Crawford Brad, Ismail Ahmed E
Department of Chemical and Biomedical Engineering, West Virginia University, Morgantown, WV 26505, USA.
Polymers (Basel). 2020 Mar 9;12(3):627. doi: 10.3390/polym12030627.
All-atom molecular dynamics simulations are utilized to determine the properties and mechanisms of cellulose dissolution using the ionic liquid tetrabutylphosphonium chloride (TBPCl)-water mixture, from 63.1 to 100 mol % water. The hydrogen bonding between small and large cellulose bundles with 18 and 88 strands, respectively, is compared for all concentrations. The Cl, TBP, and water enable cellulose dissolution by working together to form a cooperative mechanism capable of separating the cellulose strands from the bundle. The chloride anions initiate the cellulose breakup, and water assists in delaying the cellulose strand reformation; the TBP cation then more permanently separates the cellulose strands from the bundle. The chloride anion provides a net negative pairwise energy, offsetting the net positive pairwise energy of the peeling cellulose strand. The TBP-peeling cellulose strand has a uniquely favorable and potentially net negative pairwise energy contribution in the TBPCl-water solution, which may partially explain why it is capable of dissolving cellulose at moderate temperatures and high water concentrations. The cellulose dissolution declines rapidly with increasing water concentration as hydrogen bond lifetimes of the chloride-cellulose hydroxyl hydrogens fall below the cellulose's largest intra-strand hydrogen bonding lifetime.
利用全原子分子动力学模拟来确定在水含量为63.1%至100摩尔%的离子液体四丁基氯化鏻（TBPCl）-水混合物中纤维素溶解的性质和机制。比较了在所有浓度下，分别具有18股和88股的小纤维素束和大纤维素束之间的氢键。氯离子、TBP和水共同作用形成一种协同机制，能够将纤维素链从纤维素束中分离出来，从而实现纤维素的溶解。氯离子引发纤维素的分解，水有助于延缓纤维素链的重新形成；然后TBP阳离子更持久地将纤维素链从纤维素束中分离出来。氯离子提供净负的成对能量，抵消了剥离纤维素链的净正成对能量。在TBPCl-水溶液中，TBP-剥离纤维素链具有独特的有利且可能为净负的成对能量贡献，这可能部分解释了为什么它能够在中等温度和高水浓度下溶解纤维素。随着水浓度的增加，纤维素的溶解迅速下降，因为氯离子-纤维素羟基氢的氢键寿命低于纤维素最大的链内氢键寿命。
