Cellulose nanocrystal production from bleached rice straw pulp by combined alkaline and acidic deep eutectic solvents treatment: optimization by response surface methodology

The present study aims to develop a statistical model utilizing the response surface methodology (RSM) to investigate the performance of oxalic acid-choline chloride deep eutectic solvent (OA-ChCl DES) in hydrolyzing amorphous domain of the bleached rice straw pulp (BP), while liberating the oxalic acid-choline chloride DES cellulose nanocrystal (OA-ChCl DES CNC). The process parameters, including temperature, reaction time, and BP to OA-ChCl DES mass ratio, were optimized through the RSM coupled with the face-centered central composite design (FCCCD). The mathematical models were generated, while the analysis of variance (ANOVA) was conducted to determine the most significant factors influencing the response which was measured in terms of yield. The findings revealed that the OA-ChCl DES CNC yield as high as 55.08% was attained under the acidic DES hydrolysis conditions of 79.5 °C, 4 h, and 1:12.64 mass ratio. This regression model enables researchers to predict the OA-ChCl DES CNC yield with respect to the influencing parameters as well as providing an insight for further scale-up process.