Design and synthesis of waterborne light-responsive cellulose nanocrystal/fluorinated polyacrylate films toward oil/water repellent and self-healing properties

The development of environmentally friendly waterborne polymeric materials is becoming critical today. In this study, a kind of self-healing cellulose nanocrystal/fluorinated polyacrylate based on the reversible photo-induced dimerization of coumarin groups was prepared via RAFT-mediated Pickering emulsion polymerization using cellulose nanocrystal (CNC) particles modified with light-responsive amphiphilic copolymers as Pickering stabilizers. Emulsion polymerization and latex film properties were significantly varied in dependence on the amount of 7-(2-methacryloyloxyethoxy)-4-methylcoumarin (CMA) monomer. Hydrophobic, oleophobic and mechanical properties of the latex film were dynamic in response to UV light. The maximum water contact angle and CH2I2 contact angle increased by 6.1 degrees and 2.3 degrees on the irradiation of UV light at 365 nm, respectively. The tensile strength of latex film increased initially with increasing amount of CMA increased, from 0 up to 4 wt%, and then decreased. The maximum tensile value increased from 3.0 MPa to 6.4 MPa after the dimerization reaction activated by 365 nm UV light. Results from atomic force microscope (AFM) and energy dispersive X-ray spectrometer (EDX) revealed that latex film possessed a roughness structure and the fluorine had a remarkable enrichment on the film-air interface. Moreover, latex films showed an excellent surface scratch self-healing ability owing to the reversible dimerization reaction of the coumarin groups, and the reversible dimerization reaction of coumarin groups within cellulose nanocrystal/fluorinated polyacrylate polymer was extensively investigated via FT-IR spectrometer and differential scanning calorimetry (DSC). The fruitful outcomes indicated that light-responsive cellulose nanocrystal/fluorinated polyacrylate exhibited a greatly potential application as a smart material.