Silica-reinforced natural rubber tire compounds with safe compounding ingredients

For rubber compounds reinforced with a silica/silane system, the reinforcement efficiency strongly depends on the reaction between the silica surface and silane molecules, the so-called silanization reaction. DiPhenyl Guanidine (DPG) as secondary accelerator for rubber compounds vulcanized with a sulfur system gives additional positive effects in silica-reinforced rubber compounds, while DPG can act as a silanization catalyst and de-activate free silanol groups that are left over after the silanization reaction. However, DPG liberates toxic aniline which has been classified as a carcinogen, during compounding under high mixing temperatures. Concern over the aniline toxicity leads to a search for safe alternatives. In addition, Distillated Aromatic Extract (DAE) which is a petroleum-based process oil conventionally used to improve the processibility and filler dispersion of rubber compounds with high filler loadings, has been banned due to its composition that contains Polycyclic Aromatic Hydrocarbons (PAHs) of which some have been classified as carcinogenic materials. The replacement of DAE with safe process oils such as Treated Distillate Aromatic Extract (TDAE) for tire compounds has come into practice. This present thesis provides an in-depth study into the application of amines as alternatives for DPG and modified palm oils as sustainable alternatives for petroleum-based TDAE oil in silica-reinforced NR compounds, for low rolling resistance tires. Both model compound systems and practical rubber compounds were applied in order to gain information on the kinetics and performance properties of the compounds. Based on the results in this research, replacement of DPG by OCT is feasible, and EPO or mEPO are potential candidates to substitute TDAE in silica-reinforced NR compounds without scarifying the properties. With optimum loading, vulcanized rubber with OCT even shows better mechanical properties and tan δ at 60oC when compared to the DPG counterpart. The utilization of mEPOs results in compounds with enhanced reinforcement index and tensile strength, and reduced loss tangent at 60oC, compared to the mix with TDAE. Therefore, from the perspective of “safe and green” tires, the application of OCT and modified bio oils as alternatives for DPG and TDAE oil, respectively, are fulfilled and bring even lower tire rolling resistance, i.e. less fuel consumption and less CO2 emission