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Nanocellulose is a cellulose particle with a size of less than 100 nm in one dimension, which is obtained by the chemical or mechanical processing of plant fibers. Research shows that nanocellulose products have great strength and function 17 . To realize the special application of nanocellulose, they are divided into various types, including microcrystalline cellulose (MCC), microfibrillated cellulose (MFC), cellulose nanofibers (CNFs), cel- lulose nanocrystals (CNCs), nanorods, and cellulose whiskers, etc. 18–21 . Compared with plant fibers, CNFs have greater advantages in aspect ratio and specific surface area, with a diameter of 2–100 nm and a length of 500–1000 nm 22 . Turbak et al. 23 and Herrick et al. 24 first used a high-pressure homogenizer to treat wood pulp to prepare CNFs with a diameter of less than 100 nm in 1983. The raw materials for preparing CNFs are not only wood, but also seed fibers, bast fibers, grasses, etc. The properties of CNFs prepared from different raw materials are also different. In order to obtain CNFs with a purer concentration, bamboo pulp fibers with less lignin content were selected as raw materials in this paper 25 . Furthermore, Belbekhouche et al. 26 demonstrated that CNF films are more beneficial than CNC films for barrier properties. Because the surface of CNFs contains a lot of hydroxyl groups, the CNF films have better barrier properties 27 . Wang et al. 28 demonstrated that the CNF coating provided excellent hydrophobic properties to the paper. To further improve the hydrophobic properties of CNF coated paper, Mertaniemi et al. 29 sprayed CNFs on the glass surface, and then used tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (FOTS) to modify it by fluorination. Studies have shown that CNF films also have certain oil/grease resistance 30 . Koppolu et al. 31 used nanocellulose and polylactic acid (PLA) as coating raw materials to prepare barrier packaging paper with both hydrophobicity and oleophobicity. Therefore, the development of CNFs has offered a new alternative to the polymer coating to form a barrier layer 32,33 . Generally, CNFs were used as a coating to improve air resistance, oil resistance, surface strength, stiffness and tensile strength of paper, while Cobb index and roughness decreased 34,35 . In addition, there are several researchers about the use in combination of PVA and CNFs. Chaabouni et al. 36 added CNFs to PVA to prepare adhesives and found that the viscosity and water resistance of the adhesives increased, and strongly enhanced the mechanical performance in wet conditions. Deng et al. 37 prepared CNFs-PVA composite films and found that there are strong interaction and good compatibility between CNFs and PVA molecules. Furthermore, the light transmittance and thermal expansion coefficient of the composite films were decreased, while the tensile strength, Young’s modulus, glass transition temperature, and thermal stability were all improved compared with the PVA films 38 . CNFs and PVA are used in combination in some fields such as films, adhesives, and aerogels 39,40 . However, no researchers have studied the hydrophobic and oleophobic properties of PVA/CNF as coating. In this study, we investigated the properties of CNFs and the effect of CNFs on the hydrophobicity, oleopho- bicity, and strength of PVA coated paper. CNFs were prepared from bamboo pulp fibers and mixed with PVA to prepare PVA/CNF coating solution. The hydrophobic and oleophobic PVA/CNF coated paper was obtained by a coating method, which was also degradable, recyclable, and environmentally friendly. Ǥ Bleached bamboo pulp (beating degree 13.5ºSR, wet weight 15.13 g) and base paper (110 g/m 2 ) were obtained from Zhejiang Jinchang Specialty Paper Co., Ltd. (Quzhou, China). The bleached bamboo pulp composition: cellulose (94.37 wt%), hemicellulose (4.74 wt%), lignin (0.67 wt%), ash (0.10 wt%), and extractive (0.12 wt%). Bleached bamboo pulp Cellulase (enzyme activity 16,000 HCU/g) was obtained from Zhejiang Jin- jiahao Green Nanomaterials Ltd. (Quzhou, China). Polyvinyl alcohol (analytical reagent (AR) grade), citric acid (AR grade), sodium citrate (AR grade), and other chemical reagents were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). ƤǤ Bamboo pulp was dispersed in water, then 60 U/g of cellulase and citric acid-sodium citrate buffer solution were added, and the reaction was carried out at pH 5.0 and tempera- ture of 50 °C for 6 h, and the enzyme reaction was terminated at 90 °C. Then, the dispersed bamboo pulp was centrifuged at 8000 rpm for 15 min, and the undissolved part was precipitated, which was the enzyme-treatment bamboo fibers (EBFs). The EBFs were homogenized by a high-pressure homogenizer (AH-pilot2018, Shanghai Dibosi Biotechnology Co., Ltd., China) to obtain CNFs. Ȁ Ǥ PVA and CNFs were fully dissolved and mixed in 90 °C water, and then dispersed in an ultrasonic cleaner (KQ-30DE, Kunshan Ultrasonic Instruments Co., Ltd., China), then the uniform CNF/PVA composite coating was obtained. Ȁ Ǥ The prepared composite coating was coated on the surface of the base paper by a manual coater (ZAA 2300, Zehntner, Switzerland), and then dried at 80 °C to obtain the paper with hydrophobic and oleophobic properties. The preparation process and properties of PVA/CNF coated paper are shown in Fig. 1. Ǥ The morphology of bamboo fibers (BFs) and EBFs were detected by fiber analyzer (LDAO2, OpTest, Canada) and optical microscope (S800T-930HD, Jiangxi Beitekar Photoelectric Technology Co., Ltd., China). The surface morphology of CNFs was observed by atomic force microscope (XE-100E, PSIA, Korea). The atomic force microscope images of CNFs were imported into Nanoscope analysis and Nano meas- urer software, and 50 CNFs were randomly selected to measure their length and diameter. In addition, the obtained data were graphed and analyzed using Oringin software. The length and diameter of CNFs were ana- lyzed using Nanoscope analysis software. The microstructure of BFs, EBFs, and CNFs was analyzed by infrared spectrometer (Nicolet 5700, Thermo Fisher Scientific, USA) and X-ray diffractometer (ARL XTRA, Thermo
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