Preparation And Characterization Of Composite Thin Film From Cellulose Nanocrystals And Cationic Polyelectrolytes Utilizing Layer-by-layer Deposition

Cellulose, the most abundant natural polymer on the earth has been employed as a functional material because of its renewability, biodegradability, and derivatizability. It is the main component of most plant biomass, it can be found in cotton, wood, ramie tunicates (sea animals), in green algae, fungi and can as well be synthesized by cellulose producing bacteria. Acid hydrolysis of cellulose fibers yields highly crystalline rod like particles through selective degradation of the more accessible material. The cellulose nanocrystals (CNC) that result from this degradation are of colloidal dimensions, and when stabilized, they form aqueous suspensions, the properties and applications of which were our main focused in this research.The hydrolysis conditions and sources of cellulose are known to affect the properties of the resulting nanocrystals. For example, a longer reaction time leads to shorter nanocrystals. Different acids also affect the suspension properties:hydrochloric acid hydrolysis yields cellulose rods with minimal surface charge, whereas the use of sulfuric acid provides highly stable aqueous suspensions, due to the esterification of surface hydroxyl groups to give charged sulfate groups.Development of novel bio-based nanocomposites are fundamental to reduces the dependence on fossil resources and provide a sustainable future. In light of this global problem, CNC have raised interest due to their remarkable mechanical properties. Adequate design of nanocomposites requires a fundamental understanding of how the structure affects the mechanical properties of the material. However, contradictory results in the literature have revealed a lack of comprehension of this relationship for CNC based composites.In this work, CNC,3-4nm in diameter and100-300nm long, with negative charge were obtained by sulfuric acid hydrolysis from cotton cellulose pulp. The CNCs were layer-by-layer assembled with cationic polyelectrolytes, such as poly(allylamine hydrochloride)(PAH), and" poly(diallyldimethylammonium chloride)(PDDA) to prepare the composite thin films. The interaction between CNC and the polyelectrolytes were confirmed by FT-IR spectroscopy. SEM, and AFM images revealed that individual crystallites disperse uniformly exhibiting needle shaped structures and some aggregates for CNC particle, and also demonstrated the highly nanopours network on the film surface and smooth surface of PDDA/CNC, and decrease on PAH/CNC. Additionally, the wettability of coated films of PDDA/CNC was observed to be higher than PAH/CNC, which makes them suitable candidate for anti-reflective coated films. TGA curves revealed that the PAH/CNC composite exhibited higher thermal stability than the PDDA/CNC, and also suggests that the PDDA/CNC have a large amount of water than PAH/CNC.Besides synthetic cationic polyelectrolytes, CNCs were assembled with cationic polyelectrolytes from natural polymers, chitosan (CH), cationic guar gum (CGG), and cationic cellulose (Ccell). This study explored the effects of pH and salt concentration on the growth and properties of CNC films CH, CGG, and Ccell. Therefore, the results have presented that the growth of CGG/CNC and CH/CNC films and the thickness depends on the pH values. Also, Ccell/CNC film appeared to be with varied thickness with increased pH value, and we got the best thickness at pH2.