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Open AccessArticle

A Nonequilibrium Model for Particle Networking/Jamming and Time-Dependent Dynamic Rheology of Filled Polymers

1
Endurica LLC, Findlay, OH 45840, USA
2
Leibniz-Institut für Polymerforschung Dresden e.V., 01069 Dresden, Germany
3
Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik, Technische Universität Dresden, 01069 Dresden, Germany
*
Author to whom correspondence should be addressed.
Polymers 2020, 12(1), 190; https://doi.org/10.3390/polym12010190
Received: 19 November 2019 / Revised: 2 January 2020 / Accepted: 5 January 2020 / Published: 10 January 2020
(This article belongs to the Special Issue Elastomers: From Theory to Applications)
We describe an approach for modeling the filler network formation kinetics of particle-reinforced rubbery polymers—commonly called filler flocculation—that was developed by employing parallels between deformation effects in jammed particle systems and the influence of temperature on glass-forming materials. Experimental dynamic viscosity results were obtained concerning the strain-induced particle network breakdown and subsequent time-dependent reformation behavior for uncross-linked elastomers reinforced with carbon black and silica nanoparticles. Using a relaxation time function that depends on both actual dynamic strain amplitude and fictive (structural) strain, the model effectively represented the experimental data for three different levels of dynamic strain down-jump with a single set of parameters. This fictive strain model for filler networking is analogous to the established Tool–Narayanaswamy–Moynihan model for structural relaxation (physical aging) of nonequilibrium glasses. Compared to carbon black, precipitated silica particles without silane surface modification exhibited a greater overall extent of filler networking and showed more self-limiting behavior in terms of network formation kinetics in filled ethylene-propylene-diene rubber (EPDM). The EPDM compounds with silica or carbon black filler were stable during the dynamic shearing and recovery experiments at 160 °C, whereas irreversible dynamic modulus increases were noted when the polymer matrix was styrene-butadiene rubber (SBR), presumably due to branching/cross-linking of SBR in the rheometer. Care must be taken when measuring and interpreting the time-dependent filler networking in unsaturated elastomers at high temperatures.
Keywords: polymer nanocomposites; filled rubber; particle network; filler flocculation; fictive strain; structural relaxation; Tool–Narayanaswamy–Moynihan model; jamming polymer nanocomposites; filled rubber; particle network; filler flocculation; fictive strain; structural relaxation; Tool–Narayanaswamy–Moynihan model; jamming
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MDPI and ACS Style

Robertson, C.G.; Vaikuntam, S.R.; Heinrich, G. A Nonequilibrium Model for Particle Networking/Jamming and Time-Dependent Dynamic Rheology of Filled Polymers. Polymers 2020, 12, 190.

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