Foaming of Recyclable Clays into Energy-Efficient Low-Cost Thermal Insulators

Thermal insulators are crucial to reduce the high energy demands and greenhouse emissions in the construction sector. However, the fabrication of insulating materials that are cost-effective, fire resistant, and environmental-friendly remains a major challenge. In this work, we present a room-temperature processing route to fabricate porous insulators using foams made from recyclable clays that can be locally resourced at very low costs. Foams containing either pure Kaolin or a Kaolin-based clay mixture are produced through mechanical frothing or an in-situ gas-generating reaction. Surface modification of the clay particles using a cationic amphiphilic molecule leads to particle-stabilized foams that are sufficiently strong to withstand the high capillary stresses developed during water evaporation. Self-supporting insulators with up to 90% porosity and thermal conductivities as low as 0.13 W/mK can thus be obtained by simple casting and drying at ambient temperature in an ultralow energy process. Such materials can be recycled by crushing, redispersion in water, and subsequent foaming. Porous structures with higher compressive strength are optionally created by sintering the dried foams at 1000 °C. The obtained porous materials perform comparably well with existing fire-resistant insulators while offering the possibility of closed-loop processing and wide availability from local resources as well as ultralow cost and embodied energy.