CELLULOSE CHEMISTRY AND TECHNOLOGY Cellulose Chem. Technol., 55 (7-8), 755-770(2021) COMPARISON OF PROPERTIES OF CELLULOSE NANOMATERIALS(CNMs) OBTAINED FROM SUNFLOWER STALKS EKREM DURMAZ and SAIM ATE Kastamonu University, Faculty of Forestry, Department of Forest Industrial Engineering, 37150, Kastamonu, Turkey Corresponding author: E. Durmaz, edurmaz@kastamonu.edu.tr Received March 23, 2021 This study aimed to investigate the usability of sunflower stalks, which is one of the most significant agricultural residues in Turkey, in the production of cellulose nanomaterials (CNMs). Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were produced by using a grinding method and acid hydrolysis, respectively. The average width and length of CNCs were found as 13.91 ± 3.09 nm and 60.44 ± 21.06 nm, respectively. Besides, the average width of CNFs was determined as 15.03 ± 3.68 nm. The crystallinity index of CNFs and CNCs was determined as 82.64% and 83.09%, respectively. Although the main thermal degradation stage of CNCs started at higher temperature than that of CNFs, the latter were more stable than CNCs at high temperatures. Furthermore, the chemical bonds in the raw material, bleached fiber, CNCs and CNFs were investigated with FTIR analysis. Consequently, it was seen that sunflower stalks can be a suitable raw material for the production of CNMs. Keywords: sunflower stalks, agricultural residues, cellulose nanofibrils, cellulose nanocrystals INTRODUCTION Cellulose is one of the essential constituents of the cell wall of lignocellulosic biomass and it has been used in industries such as paper and packaging, 1 textiles and foods, 2 pharmaceutics and cosmetics, 3 as well as adhesive industries 4 , for many years. Nevertheless, research efforts have been made to adapt cellulose to nanotech applications in the last decades. 5 Due to their adjustable nature, cellulose nanomaterials (CNMs), alone or in combination with other polymers in the production of composites, have been extensively used in different areas, including composite films, packaging, paper, tissue engineering, bioprinting, textiles, regenerative medicine, optoelectronics, energy, environmental remediation, cosmetics, foods etc., 6-11 owing to their outstanding properties, such as three- dimensional nano-structure, advanced mechanical strength, high crystallinity, high surface area, advanced hydrophilicity, biodegradability, biocompatibility and optical transparency. 12-14 Cellulose nanomaterials are generally categorized into two basic groups related to their production process, i.e., cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). According to ISO/TS 20477, 15 cellulose nanocrystals are also called nanocrystalline cellulose (NCC) or cellulose nanowhiskers (CNWs), while cellulose nanofibrils are also referred to as nanofibrillated cellulose (NFC), nanofibrillar cellulose (NFC) or cellulose nanofibre (CNF), different terminology being used in the literature. CNFs are manufactured by a high-shear mechanical treatment of purified and bleached biomass pulp using a microfluidizer, high- pressure homogenizer or grinder. In addition, some mechanical, chemical or enzymatic pretreatments are applied to ease the defibrillation in the production of CNFs. Contrary to CNFs, CNCs are usually achieved by strong acid hydrolysis of purified and bleached biomass pulp. As a result of these various processes, CNCs exhibit rice-like shape, with only crystalline zones, whereas CNFs have spaghetti-like structure, with both crystalline and amorphous zones. 1,16 The width and length of CNFs are 3-100 nm and 100 μm, respectively, while their aspect ratio is usually greater than 10. Likewise, the width and length of CNCs are 3-50 nm and from