Functionalizing Wood Fibers with Layered Double Hydroxides for Anti-mold and Flame-retardant Properties

Abstract

Driven by global imperatives for sustainability, green building, and carbon neutrality, wood fibers and their composites have gained prominence as renewable alternatives to synthetic materials. However, their inherent susceptibility to mold growth and flammability pose significant challenges to safety, durability, and broader application. This thesis therefore focuses on endowing wood fibers with anti mold and flame retardant functionalities through an integrated approach that couples molecular dynamics (MD) simulations with experiments. Two-dimensional layered double hydroxides (LDHs) are leveraged as key modifiers to functionalize wood fibers, guided by atomistic-level insights and validated through scalable fabrication and performance testing. The objective is to deliver sustainable and innovative solutions that enhance the health, safety, and environmental compatibility of wood fiber composites throughout their life cycle.

To address mold contamination, a facile strategy is developed to fabricate anti-mold wood fibers via in situ growth of Zn-Al LDHs followed by a hydrophobic modification with stearic acid (STA). MD simulations reveal that interfacial electrostatic interactions drive the adhesion of LDH to cellulose hydroxyls, while STA organizes into low‑surface‑energy domains that reduce water uptake. The modified fibers exhibit strong anti-mold activity against common fungi, including Aspergillus, Trichoderma, and Penicillium, showing clear inhibition zones and no fungal growth in accelerated tests. Further analyses reveal that the direct antifungal effect arises from electrostatic adsorption, oxidative stress induction, and metal ion release, while the indirect effect is due to hydrophobicity.

Before engineering flame-retardant wood fibers, a fundamental understanding of cellulose combustion chemistry is established through reactive forcefield (ReaxFF) MD simulations. The detailed reaction scheme reveals that the formation of main combustion products, such as carbon monoxide, carbon dioxide, and water, highly depends on free radical reactions. Toxic species such as formaldehyde, glycolaldehyde, and carbon monoxide can be inhibited through effective control of hydroxymethyl, acetyl, and formyl radicals. Effective collisions promote combustion by enhancing the activity of free radicals such as hydroxyl groups. Kinetic analyses reveal that the decomposition follows first-order reaction kinetics. This atomistic insight provides a scientific foundation for the rational design of flame-retardant systems.

Building on atomistic insights, a hierarchical flame retardant coating is constructed by integrating MgAl LDH with reduced graphene oxide (rGO) on wood fibers. The fabrication involves dip-coating with graphene oxide (GO) followed by in situ hydrothermal growth of LDH nanosheets, during which GO is simultaneously reduced to rGO. The resulting LDH@rGO@wood fiber shows significantly improved fire safety, with reductions of 20.0% in peak heat release rate, 28.7% in total heat release, 41.5% in total smoke production, and 26.6% in peak CO production rate, alongside a 75.6% increase in char residue compared with pristine wood fibers. These enhancements arise from a synergistic interplay effect: rGO promotes uniform LDH dispersion and creates a tortuous path that impedes heat and mass transfer, while LDH catalyzes protective char formation and releases non-combustible gases to dilute flammable volatiles.

In summary, this thesis has innovatively established a simulation-driven, experiment-validated framework for engineering multifunctional wood fibers. Sustainable LDH-based strategies are developed to produce mold-resistant, flame-retardant wood fibers for enhanced safety and durability. The atomic-scale insights provide a scientific basis for rational material design. The developed functionalization routes are scalable and effective, promising to enable high-performance biocomposites for applications in green construction, automotive, and smart packaging.

Date of Award	21 Aug 2026
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Denvid LAU (Supervisor)