Influence of some antioxidants on the oxidative stability of Rimula D lubricating oil Imtiaz Ahmad, M. Shakirullah, M. Ishaq, M. Arsala Khan and Jan ullah Institute of Chemical Sciences, University of Peshawar, Peshawar, Pakistan Abstract Purpose – The purpose of this paper is to investigate some cheap and highly stable additives to improve the quality of lubricating oil. Design/methodology/approach – The study was performed using phenol, p-cresol and pyrogallol as antioxidants. The concentration of each antioxidant was varied between 0 and 1 per cent. Sample (50ml) blended with the antioxidant was taken in the same trap. The trap was placed on water both maintained at a temperature of 508C. Air was bubbled for the time duration of 6 h. After 6 h, the contents of the trap were carefully collected and characterized. The oxidation was performed in a specially designed glass made U-shaped trap in the absence and presence of antioxidants. The trap containing sample was tied with an iron stand. Air was bubbled through the sample. The bubbling was assisted by the suction pump at room temperate (248C). The sample was aerated for time duration of 6 h. After 6 h, the contents of the trap were carefully collected in a dried bottle for physicochemical tests. Findings – The results indicate that phenol is the best antioxidant in concentration of 0.5 per cent amongst the three antioxidants used at room temperature as well as at 508C. Amongst the antioxidants used, the order of suitability is phenol . pyrogallol . p-creosol. Originality/value – The antioxidants studied will help increase the service time of the lubricant to save money and to avoid environmental problems arising from careless disposal of used lubricating oils. Keywords Lubricating oils, Oxidation resistance, Physical property measurement, Chemical properties of materials Paper type Research paper 1. Introduction The quality declination of the lubricant in an internal combustion engine is a common phenomenon and believed to be a consequence of a number of factors, principal among which is the reaction with oxygen at some temperature in the range of 100 to 2008C. Oxidation has been reported to be the major factor of lubricating oil degradation (Blaine and Savage, 1992) that can produce high-molecular-weight material accompanied by deleterious changes in its physical and chemical properties. These high-molecular-weight oxidation products lead to a deleterious increase in lubricant viscosity and eventually to the formation of insoluble material that can deposit on the lubricated surfaces thereby adversely affect the performance (Blaine and Savage, 1991). Such degradation of lubricating oil carries significant economic penalties and the user has to change the oil frequently. A variety of additives such as pour point depressants, viscosity index improvers, oiliness and film strength compounds, oxidation inhibitors, corrosion inhibitors, and materials like detergents and sludge dispersers, etc. are in use. Various such additives have been documented in the literature (Barnes et al., 2001; Muraki and Wada, 2002; Jianqiang et al., 2005; Fu et al., 2005; He et al., 2005; Spikes, 2004; Kumar Saurabh et al., 2005). However, many of the additives are damaged and lose originality/value (Lin and So, 2004). Therefore, there is a need to investigate some cheap and highly stable additives to improve the quality of the lubricating oil. In the present work, phenol, p-creosol and pyrogallic acid were investigated in different concentration at room temperature and 508C as antiodidants. 2. Experimental 2.1 Sample collection The virgin sample Rimula “D” of Shell Company was obtained from the shell filling station. The sample is used to promote the lubrication function both in gasoline engine and diesel engine. It is a high-quality lubricating oil and its service duration is 3,000-4,000 km. 2.2 Effect of antioxidants 2.2.1 Effect at room temperature Sample (50 ml) was taken with the help of a clean and well dried pipette in a specially designed glass made U-shaped trap. Antioxidant was then added to the sample contained in the trap. The trap containing sample was tied with an iron stand. Air was bubbled through the sample. The bubbling was assisted by the suction pump at room temperate (248C). The sample was aerated for time duration of 6 h. After 6 h, the assembly was dismantled and the contents of the trap were carefully collected in a dried bottle for further physicochemical tests. The study was performed using phenol, p-cresol and pyrogallol as antioxidants. The concentration of each antioxidant was varied between 0 and 1 per cent. 2.2.2 Effect at 508C Sample (50 ml) blended with the antioxidant was taken in the same trap. The trap was placed on water bath maintained at a temperature of 508C. Air was bubbled for the time duration of 6 h. After 6 h, the contents of the trap were carefully collected and characterized. The current issue and full text archive of this journal is available at www.emeraldinsight.com/0036-8792.htm Industrial Lubrication and Tribology 63/4 (2011) 234–238 q Emerald Group Publishing Limited [ISSN 0036-8792] [DOI 10.1108/00368791111140440] 234