Enhancement of fines in compressible and conductive cellulose-based foams for pressure sensing

Cellulose-based foams have received increasing attention in sustainable materials due to their biodegradability and environmental friendliness. However, the poor compressive resilience and insufficient structural stability caused by the dynamic hydrogen bond between cellulose molecular chains severely restrict their applications in flexible sensing. In this study, a synergistic strategy combining Fe 3 ⁺ cross-linking and fines reinforcement is successfully developed. Specifically, carboxymethyl cellulose (CMC) serves as the matrix, which is combined with fines to reinforce the network structure. Fines are fragmented microscale pulp fractions separated from beaten bleached softwood pulp after screening with a 200-mesh sieve. And carbon black (CB) is introduced to enhance the conductivity, while Fe 3 ⁺ is introduced for cross-linking to further strengthen the stability of materials, thus yielding the multifunctional CMC/fines/CB/Fe 3 ⁺ composite foams. The resulting foams possess excellent compressive resilience, with a height retention rate of 89.25% after 1000 cycles under 40% strain. Meanwhile, the foams also exhibit ultra-low density (0.0590 g/cm 3 ), high porosity (90.3%) and low thermal conductivity (0.049 W/(m·K)). Crucially, the CMC/fines/CB/Fe 3 ⁺ foams exhibit ultrahigh sensitivity (8.55 kPa⁻ 1 ), which can work stably in both air and underwater environments, and maintain sensing stability after water immersion-drying cycles. This study provides an effective strategy for the preparation of high-performance cellulose-based foams and lays a foundation for the development of waterproof wearable electronic devices.