Aerogel beads improve rigid PU foam insulation and fire performance

The work is particularly relevant to the insulation industry. PIR foams are among the best-performing conventional insulation materials, combining low thermal conductivity with strength, low weight and established manufacturing processes. Aerogels can potentially provide still lower thermal conductivity, but their brittleness, durability and cost have limited their use in mainstream insulation products.

The new study seeks to combine the advantages of the two materials. Rather than using aerogel as a separate blanket or panel, the researchers packed chemically crosslinked aerogel beads into rigid PU foam.

The aerogel beads were designed to withstand demanding environmental conditions and provide self-intumescent fire protection. Crosslinking strengthened the aerogel structure, addressing the tendency of conventional aerogels to fracture or collapse during handling and foam processing.

The researchers used an in-situ packing method that allowed a comparatively high concentration of beads to be introduced while maintaining bonding between the aerogel and polyurethane phases. This is important because the direct addition of large quantities of particulate fillers to a PU formulation can increase viscosity, interfere with foaming and weaken the resulting cell structure.

Tests showed that the packed-bead structure reduced the thermal conductivity of the rigid PU foam while increasing its mechanical stiffness. The researchers attributed the insulation improvement to the highly porous structure of the aerogel beads and their ability to restrict heat transfer through the composite.

The beads also reinforced the foam, rather than producing the reduction in mechanical performance commonly associated with high aerogel loadings. 

According to the researchers, chemical crosslinking improved the durability of the beads and helped them maintain their structure within the foam.
Fire testing showed that the best-performing composite reduced peak heat release rate by 36.2% and peak smoke production rate by 43.2% compared with the unmodified rigid PU foam.

When exposed to fire, the aerogel beads formed an expanded protective char. This intumescent layer restricted heat and oxygen transfer and impeded the release of combustible decomposition products from the polyurethane.

The combination of lower thermal conductivity and improved stiffness could eventually allow insulation products to provide a given thermal resistance at reduced thickness. It could also offer a route to improving the fire performance of rigid PU insulation without relying solely on conventional additive flame retardants.

However, the work remains at the laboratory stage. Aerogel production cost, composite processing at industrial scale, long-term thermal aging and performance under moisture exposure will all require further investigation. Building applications would also require testing and certification of complete insulation products rather than small material samples.

The work was published in the academic journal Polymer Degradation and Stability.

Image: an AI-generated illustration for decorative purposes only that is not intend to convey an accurate depiction of the mechanism

Polymer Degradation and Stability