Production and characterization of some nanocellulose derivatives from sunflower stalks and their evaluation in different application areas

With the increase in social environmental consciousness, the interest to the production of cellulose-based nanomaterials from renewable natural resources has rapidly increased. Nanocellulosic particles allow the design of special materials with high performance that can eliminate present environmental and sustainability problems. Increasing interest for this kind of new generation products, which are called bio-based nanomaterials, will replace traditional petroleum-based materials due to fluctuations in oil prices and limited resources. Within the scope of this thesis, sunflower stalk, produced with significant amounts in Turkey, were used as raw material. This lignocellulosic raw material potential could not be used effectively in any way as industrially except for burning, leaving in the field, etc. Considering the optimum conditions in the literature, nanofibrillated cellulose (CNFs) was produced via mechanical method and nanocrystalline cellulose (CNCs) was obtained by chemical method from waste sunflower stalks. In addition to the amount of energy consumed in the grinding process stages during CNF production, turbidity, zeta potential, advanced fiber morphology analyzes, crystallinity, thermal and chemical reactive groups of both CNF and CNC samples were determined. Also some results for nanocellulose samples were analyzed comparatively both raw material and bleached fiber. Nanocomposite films were produced by mixing CNCs and CNFs with different amounts of boric acid (BA) and polyvinyl alcohol (PVA) as matrix, and the changes in chemical bond structures, thermal properties and mechanical properties of these nanocomposite films were compared each other. When chemical reactive groups of nanocomposite films reinforced with BA were examined and characteristic B–O–B, B–O–C ether bonds reflected the interactions between CNFs and CNCs with BA. Changing in PVA ratios did not affect the chemical bond structures of nanocomposite films. It was observed that the addition of BA to CNF and CNC suspensions improved the thermal resistance of nanocomposite films at high temperatures between 25% and 40%. The addition of PVA at different ratios to CNF and CNC suspensions reduced the thermal properties of nanocomposite films between 10% – 15%, in contrary to BA. Considering the mechanical properties of nanocomposite films, it was determined that the addition of BA to both CNC and CNF films decreased the tensile strength of these film samples up to 90%. The elasticity modulus of CNF and CNC film samples decreased between 15% to 90% with increasing the ratios of PVA or BA matrixes. Addition of PVA to pure CNF and CNC composite films increased the elongation at break of these nanocomposites, whereas addition of BA decreased it. In addition the gloss values of plywood surfaces coated with nanocellulose suspensions changed depending on the nanocellulose type, matrix type and number of coating layers, it was determined that the coated plywood surfaces had low (less than 10 GU) and medium (between 10 – 70 GU) gloss properties. When the surface hardness test results of the plywood were examined, it was seen that the increase in the number of coating layers using with CNF and CNC suspensions, the addition of different matrixes increased the pencil hardness values of the plywoods to the maximum level (7H). It was determined that the addition of BA, PVA and MF with different concentrations to the CNF and CNC suspensions reduced the contact angles of the plywoods coated with these nanoparticles by decreasing the surface hydrophobicity. CNF and CNC suspensions, added to the recycling papers produced from waste corrugated cardboard, newsprint and office paper pulps in different proportions, were also used in the coating of unbleached kraft papers. It was determined that the weights in unit area of the coated kraft papers and the recycled papers produced from waste pulps increased between 1% – 15% and the thickness increased between 5% – 35% with the increase in the ratio of CNF and CNC suspensions added to the papers and the number of layers in the applied coating process. It was determined that the mechanical properties of the coated papers did not show a statistically significant improvement after coating with nanocellulose suspension, the mechanical properties of the recycled papers produced by adding CNF suspension to the waste pulps were improved as a result of the statistical analyzes. Besides, the mechanical properties of the recycled papers remained at similar values with the addition of CNC suspension. It was determined that CNF suspension, added to newsprint and corrugated cardboard pulps, improved the water absorption properties of the produced papers between 3% and 18%, while the addition of CNC suspension decreased it. It was determined that the water absorption values increased with the increase in the number of layers applied in the coated papers. It was observed that the porosity properties of the paper samples increased too much with adding CNF suspension and vanished in the coating process with CNF suspension. It was seen that the nanoparticle reinforcement and the coating processes made with them did not affect the optical properties statistically. According to the results, industrial scale production possibilities of bio-based nanocellulose particles obtained from sunflower stalks, important agricultural waste, can be used as a new generation eco-friendly nanomaterials in production of composite films, covering of wooden surfaces, coating and recycling of waste paper. Thus, by encouraging the use of annual plant and agricultural wastes, which have limited usage areas, in nanocellulose production, both a way to benefit from these wastes was found and it was aimed to prevent the use of wood raw material. Consequently, some lignocellulosic raw materials like sunflower stalks can be evaluated with production for value added nano-products industrially.