Production and characterization of cellulose nanocrystals of different allomorphs from oil palm empty fruit bunches for enhancing composite interlaminar fracture toughness

Abstract

The effect of different alkaline treatments during the extraction of α-cellulose from oil palm empty fruit bunches on the properties of subsequently extracted cellulose nanocrystals are reported. Sodium hydroxide in an alkaline process step results in a change of native cellulose from type I to II. Treatment with potassium hydroxide maintains the native allomorph of cellulose I. Compared to commercial cellulose nanocrystals (CNCs), oil palm empty fruit bunch (OPEFB) CNCs type I materials have higher aspect ratios, higher crystallinity index, but lower charge, and thermal stability compared to commercial CNCs. OPEFB CNCs type II have a higher aspect ratio, but lower charge than both types of CNC. Type I CNCs exhibit intermediate charge, but higher thermal stability which might make them more suitable for processing with thermoplastic polymers. A full map of physical properties, comparing the oil palm based CNCs to both commercial and lab-based materials is presented to better understand how they might be exploited in composite applications. It is demonstrated that aligned electrospun cellulose acetate butyrate nanofibrous networks containing these CNCs can enhance the mode-II interlaminar fracture toughness of a carbon fibre-epoxy laminate.