Evaluation of physicochemical properties of extracted cellulose from the walnut shell using non-thermal plasma pretreatment
2023
Ensieh Anari | Nafiseh Soltanizadeh
The present study aims to extract cellulose fibers from the walnut shell using dielectric barrier discharge (DBD) plasma pretreatment and to evaluate its properties. For this purpose, powdered walnut shells were exposed to 18 and 20 kV DBD plasma for 10 min in three stages. First, before sodium hydroxide alkaline treatment, next, before sodium chlorite bleaching treatment, and then, before both alkaline and bleaching treatments. The extraction efficiency, FTIR, XRD, thermal properties, FESEM and diameters of the cellulose fiber were evaluated. Based on the results, the extraction efficiency was significantly affected by applied voltage (p<0.05) and due to plasma destruction of glycosidic, the efficiency was reduced. The removal of peaks related to impurities from the walnut shell and the purity of all extracted cellulose was confirmed with FTIR. The results showed that applying DBD plasma during cellulose extraction did not affect its crystal structure, but the reduction of crystallization index was observed. Furthermore, the effect of plasma on the thermal-gravimetry of the samples was observed at temperatures below 100 ° C, and after the onset temperature of degradation, the behavior of the treated and untreated fibers until the final thermal decomposition was not significantly different. The microstructure of plasma-treated samples showed an increase in cellulose fiber's roughness and swelling, followed by the transformation of microfibrils to nanofibrils with a diameter of 80 nm at the higher voltage. In general, the results showed that applying 20 kV DBD plasma in both stages before the alkaline and delignification process is a more suitable treatment for extracting cellulose and producing cellulose nanofibers.
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