Cellulose nanofibril (CNF) aerogels are promising materials for various applications because of their highly porous and ultralight characteristics. The fiber network of CNF aerogels held together by hydrogen bonding and mechanical entanglement of adjacent fibers is easily destroyed when it is exposed to water. In this study, cross-linked CNF aerogels were prepared using maleic acid and sodium hypophosphite as cross-linking agents. In the first step of treatment, CNF dispersed in water was reacted with maleic acid to form an ester linkage. Sodium hypophosphite was then added to the maleic acid-functionalized CNF suspension and the suspension was rapidly frozen using liquid nitrogen. CNF aerogel was obtained after freeze drying. The cross-linking of the cellulose was formed by the reaction between the carbon–carbon double bond of maleic acid-functionalized CNF and hypophosphite. The cross-linked CNF aerogel exhibited good network stability in water and springiness after compression.

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na⁺) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m²·day, and it decreased sharply to 1.3 g/m²·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation.

Due to the micro-sized pores on cellulosic substrate surface and the hygroscopic nature of cellulosic fibers, paper has poor barrier properties. Dispersion coating can improve the barrier properties of cellulosic paper noticeably by forming a continuous, non-porous polymer film on paper surface. In this work, the excellent film-forming performance of polyvinyl alcohol (PVA) was used to seal the surface pores of paper, thus enhancing the barrier properties. Alkyl ketene dimer (AKD) was also added as a coating component to improve the water resistance of paper. Results showed that after PVA/AKD coating hydrophilic base paper changed to hydrophobic one, as proved by water contact angle (WCA) measurements. The water vapor transmission rate (WVTR) of base paper decreased sharply from 543 g/m²·day to 2 g/m²·day in the case of PVA/AKD triple coating, where the threshold of WVTR was reached. Meanwhile, the pristinely non-grease resistant base paper converted to a product with the highest grease resistance level. Furthermore, both elongation at break and tensile strength of base paper improved markedly after PVA/AKD coating. It was concluded that these improved properties were contributed by the combined use of PVA and AKD in the coating.