Since the beginning of the 20th Century, bright stocks, which are high viscosity mineral oil fractions, have served as principal thickening agents in automotive and industrial gear oils; they have also been important viscosity-building components for mineral oils used in grease making. The future of bright stock, however, is becoming increasingly tenuous and uncertain. Projections show a tightening of the global supply because fewer conventional Group I refineries are being built. At this time, it is not premature for additive and lubricant suppliers to examine alternative thickeners for industrial and automotive gear oils and greases. Our purpose here is to review several of these fluid thickening options, with an emphasis on their performance attributes.
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