二甲基乙酰胺预活化处理时,微晶纤维素中吸附水被二甲基乙酰胺分子取代,使纤维素分子链间距离增加。预活化使纤维素分子链的氢键断裂导致微晶纤维素在氯化锂-二甲基乙酰胺体系中溶解度增加。在高温下微晶纤维素/氯化锂-二甲基乙酰胺溶液发生不可逆凝胶化,形成相互连接的丝状多孔结构。微晶纤维素的预活化路线和溶解温度影响微晶纤维素/氯化锂-二甲基乙酰胺溶液的溶胶-凝胶转变温度。微晶纤维素在溶胶-凝胶转变后再生时主要保留Ⅰ型聚集态结构,结晶度为71%。
During pre-activation using DMAc,the absorbed water inside cellulose was replaced by DMAc molecules,and the packaging of cellulose chains became more expanded.The disruption of hydrogen bonding of cellulose chains,especially inter molecule hydrogen bonding,during pre-activation was the most possible reason for the improvement of MCC's solubility in LiCl/DMAc system.The MCC/LiCl/DMAc solution became irreversibly gelled,and formed inter-connected silk-like porous structures.Also,the pre-activation routes and dissolution temperatures of MCC affected sol-gel transition temperatures of MCC/LiCl/DMAc solution.Moreover,the regenerated cellulose after sol-gel transition mainly reserved type I crystalline structure with a relatively high crystallinity of 71%.
[1] Wang S,Lu A,Zhang L.Recent advances in regenerated cellulose materials[J].Progress in Polymer Science,2016,53:169-206.
[2] Dumanli A G,Windle A H.Carbon fibres from cellulosic precursors:a review[J].Journal of Materials Science,2012,47(10):4236-4250.
[3] Jin H,Zha C,Gu L.Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution[J].Carbohydrate Research,2007,342(6):851-858.
[4] Dupont A L.Cellulose in lithium chloride/N,N-dimethylacetamide,optimisation of a dissolution method using paper substrates and stability of the solutions[J].Polymer,2003,44(15):4117-4126.
[5] Matsumoto T,Daisuke T,Tamai N,et al.Solution properties of celluloses from different biological origins in LiCl·DMAc[J].Cellulose,2001,8(4):275-282.
[6] Potthast A,Rosenau T,Sartori J,et al.Hydrolytic processes and condensation reactions in the cellulosesolvent system N,N-dimethylacetamide/lithium chloride.part 2:degradation of cellulose[J].Polymer,2003,44(1):7-17.
[7] Dan R,Dan L,Ping L,et al.Effect on dissolvability of microcrystalline cellulose through activation[J].Packaging Engineering,2012,33(9):57-60.
[8] Yanagisawa M,Shibata I,Isogai A.SEC-MALLS analysis of softwood kraft pulp using LiCl/1,3-dimethyl-2-imidazolidinone as an eluent[J].Cellulose,2005,12(2):151-158.
[9] Hiraoki R,Fukuzumi H,Ono Y,et al.SEC-MALLS analysis of TEMPO-oxidized celluloses using methylation of carboxyl groups[J].Cellulose,2013,21(1):167-176.
[10] Ruan D,Lue A,Zhang L.Gelation behaviors of cellulose solution dissolved in aqueous NaOH/thiourea at low temperature[J].Polymer,2008,49(4):1027-1036.
[11] Cai Jie,Zhang Lina.Unique gelation behavior of cellulose in NaOH/urea aqueous solution[J].Biomacromolecules,2006,7(1):183-189.
[12] Brown W,Wiskstrom R.A viscosity-molecular weight relationship for cellulose in cadoxen and a hydrodynamic interpretation[J].European Polymer Journal,1965,1(1):1-10.
[13] Duchemin B J C Z,Newman R H,Staiger M P.Phase transformations in microcrystalline cellulose due to partial dissolution[J].Cellulose,2007,14(4):311-320.
[14] Nelson M L,O'Connor R T.Relation of certain infrared bands to cellulose crystallinity and crystal lattice type.part Ⅱ.a new infrared ratio for estimation of crystallinity in celluloses I and Ⅱ[J].Journal of Applied Polymer Science,1964,8(3):1325-1341.
[15] Singh B,Gupta M,Verma A,et al.FT-IR microscopic studies on coupling agents:treated natural fibres[J].Polym Int,2000,49(11):1444-1451.
[16] Ishii D,Tatsumi D,Matsumoto T.Effect of solvent exchange on the supramolecular structure,the molecular mobility and the dissolution behavior of cellulose in LiCl/DMAc[J].Carbohydr Res,2008,343(5):919-928.
[17] Wei Y,Cheng F.Effect of solvent exchange on the structure and rheological properties of cellulose in LiCl/DMAc[J].Journal of Applied Polymer Science,2007,106(6):3624-3630.
[18] Naderi A,Lindström T,Sundström J.Carboxymethylated nanofibrillated cellulose:rheological studies[J].Cellulose,2014,21(3):1561-1571.
[19] Weng L,Zhang L,Ruan D,et al.Thermal gelation of cellulose in a NaOH/thiourea aqueous solution[J].Langmuir,2004,(20):2086-2093.
[20] Li C,Han Q,Guan Y,et al.Thermal gelation of chitosan in an aqueous alkali-urea solution[J].Soft Matter,2014,10(41):8245-8253.
[21] Deng M,Zhou Q,Du A,et al.Preparation of nanoporous cellulose foams from cellulose-ionic liquid solutions[J].Materials Letters,2009,63(21):1851-1854.
[22] Liu Z,Wang H,Li Z,et al.Characterization of the regenerated cellulose films in ionic liquids and rheological properties of the solutions[J].Materials Chemistry and Physics,2011,128(1-2):220-227.
[23] Zhao D,Li H,Zhang J,et al.Dissolution of cellulose in phosphate-based ionic liquids[J].Carbohydrate Polymers,2012,87(2):1490-1494.
[24] Cai J,Zhang L,Zhou J,et al.Multifilament fibers based on dissolution of cellulose in NaOH/urea aqueous solution:structure and properties[J].Advanced Materials,2007,19(6):821-825.
[25] Geng H,Yuan Z,Fan Q,et al.Characterisation of cellulose films regenerated from acetone/water coagulants[J].Carbohydr Polym,2014,102:438-444.
[26] El-Wakil N A,Hassan M L.Structural changes of regenerated cellulose dissolved in FeTNa,NaOH/thiourea,and NMMO systems[J].Journal of Applied Polymer Science,2008,109(5):2862-2871.
[27] Gao Q,Shen X,Lu X.Regenerated bacterial cellulose fibers prepared by the NMMO·H2O process[J].Carbohydrate Polymers,2011,83(3):1253-1256.
[28] Gao Shanshan,Wang Jianqing,Jin Zhengwei.Preparation of cellulose films from solution of bacterial cellulose in NMMO[J].Carbohydrate Polymers,2012,87(2):1020-1025.