Study on networks of vulcanizates by synchrotron X-ray-absorption fine structure measurements

Usefulness of recent synchrotron X-ray-absorption fine structure (XAFS) measurements is described for characterization of network structures of vulcanizates. The first example is related to the formation of two-phase network morphology in vulcanizates. In situ zinc K-shell X-ray-absorption near-edge structure (XANES) measurement during vulcanization is reported to support the simultaneous progress of two sulfur cross-linking reactions in the N-(1,3-benzothiazol-2-ylsulfanyl) cyclohexanamine accelerated systems under the presence of ZnO or zinc stearate. The second is a study on in situ zinc K-shell XAFS measurement for analyzing a novel intermediate, which was generated from ZnO and stearic acid during vulcanization. The intermediate [Zn₂ (μ-O₂CC₁₇H₃₅)₂]²⁺(OH^-)₂ is newly found as an active catalyst for the sulfur cross-linking reaction. The third is a study on sulfur K-shell XANES measurement to determine characteristics of sulfidic linkages in vulcanizates which were prepared by the accelerated vulcanizations using the new intermediate. The disulfidic linkage is reported to be dominantly generated in the systems. Finally, a study on scanning transmission X-ray microscopy, which provides the XANES spectra in 2D mapping, is introduced. The XAFS analysis may be a powerful tool for characterization of rubber materials. (author)