Utilisation of superheated steam in oil palm biomass pretreatment process for reduced chemical use and enhanced cellulose nanofibre production

Abstract

In this study, superheated steam (SHS) pretreatment was used as a green approach to partially remove hemicellulose from oil palm mesocarp fibre (OPMF). OPMF was treated with SHS at 260°C for 30 min prior to delignification by NaClO2 to obtain mainly cellulose fibre. Hemicellulose removal by KOH was conducted as a control experiment. Both SHS- and KOH-treated OPMF were later nanofibrillated using a wet disk mill (WDM). The characteristics of CNF produced were analysed in terms of morphological, crystallinity and thermal properties. Based on the chemical compositional analysis, SHS-treated OPMF had residual hemicellulose content of 11% (w/w), and there was no hemicellulose residue in KOH-treated OPMF. The presence of hemicellulose in SHS-treated OPMF was later found to enhance CNF formation during WDM process, whereby it was shown that nanofibrillation of SHS-pretreated OPMF occurred as early as 6th cycle, compared to KOH-pretreated OPMF (8th cycle). This observation could be explained by the presence of hemicellulose which prevented hornification of the cellulose microfibrils during milling process. This finding is significant as not only can the use of chemicals be reduced during pretreatment step, but the use of SHS pretreatment contributed greatly to the productivity of the CNF.