Decoupling the Contributions of ZnO and Silica in the Characterization of Industrially-Mixed Filled Rubbers by Combining Small Angle Neutron and X-Ray Scattering

Abstract

Scattering techniques with neutrons and X-rays are powerful methods for the investigation of the hierarchical structure of reinforcing fillers in rubber matrices. However, when using only X-ray scattering, the independent determination of the filler response itself sometimes remains an issue because of a strong parasitic contribution of the ZnO catalyst and activator in the vulcanization process. Microscopic characterization of filler-rubber mixtures even with only catalytic amounts of ZnO is, therefore, inevitably complex. Here, we present a study of silica aggregates dispersed in an SBR rubber in the presence of the catalyst and show that accurate partial structure factors of both components can be determined separately from the combination of the two scattering probes, neutrons, and X-rays. A unique separation of the silica filler scattering function devoid of parasitic catalyst scattering becomes possible. From the combined analysis, the catalyst contribution is determined as well and results to be prominent in the correction scheme. The experimental nano-structure of the ZnO after the mixing process as the by-product of the scattering decomposition was found also to be affected by the presence or absence of silica in the rubber mixture, correlated with the shear forces in the mixing and milling processes during sample preparation. The presented method is well suited for studies of novel dual filler systems.

Small Angle Scattering Techniques for the Study of Catalysts and Catalytic Processes

“…SiO 2 ) and ZnO NPs in rubber as catalyst for the vulcanization process has been analyzed using CV‐SANS, considering the unfilled rubber as a three‐component mixture made of processing oil, rubber, and ZnO NPs which lead to different scattering contrasts. This allows to discriminate the contribution of silica and ZnO in the final composite [59] …”

“…This allows to discriminate the contribution of silica and ZnO in the final composite. [59] In an impressive demonstration of the combined power of SANS and ultra-small angle neutron scattering (USANS) for material characterization, Kim et al studied the morphological features of two different commercial γ-Al 2 O 3 used as a Ptsupport and as matrix in automobile exhaust catalysts. Both techniques combined spanned almost four orders of length scales, from the nanometer to the micrometer scale, providing a complete description of both systems.…”

Recent scattering approaches to structure and dynamics of polymer nanocomposites

“…They can usually be neglected in SANS due to the low contrast and concentrations but strongly contribute to SAXS. Staropoli et al (2020) have succeeded in extracting the corresponding partial structure factors of silica and ZnO NPs by combining two probes, neutrons, and X-rays.…”

Anomalous small-angle X-ray scattering analyses on hierarchical structures of rubber–filler systems

“…Thus, the effect of ZnO on the scattering intensity makes quantitative analyses of the hierarchical structures of fillers difficult. Moreover, the particle size of ZnO in rubber-filler systems is typically 100-1000 nm and is similar to the size of aggregates of fillers (Staropoli et al, 2020;Morfin et al, 2006). Thus, we need to eliminate the effects of ZnO from the scattering intensity to analyze the hierarchical structures of rubber-filler systems quantitatively.…”