Abstract
Diphenyl guanidine (DPG) is an essential ingredient in silica-reinforced rubber compounds for low rolling resistance tires, as it not only acts as a secondary accelerator, but also as a catalyst for the silanization reaction. However, because of concern over the toxicity of DPG that liberates aniline during high-temperature processing, safe alternatives are required. The present work studies several amines as potential alternatives for DPG. Different amines (i.e., hexylamine, decylamine, octadecylamine, cyclohexylamine, dicyclohexylamine, and quinuclidine) are investigated in a model system, as well as in a practical rubber compound by taking the ones with DPG and without amine as references. The kinetics of the silanization reaction of the silica/silane mixtures are evaluated using model compounds. The mixtures with amines show up to 3.7 times higher rate constants of the primary silanization reaction compared to the compound without amine. Linear aliphatic amines promote the rate constant of the primary silanization reaction to a greater extent compared to amines with a cyclic structure. The amines with short-alkyl chains that provide better accessibility towards the silica surface, enhance the primary silanization reaction more than the ones with long-alkyl chains. The different amines have no significant influence on the rate constant of the secondary silanization reaction. The amine types that give a higher primary silanization reaction rate constant show a lower flocculation rate in the practical compounds. For the systems with a bit lower primary silanization reaction rate, but higher extent of shielding or physical adsorption that still promotes higher interfacial compatibility between the elastomer and the filler surface, the rubber compounds show a lower Payne effect which would indicate lower filler-filler interaction. However, the flocculation rate constant remained high.
Highlights
Driven by the need for more environmentally friendly and regulated products, low rolling resistance tires have been developed based on utilization of silica/silane technology for rubber reinforcement [1]
For the silica-silane-rubber mixing that required a high temperature for the silanization, it was unavoidable for aniline to be generated from Diphenyl guanidine (DPG), and so a safe alternative is needed
The kinetics of the silanization reaction in the silica/silane model systems containing various amine types reveal that such amines with different chemical structures provide quite diverse amine types reveal that such amines with different chemical structures provide quite diverse influences influences on the rate constant of the primary silanization reaction, but almost do not change the rate on the rate constant of the primary silanization reaction, but almost do not change the rate constant constant of the secondary silanization reaction
Summary
Driven by the need for more environmentally friendly and regulated products, low rolling resistance tires have been developed based on utilization of silica/silane technology for rubber reinforcement [1]. A study on the kinetics of different silanes with varying functional groups in model systems revealed that, only the alkoxy group reacted with the silanol group of the silica, the chemical structure of the whole silane influenced the rate of the reaction [17]. The rate constants of while the primary secondary silanization reactions are determined based on a study are taking silica/silane systems with and amine references. The rate of while the primary and secondary silanization reactions arepractical determined based on a study in a constants model system. Rate constants of the primary secondary silanization reactions of arepractical determined based on a study in aaconstants model with system. Rate of the primary secondary silanization reactions of arepractical determined based on a study in model system.
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