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.<br/

Unfilled Natural Rubber Compounds Containing Bio-Oil Cured with Different Curing Systems: A Comparative Study

This study focuses on the properties of unfilled natural rubber compounds containing bio-oils cured with a peroxide curing system and then discusses the comparisons to those cured using the sulfur system from our previous work. Two types of bio-oils, i.e., palm oil and soybean oil, were used, and distillate aromatic extract (DAE)-based petroleum oil was employed as a reference. The bio-oils caused no significant change in the vulcanization of rubber compounds cured using peroxide. However, the compounds containing bio-oils and cured with sulfur showed a faster vulcanization than the ones with DAE. The bio-oils strongly affected the crosslink density of rubber compounds in both curing systems. The use of bio-oils caused a low crosslink density due to the possible implication of curing agents to bio-oil molecules. The properties of rubber compounds dependent on the different levels of crosslink density were also investigated. The results revealed that when the crosslink density increased, the modulus, tensile strength, and hardness of the rubber compounds increased and the elongation at break and compression set decreased. The use of bio-oils in the rubber compounds cured with different curing systems gave low modulus at 300% strain, tensile strength, and hardness but high elongation at break and compression set when compared to the ones with DAE. However, no significant change was observed for the compression set of the rubber compounds cured using sulfur. With the presence of bio-oils, the properties of rubber compounds cured with sulfur system deteriorated less than those of the ones cured with peroxide

Role of Chemistry in the Successful Development of Low Rolling Resistance Tires for Better Sustainability

Tire development is moving towards sustainability through various approaches, for example, by developing lower rolling resistance tire tread and by utilizing more sustainable raw materials including polymers, fillers, and additives. This presentation will highlight the development of silica-reinforced natural rubber (NR) for low rolling resistance or energy-saving tires. The successful use of silica with a silane coupling agent requires an optimum silanization reaction occurring during mixing. By understanding the chemistry involved and the mechanical process, compounds with high silica-rubber interaction, low filler-filler interaction, and fine filler dispersion can be achieved. Moreover, as the silanization can be catalyzed by diphenylguanidine (DPG) which is normally used as a secondary accelerator for vulcanization but the decomposition of DPG gives toxic aniline, various amine alternatives have been investigated. Different types of aliphatic amines having alkyl or cyclic structures and similar pKa were explored. Linear aliphatic amines that have better accessibility toward the silica surface and a shielding effect provide better performance than the cyclic ones. Among various types of amines studied, octadecylamine (OCT) provides the properties of silica-reinforced NR compounds closest to the reference with DPG, showing its potential as an alternative for DPG

Verstärkung von Naturkautschuk mit Kieselsäure/Silanen in Abhängigkeit von verschiedenen Amintypen

Diphenylguanidin (DPG) ist der am häufigsten verwendete Zweitbeschleuniger für Kieselsäure/Silan-verstärkte Elastomercompounds, weil es sowohl die Silanisierungsreaktion als auch die Deaktivierung freier Silanolgruppen, die nach der ­Silanisierung übrig bleiben, begünstigt. Aufgrund von Gesundheits- und Sicherheitsbedenken bei der Verwendung von DPG, das sich bei hohen Verarbeitungstemperaturen unter Freisetzung von hochtoxischem Anilin zersetzt, sind sichere Alternativen gefragt. Diese Arbeit untersucht den Einfluss verschiedener linearer oder zyklischer aliphatischer Amine mit ähnlichem pKa-Wert auf die ­Eigenschaften von kieselsäureverstärkten Naturkautschukcompounds, wobei die DPG-haltigen Compounds als Referenz betrachtet werden. Die untersuchten Amine sind: Hexylamin (HEX), Decylamin (DEC), Octadecylamin (OCT), Cyclohexylamin (CYC), Dicyclohexylamin (DIC) und Chinuclidin (QUI). Der Einsatz von Aminen, gleich welchen Typs, führt im Vergleich zu Compounds ohne Amine zu geringeren Füllstoff-Füllstoff-Wechselwirkungen (Payne-Effekt) und verstärkter Füllstoff-Elastomer-Wechselwirkung, die sich durch den Bound-Rubber-Anteil und eine reduzierte Wärmekapazitätsdifferenz zeigt. Im Vergleich zu zyklischen Aminen haben Amine mit Alkylketten einen besserer Zugang zur Kieselsäureoberflache und zeigen durch die geringere sterische Hinderung einen gewissen Abschirmeffekt, sodass sie den Payne-Effekt besser reduzieren und die Vulkanisationsgeschwindigkeit besser steigern können. Die längeren Kohlenstoffketten der linearen Amine von HEX über DEC zu OCT führen zu einem geringeren Payne-Effekt, einer geringeren Wärmekapazitätsdifferenz, einem höheren Bound-Rubber-Anteil sowie zu ­einem größeren Modul und größerer Zugfestigkeit. Insgesamt sind kieselsäureverstärkte Kautschukcompounds mit OCT den entsprechenden Compounds mit DPG in ihren Eigenschaften am ähnlichsten, sodass OCT eine mögliche Alternative für DPG sein könnte