Potential of Thai rice straw as a raw material for the synthesis of carboxymethylcellulose
2019
Chutong, P. | Sophonputtanaphoca, S. | Cha-aim, K. | Nooeaid, P.
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 pretreated 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.
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