Facile Fabrication of Superhydrophobic and Photoluminescent Cellulose-Based Paper for Anticounterfeiting Application

　　Anticounterfeiting paper, as one of the conventional anticounterfeiting technologies, can be used in banknotes, securities, certificates, trademarks, product packaging, and other related fields due to its convenience of use and easy identification. However, most of the existing anticounterfeiting paper is prepared by adding functionally modified synthetic fibers during the paper-making process. The synthetic fibers are mainly made by mixing phosphors and polymers such as polypropylene, polyethylene, poly(vinylchloride), polyester, etc. in the melt spinning manufacturing process. Since the length of the synthetic fiber used for paper-making is much longer than that of the conventional cellulose fiber, it was much prone to flocculation, precipitation, or agglomeration during the paper-making process, resulting in poor paper uniformity. Therefore, the replacement of petroleum-based anticounterfeiting packaging materials with biomass-based fiber materials has significant sustainability. However, the inherent high hydrophilicity of the cellulose largely restricts its practical applications which require hydrophobicity (e.g., the packaging products that require cryogenic storage). Therefore, it is increasingly desirable to prepare cellulose fiber based products with hydrophobic characteristics.

　　Figure 1. Excitation (left) and emission (right) spectra of TOC@LaF3:RE3+ composites (a) TOC@LaF3:Eu3+ composites, (b) TOC@LaF3:Tb3+ composites in aqueous solution, and corresponding luminescence images of the composites excited at 365 nm.

　　Figure 2. (a) Optical images of the water droplets on the as-prepared paper surface; (b) shape of a droplet (5 μL) on the as-prepared paper surface; and the circular free-standing paper with water droplets under UV (365 nm) irradiation (c, d).

　　Based on these considerations, herein, we provided a novel cellulose fiber based luminescent and superhydrophobic paper for anticounterfeiting under a humid environment. A novel kind of TEMPO-oxidized cellulose microfibril-based luminescent paper was fabricated by a facile method using LaF3:RE3+ (RE = Eu, Tb) nanocrystals and TiO2 as building blocks. Importantly, TOC introduced abundant carboxyl groups, which are vital for RE ion coordination. Benefiting from the luminescence ability of LaF3:RE3+ and the high flexibility of TOC, the synthesized paper exhibits unique luminescence properties and excellent processability. After HDTMS modification, the as-prepared TOC@LaF3:RE3+@TiO2 paper exhibits good waterproofness and self-cleaning property, which can significantly improve the mechanical strength under a humid environment. The multiple functions of biodegradability, luminescence, and superhydrophobicity of the as-prepared paper can significantly increase the mechanical stability and security in practical anticounterfeiting applications demanding hydrophobicity.

　　The related result “Facile Fabrication of Superhydrophobic and Photoluminescent TEMPO-Oxidized Cellulose-Based Paper for Anticounterfeiting” has been published in the journal ACS Sustainable Chemistry & Engineering.

　　Link to the paper: https://doi/10.1021/acssuschemeng.0c01559