The microstructure of polymer nanocomposites made with disordered silica filler (Zeosil(R) 1165MP) of industrial relevance and various coating agents is quantitatively analyzed using a combination of SAXS, TEM, and a recently developed structural model. The polymer matrix is formed by an endfunctionalized styrene-butadiene statistical copolymer capable of covalent grafting on the silica nanoparticles. The effect of the coating agents with different alkyl chain length (C 8 , C 12 , and C 18 ) on filler structure quantified in terms of aggregate formation, for different concentrations (up to 8%wt with respect to silica), and the effect of a commonly added catalyzer, DPG, are studied using the structural model. As a result we show that a strongly synergetic effect of both DPG and coating agent exist. Our findings open the road to a fundamental understanding and rational design of model and industrial nanocomposite formulation with optimized coating agents.

We use an innovative combination of measurements to study reinforcement in a series of SBR elastomers filled with various amounts of submicrometric precipitated silica. While mechanical measurements give access to the overall response of the nanocomposite material, measurements of the chain segment average orientation induced upon uniaxial stretching give selective access to the response of the elastomer matrix only. Average segment orientation is measured by X-ray scattering. Reinforcement effects are analyzed in terms of the enhancement ratio of the mechanical modulus or induced segmental orientation in a reinforced sample over the corresponding quantity measured in the pure matrix. Cross-link densities are measured independently by NMR to account for possible impact of fillers on the cross-link density. It is demonstrated that in filled materials the orientational enhancement ratio does not decrease significantly as temperature increases, while the mechanical reinforcement ratio decreases as temperature increases, as it is known already. Also, the mechanical reinforcement ratio increases considerably as the silica fraction increases beyond a threshold, which is generally attributed to percolation or onset of filler networking, while the orientational reinforcement ratio qualitatively follows a Guth and Gold type of variation, associated solely with the geometrical (or hydrodynamical) local strain amplification contribution. Comparison of both mechanical and orientational responses thus allows discriminating and quantifying rigid network contribution from strain amplification contribution to reinforcement as a function of either temperature or filler volume fraction.

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.

An innovative rotary tribometer was developed in order to reproduce the abrasive wear of reinforced rubber materials for tire. The device allows performing accelerated, quantitative friction and wear tests which mimic real usage conditions in terms of kinematics and dynamics of the contact, temperature and open cycle conditions, specifically in low severity conditions, which often represent a challenge to mimic and study. The specific point emphasized here is the strong impact of wear debris accumulated in the contact zone on the measured wear rate. To quantify this phenomenon, the amount of wear debris in the contact was varied by changing the frequency at which debris are eliminated. It was found that the presence of more debris in the contact zone generally decreases the wear rate. Two distinct types of wear debris were identified, which are likely to correspond to two distinct mechanisms of wear. Within a transitory period at the beginning of the tests, wear debris essentially consist in a sticky layer of soluble (thus decrosslinked elastomer material). Further on, a steady regime (representative of wear in real low severity conditions) occurs, with a well established ridge pattern, in which the predominant wear mechanism consists in tearing away material fragments of micrometric sizes. The proposed test method allows discriminating quantitatively these mechanisms.

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