Strain induced nanocavitation and crystallization in natural rubber probed by real time small and wide angle X‐ray scattering

Abstract

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X‐ray scattering in a model natural rubber system. The nanocavities appear after crystallization and only when the true stress is above a critical cavitation stress σCav. The presence of crystallites alone does not influence the calculation of the void volume fraction ϕvoid. The nanocavities formed are 20–50 nm in size with a constant aspect ratio. The presence of filler shifts the critical crystallization extension ratio λCry, λCav, and σCav to lower values. The clear correlation between σCav and the crystallinity at the onset of cavitation χC(λCav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase. Under cyclic loading, nanocavitation is significant only in the first loading and in the successive loadings if the extension ratio is above its maximum historical value. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1125–1138

Nanocavitation around a crack tip in a soft nanocomposite: A scanning microbeam small angle X-ray scattering study

“…A very similar behavior was observed in a natural rubber matrix filled with the same type of CB. 35 These results have also been quantitatively confirmed by macroscopic volume variation tests [33][34][35][36] and provide a mechanistic proof of earlier reports of volume change of filled elastomers in uniaxial tension. 37,38 Such nanocavities and the associated change in volume in uniaxial extension is unusual for rubbers and was only observed for large values of extension k. In the case of the crack tip, the high stress strongly promotes the nucleation of nanovoids in the tip region, which may further lead to the ligaments structure revealed during crack propagation.…”

“…More generally, the threshold of appearance of the nanocavitation mechanism in uniaxial extension has been shown to depend on the filler volume fraction 33,34 and certainly on the nature of the filler. 35,46,47 At the crack tip, this will result in a different size of the cavitated zone for the same macroscopic loading conditions. However, our evidence strongly suggests that elastomers filled with nanoparticles will form nanocavities in a region close to the crack tip and any physically based damage models should take this feature into account.…”

“…[33][34][35] In a CB filled styrene-butadiene rubber (SBR) containing 15-20 vol % of CB nanoparticles, a sharp increase of the scattering invariant above a critical (macroscopic) strain e Cav and/or a critical (macroscopic) stress r Cav was observed in uniaxial loading. This increase in Q was attributed to the following mechanism: the rearrangement of the filler aggregates under strain generates significant triaxial stresses in locally confined regions between CB agglomerates and these local triaxial stresses then drive nanocavitation, which is detected by SAXS.…”

Thermomechanical analysis of the crack tip zone in stretched crystallizable natural rubber by using infrared thermography and digital image correlation

“…More recently, the interaction between cavitation and SIC has been highlighted and investigated in Ref. [9]. Finally, several authors have proposed mechanisms of crack growth [7,10,11].…”

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

“…As the most widely used active fillers, CB and silica particles bond among themselves to form aggregates with rich branches in the rubber matrix; strong filler–filler interactions are observed when the distance of neighboring aggregates is sufficiently close . In addition, 3D transmission electron microscopy (3D‐TEM) shows that the filler aggregates tend to form a network structure when the volume fraction of the filler exceeds a certain value, where the network structure can be tuned by external fields, such as tensile deformation and heat treatment . 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 .…”