Segmental relaxations and other insights into filler‐mediated interactions for carbon black‐filled polybutadiene rubber

Abstract

The role of interaction with filler particles in modifying segmental relaxations of elastomers is still not fully clear. This work examines the glass and melting transition of unvulcanized and vulcanized polybutadiene rubber filled with carbon black. It is found that for uncured rubbers, the calorimetric glass and melting transition temperatures are unaffected by the presence of carbon black, without invoking the concept of restricted chains near filler. In quenched vulcanizates, the increment in segmental relaxation with filler loading is detected, which is attributed to the reduction in chemical crosslink density caused by filler agglomeration. On the other hand, the crystalline part constrains the molecular motion in amorphous regions such that the glass transition temperature is raised when the crystallinity is large. This study reveals that the only effect of carbon black is to influence chemical crosslinks through filler networking and then change in segmental relaxations is detectable.

Glassy and Polymer Dynamics of Elastomers by 1H-Field-Cycling NMR Relaxometry: Effects of Fillers

“…Similarly, small variations of the correlation time for glassy dynamics, and correspondingly of T g , were observed by other authors using different experimental techniques. 22,[28][29][30]32,36 It must be pointed out that all of the investigated samples show very similar values of D res , measured by MQ-NMR experiments 86 (Table 1), in agreement with results reported by other authors. 87 D res gives a measure of local chain order arising from anisotropic fast segmental motions of the elastomer chains, which, in turn, is due to constraints to the chain motions.…”

“…On the other hand, IR_S2_CB80 shows τ s values slightly longer and shorter than those of IR_S2 at temperatures higher and lower than 283 K. The small differences observed between τ s values are in agreement with the T g values determined by DSC for the different samples, which are equal within the experimental error (216 ± 1 K). Similarly, small variations of the correlation time for glassy dynamics, and correspondingly of T g , were observed by other authors using different experimental techniques. ,− ,, It must be pointed out that all of the investigated samples show very similar values of D res , measured by MQ-NMR experiments (Table ), in agreement with results reported by other authors …”

“…In fact, highly attractive or repulsive filler–polymer interactions result in a slowdown or acceleration of dynamics, respectively. A gradient of dynamics exists on going from the interface to the bulk. − The formation of the interfacial layer is also believed to play a crucial role in determining properties of the composite, such as glass-transition temperature, fragility, elastic modulus, and rheological responses, although controversial data were reported in the literature. ,− In particular, bridging chains, that is, chains in contact with at least two particles, may interconnect the filler and polymer chains in a network when the distance between adsorption junctions is on the order of that between filler particles or aggregates. Filler–rubber interactions impose constraints to chain dynamics in elastomers, , in addition to those arising from entanglements and, in cured compounds, chemical cross-links, which constitute the microscopic origin of macroscopic properties required for specific applications.…”

Elucidation of segmental relaxations of silica‐filled cis‐polybutadiene rubber composites

“…There are a lot of voids in the samples mainly arising from strong filler agglomeration and weak rubber‐filler interaction, suggesting an increase of segmental mobility near the pores, partly to account for relatively scattered data, especially for the values of Δ C p . [ 27 ]…”

“…Finally, there are experimental results suggesting a gradual change in T g as a function of distance from the particle. [ 26 ] In our previous study, [ 27 ] we investigated cis ‐polybutadiene rubber (BR)‐carbon black N234 composites, where BR chains interact strongly with filler surfaces via Van der Waals forces. The results revealed that the only considerable influence of carbon black on segmental relaxation process of BR is through an indirect effect which is the influence of filler on chemical crosslink density.…”