Clay-Based Aerogel Composites

Clay-based aerogel composites are aerogels with remarkable features that include good fire-retardant properties, low gas permeability, and better modulus compared to neat clay aerogels. They require low energy in their production and cheap to produce compared to silica aerogels. The inherent safety and environmental friendliness in their processing make them desirable to manufacturers. However, clay-based aerogels are stymied with undesirable poor mechanical strengths and high densities. These two undesirable properties can limit their applications. Clay-based aerogels find application in the construction industry as packaging and insulating material due to their ultralow thermal conductivity and highly porous structure. This chapter presents the state-of-the-art of clay-based aerogels composites, their strength, and limitation as well as applications. Based on the main findings, a future direction of research on these interesting composites was proposed. The current review revealed that the most studied clay mineral to produce aerogel is Smectite-montmorillonite. Smectite-montmorillonite has been proven to be the best clay due to its high cation exchange capacity, swelling ability, and high surface area. Clay aerogel composites synthesis process can be summed up in three steps, namely (i) composite suspension or gel preparation, (ii) freeze-drying of gel to form ice crystals, and (iii) sublimation of ice crystals at low temperature. To improve its poor mechanical strength, commonly used enhancers and fillers for clay-based composites include natural polymers (e.g. casein, cellulose, chitin, polysaccharide, and lignin) and synthetic polymers such as epoxy, polyethyleneimine, polyamides, PVA, among few others. Clay-based composites have applications in several industries. They find application in the construction industry as insulation and adsorbent materials, microelectronics (polyamide/clay), automobile industry (epoxy/clay for tire production), thermal and acoustic insulation, catalyst support in pharmaceutical industries (casein/clay), and biomaterials (for tissue engineering and drug delivery systems, etc.). The range of potential applications of clay-based composites reinforces its importance, and the need to perfect the production process in terms of economics, sustainability, and applications. It is still very expensive to produce clay-based composites but cheaper compared to other types of aerogels. It appears that the economics of production of lignin/clay-based aerogel composites is the most attractive for now. The future research work should be directed to cheap enhancers, optimization of production techniques, and the identification of the most sustainable production routes.