Effect of alkaline pretreatment on the properties of cassava rhizome

Abstract

Lignocellulosic biomass is a complex biopolymer of cellulose, hemicellulose and lignin, which is strongly resistant to chemical and enzymatic breakdown. An efficient pretreatment process is required because it plays a vital key role to enhance chemical and enzymatic susceptibility. Alkaline pretreatment has been considered one of the most promising pretreatment methods because of its high lignin removal efficiency and polysaccharide recovery. This study aimed to investigate the effect of alkaline pretreatment on biochemical compositions of cassava rhizome (CR). The pretreatment was carried out in hot compressed water with various alkaline types including Ca(OH)2, Mg(OH)2, KOH and NaOH in three concentrations of 10, 20 and 30 wt.% dry CR at 120°C for 1 h. The pretreated CR product was analyzed for mass yield, lignocellulosic content, elemental composition, crystallinity structure, surface morphology and chemical functional groups. The analysis results showed that alkaline types and concentrations altered the pristine CR compositions substantially. The sample with maximum cellulose content was obtained when using 30 wt.% KOH, while the lowest crystallinity was obtained using 30 wt.% NaOH. These results indicated that pretreatment using KOH and NaOH significantly enhanced the chemical and enzymatic susceptibility. Chemical functional groups in the pretreated CR products changed corresponding to the changes of lignocellulosic contents. However, the contents of elemental compositions in the pretreated CR changed marginally with alkaline types and concentrations.