Stress-strain relation is one of the most basic mechanical properties of cured rubber, and it has been studied both in academia and industry for many years. It is well known that stress-strain relation of cured rubber depends on various features of rubber compounds, such as type of polymer, type of filler, loading amount of filler, cross-link density and so on. However, there remain several problems to be fully understood for stress-strain relation of filled rubber; e.g., the effect of the structure of filler-network, filler-filler interaction and filler-polymer interaction. In this review, we explain fundamental knowledge for stress-strain relation of cured rubber both for theoretical aspect and methodology for the analysis of experimental data. Firstly, stress-strain relation of unfilled rubber (rubber without filler) is explained, then that of filled rubber (rubber with filler) is explained on the basis of fundamental knowledge for unfilled rubber. Although, various models for stress-strain relation of filled rubber have been proposed and there has not been unified understanding, we explain one of the models, which, we believe, is helpful for engineer/researcher to understand and evaluate stress-strain relations of filled rubber.
This article describes the fundamentals of the measurement and analysis for linear dynamic viscoelasticity of elastomeric materials. We also introduce the linear dynamic viscoelasticity of the two types of high-damping elastomer with different characteristics of network structure.
Though the inherent elasticity of rubber materials is derived from the amorphous polymer chains, crystals are also an important factor in understanding the physical properties of rubber. For example, in natural rubber, butadiene rubber, chloroprene rubber, and some others, crystallization occurs under high elongation, which is thought to exert a self-reinforcing effect. Also the hard segments of urethane rubbers are sometimes crystalline. Dynamic change of such crystal structures has a significant effect on the physical properties of rubber, and wide angle X-ray diffraction (WAXD) is a powerful tool for analyzing such dynamic structural changes. In this paper, we aim to explain the basic principles of WAXD in as simple words as possible for readers who are not familiar with WAXD measurements.
Small-angle X-ray scattering is a method to measure scattered X-ray interference by the spatial scattering length density fluctuation in the sample. One can investigate, for example, the radius of gyration of polymer in solution, size and shape of a protein in aqueous solution, the structure of micelle (size and shape, its distribution), microphase separated structure (period and morphology), crystal lamella, the network structure of gels, nanoparticles. SAXS is a non-destructive method for observing the nanometer-scale structure and is suited for various in-situ measurements. Here, the principle of small-angle X-ray scattering is introduced, and a few examples of SAXS experiments related to the rubber materials will be given.
In this paper, fundamental knowledge for fracture of rubber is summarized. Standardized rubber testing methods and fundamental understanding of fracture mechanics for rubber is briefly discussed. Tensile strength in standardized testing method is also reviewed from fracture mechanics point of view. Throughout this paper, the important role of hysteresis energy for rubber strength is highlighted.