Dynamically bonded cellulose nanocrystal hydrogels: Structure, rheology and fire prevention performance

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Materials

Background:

• Conventional flame retardants often contain non-biodegradable synthetic polymers or inorganic nanoparticles, posing environmental and health concerns.
• There is a need for sustainable, eco-friendly alternatives with comparable or superior fire-retardant properties.

Purpose of the Study:

• To develop novel flame-retardant dynamic covalent hydrogels using wood-derived cellulose nanocrystals (CNCs).
• To address environmental and health issues associated with existing flame-retardant systems.
• To investigate the fire prevention mechanisms and potential for circular use of these plant-based hydrogels.

Main Methods:

• Fabrication of hydrogels by crosslinking CNCs with boronate ester bonds.
• Rheological analysis to determine network elasticity and self-healing properties.
• Fire performance testing on coated wood samples, including ignition delay, limiting oxygen index, and heat release rate.

Main Results:

• The developed hydrogels exhibited tunable elasticity (0.2–3.5 kPa) and immediate self-healing capabilities.
• Coating pine wood with the hydrogels delayed ignition by ~30 s and achieved a limiting oxygen index of 64.5%.
• Increased borax content enhanced fire retardancy, increasing the fire retardancy index by 277% and delaying heat release peaks.

Conclusions:

• Wood-derived cellulose nanocrystal hydrogels offer a sustainable and effective flame-retardant solution.
• The dynamic covalent crosslinking and inherent properties of CNCs contribute to significant fire resistance.
• These plant-based hydrogels demonstrate potential for circular use in preventing wood fires, even post-drying.