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Zhu, Jiaying

University of British Columbia

Cellulose, a natural polymer, has emerged as a promising alternative to petroleum-based materials, offering sustainable and environmentally friendly solutions to address climate change and plastic pollution. Leveraging its intrinsic moisture-sensitive properties, cellulose can be utilized to create a wide range of moisture-responsive materials (MRMs). However, several challenges hinder the practical application of these materials, including prolonged response times, weak interfacial bonding, and restricted hydrophilicity. This thesis addresses these limitations by utilizing cellulose nanofibrils (CNFs) in combination with innovative material design, scalable and facile fabrication techniques, and fundamental mechanism validation. The resulting CNF-based films were further integrated into functional devices to demonstrate proof-of-concept applications. This work initiates an in-depth investigation into the impact of CNF surface charge density on hygroscopicity and ionic conductivity. By manipulating the inherent properties of cellulose, humidity sensing capabilities were significantly enhanced. An increase in surface charge density led to improved water uptake and charge carrier density in CNF films, achieving high humidity sensitivity that outperforms most reported polymer-based humidity sensors. However, the dense structure of CNFs resulted in unsatisfactory response and recovery times. To address this challenge, a bilayer structure composed of CNF and microfibrillated cellulose (MFC) was developed, bonded through chitosan. This innovative design exploits the hierarchical porous structure and differential hygroscopicity of CNF and MFC to create an effective wettability gradient, facilitating rapid and stable moisture transport. The observed moisture-induced structural deformations further inspired an exploration of the hydro-swelling properties of cellulosic films. This property was harnessed to develop a hydration-driven imprinting method, enabling facile surface patterning and demonstrating the versatility of CNF-based materials. The impact of water content on the mechanical properties of CNF was systematically analyzed, revealing its potential for dynamic surface patterning through bulk deformation. A moisture-responsive film comprising a CNF top layer and a polyvinyl alcohol (PVA)/glycerol bottom layer was fabricated, enabling dynamic regulation of light and heat under varying weather conditions. Overall, the approaches outlined in this thesis highlight the immense potential of CNFs in the development of cellulose-based MRMs. These advancements address critical limitations and pave the way for broader adoption of sustainable, high-performance materials in diverse applications.

Text

2025-04-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90880

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/