Online Rheo-TD NMR for analysing batch polymerisation processes
Online Rheo-TD NMR for analysing batch polymerisation processes
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用于分析间歇聚合过程的在线 Rheo-TD NMR
DOI：
10.1016/j.micromeso.2013.03.001
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发表时间：
2013
影响因子：
5.2
通讯作者：
N. Nestle
中科院分区：
文献类型：
--
作者：
H. Herold;E. H. Hardy;M. Ranft;K. Wassmer;N. Nestle
研制了一种用于流变学和核磁共振弛豫法过程分析的小型低场核磁共振流变仪。基于NMR毛细管流变仪，在接近环境条件下，实现了具有感应耦合探头的高温（高达423 K）和高压（2 MPa）流通系统。利用双轴梯度系统对毛细管中速度相关相因子的Abel变换进行了快速测量。假设Ostwald-de Waele或Hershel-Bulkley行为，提取幂律指数和（如果适用）流变屈服点。根据来自旋转粘度计的数据验证值。在聚合过程中，不断增加的固含量提供了有关反应进展的信息，而聚合物和水相之间的相互作用则通过水相的弛豫时间表现出来。这两个参数都可以从CPMG序列后面的固体回波中确定。流动样品的溶液和分散体的NMR弛豫法面临着复杂的影响，空间依赖的激发和检测效率和不完全极化，特别是对于缓慢松弛的液体。的影响的理论描述开发和用于校正的磁化衰减曲线。它需要速度概率密度函数的知识，如果已经确定了流动剖面，则速度概率密度函数是已知的。为了减少不完全极化效应，使用使用专门设计的Halbach磁体的预极化器。
A compact low-field NMR rheometer has been developed for process analysis by means of rheometry and NMR relaxometry. On the basis of an NMR capillary rheometer for close to ambient conditions, a flow-through system with an inductively coupled probe head for elevated temperatures (up to 423K) and pressures (2MPa) was realised. A fast measurement of the Abel transform of the velocity-dependent phase factor in the capillary is performed using a 2-axes-gradient system. Assuming Ostwald-de Waele or Hershel–Bulkley behaviour the power law index and (if applicable) the rheological yield point is extracted. Values are validated against data from a rotational viscosimeter. During polymerisation the increasing solid content provides information about the progress of reaction while the interaction between the polymer and the water phase manifests itself via the relaxation time of the water phase. Both parameters can be determined from a solid echo followed by a CPMG train. NMR relaxometry on flowing samples of solutions and dispersions is confronted with complex effects as spatially dependent excitation and detection efficiency and incomplete polarisation especially for slow relaxing liquids. A theoretical description of the effects is developed and used for a correction of the magnetisation decay curves. It requires knowledge of the velocity probability density function which is known if the flow profile has been determined. In order to reduce incomplete polarisation effects, a prepolarizer using specially designed Halbach magnets is used.