Vulcanizate Structures and Mechanical Properties of Rubber Compounds With Silica and Carbon Black Binary Filler Systems

Abstract

The physical properties of rubber compounds are mainly determined by the filler dispersion within the rubber matrix, filler–rubber interaction, and chemical crosslink structure caused by sulfur. Carbon black or silica is typically used as a reinforcing filler in tire tread compounds; however, binary filler systems comprising the two types of filler are also currently being used to complement each other. This study used binary filler systems to manufacture vulcanizates and classified the vulcanizate structures as chemical crosslinks caused by sulfur, physical crosslinks caused by carbon black (carbon black–bound rubber), and silica–silane–rubber networks caused by silica and silane. The effect of each vulcanizate structure on the physical properties was also calculated. In the proposed binary filler system, silica chemically bonds with rubber molecules, unlike carbon black. Therefore, the crosslink density per unit of silica content was 19% higher than that of carbon black, in which rubber molecules were physically adsorbed on the surface. Tensile properties affected by 1 unit of crosslinking density for each filler were calculated, and silica was found to contribute more in the low-elongation range, whereas carbon black contributed more in the high-elongation range. Regarding tan δ at 60 °C and abrasion resistance per unit crosslink density of filler, carbon black made a greater contribution than silica, whereas silica had a greater contribution to wet traction and snow traction.

Effect of Epoxide Content on the Vulcanizate Structure of Silica-Filled Epoxidized Natural Rubber (ENR) Compounds

“…Thus, the silica-filled ENR compound vulcanizates had complex vulcanizate structures, which were analyzed based on the total crosslink density ( Figure 5 and Table 6 ). This was calculated as the sum of the filler–rubber interaction and chemical crosslink density based on a vulcanizate structure analysis of the compounds with different filler contents [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. When ENR was used as the base rubber, the silica–TESPT–ENR interactions and silica–ENR interactions due to the epoxide groups were quantitatively calculated based on the difference in filler–rubber interactions between the compounds with and without 8 wt% TESPT.…”

“…The Kraus equation was proposed based on this work, where the density was found to be proportional to the filler volume fraction. Furthermore, recent studies quantitatively distinguished the vulcanizate structure of compounds with silica as a filler as networks of silica–silane–rubber and sulfur chemical crosslinking [ 19 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Consequently, the filler–rubber network of silica-filled compounds can be quantitatively differentiated, the detailed vulcanizate structure of rubber with functional groups (e.g., ENR) can be identified, and the effects of functional groups on the properties of the compounds were better understood.…”

Effect of the Epoxide Contents of Liquid Isoprene Rubber as a Processing Aid on the Properties of Silica-Filled Natural Rubber Compounds

“…To determine the effect of the epoxide content of E-LqIRs on the vulcanizate structures of the rubber compounds having various filler contents, the total crosslink density was calculated as the sum of the filler–rubber interactions and chemical crosslink density via vulcanizate structure analysis [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Figure 6 and Table 6 present the results of the analysis.…”

Vulcanizate Structures of SBR Compounds with Silica and Carbon Black Binary Filler Systems at Different Curing Temperatures

“…Lee et al conducted swelling tests and used Equations (1) and (2) for vulcanizates filled with silica or carbon black in order to separate the total crosslink density into the filler–rubber interaction and chemical crosslink density [ 21 ]. In addition, a previous study by Kim et al categorized SBR compounds with carbon black and silica as binary fillers into CBBR, SSRN, and CCDS by employing the swelling test as well as Equations (1) and (2), as demonstrated in Figure 2 [ 25 ]. In this study, we determined the effect of cure temperature on the vulcanizate structure.…”

“…In recent studies, vulcanizate structures in compounds using silica as the filler were classified quantitatively according to the network from silica-silane–rubber and the chemical crosslink by sulfur [ 20 , 21 , 22 , 23 , 24 ]. In addition, as shown in Figure 1 , there are existing studies on compounds using carbon black and silica as binary fillers that are distinguished based on the chemical crosslink density by sulfur (CCDS), carbon black bound rubber (CBBR) (i.e., the physical crosslink due to carbon black), and silica-silane–rubber network (SSRN) [ 25 ]. As the filler–rubber network could not be subdivided prior to these research findings, it was difficult to characterize the detailed vulcanizate structure based on cure temperature and determine the effect of cure temperature on the physical properties of the material.…”