Fabrication of Environmental Friendly Cellulose/Cellulose Derivative Based Functional Materials and Their Applications

環境友好型纖維素和纖維素衍生物基功能材料的製備及其應用

Student thesis: Doctoral Thesis

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Award date20 Oct 2020

Abstract

Cellulose, as the most abundant polymer from nature, has attracted a lot of research and application interest due to its renewability, biocompatibility and biodegradability. When cellulose is disintegrated into microfibril level, nanocellulose exhibits its superiority of excellent mechanical properties, high aspect ratios and self-assembly or optical transparency under certain conditions. However, the difficulty of dissolving cellulose in most of industrial solvents owing to its strong hydrogen bonds has limited its industrial processing and application. Therefore, the modification of cellulose/nanocellulose and the development of cellulose derivatives provide means at expanding the applications of nanocellulose. In this research, functional cellulose and cellulose derivatives have been fabricated. Two new attempts have been studied to push the application of cellulose into frontier areas:

(1) Cellulose-based composite aerogels modified by aluminium hydroxide and silane as multifunctional acoustic absorbing material. Aerogels with porous structure have high surface area and can benefit acoustic absorption property. In this part of the research, nanocellulose is initially modified by TEMPO-mediated oxidation method and subsequently treated by in-situ synthesis of aluminium hydroxide. The composite cellulose aerogels are prepared by freeze-drying and followed by silanization modification. The composites exhibit favorable acoustic adsorption, especially a maximum sound absorption coefficient of 0.98 at the high frequency range due to its appropriate porosity (48.5±4.0 %) and the porous structure. The existence of aluminium hydroxide not only improves the thermal stability and flame retardant behaviour of the composite aerogels, but also synergistically enhances the mechanical properties. Furthermore, the silanization allows the hydrophilic cellulose material change to hydrophobic. The whole material processing can be carried out under a mild aqueous and facile condition.

(2) Cellulose acetate reinforced PEG-based all-solid-state polymer electrolyte in lithium battery. Cellulose acetate is derived from the cellulose by acetylation of the hydroxyl groups in the molecules with acetic acid and acetic anhydride which makes it soluble in many organic solvents. Due to its processability and good mechanical property, cellulose acetate can be applied as separator in batteries. In this part of the work, cellulose acetate is added in the Si doped PEG-based solid polymer electrolyte to balance the mechanical strength and ion conduction of the membranes. It can be made homogeneous with the electrolyte and lithium salt. The addition of cellulose acetate improves the tensile strength and thermal stability of the membranes, while it also hinders the crystallization of PEG in order to maintain the ion conductivity. The electrochemical window of the membranes reaches over 5.0 V (vs. Li/Li+). More importantly, Li/LiFePO4 cells assembled with the membranes deliver the capacity retention from 46.8% to 66.7% after 100 cycles with the judicious addition of cellulose acetate, which can be explained by the formation of more stable solid electrolyte interface and the suppression of lithium dendrite and dead lithium.

In summary, the functional modification of cellulose and its derivative have been demonstrated to playing important roles as matrix frame or enhancement filler. With functional modifications, the materials exhibit outstanding performances as acoustic adsorption material and energy storage material to relieve environmental pollution and energy crisis.