On the Filler Flocculation in Silica-Filled Rubbers Part I. Quantifying and Tracking the Filler Flocculation and Polymer-Filler Interactions in the Unvulcanized Rubber Compounds

Abstract

Filler flocculation was followed for silica filled compounds containing various alkoxy silanes and non-silane type polar additives. The methodology employed in this paper permitted a quantitative characterization of filler flocculation and polymer-filler interactions after heating the compound under conditions that simulated vulcanization. With the addition of trialkoxy silanes, the reduction of filler flocculation and the degree of polymer-filler interactions were found to depend on the type and the concentration of silane added, and on the mixing drop temperature (Td) used. Greater polymer-filler interactions and flocculation suppression were obtained with a compound containing a tetrasulfane when compared to that containing either a disulfane or a monofunctional-silane. Polar additives such as an amine compound and a sugar alcohol did not reduce the silica flocculation during simulated vulcanization because they were dewetted from the silica surface upon heating. The filler flocculation process was monitored by following the change of dynamic storage moduli using an on-line rheometer. The flocculation process order and process constant were extracted from the non-linear regression analysis of the kinetic data. These kinetic parameters were used to quantify the suppression of filler flocculation by the additives used. Filler flocculation was found not to be affected by the vulcanization process because it occurred prior to the onset of cure.

Flocculation, Reinforcement, and Glass Transition Effects in Silica-Filled Styrene-Butadiene Rubber

“…8 Examples of the strain dependence of G are presented in Figure 4 for as-mixed and annealed silica-filled SBR compounds (no curatives), and Table I summarizes the results for all of the samples. A large increase in the Payne effect was noted upon annealing the unmodified silica-filled SBR, and this silica flocculation was greatly suppressed by addition of both OTES and MPTMS, with the latter silane demonstrating better effectiveness ( Figure 5).…”

“…Böhm and Nguyen 13 were the first to highlight this feature, and more details about this flocculation phenomenon were revealed in later papers. 8,9,14,15 In particular, introducing various silanes, which modify the surface of the silica for better compatibility with the polymer or create chemical links between the polymer backbone and the silica particles, can greatly suppress the filler flocculation process. 8,9 The nature of the polymer-silica interface, as altered by silanes, may also influence the molecular mobility of the polymer chains near the filler.…”

“…8,9,14,15 In particular, introducing various silanes, which modify the surface of the silica for better compatibility with the polymer or create chemical links between the polymer backbone and the silica particles, can greatly suppress the filler flocculation process. 8,9 The nature of the polymer-silica interface, as altered by silanes, may also influence the molecular mobility of the polymer chains near the filler. The effects of nanoconfinement, free surfaces, and interaction with particles on the glass transition of polymers have been reviewed in recent years with no general consensus revealed.…”

“…In the case of silica as a reinforcing filler, silanes can be incorporated into rubber formulations to lessen the filler-filler contacts and reduce the loss tangent (tanδ = G /G ) in the final vulcanizate. [7][8][9][10] Silanes can also improve the processability of silica-filled rubber in the uncured state. 11,12 Much of the filler network develops post-mixing when the rubber is annealed at elevated temperatures (e.g., during the early part of the cure process before the polymer network is established).…”

Chain Scissions of Rubber Molecules by a Tensile Force in Filled Rubber Systems

“…On the other hand, the tensile stress for the TM-1 and TM-2 steadily increased with increasing the strain, similar to the case of carbon black filled vulcanizates 20,21) . It is well known that the strong interfacial bondings between carbon black and rubber matrix enhanced the tensile stress at a larger strain [20][21][22] . As seen in Table 2, ethoxy groups of TESPT react with silanol groups on silica 14,22) .…”