Rancidity of soaps is generally understood as an oxidative, catalytic & hydrolytic process, which impairs the odor & unfavorably influences the appearance of the soap. The causes of rancidity are various and depend on the use of inferior or indeed unsuitable fats or fatty acids, or on manufacturing faults such as incomplete saponification, insufficient separation of the soap mass from the lower lye in soap manufacturing or fault adjustments.
In addition to the impurities arising from the raw materials, the most important factor affecting the quality of soap is presence of traces of metals (e.g. copper & iron) arising from the apparatus (e.g. dies, kettles, containers, pipes, armatures), which have a powerful catalytic action on oxidation. The oxidation is further assisted by light, humidity and heat and also by the large surface area such as is possessed by flakes or chips.
After prolonged storage, the presence of one or more of the factors described above can cause discoloration and rancidity symptoms in soaps, which initially have a good appearance and fully satisfactory odor. Hence the stabilization of soaps is always an important and acute problem, and the addition of an antioxidant, if only as a preventive measure, is regarded by manufacturers as essential.
[1- (O-TOLYL) BIGUANIDE] (CAS # 93-69-6)
CRISTOL–OTB largely prevents harmful oxidation and the catalytic influence of traces of metal. It has all the features expected of a stabilizer. It is white in colour, odorless & non-volatile. It does not change the properties of the soap. It does not react with the soap or the free alkali in it. Very low dosages are required.