Silica-filled rubber compounds quietly change while they sit in storage. In uncured compounds made with solution styrene-butadiene rubber (SSBR), polar silica clusters slowly migrate toward one another, forming irreversible physical bonds that raise the compound’s storage modulus over time. This storage hardening contaminates a standard rheological measurement, the Payne effect, and makes comparisons between freshly prepared and stored materials unreliable. A new open-access study in Discover Polymers reports a strikingly simple fix: performing the strain amplitude sweep from high to low strain eliminates the storage-time influence in a single measurement, offering a practical alternative for industrial quality control.
The Payne effect reflects the breakdown of filler-filler networks in rubber compounds under deformation. It is quantified as the difference between the storage modulus (G’) measured at low and high strain amplitudes, denoted ΔG’. At low strain, a connected filler network keeps the modulus high; as strain amplitude increases, the network breaks down and the modulus drops sharply. The effect appears in both unvulcanized and vulcanized compounds, but it is significantly more pronounced in unvulcanized materials, where the absence of a permanent crosslinked network allows greater mobility and reorganization of filler structures over time.
The complication arises because two distinct mechanisms contribute to the measured ΔG’ in uncured silica-filled compounds. Filler flocculation, the aggregation of filler particles driven by polar interactions and van der Waals forces, is an irreversible process that depends on both time and temperature. During storage, gradual reformation of filler networks increases the modulus, inflating ΔG’ values. Conventional one-sweep measurements therefore bundle together the strain-dependent breakdown of the intrinsic filler network and the time-dependent contribution from flocculation, potentially overestimating actual filler-filler interactions.
Anmol Aggarwal, Fabian Grunert, Sybill Ilisch and Anke Blume set out to separate these contributions and develop a simplified, time-efficient test method. They prepared two compounds with identical formulations based on SSBR SPRINTAN 4602, reinforced with 80 phr of precipitated silica ULTRASIL 7000 GR, a loading deliberately set above the percolation threshold to guarantee a full silica network. A bis(triethoxysilylpropyl)disulfide (TESPD) coupling agent linked the polar silica to the non-polar polymer, with the silane amount calculated from the silica’s CTAB surface area of 160 square meters per gram.
Compounding was carried out in a three-stage mixing process in a 390 ml Brabender internal mixer with tangential rotors, an extra stage added beyond typical industrial two-stage practice to improve the extent of silanization. Although the mixer temperature for the silanization reaction was set at 140 degrees Celsius, actual dump temperatures reached 145 to 150 degrees Celsius due to shear heating and the exothermic reaction, conditions within the recommended industrial range. Repeated mixing runs produced consistent rheological responses, confirming reproducible conditions.
To probe storage effects, Compound A was stored at room temperature of 20 degrees Celsius and Compound B at 7 degrees Celsius for up to 29 days. Uncured Payne effect measurements were performed on a Rubber Process Analyzer from TA Instruments at 60 degrees Celsius and 1 Hz, with low strain at 0.074 percent and high strain at 100 percent. In the first low-to-high sweep, ΔG’ values rose steadily with storage time under both conditions, but the increase was markedly larger at room temperature: after 29 days, RT-stored compounds showed roughly 40 percent higher ΔG’ than their initial value, while refrigerated samples showed a smaller but consistent increase of about 25 percent.
The two-sweep protocol revealed the underlying structure of the phenomenon. When a second sweep from high to low strain was performed immediately after the first, its ΔG’ values remained consistent across all storage times and temperatures, matching those of freshly prepared compound. The first sweep destroys both the flocculated network built up during storage and the intrinsic strain-dependent network; the flocculated part cannot reform within the short interval between sweeps, while the intrinsic network reforms quickly. The second sweep therefore captures only the strain-dependent component, and the difference between the two sweeps serves as a direct measure of the extent of flocculation.
Quantifying that difference over the 29-day period showed flocculation accelerating with temperature. By Day 29, the ΔG’ difference between sweeps for RT-stored compounds reached approximately 360 kilopascals, while samples stored at 7 degrees Celsius stayed below 250 kilopascals. Room-temperature samples showed a sharp rise between Day 0 and Day 5, suggesting rapid early aggregation of silica clusters, followed by a slower, near-linear accumulation as mobile clusters became scarce. The refrigerated samples increased more gradually from the start and plateaued beyond 20 days, indicating that cold storage suppresses but cannot completely prevent flocculation.
The team then tested whether both sweeps were even necessary. Four samples of Compound A, stored at room temperature for 30 days, were measured in all four sweep-order combinations: low-to-high followed by high-to-low, low-to-high followed by low-to-high, high-to-low followed by low-to-high, and high-to-low repeated. In every case, the second sweep, regardless of direction, gave consistent modulus values, confirming that the initial sweep breaks down the storage-induced flocculation. Most importantly, when the first sweep ran from high to low strain, the two sweeps overlapped entirely: starting at 100 percent strain destroys both the flocculated and intrinsic networks at once, so the time-dependent contribution is eliminated immediately.
The practical conclusion is that a single high-to-low strain sweep is sufficient to isolate the strain-dependent, storage-history-independent Payne effect, making two-sweep measurements unnecessary for routine work and providing a fast, reliable alternative for compound development and quality control. The authors note limitations and future directions: only two storage temperatures were studied, and extending the range, adding shorter and more frequent early-stage measurements, and validating the approach across different polymer-filler systems would enable kinetic modeling and confirm broader applicability. For an industry that stores large quantities of uncured silica-filled compounds for extended periods, the finding offers a straightforward way to keep measurements comparable regardless of storage history.
Subject of Research: Storage-time-dependent silica flocculation and strain sweep protocols for measuring the Payne effect in uncured silica-filled SSBR compounds.
Article Title: Influence of storage time and amplitude sweeps on flocculation behavior in silica-filled SSBR compounds
Article References: Aggarwal, A., Grunert, F., Ilisch, S., & Blume, A. (2026). Influence of storage time and amplitude sweeps on flocculation behavior in silica-filled SSBR compounds. Discover Polymers, 3(1), Article 12. https://doi.org/10.1007/s44347-026-00048-6
Image Credits: AI Generated
DOI: 10.1007/s44347-026-00048-6
Keywords: Payne effect, silica filler, SSBR, filler flocculation, rubber compounding, Rubber Process Analyzer, storage hardening, strain amplitude sweep, storage modulus, quality control, silanization, unvulcanized rubber
News Source: Bethany Barker. (November 5, 2026). A Single High-to-Low Strain Sweep Strips Storage Effects from Silica Rubber Payne Effect Tests. Scienmag.
