Understanding the effects of alkali pretreatment and acid treatment of oil palm trunk fibres

Abstract

Cellulose is becoming a super-material due to its excellent properties and renewability. Understanding its resistance to chemical treatments is important to boost the usage and accessibility. In this study, oil palm trunk fibre (OPTF) was pretreated with NaOH and NH4OH either in an autoclave or in a water bath. The optimised alkaline pretreated samples were then subjected to acid treatment with acetic acid (AA). The results showed the highest delignification was achieved by using 12% of NaOH via the autoclaving process, with 10685.4 mg/L of lignin and 7.8% of acid insoluble lignin (AIL). The Fourier-transform infrared (FTIR) analysis confirmed the removal of lignin by the reduction of the peaks at 1250 and 1750 cm-1, representing C=O and C-O-C, respectively, from lignin. The delignification was pronounced when concentrated AA was used and the lignin-to-cellulose ratio decreased to about 52%. Other than lignin, amorphous celluloses were also removed during the AA treatment, causing an increment in the crystallinity index (CrI) and crystallite size (L). Consequently, the AA treatment had led to the depolymerisation of crystalline cellulose and affected the viscosity-average molecular weight (Mn).