Construction of Nanocellulose Aerogels with Mechanical Flexibility and pH-Responsive Properties via a Cross-Linker Structure Design Strategy

Although chemical cross-linking could greatly improve the mechanical flexibility of nanocellulose aerogels, current cross-linking strategies still have some shortcomings, such as a complex cross-linking process or toxic cross-linking agents. Herein, a copolymer (PDMAEMA-co-PVTMS) containing polyorganosiloxane and a pH-responsive segment was designed and synthesized via free-radical polymerization. The polyorganosiloxane could covalently cross-link to a cellulose nanofiber (CNF) and the dimethylaminoethyl methacrylate (DMAEMA) section could endow the aerogel with pH-responsive properties. The prepared aerogel showed a three-dimensional (3D) porous structure with a specific surface area as high as 53.88 m2/g. Furthermore, the cross-linked aerogel had excellent mechanical flexibility and its maximum stress could be maintained above 71.3% of the initial value (11.88 kPa) after 50 cycles. More importantly, the aerogel could turn from a positive charge to a negative charge when the environment changed from acidity to alkalinity. It could be used to adsorb bovine serum albumin (BSA) in an acidic environment and adsorption capacity could reach 107 mg/g. It also could release 97% of adsorbed BSA in an alkaline environment. This work provided a new strategy to construct functional cellulose aerogels with excellent mechanical properties through structural design of a cross-linking agent containing organosiloxane.