A novel practical approach for monitoring the crosslink density of an ethylene propylene diene monomer compound: Complementary scanning acoustic microscopy and FIB-SEM-EDS analyses

Abstract

Tuning of the crosslink density (CLD) in the rubber compounds is very crucial for optimizing the physical and mechanical properties of the ultimate rubber products. Conventionally, CLD can be measured via rheological methods such as moving die rheometer (MDR), via mechanical tests such as temperature scanning stress relaxation analysis (TSSR), or via direct swelling experiments using Flory–Rehner approach. In the current study, two novel techniques, focused ion beam - scanning electron microscopy (FIB-SEM) processing, with simultaneous energy dispersive X-ray spectrometry (EDS) mapping analysis and scanning acoustic microscopy (SAM) were combined and correlated to conventional methods on a model recipe of ethylene propylene diene monomer (EPDM) compound having different sulphur contents. Depending on the applied technique, the increase in the crosslink density with sulphur content was found to be 1.7 fold for the Flory–Rehner approach and 1.2 fold for both TSSR and MDR. It is directly monitored from the FIB-SEM-EDS analysis that the sulphur distribution and agglomeration behavior increased in line with ZnO content, which is an indirect indication of the rise in crosslink density. The impedance maps of the crosslinked samples obtained through SAM analysis revealed that the impedance of the samples increased with the increasing sulphur content, which can be attributed to higher level of crosslink density. A quantified correlation was obtained between SAM images and the crosslink density of the samples. It was shown that SAM is a promising tool for practical and non-destructive analysis for determining the formation of crosslink density of the rubbers.

Improved Heat Dissipation of NR/SBR-Based Tire Tread Compounds via Hybrid Fillers of Multi-Walled Carbon Nanotube and Carbon Black

“…This can be attributed to the improved distribution of MWCNT in the rubber matrix, an enhanced interfacial area between MWCNT and NR/SBR resulted in improved initial relaxation modulus and increased physical desorption [62,63]. At a constant strain, the slope of the stress versus temperature plot can be used to determine the cross-link density (CLD) of a material [64,65]. As shown in Table 5, the CLD of MWCNT-reinforced tire tread NR/SBR compounds is higher than that of CB-reinforced compounds.…”

“…* T10 stands for the temperature at which the force (F) decreased by 10% from its initial value (F0). At a constant strain, the slope of the stress versus temperature plot can be used to determine the cross-link density (CLD) of a material [64,65]. As shown in Table 5, the CLD of MWCNT-reinforced tire tread NR/SBR compounds is higher than that of CBreinforced compounds.…”