Glass bubbles (also known as hollow glass microspheres) can significantly contribute to fire hazard reduction in polymers and composites. Though inherently non-flammable, their real advantage lies in how they influence thermal insulation, flammability behavior, and smoke suppression when used as fillers.
How Glass Bubbles Help Reduce Fire Hazards:
1. Inherently Non-Combustible
Glass bubbles are made from soda-lime-borosilicate glass — an inorganic, non-flammable material. They do not contribute fuel to a fire, unlike organic fillers.
2. Thermal Insulation Barrier
Their hollow structure lowers the overall thermal conductivity of the host material. This creates a thermal barrier that:
Slows down heat transfer through the material.
Delays ignition.
Reduces the heat release rate (HRR) during combustion.
3. Dilution Effect on Combustible Polymers
When mixed into thermoplastics or thermosets:
The glass bubble content replaces part of the flammable organic resin.
This results in reduced fuel availability, effectively lowering the total heat of combustion.
4. Char Promotion and Structural Integrity
In some systems, glass bubbles help maintain structural stability after burning by supporting the formation of a protective char layer.
This char acts as a barrier to oxygen and heat.
Less dripping and flame propagation is observed.
5. Smoke Suppression
Glass bubbles do not decompose into smoke-producing volatiles.
When used in flame-retardant composites, they can help achieve lower smoke density and toxicity — essential for transportation and construction sectors.
Supporting Studies and Applications:
Epoxy/glass bubble composites: Show improved LOI (Limiting Oxygen Index) and delayed time to ignition.
TPU or polyethylene + glass bubble systems: Demonstrate reduced peak HRR and total smoke release.
Often used in fire-rated panels, cable insulation, transportation interiors, and low-flame spread building materials.
Key Considerations:
Glass bubble type (crush strength, particle size, wall thickness) matters.
Synergistic effects are observed when combined with other flame retardants (e.g., aluminum hydroxide, intumescent agents, or phosphorus-based additives).
They also help reduce weight while improving fire safety — crucial for aerospace and EV industries.
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