微聚焦三维SAXS技术及其在聚乳酸注塑成型中的应用研究

Micro focused three-dimensional X-ray small angle scattering (3D-SAXS) is a new experimental methodology for nondestructive reconstruction of internal 3D nanoscopic structure in multiphase and non-uniform object. This method has an in-situ and nondestructive performance with a wide potential applications in the characterization of 3D mesoscopic structures. A key to achieve this method is the condition of high-resolution high-luminance x-ray source. Currently, 3D-SAXS is a positive developing method in the international advanced synchrotron radiation facilities and preliminarily has been applied to the study of structural properties and functions in soft material. By contrast, research about 3D-SAXS in domestic is still in the blank. Based on the small angle x-ray scattering beamlines (BL19U2, BL16B1) in domestic third-generation synchrotron radiation facility (Shanghai synchrotron radiation facility), this project plans to establish the high-resolution 3D-SAXS experimental methodology and develop an efficient computer tomography reconstruction algorithm for vector information reconstruction to achieve the reconstruction of mesoscopic structures in multiphase samples. Furthermore, It will be applied to characterize the structure changes in the polylactic acid injection molding process. It will give a chance to form a "fine" control of internal structure of materials during the injection molding process and establish the relationship between the final performance and the processing parameters as well as the product structure. This will help us to open up the "process - structure - performance" internal relations and to achieve the initial realization of the so-called "fixed configuration process " in polylactic acid injection molding applications.

微聚焦三维X射线小角散射（3D-SAXS）技术是一种可以无损重建多相非均匀物质内部三维纳米结构信息的新型实验方法。该方法在表征三维介观尺度结构方面具备实时无损等特点，拥有广泛的实验用途。实现这一方法的必要关键条件是需要有高分辨高亮度的X射线光源作为基础。目前国际上3D-SAXS方法学正处于发展阶段，也是当前相关先进同步辐射光源积极发展的新方法；国内有关3D-SAXS方面的研究则尚处于空白阶段。本研究基于国内第三代同步辐射装置（上海光源）小角散射相关线站拟建立三维空间高分辨3D-SAXS实验方法学，针对矢量信息重建发展一套相应的高效层析重建算法，以实现在线分析重构样品介观尺度结构并将其应用于聚乳酸注塑成型过程的结构表征。期望对注塑成型过程中材料内部结构形成“精细化”控制，打通“加工-结构-性能”的内在联系，初步实现所谓的“定构加工”。

本课题基于第三代同步辐射装置初步建立微聚焦SAXS实验方法，并采用有序子集最大期望值（OSEM）算法，成功实现了散射CT数据的重建。研究发现使用OSEM重建算法能在有限的投影角度下很好的抑制条形伪影的产生，并且在保证重建质量的前提下降低投影数目，从而提高数据采集效率。使用微聚焦SAXS实验方法对毛竹、聚乳酸（PLA）、己二酸丁二醇酯-对苯二甲酸丁二醇酯共聚物（PBAT）等高分子材料内部三维结构进行了分析，初步探讨了这些高分子材料注塑成型过程中的“结构-性能”关系。对于毛竹样品，使用散射CT方法能正确得到具有典型散射特性的维管束和薄壁细胞空间分布。对PLA试样内部横向及纵向结构进行完整的三维无损表征，得到了内部晶体结构完整的分布情况以及随着剪切过程的演化规律。初步重构了注塑PBAT样品的三维结构和三维微区散射图样。研究了促进剂对高分子量注塑PLA共混物立体复合晶形成的诱导促进作用以及注塑加工中高冷却速率和高剪切速率下聚酰胺6/聚对苯二甲酸乙二醇酯（PA6/PET）共混物的结构及其湿敏性能。初步获取了典型加工外场（压力-剪切-温度场）下注塑加工高分子材料中shish-kebab的生成规律。本研究可为高分子材料结构分析和提高相应注塑品宏观性能提供相应科学依据。