Lubricants Degradation mechanisms

The conditions that most commonly lead to sludge and varnish problems vary, which complicates the process of identifying the root cause analytically. There are at least 25 unique lubricant degradation mechanisms leading to sludge or varnish formation, including ... 

Zhao, X., Bhushan, B., andKajdas, C., Lubrication Studies of Head-Disk Interfaces in a Controlled Environment, Part 2 Degradation Mechanisms of Perfluoropolyether Lubricants," Proc. Inst. Mech. Eng., Part J J. Eng. Tribal., Vol. 214, 2000, pp. 547-559. 

Wright, B. and du Parquet, J.PR. (1983) Degradation of polymers in multigrade lubricants by mechanical shear. Polym. Degrad. Stab. 5 425-447. 

Often, the surface modification of biomedical devices is required to maximize performance. The surface can be modified in many ways, including plasma modification and application of coatings to the substrate. Surface modifications can be used to affect surface energy, cell adhesion, mechanical performance, chemical inertness, lubricity, degradation, bioactive agents release, and hydrophilicity. 

Since reducing friction is paramount in the choice of socket material, a logical first choice (and one that was made 40 years ago) would be PTFE. However, the cold flow of the polymer near body temperature (see Section 9.7) is undesirable. UHMWPE has a good combination of lubricity and mechanical stability. There are still problems of degradation, especially along grain boundaries that may remain from the compression molding process as well as persistent by-products from the sterilization step. 

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

The first method used for wear particle analysis is routine monitoring and trending of the solids content of machine lubricant. In simple terms the quantity, composition and size of particulate matter in the lubricating oil is indicative of the mechanical condition of the machine. A normal machine will contain low levels of solids with a size less than 10 microns. As the machine s condition degrades, the number and size of particulate matter will increase. 

In summary, the degradation of the PFPE lubricants is a complex process involving several mechanisms, including thermal decomposition, catalytic decomposition, tribo-chemical reactions activated by exoelectron emission, and mechanical scission, which comes into the play simultaneously. 

Polyethers. Acetal Resins. These stabilized polyoxymethy-lenes were introduced dramatically by DuPont and Celanese as engineering plastics to replace non-ferrous metals. Good mechanical strength, resilience, fatigue-resistance, lubricity, abrasion-resistance, heat distortion temperature, water and solvent-resistance can approach the behavior of metals on a volume basis, while processability, color possibilities, and corrosion-resistance are superior. Major weakness is sensitivity to thermal, oxidative, and ionic degradation. 

A simple compounding recipe was used to minimize the influence on mechanical and rheological properties of the polymer under examination. A commercial powdered Ba-Cd stabilizer (2%), an antioxidant (0.1%) especially suited to prevent the degradation of the elastomeric phase, and 0.5% of a stearic-based lubricating mixture were used. 

Degradation of lubricants by oxidative mechanisms is potentially a very serious problem. Although the formulated lubricant may have many desirable properties when new, oxidation can lead to a dramatic loss of performance in service by reactions such as ... 

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. 

Fabric softeners remedy these degradations and improve the feel by coating the fibers with a protective film of fatty material that reconstitutes the finish, maintains the microfibrils close to the fibers [23], masks fiber alterations, and covers the mineral deposits. Hence, the main mechanism for fabric softening is fiber lubrication. 

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