Carboxymethyl cellulose aerogels with Laponite, halloysite or kaolin: effect of clay type on shrinkage, compressive and heat-transfer behavior

Abstract Freeze-dried carboxymethyl cellulose aerogels are light but can shrink during drying and are mechanically weak. This study examined how the type of clay changes the structure and properties of these aerogels, comparing the synthetic smectite Laponite (2:1 layered discs) with the 1:1 aluminosilicates halloysite (nanotubes) and kaolin (platelets). A 0.8% (w/v) carboxymethyl cellulose solution was mixed in equal volumes with clay dispersions of 0.4–2.0% (w/v) and freeze-dried. Compressive behavior was assessed by uniaxial compression, heat transfer by infrared thermography on a 200°C hot plate, and polymer–clay interactions by Fourier-transform infrared spectroscopy. Aerogels containing Laponite retained about 37% of their cast volume, compared with about 20% for those containing halloysite or kaolin. Because the compression tests ended at very different strains, the composites were compared at 10% strain. At this strain, the Laponite composites carried 2.6–10.3 kPa, 2.0–7.7 times more than the halloysite and kaolin composites, and the stress increased with Laponite concentration, whereas the halloysite and kaolin composites, which have nearly the same composition but different shapes, behaved similarly (1.2–1.6 kPa). After 30 min on the hot plate, the lowest top-surface temperatures (81.6–82.9°C, compared with 90.1°C for the neat aerogel) were recorded for 2.0% halloysite and 1.2–1.6% kaolin. The results suggest that Laponite forms a continuous network with the polymer that limits shrinkage and stiffens the aerogel, whereas halloysite and kaolin act mainly as fillers. As thermal conductivity and porosity were not measured and heights and densities were estimated, the results describe comparative trends.