Unveiling Reinforcement and Toughening Mechanism of Filler Network in Natural Rubber with Synchrotron Radiation X-ray Nano-Computed Tomography

Abstract

Double network structure constructed with filler network of carbon black and molecular network of natural rubber possesses excellent toughness and strength. However, due to lack of proper in situ imaging techniques to detect the structural evolutions under loading, the reinforcement mechanism of filler network is still under debate. Here in situ synchrotron radiation X-ray nano-computed tomography with high spatial resolution (100 nm) is employed to study structural evolution of carbon black in a large volume of natural rubber matrix. For the first time, strain-induced deformation, destruction, and reconstruction of filler network are directly observed under cyclic loading. Combining mechanical test, the reinforcing and toughening effect of filler network is quantitatively assigned to three mechanisms, namely elastic deformation, destruction, and friction of filler network. Elastic deformation mainly occurs at low strain for energy storage, while network destruction plays the dominant role at larger strain to dissipate strain energy. Additionally, friction is another energy dissipation mainly at low strain.

From the Volume‐Filling Effect to the Stress‐Bearing Network: The Reinforcement Mechanisms of Carbon Black Filler in Natural Rubber

“…Some special mechanical features, such as the well‐known Payne effect, are also considered to play a role in the construction and destruction of the filler network under loading . Using “X‐ray nano‐CT”, where computed tomography can have nanoscale resolution as a result of synchrotron‐radiation X‐rays, we observed the destruction and reconstruction of a CB filler network in a NR matrix under cyclic loading . All results reflect the common view that the filler in the rubber matrix tends to form a network, which undergoes a structural evolution to store and dissipate external strain energy and is considered the main reason for the excellent toughness and strength of the rubber composites …”

“…Similar to the previously described method, the 3D imaging slices were segmented and reconstructed using the Amira software from TGS Inc.; the components were made different colors to easily distinguish them according to their contrast values. In 3D segmentation and reconstruction, the selected threshold is very important in determining the aggregate size and CB volume fraction in the rubber matrix.…”

“…The method to calculate m // and m ┴ is shown in Figure ; the network is assumed to be composed of a series of quadrilateral meshes. Using our software, lines with identical spacings (dashed lines in Figure ) along and perpendicular to the loading direction are drawn to outline the quadrilateral meshes . For each image, a set of 20 lines are used for the perpendicular calculation, and another set of 20 for the parallel calculation.…”

“…Filled rubber with multiple components is so complex that many factors—such as the filler volume fraction, formulation, mixing and storing conditions—can affect the network structure, toughness, and strength . Moreover, under mechanical loading, the filler network experiences elastic deformation, sliding, destruction, and reconstruction, which are essential for the non‐linear mechanical behavior of filled rubber composites. Evidently, without direct structural information of the network and the evolution during mechanical tests, it is difficult to construct quantitative relationships between the filler network and the mechanical properties of the rubber composites.…”

“…3D‐TEM has high resolution, but it is limited to a small imaging field; in contrast, optic microscopy is restricted by the resolution and penetration depth . In previous studies, we demonstrated that synchrotron‐radiation X‐ray nano‐CT is an effective technique for obtaining a CB filler network in large volume; it can also be performed on samples under loading at different strains. By considering the mechanical behavior and structural evolution of the filler network, the reinforcement can be attributed to elastic deformation, sliding, and destruction of the filler network.…”