Lubricant oxidative degradation

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

Due to the very flexible synthetic approach, imprinted layers are highly suitable for sensor measurements in complex mixtures Sensor coatings consisting of a carbonic-acid-imprinted sol-gel material e.g. incorporate oxidative degradation products from engine oil leading to a chemical lubricant sensor. 

Hindered phenol and phenylenediamine (PDA) compounds are commonly used and quite effective at preventing free-radical oxidative degradation of fuel. They can be used in gasoline, kerosene, jet fuel, and certain distillates and lubricants. Often, a synergistic effect can be obtained by using a combination of a hindered phenol and a phenylenediamine antioxidant in the same application. 

After a short period of use in the average engine, changes start to occur. Initially, a loss of the zinc based antiwear/antioxidant additive ZDDP is observed by negative absorptions at 1000 cm 1 and 715 cm 1. Oxidative degradation of oil follows soon after and this is observed by positive absorptions, represented by carbonyl, hydroxy, nitro and C-O- species. The ER spectroscopy of lubricants can reflect additive depletion and the formation of oxidation products (Coates and Setti, 1984 Coates etal., 1984). 

Zeman, A., Stuwe, R., and Koch, K. 1984. The DSC Cell A Versatile Tool to Study Thermal-Oxidative Degradation of Lubricants and Related Problems. Thermochim. Acta, 80,1-9. 

VISCOSITIES, POUR POINTS, AND OXIDATIVE DEGRADATION TENDENCIES OF MAJOR LUBRICANT BASESTOCKS... 

Oxidative Degradation and Stabilisation of Mineral Oil-Based Lubricants... 

This contribution presents the degradation reaction mechanisms and processes of lubricants and the factors influencing them. In addition, mechanisms by which antioxidants inhibit lubricant oxidation with respect to specific industrial and engine oil applications are suggested. 

Organophosphorus compounds Phosphites are the main organophosphorus compounds used to control oxidative degradation of lubricants. They eliminate hydroperoxides, peroxy and alkoxy radicals, retard the darkening of lubricants over time and also limit photodegradation. These performance characteristics may be of importance for polyalphaolefins, hydrocracked or severely hydrotreated base stocks and white oils. 

Industrial lubricants have to prevent damage to the machinery which arises from friction between moving parts in service. Oxidation stability is one of the key requirements of the lubricant because the oxidation degradation products, e.g. per-oxy radicals, hydroperoxides and organic acids as well as sludge and deposits, are detrimental to the equipment. The important role of antioxidants, to protect the various types of base oil under different operation conditions, is outlined in the following sections. 

Refrigerating compressors operate with the exclusion of air therefore, lubricant oxidation is low and consequently refrigerator lubricants are generally free of additives. The absence of additives removes the possibility of additive degradation products reacting with the refrigerant. 

Some metals such as copper can act as oxidation catalysts and their presence increases the rate of oxidative degradation of the lubricant. Other metals such as zinc can be corrosive to silver machinery parts such as bearings and bushings. Determining the oil s metallic concentration, the accumulation rate and the sources of the individual metals is an important part of oil analysis. 

In lubrication systems, organic compounds are exposed to high temperatures and stresses in the presence of oxygen and nitrogen (atmospheric air), resulting in the formation of partially oxidized and nitrated compounds. There are a wide variety of oxidation degradation by-products produced during machinery operation and the exact composition and distribution of these compounds are complex [17]. 

Typically, composite deck boards are porous. The pores are formed by steam and by volatile organic compounds (VOC) during extrusion. Composite boards are partly foamed, and the pores are typically opened and connected to each other, forming chains of cavities. That is why composite materials absorb water, unlike many plastics. Air oxygen flows in, through these pores, and effectively oxidizes composite materials from inside, particularly at elevated temperatures, which often takes place on decks. Water, which is always present in composite materials, serves as a catalyst for the oxidation. Metals, which are often present in composites (as constituents of colorants, lubricants, biocides, fillers), also serve as efficient catalysts of oxidative degradation of composites. As a result, rates of oxidative degradation of composites are 50-100 times faster than those for their constituent plastics. 

Low resistance to oxidative degradation (Asadauskas et al., 1996, 1997, 2000) and poor low-temperature behavior (Erhan Asadauskas, 2000 Hagemann Roth-fus, 1988 Rhee, 1996) remain the major impediments to using soybean oil as a base stock in biobased lubricants. Soybean oil is the most widely available and least expen-... 

The useful lifetime of an organic product (e.g. polymers, lubricants) is often related to its resistance to oxidative decomposition, the so-called oxidative stability of the material [1,4]. Oxidative degradation of polymers is an exothermic process and is detectable by differential scanning calorimetry (DSC). In order to determine oxidative stability by DSC, a small, unweighed sample is raised to an elevated temperature in an inert atmosphere. After reaching the desired temperature, the inert atmosphere of the sample is rapidly changed to an oxidizing atmosphere. The time to onset of the exothermic oxidation of the material is a measure of the oxidative stability of the product. 

Rasberger, M. Oxidative degradation and stabilization of mineral oil based lubricants. In Mortier, R.M., Orszulik, S.T. (eds.) Chemistry and Technology of Lubricants, pp. 98-143. Blackie Academic Professional, London (1997)... 

EIS has been used for general characterization of engine oils [2], studies of lubricants oxidation [5], and monitoring oil degradation due to its contamination by glycol [3], water [11], and soot [12]. The combination of EIS and multivariate data analysis can be used to simultaneously determine the amotmts of soot and diesel in engine oil [13] as well as the concentration and pH of an industrial cutting fluid [14]. 

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