壳聚糖在4种咪唑型离子液体中溶解性的研究

STUDY ON DISSOLUBILITY OF CHITOSAN IN FOUR KINDS OF IMIDAZOLE-BASED IONIC LIQUIDS

研究、比较了壳聚糖在4种咪唑型离子液体氯化1-丁基-3-甲基咪唑([BMIM]Cl)、1-丁基-3-甲基咪唑醋酸盐([BMIM]Ac)、1-乙基-3-甲基咪唑醋酸盐([EMIM]Ac)和氯化1-烯丙基-3-甲基咪唑([AMIM]Cl)中的溶解性,提出了可能的溶解机理,并利用红外光谱(FTIR)、热重分析(TGA)和X-射线衍射(XRD)等研究了溶解后再生的壳聚糖的结构和性能的变化.结果表明,这4种离子液体对壳聚糖的溶解能力不仅与阴离子有关,也受阳离子结构的影响,其中[EMIM]Ac对壳聚糖的溶解能力最强,在[EMIM]Ac中110℃下壳聚糖的溶解浓度达到15.5 wt%;随着溶解温度的升高和溶解时间的延长,壳聚糖在离子液体中的溶解浓度增加,但黏均分子量下降;溶解后再生的壳聚糖热稳定性有所降低,结晶结构也发生了转变,从α型转变成β型.

The dissolubility of chitosan was studied in four kinds of imidazole-based ionic liquids 1-butyl-3-methylimidazolium chloride（Cl）,1-butyl-3-methylimidazolium acetate（Ac）,1-allyl-3-methylimidazolium chloride（Cl） and 1-ethyl-3-methylimidazolium acetate（Ac） respectively.The possible dissolution mechanism of chitosan in these ionic liquids was suggested,and the chemical structures,thermal stabilities and crystalline forms of the native chitosan and regenerated chitosan from these ionic liquids were analyzed by FTIR,TGA and XRD,respectively.The results show that,chitosan can be dissolvd without derivatization by all the four kinds of ionic liquids,and the dissolubility of chitosan in these ionic liquids is mainly related to the anions of ionic liquids,but also influenced by cations of ionic liquids.The dissolving power of the two kinds of acetate ionic liquids for chitosan is stronger than that of the two kinds of chloride ionic liquids,and that of Ac is the strongest.15.5 wt% of chitosan dissolved in Ac can be achieved at 110℃.The dissolution concentration of chitosan in these ionic liquids increases,but the viscosity-average molecular weight of it decreases with the increasing of temperature and the prolongation of time.The thermal stability of the regenerated chitosan from Cl,Cl,-Ac and Ac respectively increase gradually,which is consistent with the dissolving power of these ionic liquids for chitosan,but the thermal stability of the regenerated chitosan from the four kinds of ionic liquids decreases compared with that of native chitosan.A transition of α-chitosan to β-chitosan may occur during the dissolving and the recovering processes.