CONTRIBUTION OF CROSSLINK NETWORK STRUCTURE TO THE VISCOELASTIC CHARACTERISTICS OF EPDM: TUNING DYNAMIC PROPERTIES THROUGH HYBRID CURING
EPDM is the fourth most widely used general-purpose elastomer, accounting for approximately 10% of total synthetic rubber production. With its broad applications in the automotive and construction industries, the analysis of EPDM’s dynamic viscoelastic properties is critical for optimizing product performance. Although the effects of various fillers and their structures on EPDM’s viscoelastic behavior have been widely studied, the impact of crosslink network architecture on long-term viscoelastic properties is seldom explored. To investigate the influence of different crosslink types and their compositions on the long-term viscoelastic behavior of EPDM, we have used thiol-amine analysis, time–temperature superposition for frequency-dependent properties, and temperature scanning stress relaxation. We establish correlations between crosslink features and the viscoelastic properties of carbon black–filled EPDM. In addition, we explore the effects of unique crosslink networks formed through hybrid cure systems containing accelerated sulfur and peroxide on the viscoelastic performance of EPDM. Our findings indicate that the frequency dependence of viscoelastic properties is governed by crosslink length, whereas temperature dependence is influenced by crosslink type. The results also indicated a strong correlation between plateau modulus and polysulfide crosslinks. These insights offer valuable guidance for optimizing the viscoelastic characteristics of next-generation elastomeric materials.ABSTRACT
Proposed hybrid curing reaction mechanism in ENB-EPDM.
Thiol-amine treatment for selective breaking of (a) polysulfidic crosslinkages; (b) disulfidic crosslinks; and (c) unaffected crosslinks on treatments 1 and 2. (d) Schematic of TSSR measurement.
(a) Crosslink density of the samples from Flory–Rehner equation. (b) Composition of different structures (types) of crosslinks in samples.
G′ (a) and G′′ (b) in strain sweep of samples and G′ (c) and G′′ (d) of 504-h thermally aged samples at 125 °C.
(a) Temperature dependence of G′ of samples. (b) Temperature dependence of G′′ of samples. (c) Tan δ of samples in temperature sweep. (d) Correlation between quantity of polysulfidic linkages and G′ at 30 °C.
(a) Isothermal G′ curves in frequency sweep at various temperatures of sample S-link. (b) Master curve of G′ at −40 °C of the sample S-link. (c) Master curve of G′′ at −40 °C of the samples S-link. (d) G′′ in frequency sweep at various temperature of samples S-link. Double asterisk (**) is Tr.
Master curves of G′, G′′, and tan δ obtained by shifting the isothermal frequency sweep data, giving the viscoelastic behavior over an extended frequency scale at Tr of approximately −40 °C of samples: (a) S-link, (b) SP-hybrid, (c) SP-plus, and (d) P-link. (e) vGP plot of all samples. (f) Cole–Cole plot of G′′ vs G′ of all samples.
Comparison of master curve of (a) G′, (b) G′′, (c) tan δ of all samples at 25 °C; (d) temperature dependence of horizontal shift factor (aT of samples) and their fit to WLF equation and (e) C1 and C2 values from WLF equation. (f) Schematic representation of polysulfidic and CIMB-based crosslink lengths.
(a) Continuous relaxation spectra from complex modulus. (b) Relaxation spectra from TSSR. (c) Force ratio curves from TSSR. (d) Stress vs temperature curve from TSSR. (e) T10 values from TSSR. (f) Crosslink density of samples from TSSR.
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