Crosslinked Elastomers: Structure-Property Relationships and Stress-Optical Law.

Paul Sotta,Caroline Fayolle,Pierre-Antoine Albouy,Benoit Moreaux,Mohammad Abou Taha

doi:10.3390/polym14010009

Abstract

We present a combination of independent techniques in order to characterize crosslinked elastomers. We combine well-established macroscopic methods, such as rheological and mechanical experiments and equilibrium swelling measurements, a more advanced technique such as proton multiple-quantum NMR, and a new method to measure stress-induced segmental orientation by in situ tensile X-ray scattering. All of these techniques give access to the response of the elastomer network in relation to the crosslinking of the systems. Based on entropic elasticity theory, all these quantities are related to segmental orientation effects through the so-called stress-optical law. By means of the combination of these techniques, we investigate a set of unfilled sulfur-vulcanized styrene butadiene rubber elastomers with different levels of crosslinking. We validate that the results of all methods correlate very well. The relevance of this approach is that it can be applied in any elastomer materials, including materials representative of various industrial application, without prerequisite as regards, e.g., optical transparency or simplified formulation. Moreover, the approach may be used to study reinforcement effects in filled elastomers with nanoparticles.

Highlights

In this paper, we present a combined experimental approach that allows characterizing the relationship between the response to various types of constraint and the structure of the crosslinking network in elastomer materials
Beyond the present styrene butadiene rubber (SBR) samples, it has been applied in a limited set of materials yet, namely natural rubber and polychloroprene [22,23], the technique may potentially be applied in any elastomer material due to the intrinsically anisotropic scattering at the scale of the Kuhn segment in network chains
It was shown that the stress-optical law, Equation (2), is no longer verified in elastomers reinforced by nanometric silica aggregates [24,25], as the stress in reinforced materials no longer follows the same variation as the orientation parameter in the elastomer matrix

Summary

Introduction

We present a combined experimental approach that allows characterizing the relationship between the response to various types of constraint and the structure of the crosslinking network in elastomer materials. Elastomers are very important polymeric materials as they exhibit unique mechanical properties. For practical applications, they generally need to be reinforced by adding solid particles or aggregates (fillers) of submicrometric sizes. The most commonly used reinforcing nanoparticles are carbon black or either fumed or precipitated silica [1,2,3,4,5,6,7], which brings qualitatively new mechanical behavior and drastically improves the properties of the obtained materials in terms of elastic modulus and energy at break [8]. The relative quantitative importance of these various factors in various elastomer materials is frequently debated still For these reasons, it is essential to be able to discriminate and quantify each of these factors

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Conclusion