Potential of Thai rice straw as a raw material for the synthesis of carboxymethylcellulose

Abstract

Ten different Thai rice straw cultivars were used to evaluate their potential as a raw material for the synthesis of carboxymethylcellulose (CMC). The native straw samples contained 22.4-37.5% cellulose by weight of the native biomass. After cellulose extraction by alkaline peroxide pre-treatment (5% sodium hydroxide in 2.5% hydrogen peroxide), total solid recovery ranged from 38.7-49.5% of the biomass by dry weight. In these solid samples, cellulose was the main component of the materials. Cellulose content accounted for 59.8-81.2% by weight of the pre-treated biomass depending on the specific rice straw sample. Alkalisation and methylation by sodium hydroxide and sodium monochloroacetate in the presence of solvent gave CMC yields higher than 90% by weight of extracted cellulose. The characterisation of CMC revealed that Fourier-transform infrared (FT-IR) spectra of all CMC samples showed differences in terms of carboxymethyl substitution as compared to that of cellulose. X-ray diffraction analysis suggested that crystallinity of the synthesised CMC samples was reduced as compared to that of cellulose. The CMC had a degree of substitution ranging from 0.63-0.87. The highest viscosity of CMC was found in the sample of rice straw RD 6, which had a measured viscosity of 100 cP. Scanning electron microscope analysis showed that all CMC samples had a smooth surface, indicating a high level of carboxymethylation. © 2019, Universiti Putra Malaysia.