Silica-Reinforced Natural Rubber: Synergistic Effects by Addition of Small Amounts of Secondary Fillers to Silica-Reinforced Natural Rubber Tire Tread Compounds

Abstract

Modern fuel-saving tire treads are commonly reinforced by silica due to the fact that this leads to lower rolling resistance and higher wet grip compared to carbon black-filled alternatives. The introduction of secondary fillers into the silica-reinforced tread compounds, often named hybrid fillers, may have the potential to improve tire performance further. In the present work, two secondary fillers organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the mixing procedure commonly in use for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior, and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent with silica and elastomer are significantly influenced by organoclay due to an effect of its modifier: an organic ammonium derivative. This has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this behavior. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the high specific surface area of the carbon black used. The dynamic properties indicate that there is a potential to improve wet traction and rolling resistance of a tire tread when using organoclay as secondary filler, while the combination of carbon black in silica-filled NR does not change these properties.

Synergistic effect by high specific surface area carbon black as secondary filler in silica reinforced natural rubber tire tread compounds

“…The presence of small molecules like amine-based substance such as aliphatic amines and DPG in this work has been reported to help shielding off those left-over silanol groups and reduce the cure retardation [9,10]. Nevertheless, the pure silica-filled compound still shows longer scorch and cure times with lower cure rate index compared to the systems with silica/CB mixed fillers as corresponded to the previous works for silica/CB [23,30], silica/bentonite [31] and silica/nanoclay [14,23]. The addition of CB reduces both scorch and cure times especially in the range of 0-40 wt% relative to total filler, thereafter the values decrease slightly with increasing amount of CB.…”

“…This is also due to the filler network of CB. Moreover, it is well established that the dump temperature is a key parameter affecting the silanization reaction for silicasilane compounds [7,8,23]. The higher dump temperature promotes a greater extent of the silanization and filler-rubber interactions and thus increases the viscosity.…”

“…Although the use of CB in combination with silica has been widely studied and previously reported, the use of CB as secondary filler in silica-reinforced NR compounds aiming to enhance tire performance has not been considered. Our previous report on the effect of addition of small amounts of organoclay and CB as secondary fillers to silicareinforced natural rubber tire tread compounds [23] shows that the properties of compounds are affected by the mixing dump temperature. An increased dump temperature leads to a better silanization reaction between the silica and the coupling agent TESPD, but at too high mixing temperatures NR degradation can occur.…”

“…There is a growing interest to use a filler combination or hybrid fillers making use of the benefits provided by the individual components. Silica has been used in combination with secondary fillers such as China clay [13], montmorillonite [14,15], kaolin [16], organically modified nanoclay [17] and CB [18][19][20][21][22][23] aiming for a synergistic effect on the rubber properties. The simplest combination should be silica/CB as both types of fillers are already commonly used in tire compounds.…”

Influence of Fillers and Ionic Liquids on the Crosslinking and Performance of Natural Rubber Biocomposites

“…Elastomer compounds for potential applications such as the tire industry generally contain at least 30 phr of active fillers, i.e., carbon black or silica. Various types of silica are conventionally used as reinforcing fillers, since they improve the mechanical properties of elastomers, i.e., tensile strength, modulus, tear strength, heat build-up, flex fatigue, chunking resistance, as well as abrasion and skid resistance [40,41]. However, the addition of silica to rubber compounds has some disadvantages, which arise from weak elastomerfiller interaction and the incompatibility of silica with rubbers [42].…”