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Effects of CMC molar mass on mechanical properties of CMC-acid gel

CMC-酸ゲルの機械的特性に及ぼすCMCの分子量の影響

瀧上 眞知子*; 廣木 章博; 長澤 尚胤; 笠原 崇光*; 瀧上 昭治*; 玉田 正男

Takigami, Machiko*; Hiroki, Akihiro; Nagasawa, Naotsugu; Kasahara, Takamitsu*; Takigami, Shoji*; Tamada, Masao

121$$^{circ}$$Cでの酸加水分解により分子量の異なるカルボキシメチルセルロース(CMC)を調製し、クエン酸と混合、所定温度で保管することで、CMC-酸ゲルを得た。保管している間にカルボキシメチル基末端がNa型からH型に変わることで水素結合形成とCMC分子鎖の絡み合いにより弾性ゲルとなる。今回、弾性ゲルのゲル分率,吸水性及び機械的特性に及ぼす分子量の影響を検討した。その結果、保管時間が一定の場合、分子量の高いCMCほどゲル分率は高くなった。しかし、低分子量CMCであっても混合後の保管時間を長くすると、ゲル分率は高分子量CMCのときと変わらなかった。低分子量CMCゲルは、高分子量のモノに比べ、より柔らかく吸水力が高いことがわかった。高分子量CMCゲルでは、保管時間を長くするとますます硬くなったが、低分子量CMCゲルの柔らかさと高吸水性は、保管時間に依存せず、変化しないことが明らかとなった。

Carboxymethyl cellulose (CMC) with different molar mass was prepared by acid hydrolysis at 121$$^{circ}$$C. CMC thus prepared was mixed with citric acid aqueous solution to form CMC-acid gel. By replacing sodium existing as counter ion in carboxymethyl group with hydrogen, CMC molecules coagulate and hydrogen bonds are formed among CMC molecules. The CMC-acid gel prepared in that way was subjected to evaluation of gel fraction, water absorption and mechanical properties. Gel fraction was higher in CMC with higher molar mass than that in CMC with lower molar mass at short incubation time. However, there was no difference in gel fraction attributable to molar mass of CMC after long time incubation. CMC with higher molar mass crosslinked more easily than CMC with lower molar mass. The gel made of CMC with lower molar mass was softer and absorbed more amount of water than that with higher molar mass. All the results were elucidated by number of hydrogen bonds in CMC molecule. The gel made of higher molar mass CMC becomes stiff and brittle after long time incubation, however, the gel made of lower molar mass CMC keeps softness and strength longer.

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