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Paper materials are well-known to be hydrophilic unless chemical and mechanical processing treatments are undertaken. The relative humidity impacts the fiber elasticity, the interfiber joint behavior and the failure mechanism. In this work, we present a comprehensive experimental and computational study on mechanical properties of the fiber and the fiber network under humidity influence. The manually extracted cellulose fiber is exposed to different levels of humidity, and then mechanically characterized using atomic force microscopy, which delivers the humidity dependent longitudinal Young’s modulus. We describe the relation and calibrate the data into an exponential function, and the obtained relationship allows calculation of fiber elastic modulus at any humidity level. Moreover, by using confoncal laser scanning microscopy, the coefficient of hygroscopic expansion of the fibers is determined. We further present a finite element model to simulate the deformation and the failure of the fiber network. The model includes the fiber anisotropy and the hygroscopic expansion using the experimentally determined constants, and further considers interfiber behavior and debonding by using a humidity dependent cohesive zone interface model. Simulations on exemplary fiber network samples are performed to demonstrate the influence of different aspects including relative humidity and fiber-fiber bonding parameters on the mechanical features, such as force-elongation curve, strength and extensibility. Finally, we provide computational insights for interfiber bond damage pattern with respect to different humidity level as further outlook.

Developing a feasible and efficient separation membrane for the purification of emulsified oily wastewater is challenging due to the critical limitations of serious fouling during membrane preparation. Herein, underwater superoleophobic paper-based materials with high wet strength were prepared by low cost and green papermaking technology. The fibrillation of cellulose fibers was achieved by beating to optimize the pore structure of paper sheets. Simple modification of paper sheets with 1,2,3,4-butanetetracarboxylic acid significantly improves the surface hydrophilicity and the wet strength through the crosslinking reaction between fibers. The maximum underwater oil contact angle and wet strength of the modified paper sheets are high up to 167.8°and 36.5 N·m/g, respectively. The water flux can be adjusted in the range of 25.8 L m−2 h−1–4920 L m−2 h−1 by controlling the average pore size from 6.64 μm to 18.9 μm. Lower pore size and higher carboxyl content of the paper-based materials are beneficial to improve the oil rejection, which can reach more than 99.3% even for submicron emulsified oils. Most of the paper sheets achieve efficient oil–water separation although the average pore size is remarkably larger than the emulsified oil droplet. The reason can be attributed to the zigzag pore structure of paper sheets, which is favorable to form liquid bridge on the surface as well as collision demulsification in the Z-direction channel, thereby promoting the mechanical interception effects. The low-cost, eco-friendly, easily-manufactured and highly efficient paper-based separation materials possess wide applications in oily wastewater treatment.

Cheap, rapid, simple and equipment-free nucleic acid extraction (NAE) is highly preferred for implementing nucleic acid detection at point-of-care (POC). Paper-based NAE materials have been extensively utilized due to their low cost, abundance, portability, biocompatibility and ease of chemical modification. However, it is challenging for users to choose the proper one from existing paper-based NAE materials for specific POC applications, which is determined by their physical and chemical properties. Additionally, building the relationship between the physical and chemical properties and the NAE efficiency of paper-based materials is instructive for development of new paper-based NAE materials. In this study, we first systematically compared the physical and chemical properties of six widely used paper-based NAE materials (namely Whatman filter paper #1, FTA card, FTA elute card, Fusion 5, silica membrane and polyethersulfone (PES) membrane), and then evaluated their NAE efficiency. The obtained results indicated that pore uniformity, wet strength, porosity and functional groups are key parameters to affect the efficiency of NAE. The NAE performance of FTA card is the best with high concentration and purity. Finally, we envision that more cost-effective paper-based NAE materials will be developed for POCT application in the future. Graphic abstract

As non-biodegradable single-use plastic packaging products have been restricted in recent years, paper-based materials have attracted considerable attention owing to their environmental benefits. However, the hydrophilic nature of paper-based materials limits their application as replacements for non-biodegradable plastics. In this study, an environmentally friendly and multifunctional superhydrophobic paper was developed using silane-modified superhydrophobic nanofibrillated cellulose (M-NFC) via a simple spraying method. This paper can reduce the white pollution caused by non-degradable single-use plastic packaging products. Upon spraying the base paper with 1.5 g/m2 of M-NFC, the coated paper (CP) exhibited excellent superhydrophobicity (water contact angle of 160°), water repellency (Cobb value of 7.5 g/m2), strong durability to sandpaper abrasion, finger-wipe, bending, folding, and sustained exposure to corrosion media (HCl with a pH of 1, NaOH with a pH of 10, high temperature treatment at 180 °C, and ultraviolet irradiation). Additionally, the CP surface directly prevented the adhesion of S. aureus and E. coli and also indirectly repelled solid contaminants upon washing with water, thereby demonstrating highly efficient antibacterial and anti-fouling properties. The durable and multifunctional superhydrophobic paper developed in this study provides a novel direction for solving white pollution and also presents a new research pathway for the potential applications of paper-based materials.

Activated carbon paper-based materials were prepared from softwood pulp, activated carbon powder, and polyester fiber through wet forming process. Then polyethyleneimine was loaded on the activated carbon paper-based materials using physical impregnation method to fabricate green, low cost, and degradable PEI/activated carbon composite paper-based adsorbent materials (PPCA) for the removal of Cr(VI) from drinking water. The surface characteristics of the adsorbent were analyzed by SEM, EDX, BET, FT-IR, and XPS. It was found that the maximum adsorption capacity of Cr(VI) could reach up to 1.58 mg g −1 when the PEI immersion concentration is 1%, the contact time is 180 min, the temperature is 30 °C and pH = 2. The adsorption of Cr(VI) on PPCA conformed to both the freundlich isotherm model and the quasi-second-order kinetic model, indicating that the adsorption was multi-molecular layer adsorption controlled by chemical reaction process. The adsorption mechanism of Cr(VI) on PPCA included electrostatic attraction, redox and chelation. Overall, this study provides a green, large-scalable production way for the preparation of biodegradable adsorption materials for the efficient removal of Cr(VI) from drinking water aiding the safe management of aqueous system. Graphical abstract

Since oily wastewater has serious harm to the environment and human health, a green paper-based material with underwater superoleophobicity, high wet strength and high flux was developed for the efficient oil–water emulsion separation. A series of key steps, including fiber beating, citric acid (CA) crosslinking, and dielectric barrier discharges (DBD) plasma treatment, were successfully adopted to control the pore size in micron scale, enhance the wet strength, and improve the underwater superoleophobicity, respectively. Moreover, DBD plasma treatment led to a significant increase in the porosity while maintaining the pore size, which is beneficial to improve the flux with high separation efficiency. The maximum porosity and flux can reach 59.7% and 106 L/m2∙h, respectively. The separation efficiency of emulsified oil is high up to 99.60% even when the average droplet size is as low as 0.98 µm. This high-efficiency, low-cost, environmentally-friendly, and recyclable paper-based separation material possesses potential applications in oily wastewater treatment.

The development and optimization of structured materials, such as tissue paper materials, benefit from modeling strategies that take into consideration its structural hierarchy at the fiber and the paper levels. The use of an innovative three-dimensional voxel approach to model both the fiber and the 3D paper structure were validated by comparison of the computational structures with the laboratory-made structures. The main goal of this work was to model tissue structures and obtain a computational implementation adapted for tissue products. The fibers were modeled in 3D according to their dimensions, and the structures produced by them were characterized using the Representative Elementary Volume (REV) and image analysis computational tools. This methodology made it possible to model the fibers according to their morphology, flexibility, and collapse, resulting in a tissue structure with thickness, porosity, relative bonding area, coverage, among other properties. The experimental design plan included the production and characterization of isotropic laboratory structures with basis weights of 20, 40, and 60 g/m2 with different eucalyptus fibers and beating degrees. With the aid of these advanced computational tools, mathematic models with predictive capacity for tissue properties such as softness, strength, and absorption can be developed.

As a global environmental problem, plastic pollution has attracted worldwide attention. Plastic wastes not only disrupt ecosystems and biodiversity, but they also threaten human life and health. Countries around the world have enacted regulations in recent years to limit the use of plastics. Paper products have been proposed as promising substitutes for plastics, which undoubtedly brings unprecedented opportunities to the pulp and paper industry. However, paper products have some deficiencies in replacing certain plastic products. Research and development to improve paper properties and reduce production costs is needed to meet such challenges.

Solar-driven water splitting by inorganic semiconductor photocatalysts is considered a promising method to produce hydrogen fuel. Loading inorganic semiconductor on cellulose fiber to construct photocatalytic paper contributes to the dispersion and recycling of photocatalyst. In addition, the photocatalytic paper floating on water can build a solid–gas biphase photocatalytic interface (photothermal-generated steam/photocatalytic paper/hydrogen), replacing the traditional liquid–solid–gas triphase photocatalytic interface (liquid water/photocatalyst/hydrogen) for improving photocatalytic kinetics. Here, we design and synthesize a photocatalytic composite paper with zinc sulfide (ZnS) anchored onto cellulose fibers (CF) with the help of polydopamine (PDA). PDA achieves high load and uniform distribution of ZnS on cellulose fibers, and forms the ZnS/PDA heterojunction to increase photogenerated charge separation efficiency and photocatalytic stability. Solid–gas biphase photocatalytic interface constructed by the CF/PDA/ZnS composite paper minimizes the interface barriers of hydrogen transport and water molecular adsorption for improving hydrogen evolution rate. The CF/PDA/ZnS composite paper shows a high hydrogen production rate up to 18706.8 μmol h−1 g−1. Stable loading of ZnS/PDA heterojunction in composite paper contributes to the photocatalytic stability. In the third photocatalytic cycle, the hydrogen evolution rate of CF/PDA/ZnS composite paper remains 96.4%. This work inspires that anchoring of inorganic semiconductor on cellulose fibers with the help of PDA can be a promising strategy for designing efficient photocatalytic paper for solar hydrogen production.

In the cellulose scientific community, hydrogen bonding is often used as the explanation for a large variety of phenomena and properties related to cellulose and cellulose based materials. Yet, hydrogen bonding is just one of several molecular interactions and furthermore is both relatively weak and sensitive to the environment. In this review we present a comprehensive examination of the scientific literature in the area, with focus on theory and molecular simulation, and conclude that the relative importance of hydrogen bonding has been, and still is, frequently exaggerated.