The chemical and physical characteristics of bar soap / Nur Ameera Amnudin

Soap is made of alkaline solutions to release glycerol by the process of saponification of fatty oils. Soaps are able to dissolve the dirt on the surface of the skin and cleanse it well. There is not much difference between bar soaps and liquid soaps, both can clean well. However, bar soap is more ecofriendly and also cheaper than liquid soap, making it a better choice for certain people. There are two characteristics of soap that are used to determine a good soap. They are chemical and physical characteristics. The chemical characteristics include free fatty acid, total free alkali, free caustic alkali, total fatty matter, pH, and moisture content and the physical characteristics include foam stability, and weight loss on curing (hardening process). These characteristics are important to determine the quality of soap. Some of these characteristics are good in high value but there are also some parameters that are required in small quantities to make a good quality of bar soap. The objective of this review is to study the chemical and physical characteristics of different type of bar soaps from the data obtained from the articles. The moisture content will affect the hardness of the soap and the soap's shelf life while pH, total free alkali, and free caustic alkali may influence the side effects of soap to irritate the skin, cause skin scraping and also make the skin oilier. TFM value also has an effect on the skin as low TFM are not suitable for certain skin conditions. The foam stability of soap can be affected by the moisture content and the addition of suitable types of oil added to the oil blends and the addition of additives during the saponification process could influence the free fatty acid level of soap. In the chemical characteristics, the values of free fatty acid from the chosen data were ranged between 0.171
-0.426%, total free alkali ranged between 0.13 - 1.6%, free caustic alkali ranged between 0.01 - 0.62%, the total fatty matter was found between 13.3 to 80.5%, pH ranged between 9.6 - 10.4 value and moisture content was found between 1.9 - 5.8%. Meanwhile, in physical characteristics, the value of foam stability and weight loss on curing (hardening process) were ranged from 5.45 - 6.30 min and 13 -18g respectively. Free fatty acid and foam stability values were obtained from palm kernel oil : beef tallow oil blends samples while total free alkali and free caustic alkali were both obtained from commercial soap samples. For pH and total fatty matter, soap samples from coconut oil, gee oil, olive oil, castor oil, and palm oil were used. Lastly, palm kernel oil, palm oil, shea butter oil, peanut oil, and tallow oil soap samples were used to analyze the hardening process and moisture content characteristics in soap. As a conclusion, a good soap contains low free fatty acid level, low total free alkali, low free caustic alkali, low moisture content, high total fatty matter, high value of foam stability, has a hard texture, and a good pH soap standard range from 9 to 11.