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首页> 外文学位 >Crystallization and birefringence studies on fast structural changes followed by non-contact spectral birefringence and Raman spectroscopy techniques.
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Crystallization and birefringence studies on fast structural changes followed by non-contact spectral birefringence and Raman spectroscopy techniques.

机译：快速结构变化的结晶和双折射研究，然后进行非接触光谱双折射和拉曼光谱技术。

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The structural characteristics of the manufactured polymers such as crystallinity and orientation are controlled by the thermal-deformation history imposed by the processing machinery. Therefore it is essential to monitor these structural characteristics and use the information advantageously to optimize the properties of interest by controlling the process conditions. The focus of this study is to develop robust automated techniques to monitor birefringence and crystallization in real-time.; In many of the polymer processing operations involving film stretching where the polymer undergoes a series of thermal deformation treatments, the quantitative changes that take place during the course of these processing operations is poorly understood partly as a result of very rapid structural changes that occur when the polymer's initial condition is not isotropic melt of isotropic solid. There is a great need to quantify the kinetics of the structural changes from preoriented/partially-crystallized states. As part of this dissertation, the birefringence development of preoriented polyethylene terephthalate (PET) films is monitored on-line by the developed spectral birefringence technique with the intent of simulating the heat-setting stage of a tenter film stretching process. Theoretical improvements, software development and optimization, and the equipment design and construction are some of the major tasks accomplished in this dissertation. The automated spectral birefringence technique not only allows the measurement of retardations to very high values, but also enables one to detect the changes in the trend in birefringence (such as a decrease as a result of relaxation, or an increase as a result of crystallization) and to investigate changes that occur very rapidly in the order of a few hundred milliseconds.; The effects of stretching conditions on the kinetics of the structural changes in PET films were also investigated using characterization techniques such as differential scanning calorimetry (DSC), wide-angle and small-angle X-ray scattering. In general, it was found that the heat setting for samples stretched to low stretch ratios (2.0X) results in partial or complete relaxation of orientation. This relaxation disappears above certain conditions (≥2.5X) followed by rapid increase in birefringence and long-term slow increase. At higher stretch ratios where the precursor films attain high crystallinities, the rate of structural changes slows down. These results are attributed primarily to the establishment of highly constrained network structure where nodes are composed of crystallized regions formed during stretching stage. The measurements are performed at temperatures, where the crystallization rates are the fastest and our technique performed exceptionally well to follow these structural changes.; As part of this dissertation, we also developed another robust, non-contact on-line measurement technique to monitor crystallinity of semicrystalline polymers (low-density polyethylene and polyoxymethylene) using laser Raman spectroscopy. In this technique, Raman instrument is calibrated off-line by partial least squares calibration method using the data from independent dynamic techniques such as small-angle light scattering, depolarized light intensity and DSC. The utility of this technique as an on-line measurement technique was illustrated by its application on the melt spinning of LDPE tape. In these experiments, the non-contact Raman spectroscopy technique successfully predicted the development of crystallinity along the spinline.
机译：所制造的聚合物的结构特征，例如结晶度和取向度，是由加工机械施加的热变形历史来控制的。因此，有必要监视这些结构特征并有利地使用信息来通过控制工艺条件来优化所关注的特性。这项研究的重点是开发强大的自动化技术来实时监控双折射和结晶。在许多涉及膜拉伸的聚合物加工操作中，其中的聚合物经历了一系列的热变形处理，因此，人们对这些加工操作过程中发生的定量变化知之甚少，部分原因是由于在加工过程中发生了非常迅速的结构变化。聚合物的初始条件不是各向同性固体的各向同性熔体。非常需要量化来自预取向/部分结晶状态的结构变化的动力学。作为论文的一部分，通过开发的光谱双折射技术在线监测预取向聚对苯二甲酸乙二醇酯（PET）薄膜的双折射发展，以模拟拉幅机薄膜拉伸过程的热定型阶段。理论上的改进，软件的开发与优化以及设备的设计与建造是本文所要完成的主要任务。自动化光谱双折射技术不仅可以将延迟测量到非常高的值，而且还可以检测双折射趋势的变化（例如，由于弛豫导致的减少或由于结晶导致的增加）并调查几百毫秒内迅速发生的变化。还使用诸如差示扫描量热法（DSC），广角和小角X射线散射等表征技术研究了拉伸条件对PET膜结构变化动力学的影响。通常，发现拉伸至低拉伸比（2.0X）的样品的热定型会导致部分或完全松弛取向。在某些条件下（≥2.5X），这种松弛消失了，随后双折射迅速增加，长期缓慢增加。在前体膜达到高结晶度的较高拉伸比下，结构变化的速度变慢。这些结果主要归因于高度约束的网络结构的建立，其中节点由在拉伸阶段形成的结晶区域组成。测量是在结晶速率最快的温度下进行的，并且我们的技术在跟踪这些结构变化方面表现出色。作为本论文的一部分，我们还开发了另一种健壮的非接触式在线测量技术，以使用激光拉曼光谱法监测半结晶聚合物（低密度聚乙烯和聚甲醛）的结晶度。在这项技术中，拉曼仪器是通过偏最小二乘校准方法离线校准的，该方法使用了来自独立动态技术的数据，例如小角度光散射，去偏振光强度和DSC。该技术在LDPE胶带的熔融纺丝中的应用说明了该技术作为在线测量技术的实用性。在这些实验中，非接触拉曼光谱技术成功地预测了沿着纺丝线的结晶度的发展。

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