Stretchable and Thermally Stable Cellulose Film

Abstract

Glass has been widely used as a substrate for display, because of its high transparency and low thermal expansion coefficient. However, glass is not suitable for stretchable displays because it is easily broken and has no ductility. Instead of glass, synthetic polymers can be alternative. However, most synthetic polymers have low transparency and high thermal expansion coefficient. Therefore, as a substitute for glass or synthetic polymer, cellulose nano-fiber was used to make transparent, stretchable and thermally stable film.1 Cellulose is composed of β-(1,4) linked D-glucose unit. Glucose has three hydroxyl groups on surfaces and it can form hydrogen bonds with Nitrogen, Oxygen and Fluorine. Cellulose composed of glucose has many hydroxyl groups. Due to these hydroxyl groups, they are dense with strong hydrogen bonds between the fibers. The cellulose is formed by bundles of many nano-fibers. And it can be used to make a flexible film like paper. However, there is no elasticity because of the intense hydrogen bonding between the molecules.2 In order to impart elasticity to the cellulose, it is necessary to loosen the molecular structure and a network structure. Loosening the molecular structure is possible by modifying the hydroxyl group to another functional group so that the cellulose does not allow hydrogen bonding, or by using a solvent that interrupts and breaks hydrogen bonds between molecules. It is not enough to break hydrogen bonds to give elasticity, so that cross-linking was used to form a network structure. Prior to cross-linking, cellulose fiber was treated by homogenizer to increase the surface area and reaction efficiency of the cellulose. In this process, cellulose are nano fibrillized. Then, polymeric aldehyde was added as a cross-linking agent to the cellulose nano fiber. In this work, the properties of the stretchable cellulose will be presented. To investigate thermal stability, DSC and TGA analyzes were performed. Tg was measured by DSC analysis and thermal decomposition temperature of cellulose film was measured by TGA anaylsis. Transparency was measured by the transmittance at various wavelengths. To determine the strength and elongation, tensile strength and strain were also measured. REFERENCES(1) Nogi, M; Iwamoto, S; Nakagaito, A; Yano, H. Optically Transparent Nanofiber Paper. 2009, Adv. Mater. 21, 1595–1598(2) Striegel, A. Theory and applications of DMAc/LiCl in the analysis of polysaccharides. 1997, Carbohydrate Polymers 34, 267-214