Simple centrifugal fractionation to reduce the size distribution of cellulose nanofibers

Abstract

Since cellulose nanofiber (CNF) has unique characteristics in terms of renewability, high specific elastic modulus and strength and transparency, it is attractive for a building block of future materials. cnf can be extracted from various natural resource by several means. However, the size of the extracted cnf is very broad and uniformity of the extracted cnf is very important for many applications. thus, a fractionation process is necessary to obtain a uniformly sized cnf. in this paper, a simple centrifugal fractionation was carried out to reduce the size distribution of the extracted cnf suspension from hardwood pulp by the combination of TEMPO oxidation and aqueous counter collision methods. The original CNF suspension was diluted and centrifuged under low speed to remove cellulose microfibers then centrifuged under high speed to separate very small CNF. The centrifugation condition is 10 k rpm for 1 h followed by 45 k rpm for 4 h. The fractionated CNF was analyzed by an atomic force microscopy, and the length and width distribution histogram analysis was utilized. UV-visible analysis, ft-iR and XRD crystallinity analysis were carried out to analyze all fractionated cnfs and the original cnf. After centrifugal fractionation, the width and length distribution range were reduced by 62% and 70%, respectively. It is shown that the centrifugal fractionation is an easy and efficient method to fractionate a uniform cnf suspension. The tallest tree in the world which is 115 m high sustains itself for more than 600 years under its own weight and harsh environment of winds, snows, and rains 1. Wood is a fiber reinforced polymer composite produced in nature, which exhibits marvelous structural behaviors. It is a natural composite of cellulose fibers embedded in a matrix of lignin and hemicellulose. Typically, cellulose fibers in the wood are hierarchically composed of macrofibrils and microfibrils surrounded by hemicellulose and lignin. The microfibril is formed with crystalline domain and short amorphous domain 2. The microfibril, so called cellulose nanofiber (CNF), has unique characteristics in terms of renewability, high specific elastic modulus and tensile strength, low thermal expansion coefficient 3. During the biosynthesis process, cellulose molecules can form into microfibrils through the formation of inter-and intra-molecular hydrogen bonds 4. CNF is a material composed of nanosized cellulose fibrils with a high aspect ratio (length to width ratio). The width of CNF is typically in the range of 5-20 nm and length is typically up to microns 5,6. CNF is attractive for many applications, for instance, coatings, fillers, additives, structural composites, cosmetics, flexible electronics and flexible displays 7-12. CNF extracted from plants by top-down approach can be a building block of future materials. CNF can be extracted by mechanical, chemical and biological methods 13-16. However, the length of the extracted CNF is very broad depending on the extraction method and pretreatment of cellulose resources. Uniform...

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