermal properties

Abstract

A low-cost waste biomass generated from a food industry, apricot shells, was subjected to alkali modification in order to compare morphology, crystalline structure and thermal stability of native and modified biomass, accompanied by their cellulose-rich fractions. The surface morphology and structure of compared samples were analysed by the scanning electron microscopy (SEM) and mercury porosimetry. Furthermore, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermal analysis (TG/DTA) were applied. The results have shown that after alkaline treatment, inter- and intra-particle porosity in the material rises, resulting in increase of the total surface area. The XRD diffractograms showed that crystallinity index increased together with crystallite size, suggesting that modified sample has more ordered crystalline structure than native sample (also confirmed by the FTIR analysis). Although the cellulose-rich fraction extracted from the alkali-modified sample showed higher thermal stability, the overall thermal analysis revealed that alkali-modified biomass has lower thermal stability than the native sample. This indicates that this type of modification will improve the fuel properties of this lignocellulosic biomass and imply its possible application in energy recovery process.