Abstract Walnut shell with about 22% cellulose is a good source for cellulose fibers extraction. Despite different techniques applied for cellulose extraction from agricultural wastes, most of these treatments are low-efficient and cause environmental problems. In this regard, considering alternative methods for cellulose extraction is necessary. The present study aims to extract cellulose fibers from the walnut shell using dielectric barrier discharge (DBD) plasma pretreatment and to compare its properties with commercial microcrystalline cellulose. For this purpose, powdered walnut shell were exposed to 18 and 20 kV DBD plasma for 10 min before sodium hydroxide alkaline treatment, before sodium chlorite bleaching treatment, and before both alkaline and bleaching treatments. Also, commercial microcrystalline cellulose was treated by cold plasma at 20 kV for 10 min. The chemical composition of walnut shell and extracted cellulose, extraction efficiency, color, Fourier transform infrared spectroscopy, crystal structure, thermal properties, microstructure, and elemental analysis of the samples were eva‎luated. Based on the results, the applied voltage significantly reduced the cellulose extraction efficiency (p<0.05) due to the distruction of glycosidic bonds in cellulose which is related to plasma treatment; however, the difference between the extraction efficiency of plasma-treated samples and control was negligible. In addition, glucose and lignin of extracted cellulose significantly changed with plasma pretreatment (p<0.05). The purity of all extracted cellulose was confirmed with Fourier transform infrared spectrometer. Plasma treatment considerably increased the lightness of extracted cellulose (p<0.05). 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 exposure of lignocellulosic fiber to DBD plasma reduced the thermal stability of extracted cellulose compared to commercial microcrystalline cellulose. The main effect of plasma on thermal-gravimetry was observed at temperatures below 100 oC. The microstructure of plasma-treated samples showed an increase of cellulose fiberʹs roughness and swelling, followed by the transformation of microfibrils to nanofibrils with a diameter of 80 nm. The elemental analysis also confirmed sulfur and calcium removal from walnut shell, carbon amount decrement, and the oxygen level increment in extracted cellulose. An increase in carbon and a decrease in oxygen amount were observed in plasma-treated samples compared to the control. Based on the results, although plasma pretreatment did not significantly affect extraction efficiency, the physicichemical properties of extracted cellulose considerably changed after exposure to DBD plasma. This pretreatment could result in the production of nanofibril without the application of chemical treatment. Keywords: DBD plasma, Cellulose, Walnut shell, Structural features.

نفيسه سلطاني زاده

ميلاد فتحي

هاجر شكر چي زاده، محمد ديناري