Preparation And Characteristics Of Nanocellulose-based Barrier Materials Reinforced With Inorganic Materials

In recent years,barrier materials have developed rapidly and have been widely used in various fields such as packaging,anti-fouling and oil-water separation due to their excellent barrier properties.However,the raw materials for barrier materials are mainly derived from petroleum-based polymers,which have the shortcomings including unsustainable raw materials,difficult to biodegrade and easy to cause secondary pollution.Nanocellulose,as a natural biomass resource,has the advantages of biodegradability,large specific surface area,high aspect ratio as well as high elastic modulus,and is considered a promising raw material to replace petroleum-based polymers in the preparation of barrier materials.Nevertheless,nanocellulose materials suffer from low mechanical properties,inadequate barrier properties,and no antibacterial properties.In this regard,this research introduced two-dimensional material Ti₃C₂T_x（MXene）and metal nanoparticles（Ag NPs,Au NPs）as reinforcing fillers to regulate the mechanical and barrier properties of nanocellulose,and endow it with antimicrobial properties.Nanocellulose-based antibacterial composites with different barrier properties were constructed by designing the surface properties and microstructure,and their barrier enhancement mechanisms,antibacterial mechanisms,and potential multifunctional applications were explored.The main findings and conclusions are as follows:（1）Preparation of nacre-inspired nanocellulose-based inorganic composite film with superior oxygen barrier propertiesMXene/nanosilver was prepared using MXene as a template and tea polyphenol as a reducing agent.The nanocellulose-based film was prepared through the casting film method,in which TEMPO cellulose nanofibers（TNF）were utilized as substrates and MXene immobilized nanosilver as reinforcing fillers.The results showed that the composite film had a tightly stacked layered structure due to the strong interfacial interaction between nanocellulose and MXene as well as the filling of Ag NPs.The TNF-based film exhibited excellent mechanical properties（Young’s modulus up to 4.4 GPa）far superior to PE films and acid-base stability（remaining unchanged after 120 days under different p H conditions）.Importantly,the composite film not only presented ultra-low oxygen permeability（below the detection limit of the instrument）and nitrogen permeability measurements（2.274 cm³/m²·24h·0.1MPa）,but also had better barrier properties to ethyl acetate,ethanol and ethyl ether than PE films.It is here considered the diffusion mechanism through the tortuous path of the composite film responsible for the enhanced gas barrier performance.In addition,the composite film possessed excellent antibacterial properties,biocompatibility and biodegradability as it is completely degraded after150 days in soil.This study provides innovative insights for the design and manufacture of biodegradable and high oxygen barrier packaging materials.（2）Preparation of sandwich-like nanocellulose-based inorganic composite film with superhydrophobicity propertiesAlthough the nanocellulose-based composite films studied above have excellent gas barrier properties,the hydrophilic nature of nanocellulose tends to limit its application.Herein,perfluorosilane（PFOTS）was used to modify MXene with superhydrophobicity.The superhydrophobic nanocellulose-based antimicrobial composite film with sandwich structure was successfully prepared through layer-by-layer self-assembly method under alternating vacuum filtration,in which superhydrophobic MXene was used as a hydrophobic barrier for TEMPO-oxidized nanocellulose.The results showed that surface functionalization using PFOTS was applied to endow MXene with super-hydrophobicity,improving its stability,and the resulting materials remained unaltered after at least 150 days.The resulting hybrid film exhibited exceptional flexibility and strength,which could be folded into various shapes and easily support a considerable weight（ca.1 kg）.The superhydrophobic composite film displayed a high-water contact angle of over 153°,showing excellent self-cleaning ability,water repellency and durability.The composite film also showed high photothermal conversion capacity and stability,being able to rapidly increase the temperature over 100°C under NIR laser irradiation,maintaining it for a long time.Interestingly,the combination of super-hydrophobicity and photothermal conversion ability of the composite film successfully achieved controllable light-driven motion and enhanced antibacterial properties by the simultaneous integration of super-hydrophobicity,antiadhesion and long-lasting photothermal sterilization properties.This study provides a valuable strategy for the preparation of highly water barrier nanocellulose-based antimicrobial composite films.（3）Preparation of directionally aligned nanocellulose-based inorganic composite aerogel with hydrophobic propertiesAlthough the above studies can effectively avoid the effect of moisture on nanocellulose materials,their hydrophobic modification methods are complicated to operate and difficult to prepare membrane materials.Herein,the multifunctional nanocellulose-based antimicrobial aerogel with super-elasticity,hydrophobicity and superior photothermal conversion was fabricated through directional freeze-drying.MXene/Au NPs（MX/Au NPs）was synthesized via green mechanochemistry,where MXene served as a template.TEMPO-oxidized nanocellulose（TNF）was applied to construct functional networks,MX/Au NPs as photothermal absorbers,and methyltrimethoxysilane（MTMS）as hydrophobic coatings.The experimental analysis of the aerogels revealed that the as-prepared aerogel shows mechanical superelasticity（85.7%strain remaining after 30 compress-release cycles at a constant strain of 90%）,durable hydrophobicity（145°and a certain degree of resistance to water adhesion and water barrier）,highly efficient absorption capacity of oil/organic solvents（45.7-85.6 g/g）and superior photothermal conversion ability.More importantly,through the simultaneous integration of hydrophobicity and photothermal conversion capabilities,the aerogel showed rapid and efficient absorption capacity of viscous crude oil（within 10 s）.Also,the obtained aerogel successfully achieved controlled and rapid light-driven motion,as well as long-lasting photothermal sterilization performance.This study provides a promising preparation method as well as potential applications for the development of nanocellulose-based antimicrobial materials with hydrophobic properties.（4）Preparation of three-dimensional porous nanocellulose-based inorganic composite aerogel film with underwater oil barrier propertiesCompared to the oven-dried films and freeze-dried aerogels described above,the aerogel films combine the advantages of oven drying and freeze-drying,which are more conducive to material interactions and control of porosity.Herein,the nano-silver was prepared by using MXene as a template.A double drying strategy was introduced via oven drying and freeze-drying to fabricate the nanocellulose-based aerogel film with high oil resistance and environmental degradability using TEMPO-oxidized nanocellulose（TNF）and MXene/Ag NPs.Based on the regular nacre-like structures developed in the drying process and the pores formed by freeze-drying,the aerogel film finally obtained regularly arranged porous structures after double drying.Moreover,the aerogel film possessed excellent underwater superoleophobicity with a contact angle above 168°and outstanding antifouling properties due to the natural hydrophilicity of cellulose and MXene.Based on its well-ordered pore structures and superwetting properties,the aerogel film could separate different kinds of oil-water mixtures as well as highly emulsified oil-water dispersions with an efficiency of up to 99%under gravity-driven conditions only,while being recyclable.In addition,the aerogel film also showed excellent photothermal conversion performance,long-lasting antibacterial properties（photothermal sterilization up to 6 times）and biodegradability（completely degraded after 50days in soil）.This study provides a new direction for the development of multifunctional oil-water separation materials.