High strength, anti-freezing and conductive silkworm excrement cellulose-based ionic hydrogel with physical-chemical double cross-linked for pressure sensing

Recently, ionic conductive hydrogels have attracted extensive attention in the field of flexible pressure sensors due to their mechanical flexibility and high conductivity. However, the trade-off between the high electrical and mechanical properties of ionic conductive hydrogels and the loss of mechanical and electrical properties of traditional high water content hydrogels at low temperature are still the main hurdles in this area. Herein, a rigid Ca-rich silkworm excrement cellulose (SEC-Ca) extracted from silkworm breeding waste was prepared. SEC-Ca was combined with the flexible hydroxypropyl methylcellulose (HPMC) molecules through hydrogen bonding and double ionic bonds of Zn2+ and Ca2+ to obtain the physical network SEC@HPMC-(Zn2+/Ca2+). Then, the covalently cross-linked network of polyacrylamide (PAAM) and the physical network were cross-linked by hydrogen bonding to obtain the physical-chemical double cross-linked hydrogel (SEC@HPMC-(Zn2+/Ca2+)/ PAAM). The hydrogel showed excellent compression properties (95 %, 4.08 MPa), high ionic conductivity (4.63 S/m at 25 degrees C) and excellent frost resistance (possessing ionic conductivity of 1.20 S/m at -70 degrees C). Notably, the hydrogel can monitor pressure changes in a wide temperature range (-60-25 degrees C) with high sensitivity, stability and durability. This newly fabricated hydrogel-based pressure sensors can be deemed of great prospects for large-scale application of pressure detection at ultra-low temperatures.