Optimization of cellulose extraction process from sugar beet pulp and preparation of its nanofibers with choline chloride–lactic acid deep eutectic solvents

In this novel bench-top experimental and statistical investigation, the effects of influencing parameters on cellulose extraction have been studied and optimized. Chemically isolated cellulose was used at the optimum condition for the purpose of cellulose nanofiber preparation by deep eutectic solvent (DES) application. For this purpose, the Taguchi method was applied for experimental design. Six parameters which have more signal-to-noise ratio were selected as influencing parameters. These parameters consist of solvent ratio for dewaxing, depectinization pH and time, delignification pH and time, and pH of hemicellulose removal. The effect of these parameters on the cellulose extraction was modeled and optimized by the application of artificial neural network (ANN), coupled with genetic algorithm (GA). The ANN model, by establishing of feedforward backpropagation network with topologies 6, 13, and 1, was applied to model the relation between the extraction condition and cellulose extraction. The results confirmed that the best neural network structure has the ability of cellulose extraction yield prediction with an acceptable level of accuracy. The optimization results show the maximum cellulose extraction would be achieved at the following conditions: pectin extraction time of 1.62 h, delignification time of 2.19 h, the solvent ratio for dewaxing of 0.89 (V/V%), depectinization pH of 2.06, delignification pH of 5.48, and hemicellulose removal pH of 11.36. Under these conditions, the experimental extraction condition yield was 91.7% for cellulose extraction, which matched with the predictive extraction yield of 92.3%. Chemically extracted cellulose at the above condition was applied to prepare cellulose nanofibers. For this purpose, choline chloride–lactic acid–based DES pretreatment was used. The structure of the extracted cellulose and prepared cellulose nanofibers by the application of FTIR, XRD, Fe-SEM, and TEM methods was characterized. The XRD diffractograms alongside with FTIR analyses show that in the extraction process by impurity elimination, the crystallinity index increases. Also, as the characterization results show, by the DES application, glyosidic bonds were cleaved, enhancing the crystallinity and nanofibrilization.