Abstract The Rietveld method has been used to refine the polyvinyl alcohol (PVA) structure. The PVA is a polymeric material exhibiting a semicrystalline “head-to-tail” arrangement of repeating units. Experimental X-ray pattern of PVA was adjusted considering a model based on monoclinic symmetry, but using the P21/m and P21/c spatial groups. The lattice parameters and atomic positions were adjusted in each case. The P21/c based model showed a better Rietveld adjust than the P21/m. Then, the P21/c model was used to analyze the structural behavior of the PVA subjected to different pH environments. From refinement results, the PVA subjected to acid environment remained unchanged and suffered a regalement of its crystalline structure when it is subjected to a basic pH, causing a loss of its permanence and crystallinity. The results provide a powerful model to evaluate the crystallinity degree of the PVA and its structural variations using the Rietveld refinement method.

中文翻译：

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聚乙烯醇的 X 射线分析和 Rietveld 精修

摘要 Rietveld 方法已被用于改进聚乙烯醇 (PVA) 结构。PVA 是一种聚合物材料，呈现出重复单元的半结晶“头对尾”排列。考虑到基于单斜对称性的模型，但使用 P21/m 和 P21/c 空间组，对 PVA 的实验 X 射线图进行了调整。在每种情况下调整晶格参数和原子位置。基于 P21/c 的模型显示出比 P21/m 更好的 Rietveld 调整。然后，利用P21/c模型分析了PVA在不同pH环境下的结构行为。细化结果表明，PVA在酸性环境下保持不变，在碱性pH条件下其晶体结构发生变化，导致其稳定性和结晶度下降。