Thermo-responsive nanofibrillated cellulose by polyelectrolyte adsorption

In this study, thermo-responsive nanofibrillated cellulose (NFC) has been produced by the adsorption of thermo-responsive polyelectrolytes to the NFC. Three block copolymers were synthesized in which the polyelectrolyte block was composed of quaternized poly(2-(dimethylamino)ethyl methacrylate) (qPDMAEMA) and the thermo-responsive block was composed of poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA). The block copolymers were synthesized employing atom transfer radical polymerization (ATRP) and the PDMAEMA block was utilized as a macroinitiator for the polymerizations of PDEGMA. The length and charge of the PDMAEMA block were kept constant in all three block copolymers, while three different molecular weights of the PDEGMA block was synthesized. The PDMAEMA block was quaternized to introduce positive charges and the block copolymers were subsequently adsorbed onto the negatively charged NFC that was dispersed in water. The lower critical solution temperatures (LCSTs) of the free block copolymers in solution were analyzed by dynamic light scattering (DLS). The composites were analyzed by QCM-D, FT-IR and TGA, which clearly showed an adsorption of the block copolymer onto the NFC. The grafted NFC showed a thermo-responsive behavior in solution upon heating and cooling, thus supporting that the properties of the polyelectrolyte can be transferred to the cellulose. By this methodology, thermo-responsive NFC materials can be produced in a straight-forward manner in water dispersions, without performing any chemical reactions on the NFC.