Mechanical Properties and Cross-Link Density of Styrene–Butadiene Model Composites Containing Fillers with Bimodal Particle Size Distribution

Abstract

Mechanical properties and cross-link density of model composites being solution styrene–butadiene rubbers filled with different amounts of nanosized silica particles or mixtures of nanosized silica particles and micrometer-sized borosilicate glass particles are studied. The cross-link density of the rubber matrix is measured based on a double-quantum NMR spectroscopy method. Shear data show that reinforcement and dissipation G″ in the rubber plateau range depend systematically on the total surface area of the filler per unit composite. Different contributions to reinforcement due to hydrodynamic effects, “filler network”, glassy polymer layer, and “occluded rubber” are quantified based on a comparison of linear response measurements with strain sweeps performed at different temperatures. The results show a percolation threshold at silica volume fractions of about 0.15. The load-carrying capacity of the “filler network” decreases significantly with temperature. This may indicate the existence of a glassy polymer layer on the surface of the filler particles which softens several ten degrees above the bulk T g of the rubber matrix. Two regimes are found in the dissipation above T g which both depend systematically on the surface area of the filler system: A strongly frequency-dependent dissipation regime with power-law behavior is observed in G″(ω) at temperatures up to 70 K above the bulk T g, and a nearly frequency-independent G″ regime dominates at higher temperatures. The molecular nature and importance of this finding for tire applications are discussed.

Translation of segment scale stiffening into macroscale reinforcement in polymer nanocomposites

“…The negligible effect of the nanoparticles and their assemblies on the mechanical response is observed below the glass transition of the system (40°C) while a substantial difference in the modulus enhancement is observed above the glass transition and in the rubbery plateau region. This is in good agreement with other experimental works reporting the thermomechanical response of PNCs . The temperature was expressed as a distance from the actual T g of each system as a reference point by the parameter T − T g .…”

Synergistic effects of rubber band infused graphene nanocomposite on morphology, spectral, and dynamic mechanical properties

“…A region where temperature more 45°C shows an apparent decrease of reinforcement with decreasing graphene content (inset figure). This phenomenon can be interpreted that at a certain fraction of the RB matrix which has a significantly higher softening temperature than bare RB …”

Depercolation of aggregates upon polymer grafting in simplified industrial nanocomposites studied with dielectric spectroscopy

“…In this context, distinct contributions have been detected: one part of the chain segments is not affected by the filler, whereas an interfacial polymer layer with frozen dynamics at nanosecond time scales has been evidenced by solid-state NMR experiments, the so-called "glassy" fraction [13,14]. Such an immobilized layer with a thickness of 1 to 2 nm at the particle surface close to T g would lead to an increase of the solid-like fraction within the nanocomposite and is thus of utmost importance for filler network percolation [32,48,49].…”