Shinzawa Hideyuki, Togo Azusa, Hagihara Hideaki
Research Institute for Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.
Appl Spectrosc. 2024 Sep 5:37028241272257. doi: 10.1177/00037028241272257.
In this study, a new system was developed to carry out simultaneous near-infrared (NIR) and small-angle X-ray scattering (SAXS) measurements. Aged polypropylene (PP) was examined with the NIR-SAXS system to demonstrate how it can be utilized to derive pertinent information about the polymer structure. Pairs of SAXS profiles and NIR spectra of PP in its initial state and after aging were measured to derive an in-depth understanding of the aging phenomenon. The SAXS profiles of the PP samples showed a clear shift of the SAXS peak to the lower q direction induced by the thermal aging, indicating an increase in the length of the long-period structure. Two-trace two-dimensional (2T2D) asynchronous correlation spectra derived from NIR spectra clearly revealed that the aging treatment leads to a substantial increase in the spectral intensity of the regularity bands representing the longer helix present in a folded lamellar structure. In other words, it suggests that the long helix structure is more abundantly present than the short helix structure in the aged PP than in the initial PP. By combining the information derived from the SAXS profiles and NIR spectra, the details of the aging-induced variation were clearly determined. Namely, aging causes additional crystallization of the PP by developing more helical structures, which involves an increase in the lamellar thickness as well as a decrease in the amorphous region. The growth of the rigid crystalline phase restricts the elastic deformation in the amorphous structure, which eventually induces the deterioration of PP by making the polymer hard but brittle. Such observation, in turn, implies that retarding or accelerating the crystallized structure of PP substantially works to control the progress of aging.
在本研究中，开发了一种新系统，用于同时进行近红外（NIR）和小角X射线散射（SAXS）测量。使用NIR-SAXS系统对老化聚丙烯（PP）进行了检测，以证明如何利用该系统获取有关聚合物结构的相关信息。测量了PP初始状态和老化后的SAXS谱图与NIR光谱对，以深入了解老化现象。PP样品的SAXS谱图显示，热老化导致SAXS峰明显向低q方向移动，表明长周期结构的长度增加。从NIR光谱导出的双迹二维（2T2D）异步相关光谱清楚地表明，老化处理导致代表折叠片层结构中较长螺旋的规则带的光谱强度大幅增加。换句话说，这表明在老化的PP中，长螺旋结构比初始PP中的短螺旋结构更丰富。通过结合从SAXS谱图和NIR光谱获得的信息，清楚地确定了老化引起的变化细节。也就是说，老化通过形成更多的螺旋结构导致PP额外结晶，这涉及片层厚度的增加以及非晶区的减少。刚性结晶相的生长限制了非晶结构中的弹性变形，最终通过使聚合物变硬变脆而导致PP劣化。反过来，这种观察结果意味着延缓或加速PP的结晶结构对控制老化进程有很大作用。
