Study of Filled SBR Elastomers Using NMR and Mechanical Measurements

Abstract

The effects of different kinds and amounts of fillers, e.g., carbon black N220 and silicasilane, on molecular structure and dynamics of styrene-butadiene rubber (SBR) and the effects of vulcanization on filled SBR systems are studied by Hahn echo and rotating-frame longitudinal relaxation T 1F NMR techniques as well as mechanical measurements, with the emphasis of quantitative comparison between microscopic and macroscopic results. The calculation based on a theoretic model for transverse relaxation in elastomeric networks reveals that filler aggregates or clusters behave like additional crosslinking points and thus lead to a decrease in the molecular mass between cross-linking points M c, an increase of intercross-link chains, or accordingly a decrease of dangling and free chains, ultimately to the increasing cross-link modulus G c, to the extent that depends on the type and, in particular, content of fillers. Compared with SBR filled with silica-silane, SBR filled with carbon black N220 shows more network chains due to its stronger binding ability or adsorbability but results in less cross-link density due to its higher inhomogeneity. The filler dependence of segmental and overall chain mobility is definitely different for both SBR systems, cross-linked and un-cross-linked, which is attributed to the restriction of filler on chemical cross-linking reaction occurred in a SBR matrix. A recent concept of hydrodynamic reinforcement by filler clusters and stress-induced cluster breakdown is combined with a tube model of rubber elasticity for modeling the typical stress softening effect of filled rubber for uniaxial stress-strain measurements. The evaluated material parameters deliver information about cross-link densities and filler specific polymer-filler couplings. The resulting densities ν mech of network junctions are fairly consistent with NMR-derived ones within experimental errors; the differences can be used to estimate the content of different types of cross-links and chain entanglements. Finally, the related observations have been schematically represented using different physical models.

Physical interpretation of the Mullins softening in a carbon-black filled SBR

“…According to [10], heating a carbon-black filled SBR at 80 °C increases its chain free motion, boosting adsorption at the filler surface. Therefore, virgin samples were exposed to heating in vacuo at various temperatures during three days.…”

“…A degradation of this layer, by desorption for instance, may have a significant impact on the material stiffness. Moreover, Luo et al [10] noticed, thanks to NMR observations, that when heated at 80 °C, free chains adsorbed at the carbon-black aggregates surface, which could explain the Mullins recovery at high temperature in vacuo [2].…”

Silica nanoparticles dispersed in a self-assembled viscoelastic matrix: structure, rheology, and comparison to reinforced elastomers

“…At higher deformations, the reinforcement factor decreases in all cases, but stays still superior in the case of the low-pH samples. A simple interpretation of this λ-dependence is that big aggregates contribute strongly to reinforcement, and that they break up under deformation, thereby reducing the reinforcement factor of the composites [36]. At large deformation, finally, only small aggregates and potentially slightly different interfacial interactions contribute to the reinforcement.…”

Radiation-Induced Cross-Linking in a Silica-Filled Silicone Elastomer As Investigated by Multiple Quantum 1H NMR

“…28 These effects have been observed to be large enough to reverse trends of <Ω d > vs crosslink density at different fields. 29,30 MQ based approaches, have so far, been shown to be insensitive to these effects. 30 Since the network topology and the filler-particle interactions determine to a significant part the engineering properties, 31 including tensile, shear, and creep moduli, MQ methods offer the potential for model free insight into the origins of degradation in material performance.…”

“…It should be noted that due to the number of competing contributions to the echo decay rate, <Ω d 2 > can usually only be diagnostic of trends in crosslink density or molecular order and even these trends must be interpreted with care given previous observations that the trends can be field dependent. 29,30 Multiple quantum NMR experiments were performed using the refocused multiple quantum excitation and reconversion pulse sequence shown in Figure 1B. This sequence was shown to be a versatile method for exciting MQ coherences in silicone systems.…”