Abstract
Rheological and physicochemical characteristics of edible oils used for biodiesel production are well established; nonetheless, the rheological and physicochemical characteristics of nonedible oils are yet to be established. The present study therefore focuses on rheological and physicochemical characterization of nonedible vegetable oils that can be used as biodiesel feedstock. The selected vegetable oils studied include cashew nut shell liquid (CNSL), castor oil (CO), Croton megalocarpus oil (CMO), Podocarpus usambarensis oil (PUO), and Thevetia peruviana oil (TPO). Physicochemical parameters analyzed were free fatty acids, acid value, saponification value, peroxide value, iodine value, specific gravity, and moisture content using methods by the Association of Official Analytical Chemists (AOAC). Rheological properties were analyzed using a VT-550 Thermo Haake Viscotester operated by the Rheowin 3 Job Manager software. The preset parameters in the Viscotester were shear rate and temperature. The shear rate increased uniformly from 5 to 100 s(-1) at the temperature range of 30-60 °C. The experimental data were fitted into rheological models of Newton, Bingham, Ostwald-de Waele (power-law), and Herschel-Bulkley using Rheowin 3 Data Manager. The oil yield was 29-65%, highlighting the feedstock's potential for commercial biodiesel production. At a constant temperature, all oil samples exhibited a Newtonian flow behavior. In contrast to edible oils, nonedible oils exhibited high shear stress, emphasizing the reconstruction of new appropriate designs of production systems. The rheological models appropriate to represent the flow behavior of the samples were the Newton and Ostwald-de Waele models, with a fit of R (2) = 0.990-1.000.