Organic Solvent-Free Fabrication of Durable and Multifunctional Superhydrophobic Paper from Waterborne Fluorinated Cellulose Nanofiber Building Blocks

Abstract

In view of a great demand for paper-based technologies, nonwettable fibrous substrates with excellent durability have drawn much attention in recent years. In this context, the use of cellulose nanofibers (CNFs), the smallest unit of cellulosic substrates (5-20 nm wide and 500 nm to several microns in length), to design waterproof paper can be an economical and smart approach. In this study, an eco-friendly and facile methodology to develop a multifunctional waterproof paper via the fabrication of fluoroalkyl functionalized CNFs in the aqueous medium is presented. This strategy avoids the need for organic solvents, thereby minimizing cost as well as reducing safety and environmental concerns. Besides, it widens the applicability of such materials as nanocellulose-based aqueous coatings on hard and soft substrates including paper, in large areas. Water droplets showed a contact angle of 160° (±2°) over these surfaces and rolled off easily. While native CNFs are extremely hydrophilic and can be dispersed in water easily, these waterborne fluorinated CNFs allow the fabrication of a superhydrophobic film that does not redisperse upon submersion in water. Incorporated chemical functionalities provide excellent durability toward mechanochemical damages of relevance to daily use such as knife scratch, sand abrasion, spillage of organic solvents, etc. Mechanical flexibility of the chemically modified CNF composed paper remains intact despite its enhanced mechanical strength, without additives. Superhydrophobicity induced excellent microbial resistance of the waterproof paper which expands its utility in various paper-based technologies. This includes waterproof electronics, currency, books, etc., where the integrity of the fibers, as demonstrated here, is a much-needed criterion.

Water‐Based Robust Transparent Superamphiphobic Coatings for Resistance to Condensation, Frosting, Icing, and Fouling

“…Owing to the competition between transparency and surface roughness, realizing high transparency of most superamphiphobic coatings, especially water‐based superamphiphobic coatings, is difficult. [ 39 ] Figure 1d reveals that the transmittance of the pristine glass and the WSC‐coated glass is similar, and the coated glass is even antireflective at wavelengths ranging from 440 to 800 nm. In addition, the clear university logos beneath the coated glass and spherical droplets of water, olive oil, and hexadecane on the coated glass demonstrate that the coated glass is simultaneously transparent and superamphiphobic.…”

“…A few strategies have been reported about preparing water‐based superhydrophobic coatings and even water‐based superamphiphobic coatings. [ 37–44 ] The focus of the present studies is on the preparation of these coatings. However, high performances of water‐based superhydrophobic coatings are neglected which are the key factors in wide, long‐term, and efficient application, due to the difficulty in achieving them.…”

Drying of the Natural Fibers as A Solvent-Free Way to Improve the Cellulose-Filled Polymer Composite Performance

“…It has been found that cellulose requires some specific surface treatments in order to obtain a polymer composite of a sufficient performance. Fortunately, there are many known examples of chemical modifications that are carried out in neat conditions and in solvent-free environments, e.g., acetylation [41,42], carboxylation [43,44], and fluorination [45]. Moreover, cellulose is not only being modified in mild conditions; other treatments include lignocellulose acetylation [46] and lignin acetylation [47].…”

Development of a Transparent Coating to Enhance Self-Cleaning Capability and Strength in Conventional Paper

“…For these reasons, researchers have attempted to design a superhydrophobic coating that is self-cleaning, dust-proof, moisture-proof, and anticorrosion [2][3][4][5]. Examples of such studies include Ogihara et al [6], who reported that superhydrophobic coatings can be deposited on paper by spraying alcohol suspensions of SiO 2 nanoparticles; Baidya et al [7] described a simplistic methodology to develop a superhydrophobic paper via manufacture of fluoroalkyl functionalized cellulose nanofibers (CNFs); Shi et al [8] prepared a superhydrophobic nanocomposite coating using hydrophobic silica nanoparticles as a filter and polyvinylidene fluoride (PVDF) as a film-forming material, which was applied to the paper's surface through a simple, one-step spray dispersion method; Wang et al [9] manufactured a superhydrophobic paper by coating it with silica sol using tetraethylorthosilicate (TEOS) and trimethylethoxysilane (TMES) as a precursor and coprecursor, respectively. However, the superhydrophobic coatings prepared by the above methods are lacking resistance to oily substances and thus do not have a selfcleaning effect [10].…”