ABSTRACT: The experimentally determined kinematic vis- cosities of simple triacylglycerols [trilaurin, trimyristin (MMM), tripalmitin (PPP), tristearin (SSS), triolein (OOO), and trilinolein (LiLiLi) were correlated to a modified Andrade-type equation. The constants for the modified equation were derived for each simple triacylglycerol. The method was also used to estimate the viscosity of mixed triacylglycerols [1,2-dimyristoyl-3-palmi- toyl (MMP), 1,2-dioleoyl-3-palmitoyl (OOP), 1,2-dimyristoyl-3- oleoyl (MMO), and 1,2-dipalmitoyl-3-oleoyl (PPO)], binary tri- acylglycerol mixtures (PPO/OOP, PPP/SSS, and OOO/SSS of different portions), and three types of vegetable oils [refined, bleached, and deodorized palm oil; cocoa butter; and canola oil] by applying modified Kay’s rule utilizing the simple triacyl- glycerol constants derived earlier. In all cases, the estimated val- ues for liquid viscosity were compared with experimental val- ues determined in this work and with previous work from the literature. When applied to vegetable oils, the method requires knowledge of their triacylglycerol composition. Despite its sim- plicity, the method gives a reasonable estimate. The method may be used to predict the viscosity of different blends of vegetable oils, and the accuracy is expected to increase when more ex- perimental data on simple triacylglycerols become available. Paper no. J9813 in JAOCS 78, 1001–1005 (October 2001). KEY WORDS: Triacylglycerol, vegetable oil, viscosity esti- mation. Viscosity is an important transport property of fluids, and it must be considered in chemical engineering design. Viscosity strongly affects flow behavior at different temperatures and significantly affects the design of pipelines and equipment. Oils owe their relatively high viscosities to the intermolec- ular attractions of the long chains of the glyceride molecules. In general, viscosity increases with molecular weight but de- creases with increases in unsaturation and temperature. Therefore, oils containing triacylglycerols of low molecular weight are slightly less viscous than oils of an equivalent de- gree of unsaturation containing only high molecular weight triacylglycerols (1). A critical review of methods for determining viscosity sug- gests that most of the generalized methods, which are based on group contributions or which utilize critical properties and den- sity, give large errors when applied to triacylglycerols and veg- etable oils. This category includes the Orrick and Erbar and the Van Velzen, Cardozo, and Lagenkamp methods as reviewed by Reid et al. (2). The deviation of the calculated values, derived using these two methods, from the experimental values in this work approaches ± 100% (3). The generalized UNIMOD model for the estimation of viscosity for fatty mixtures gives high accuracy (4). This model is based on a group contribution method and requires a multitude of steps to calculate the pa- rameters in the model. Andrade-type equations tend to give a better estimate since the constants are derived from experimen- tal values; however, the constants are specific to the respective triacylglycerol or oil type, as shown previously (5,6). A quick method for estimating viscosity of vegetable oil at varying temperatures with reasonable accuracy is the ob- jective of this work. The constants for the modified Andrade- type equation were first derived from the experimental values for the range of triacylglycerols commonly found in vegetable oils. The method described below utilizes these constants to estimate viscosity of vegetable oil mixtures once their tri- acylglycerol composition is known. The method established in this work is similar to the gener- alized method for estimating vegetable oil properties such as density (7) and specific heat capacity (8). However, for those two properties (density and specific heat capacity), the fatty acid compositions of the vegetable oil mixture were required, which therefore required inclusion of correction factors. EXPERIMENTAL PROCEDURES The kinematic viscosities of simple triacylglycerols [trilaurin (LLL), trimyristin (MMM), tripalmitin (PPP), and tristearin (SSS)], mixed triacylglycerols (MMP, MMO, PPO, and OOP), a binary triacylglycerol mixture (PPO/OOP, 55:45 w/w), and refined, bleached, deodorized palm oil (RBDPO) were determined in this laboratory (3). The kinematic viscos- ity of cocoa butter was determined in this laboratory (9). Pure triacylglycerols obtained from Sigma Chemical Co. Ltd., (Poole, United Kingdom) had a nominal purity of >99%; the binary triacylglycerol PPO/OOP was made up from the pure triacylglycerols. The RBDPO was obtained from Pandama- ran Oil Product (Felda Refinery Corp., Port Klang, Malaysia). Cocoa butter was obtained from Malaysia Cocoa Manufac- turing, Sdn. Bhd. (Petaling Jaya, Malaysia). The kinematic viscosity of the above-mentioned triacylglyc- Copyright © 2001 by AOCS Press 1001 JAOCS, Vol. 78, no. 10 (2001) *To whom correspondence should be addressed at Centre of Lipids Engi- neering & Applied Research (C.L.E.A.R.), Universiti Teknologi Malaysia, J. Semarak, Kuala Lumpur, 54100, Malaysia. E-mail: azian@utmkl.utm.my Viscosity Estimation of Triacylglycerols and of Some Vegetable Oils, Based on Their Triacylglycerol Composition M. Noor Azian*, A.A. Mustafa Kamal, F. Panau, and W.K. Ten Centre of Lipids Engineering & Applied Research (C.L.E.A.R.), Universiti Teknologi Malaysia, Kuala Lumpur, 54100, Malaysia