Swelling behaviour and methylene blue absorption of carboxymethyl cellulose hydrogels prepared from malaysian agricultural wastes by electron beam irradiation

Abstract

Malaysia is the second largest producer of palm oil and generates 18 million tons of empty fruit bunches annually. Sugarcane is another important crop that is widely planted throughout Southeast Asia for sugar production. Both crops generate large amounts of lignocellulosic waste biomass in the form of sugarcane bagasse (SCB) and oil palm fibres (OPF), which can be converted into carboxymethyl cellulose (CMC) and subsequently cross-linked into hydrogels using electron beam irradiation. The irradiated CMC yielded hydrogels with up to 40% gel fraction, which can be increased to 50% with the addition of acrylamide as copolymer. The addition of acrylamide increased hydrogel yields and protected the polymer from chain scission at high radiation doses, up to 40 kGy. Furthermore, the hydrogels produced were stable at pH 3-10, suggesting that pH had a minimal impact on swelling, which affects their performance as absorbents. The methylene blue absorption of all SCB and OPF hydrogels examined in this study ranged from 0.722-0.987 mmol/g, which far exceeded that of bamboo-based activated carbon (0.142 mmol/g). This makes these hydrogels suitable for cationic dye removal and may be applied for the absorption of fertiliser ions in the future.