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Ashless Antiwear and Antiscuffing (Extreme Pressure) Additives
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Liehpao Oscar Farng, Tze-Chi Jao
Phosphites are the main organophosphorus compounds used to control oxidative degradation of lubricants. They eliminate hydroperoxides and peroxy and alkoxy radicals, retard the darkening of lubricants over time, and also limit photodegradation. In addition to their important role as antioxidants, phosphites are also found to be useful antiwear additives. Dialkyl hydrogen phosphites and diaryl hydrogen phosphites are neutral esters of phosphorous acid. These materials have two rapid equilibrating forms: the keto form, (RO)2P(═O)H, and the acid form, (RO)2P–O–H. Physical measurements indicate that they exist substantially in the keto form, associated in dimeric or trimeric groupings by hydrogen bonding. Trialkyl phosphites and triaryl phosphites are neutral trivalent phosphorus esters. These materials are clear, mobile liquids with characteristic odors.
Retarding thermal-oxidative aging of anhydride-cured epoxy asphalt binder and mixture by incorporating antioxidant Irganox 1010
Published in International Journal of Pavement Engineering, 2023
Qichang Wang, Zhaohui Min, Wei Huang, Yiik Diew Wong, Mingyue Li
Introducing antioxidants into the EA system is considered the most effective and convenient method to address the aging problem. Currently, organic antioxidants on the market are mainly divided into hindered phenolic and phosphite additives (Tauste et al.2018). Hindered phenolic additives (e.g. Irganox 1010, Irganox 1330, Irganox 1076, Irganox 1098) are the primary antioxidants and function as free radical scavengers. Phosphite additives (e.g. Irgafos 168) are secondary antioxidants and function as peroxide or hydroperoxide decomposers. Irganox 1010 is one of the hindered phenolic antioxidants that belongs to a chain terminator according to the mechanism (Apeagyei 2008). Irganox 1010 has several key advantages, including high resistance to extraction, low volatility, and a similar melting range as anhydride-cured epoxy asphalt (110–125°C) (Apeagyei 2011). Thereby, Irganox 1010 has attracted the attention of researchers earlier than other antioxidants, and numerous stabilisation results on asphalt or polymer have been obtained. Recent studies on asphalt have reported that Irganox 1010 can improve the oxidative aging resistance of base asphalt more than Irgafos 168 (Feng et al.2011). Zhao et al. (2015) revealed that Irganox 1010 could peptize the asphaltenes in asphalt systems and enhance the short-term oxidative resistance of base asphalt. Feng et al. (2011) showed that Irganox 1010 might have different effects with different asphalt binders. They also suggested that asphalt binders incorporating Irganox 1010 need to focus on their anti-rutting properties. Cong et al. (2021) proposed that Irganox 1010 does not undergo a chemical reaction with SBS-modified asphalt and can effectively inhibit the oxidation process of SBS-modified asphalt binders. Hu et al. (2022) confirmed that adding antioxidants can prevent high-viscosity modified asphalt from undergoing more severe oxidation. It is worth noting that the combination of Irganox 1010 and UV absorbers have a synergistic enhancement effect on the environmental aging resistance of asphalt (Hu et al.2022). These studies all demonstrate that Irganox 1010 can effectively improve the thermal-oxidative aging resistance of asphalt materials. Therefore, it is reasonable to adopt Irganox 1010 as an antioxidant for EA materials.