Proceedings of the 1 st International Conference on Natural Resources Engineering & Technology 2006 24-25 th July 2006; Putrajaya, Malaysia, 638-645 638 Rheology of Environmental Friendly Hydraulic Fluid: Effect of Aging Period, Temperature and Shear W. B. Wan Nik 1,∗ , F. N. Ani 2 , and H.H. Masjuki 3 1 Engineering Science Department, Faculty of Science and Technology, University College of Science and Technology Malaysia (KUSTEM), 21030 Kuala Terengganu, Terengganu, Malaysia. 2 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. 3 Department of Mechanical Engineering, University Malaya (UM), 50603, Kuala Lumpur, Malaysia. Abstract Limitations of petroleum oil in the aspect of non-renewable, not environmental friendly and its non-sustainability in the future have prompted a search for more stable and environmentally friendly alternatives. Bio-oils are potential to be used as industrial fluids. Currently rheological and tribological aspects of bio-oil are being investigated. Rheological properties of bio-oils used as hydraulic fluid were determined at different aging periods, temperatures and shear rates using a concentric cylinder rotational viscometer. Apparent viscosity versus shear rate was successfully fitted to the generalized Ostwald de-Waele, modified power law, Cross, Carreau and Herschel-Bulkley rheological models. The oils were found to exhibit non-Newtonian, shear thinning behavior at all aging periods and temperatures. The flow behavior index, n, varied in the range of 0.6 to 0.9. The consistency index, K, was in the range of 0.0102 to 0.0485 Pa.s n . Both parameters were significantly affected by temperatures and aging periods. Keywords: Rheology, bio-oil, palm oil, environmental friendly alternative, flow index 1.0 Introduction Recently, environmental related issues that include biodegradability, toxicity, occupational health and safety, and emissions have created an important issue to be considered especially the use of mineral oils in environmental sensitive areas [1,2]. The European Union (EU) has set an objective of 10% of hydraulic fluid from environmental friendly raw material. This has encouraged number of researchers to involve in the research of vegetable oil as alternative base oils for environmentally benign hydraulic fluids. Mostly, vegetable oils are applied in situation where accidental spillage and leakage would cause serious impact on environment. Such applications include marine, construction and agriculture activities. In another words, with the increasing environmental consciousness, the use of agricultural oils in non-food applications arises considerable interest. This is also due to their renewable character, biodegradability and aptitude to facile chemical modifications [3]. Furthermore, expanded use of this vegetable-based oil could provide developing countries such as Malaysia with inexpensive and renewable energy from domestic sources. ∗ Corresponding author: e-mail: a, * niksani@kustem.edu.my