SusChEM: Rheology of Cellulose and other Biopolymers in Ionic Liquids

摘要非技术：纤维素是地球上最丰富的可再生聚合物自然资源。多年来，纤维素一直被化学修饰，使其成为水溶性的，或者至少是可水分散的，从而使纤维素的溶液加工成为可能。然而，这些改性是昂贵的，并且抑制了赋予最终机械性能的纤维素的结晶。离子液体是一种非挥发性溶剂，最近发现某些离子液体可以溶解天然纤维素。针对未改性纤维素的纤维纺丝和其他溶液加工操作，各公司正在开发纤维素/离子液体解决方案的大型专利组合，进行了大量的诱导研究工作。为了支持这些技术，计划对纤维素溶液在离子液体中的流动特性进行基础研究。由于纤维素/离子液体流变学有几个不寻常的方面，包括看起来很大的微量水的影响，这项研究可能是变革性的和可行的。这项研究将为了解天然纤维素的流变性，使其能够在离子液体溶液中进行加工提供基础。这种绿色加工方案允许在不进行化学修饰的情况下加工纤维素，这已被认为可以产生具有优异机械性能的纤维，而离子液体是非挥发性的，通常从纤维素中提取水，无需使用任何挥发性有机溶剂即可回收99%。因此，离子液体溶液可能提供一种可行的途径，从非石油为基础的可再生资源中获得高模聚合物产品。技术：在给定浓度下，离子液体溶液比水溶液具有更高的粘度，并且略有更大的弹性(松弛时间更长)；两者都有利于涂层和纤维纺丝操作的稳定性。计划中的流变学实验将彻底表征纤维素在三种离子液体(一种似乎是theta溶剂，另一种初步数据表明是良好溶剂)在广泛的温度和浓度范围内的粘弹性反应。在线性响应中，干纤维素/离子液体溶液的粘度、松弛时间和末端模数的浓度依赖关系具有预期的标度，而线性粘弹性对少量水非常敏感。此外，在与涂层、纤维纺丝和其他溶液加工相关的更强的剪切流动中观察到了意想不到的结果；剪切粘度显著大于振荡剪切的线性粘度，而传统的聚合物溶液要么显示两者相同，要么发现剪切时链对齐的剪切粘度较低。这将用剪切流动中的X射线散射来检测纤维素链的排列来详细研究。PI和他的团队还将开始探索离子液体中其他多糖(甲壳素/壳聚糖，地球上第二丰富的聚合物自然资源)的溶液流变学。

AbstractNon-Technical: Cellulose is the most abundant renewable polymeric natural resource on our planet. For many years cellulose has been chemically modified to make it water-soluble or at least water-dispersible, enabling solution processing of cellulose. However, the modifications are expensive and inhibit the crystallization of cellulose that imparts final mechanical properties. Ionic liquids are nonvolatile solvents and recently, certain ionic liquids have been found to dissolve native cellulose. There is a large inductrial research effort aimed at fiber spinning and other solution processing operations on unmodified cellulose with companies developing large patent portfolios on cellulose/ionic liquid solutions. In support of such technologies, a fundamental study of the flow properties of cellulose solutions in ionic liquids is planned. Since there are several unusual aspects of cellulose/ionic liquid rheology, including a seemingly large effect of trace amounts of water, this research may be transformative and enabling. This study will provide a basis for understanding the rheology of native cellulose, enabling it to be processed in ionic liquid solutions. This green processing scheme allows cellulose to be processed without chemical modification, which is already known to produce fibers with superior mechanical properties, and ionic liquids are nonvolatile and routinely water-extracted from the cellulose to be 99% recovered without use of any volatile organic solvents. Consequently, ionic liquid solutions may provide a viable pathway to high modulus polymer products from renewable resources that are non-petroleum based.Technical: At a given concentration, ionic liquid solutions have higher viscosity than aqueous solutions and are slightly more elastic (longer relaxation time); both are advantageous for stability of coating and fiber spinning operations. The planned rheology experiments will thoroughly characterize the viscoelastic response of cellulose in three ionic liquids (one that appears to be a theta-solvent and another that preliminary data suggests to be a good solvent) over wide ranges of temperature and concentration. While the concentration dependences of viscosity, relaxation time and terminal modulus of dry cellulose/ionic liquid solutions in linear response have the expected scalings, the linear viscoelasticity is quite sensitive to small quantities of water. Additionally, unexpected results are observed in stronger shear flows relevant to coating, fiber spinning and other solution processing; the shear viscosity is significantly larger than the linear viscosity from oscillatory shear, whereas conventional polymer solutions either show the two to be identical or find the shear viscosity is lower from chain alignment in shear. This will be explored in detail using X-ray scattering in shear flow to detect alignment of cellulose chains. The PI and his team will also begin to explore the solution rheology of other polysaccharides (chitin/chitosan, the second-most abundant polymeric natural resource on the planet) in ionic liquids.