Effects of Molecular Weight of Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of SSBR/Silica Compounds

Abstract

Liquid butadiene rubber (LqBR) which used as a processing aid play a vital role in the manufacturing of high-performance tire tread compounds. However, the studies on the effect of molecular weight, microstructure, and functionalization of LqBR on the properties of compounds are still insufficient. In this study, non-functionalized and center-functionalized liquid butadiene rubbers (N-LqBR and C-LqBR modified with ethoxysilyl group, respectively) were synthesized with low vinyl content and different molecular weights using anionic polymerization. In addition, LqBR was added to the silica-filled SSBR compounds as an alternative to treated distillate aromatic extract (TDAE) oil, and the effect of molecular weight and functionalization on the properties of the silica-filled SSBR compound was examined. C-LqBR showed a low Payne effect and Mooney viscosity because of improved silica dispersion due to the ethoxysilyl functional group. Furthermore, C-LqBR showed an increased crosslink density, improved mechanical properties, and reduced organic matter extraction compared to the N-LqBR compound. LqBR reduced the glass transition temperature (Tg) of the compound significantly, thereby improving snow traction and abrasion resistance compared to TDAE oil. Furthermore, the energy loss characteristics revealed that the hysteresis loss attributable to the free chain ends of LqBR was dominant.

Effect of the Functional Group Position in Functionalized Liquid Butadiene Rubbers Used as Processing Aids on the Properties of Silica-Filled Rubber Compounds

“…Figure 2 and Figure 3 , and Table 4 show the results of GPC and 1 H NMR of the polymerized LqBRs. Kim et al, reported that most LqBRs can be crosslinked to the base polymer by sulfur when the molecular weight of the LqBR is 25,000 g/mol or higher [ 19 ]. In addition, Salort et al, reported that low-molecular-weight di-functionalized LqBRs can be crosslinked to the base polymer by sulfur through higher molecular-weight structure formation by self-condensation [ 2 ].…”

“…Sufficient viscosity and shearing force are required during the mixing process to achieve excellent silica dispersion within the compound [ 1 , 19 ]. Due to the fact that LqBRs, which have higher molecular weights than TDAE oils (molecular weight < 500 g/mol), possess higher viscosity, high peak torque values were obtained in the first stage of the mixing process, as shown in Figure 4 and Table 5 .…”

“…The Mooney viscosity results, and the cure characteristics obtained using an MDR are shown in Table 7 and Figure 6 . LqBRs not only improve silica dispersion, but also show lower Mooney viscosity and minimum torque (T min ) values, as compared with the TDAE compound, because chain slippage is facilitated by acting as a lubricant between the base polymer chains [ 1 , 19 ]. The compounds with OF-LqBR and CF-LqBR exhibited lower Mooney viscosity and T min values than NF-LqBR owing to the improved silica dispersion.…”

“…However, the OF-LqBR and CF-LqBR compounds showed similar M 300 values, as compared with those of the TDAE compound, even though the crosslink density was lower. This is caused not only by increased filler–rubber interactions owing to the coupling reaction of OF-LqBR and CF-LqBR, but also by increased modulus owing to the effect of chain entanglement [ 19 , 35 ]. In the case of DF-LqBR, the crosslink density increased because of the network structure formed by self-condensation, which resulted in the highest M 300 value.…”

“…Salort et al, reported that low-molecular-weight silane-functionalized LqBRs can be crosslinked to the base polymer by sulfur through higher molecular-weight structure formation by self-condensation [ 2 ]. Kim et al, reported that silane-functionalized LqBRs can perform a role similar to that of a silane coupling agent in the compound because the ethoxysilyl group not only reacts with the silanol group of silica, but also crosslinks with the base polymer by consuming sulfur [ 19 ]. In addition, when processing oils and NF-LqBRs are replaced by silane-functionalized LqBRs, hysteresis can be greatly reduced owing to the decrease in the chain mobility due to the functional groups and the decrease in the number of free chain ends.…”