Low temperature dissolution of microcrystalline cellulose in quaternary ammonium base aqueous solution
Three kinds of quaternary ammonium base aqueous solutions,namely tetramethylammonium hydroxide(TMAH),tetraethylammonium hydroxide(TEAH)and tetrapropylammonium hydroxide(TPAH),were selected as solvents to dissolve mi-crocrystalline cellulose(MCC)through low-temperature freezing and room-temperature thawing.The dissolution effect of MCC was studied at different temperatures and solvent concentrations,and the dissolution behavior of MCC treated with different qua-ternary ammonium base aqueous solutions was characterized.The results showed that the solubility of MCC in all three solvents showed an overall trend of first increasing and then gradually stabilizing as the freeze-thaw temperature decreased;the solubility of MCC showed an increasing trend with the increase of quaternary ammonium base concentration in different solvent systems;the dissolution effect of MCC was optimized when the freeze-thaw temperature was-30℃and the mass fraction of quaternary ammo-nium base was 35%in the solvent,and the solubility of MCC in TMAH,TEAH and TPAH aqueous solutions was 1.2%,11.5%and 7.25%,respectively;the quaternary ammonium base aqueous solution system was a non-derivative solvent system for MCC,in which TEAH could weaken the internal hydrogen bonds of MCC and offer the strongest solubility;the crystallinity of MCC treated with TEAH and TPAH both decreased,the crystallinity of MCC decreased from 63.11%to 43.71%after TEAH swelling treatment,and the crystallinity of regenerated MCC decreased to 30.46%after TEAH dissolution,and the crystal form of MCC transformed from cellulose crystal form Ⅰ to cellulose crystal form Ⅱ;and TEAH had the strongest ability to decrystallize and contributed the best dissolution effect to MCC among the three quaternary ammonium base aqueous solutions.
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