TEMPO 酸化セルロースナノファイバーの調製と特性解析

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2,2,6,6一テトラメチルピペリジニルー1一オキシルラジカル(TEMPO)を用いることにより,多糖の1級水酸基を選択的にカルボキシル基に変換できる。このTEMPO触媒酸化反応を木材パルプに適用すると,ミクロフィブリル表面に露出しているC6位の1級水酸基を選択的に酸化でき,カルボキシル基のNa塩が生成する。十分なカルボキシル基量を有するTEMPO酸化木材セルロースを水中で角繊処理することで,約4㎜の均一幅で,長さ数ミクロンの擬集せずに)孤立したナノファイバーに変換できる。TEMPO酸化によりミクロフィブリル上に高密度で負電荷が生成するため,水中で荷電反発浸透圧効果が作用し,高アスペクト比で高結晶性のTEMPO酸化セルロースナノファイバー(TOCN)が得られる。　TOCN/水分散液からキャスト成形したフィルムは高い光学透明性,極めて低い酸素透過度と線熱膨張率,高強度等の特性を有する。TOCNは豊富な木質バイオマスから製造可能であり,環境適合型の新規バイオナノ素材として,食品医薬品用の高ガスバリア包装用材料,表示体フィルム,電子部材,ヘルスケア材料等の先端分野への利用が期待される。 | Selective conversion of primary hydroxyls of polysaccharides to carboxyl groups can be achieved by TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl radical)-mediated oxidation in water under moderate conditions. Fundamental and applied studies of TEMPO-oxidized cellulose nanofibers and their related researches are reviewed, primarily based on the results obtained in our laboratory and by collaboration. When TEMPO-mediated oxidation in water is applied to bleached wood kraft pulps for papermaking, C6-carboxylate groups are efficiently and position-selectively formed on the surfaces of wood cellulose microfibrils. TEMPO-oxidized wood celluloses having sufficient amounts of sodium carboxylate groups can be converted to individualized cellulose nanofibers with almost uniform widths of 4 nm and lengths >1 µm by mild mechanical disintegration in water. Electrostatic repulsion and/or osmotic effect efficiently work between anionically charged TEMPO-oxidized wood cellulose microfibrils, resulting in the formation of the individual nanofibers with high aspect ratios and high crystallinity. Cast films prepared from the TEMPO-oxidized cellulose nanofiber (TOCN)/water dispersions have high optical transparency, extremely low oxygen permeability, low thermal expansion coefficients, high strengths and other unique properties. The new cellulose-based nanofiber films are expected to be applied as transparent packaging materials with a high oxygen barrier for foods and medicines, flexible display panels, electronic devices, health care and other uses. Thus, TOCNs prepared from abundant wood biomass have great potential as novel bio-based nanofibers in state-of-the-art material fields required for the establishment of a sustainable society.Selective conversion of primary hydroxyls of polysaccharides to carboxyl groups can be achieved by TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl radical)-mediated oxidation in water under moderate conditions. Fundamental and applied studies of TEMPO-oxidized cellulose nanofibers and their related researches are reviewed, primarily based on the results obtained in our laboratory and by collaboration. When TEMPO-mediated oxidation in water is applied to bleached wood kraft pulps for papermaking, C6-carboxylate groups are efficiently and position-selectively formed on the surfaces of wood cellulose microfibrils. TEMPO-oxidized wood celluloses having sufficient amounts of sodium carboxylate groups can be converted to individualized cellulose nanofibers with almost uniform widths of 4 nm and lengths >1 µm by mild mechanical disintegration in water. Electrostatic repulsion and/or osmotic effect efficiently work between anionically charged TEMPO-oxidized wood cellulose microfibrils, resulting in the formation of the individual nanofibers with high aspect ratios and high crystallinity. Cast films prepared from the TEMPO-oxidized cellulose nanofiber (TOCN)/water dispersions have high optical transparency, extremely low oxygen permeability, low thermal expansion coefficients, high strengths and other unique properties. The new cellulose-based nanofiber films are expected to be applied as transparent packaging materials with a high oxygen barrier for foods and medicines, flexible display panels, electronic devices, health care and other uses. Thus, TOCNs prepared from abundant wood biomass have great potential as novel bio-based nanofibers in state-of-the-art material fields required for the establishment of a sustainable society.
2012-02-25

TEMPO 酸化セルロースナノファイバーの調製と特性解析

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