Preparation And Properties Of Cellulose Nanofibers Membrane Material With High Strength Performace

An important component of the cell wall of the timber is the cellulose molecule aggregates that the diameter is in the nanometer scale, having a high aspect ratio, high specific surface area and rich surface groups. By a suitable method, we can get the fibrillating cellulose, and then through the "Nano construction" approach to prepare the cellulose into a high performance, functionalization and high value-added cellulose-based products.In recent years, the biomass materials research has being the international hot spots and cutting-edge issues.This article is based on a "bottom-up" academic thinking. Firstly, by chemical pretreatment, high-intensity ultrasound treatment and high-pressure homogenization treatment, we isolated nano-fibrils from the cell walls of the wood cellulose to prepare (CNF). And then, CNF was further assembled into high strength nanopaper by the vacuum filtration-drying method. Finally, the CNF reinforced polymer PMMA, obtaining a nanocomposite material with excellent optical transparency and mechanical strength properties. The main conclusions are as follows:(1) Based on the method of high-intensity ultrasonication combined with high-pressure homogenization to obtain a uniformly fibrillating CNF, retained the native cellulose I type crystal structure, a low diameter size distribution (fibril diameter from1to3nm) and high aspect ratio features. The nanofiber surface was hydrogen bonding with each other more strongly, and it was easy to form a ribbon nest sets and network structure. The nanocellulose rheological analysis is further proof for these characteristics, in which homogeneous treatment can increase the aggregation of the fibrils and the degree of the connection between the fibrils. The storage modulus G’and loss modulus G" were significantly increased, while the tan delta was less than0.2. It showed obvious viscoelastic properties, and was not susceptible to shearing force and thermal effects more significantly. This characteristic was more evident with increasing concentration.(2) Preparation of a controlled thickness of nanometer paper was through the vacuum filtration-moisture evaporation similar to the papermaking process, that is, on the basis of doing not change the the CNF itself inherent properties. The method was based on the high-intensity ultrasonication combined with high-pressure homogenization processing CNF. Nanopaper was constituted by the intertwining lamellar nanofibrils, that is, nanofibrils were randomly arranged in the plane and had good dispersibility. The nanofibrils are closely connected and a small pitch to3%of a low porosity, having a density similar to cellulose.According to the type of nanometer thickness of the paper, its Young’s modulus of13to20GPa variation, mechanical tensile strength at140to173MPa, the maximum strain (0.5%to 2.5%) and the work of fracture (50KJ/m2～250KJ/m2) small changes. In a wide range of test temperature (25°C to260°C), the dynamic mechanical properties of nano paper was smaller temperature-dependent properties. The storage modulus of about10GPa and the Tanδ value remain stable. Herefore. nanopaper have good thermal mechanical stability.(3) The CNF nanopaper as the reinforcing material composite with poly (methyl methacrylate)(PMMA) to prepare nanocomposites material. The material have good optical properties as well as high mechanical strength. CNF concentration and volume changes in the content, it is possible to change the thickness of the nanopaper and the mechanical properties of the preparation of composite materials(the tensile strength of27.18to33.67MPa, Young’s modulus of2.91-3.97GPa,0.96to2.21while the ultimate strain. For the same CNF concentrations nanocomposites, with the increase of the content of nanofibrils diameter sizes, the nanocomposite tensile strength, Young’s modulus and ultimate strain increases gradually. CNF nanopaper/PMMA composites due to its significant flexibility, optical transparency and mechanical strength, can be widely used in the field of packaging materials, the AMOLED display substrate material and flexible OLED encapsulating material, etc.