Abstract
Palm oil is commonly used to prepare laundry soap by treating it with alkaline solutions. However, using it for this purpose is becoming expensive as palm oil is imported from few major exerting countries. Moreover, it is used for biodiesel production. Therefore, looking for alternative raw material that substitutes palm oil for soap production is imperative. Used cooking oils (UCOs) are good candidates in this regard. In the present study, laundry soaps were prepared using UCOs and sodium hydroxide solution. The cleaning actions and physicochemical properties were evaluated and compared with that commercial soaps purchased from local market. The pH, moisture content, free caustic alkali, % chloride and total alkali content values of the prepared soap materials were found to be in range of 9.31 to 10.56, 6.67 to 14.47%, 0.19 to 0.22%, 0.12 to 0.21%, 0.78 to 1.09%, 75.42 to 88.53%, 70.35 to 84.68%, 0.98 to 1.52%, and 0.28 to 0.67%, respectively. The results obtained in this study were comparable with the physicochemical properties of the commercial soap products used in the study. Moreover, the observed data were comparable with similar data reported in literature and East African Standards (EAS) suggesting that UCOs can be used as raw materials to prepare good quality laundry soap by replacing imported palm oil. Key words: Laundry soap, used cooking oil, saponification, physicochemical properties, saponification.
Highlights
Soap is the sodium (Na) or potassium (K) salt of a long chain fatty acid
The finding of the study showed that 30±1.00g I2/g for Used cooking oils (UCOs) was obtained from restaurants, 31.03± g I2/g for UCOs was obtained from hotels and 32.3±0.62g I2/g for UCOs was obtained from street food venders (Table 1)
The observed iodine values of the oils were lower than reported iodine value of palm oil (53.87) (Adulkadir and Jimoh, 2013) suggesting that the UCOs can be used as suitable raw materials for soap making
Summary
Soap is the sodium (Na) or potassium (K) salt of a long chain fatty acid (at least 12 carbons hydrocarbon chain and linked with carboxylic acid functional group). Solid soaps typically consist of sodium salts of fatty acids and liquid soaps consist of potassium salts of fatty acids (Schuman and Siekman, 2005; Gunstone et al, 1986; Head et al, 1995). Their cleansing action can be attributed to the presence of long hydrocarbon chains attached to a carboxyl group (carboxylate anion). The general saponification reaction used in soap preparation is shown below (Figure 1)
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