Two principal routes are used to manufacture soap on a large scale: direct saponification of oils and fats and neutralization of fatty acids.
Direct saponification, the most traditional method, uses large stainless steel “kettles” operated batchwise. Slow saponification of the oils and fats with caustic soda is followed by repeated washing with salt solutions, which separates the curd soap from excess water and glycerine formed in the reaction. A batch takes several days before it is ready for drying and finishing.
In the neutralization of fatty acids, fatty acids react rapidly with alkalis to form soap. There is no glycerine stream to recover – indeed, glycerine is often added back to the soap base in a purified form for its benefits in processing and appraisal properties.
A soap-making process based on fatty acid neutralization is more straightforward and less capital-intensive than direct saponification and produces soap bases of higher purity. Plant designs exist for batch or continuous operation of both routes, although the long reaction time of direct saponification makes it more suited practically to batch operation.The neat soap is dried in a vacuum chamber and extruded to improve plastic properties and texture. At this stage, it can be chopped into “noodles” and sold as a base for finishing.
At the finishing line, the soap is intensively mixed with perfume, colorants, and any ingredients sensitive to alkali or heat. Further extrusions, stamping, and packaging complete the soap bar manufacturing process.
What are bar soaps made of?
Generally, a wide range of raw materials can be used in soap production. Still, when discussing mass-market production, one has to consider the practical demands of finishing lines, raw material costs, and shelf life—the choices then reduce considerably.
A blend of 15 to 25% lauric oils (coconut or palm kernel) with 75 to 85% harder fats (usually tallow or palm oil) achieves a good balance of properties, and indeed, most commercial products fall into this composition band.
How is transparent soap made?
Recipes for transparent soaps have been known for many years. A famous example is the ‘Pears’ soap, invented in 1789. Unilever still produces a version in India. Clarity is achieved by adding crystal inhibitors, synthetic surfactants, and solubilizers to a standard soap base.
The soap is made as a hot solution, poured into molds, and allowed to set. Producing on a standard soap line is impossible, although patents exist to automate the process. Consumers today equate transparency with “naturalness” and “purity,” and marketers have been quick to apply this association to bar soap products containing, for example, natural fragrances and skincare ingredients.
The desire to make clear soaps on a larger scale led to the development of translucent soap bases.” Translucent represents a practical limit on the level of clarity achievable on a high-speed, automated finishing line. Formulations use the same basic ingredients as transparent recipes but contain higher soap levels.
Translucency develops through applying high shear during extrusion and must be carefully controlled to ensure that it is retained in the end product. Colgate’s successful multinational launch of a mass-market translucent soap, the ‘Naturals’ range, has helped to stimulate this market segment and encourage others to extend their traditional products with translucent bars.How is liquied soap made?
Liquid soaps can be produced from the saponification of oils or neutralization of fatty acids with a base such as potassium hydroxide, typically to a concentration of 15 to 20% active.
However, there are very few natural liquid hand soaps on the European and US markets, which are dominated by synthetic soaps based on fatty alcohol ether sulfates, with the addition of milder coactives such as lauryl betaines and coco glucosides.
Examples of manufacturers offering natural liquid soaps include L’Occitane (France), Gal (Spain), and Vermont Soapworks (US).
What are Syndets?
Natural soaps have certain disadvantages—they exhibit poor hard water tolerance, leading to the formation of insoluble calcium soaps. In addition, their inherently high pH in solution is associated with harshness and a dry after-feel; this can be compensated to some extent by adding skincare ingredients, super-fatting agents, and others, but it cannot be completely alleviated.
Syndets (synthetic detergents) are mild surfactants developed for use in toilet soaps. While more costly than natural soap, they have perceivable benefits in skin mildness and elimination of calcium soaps, giving a pH close to neutral.
Essential ingredients in use today include sodium acyl isethionate and disodium lauryl sulphosuccinate; these combine the benefits of syndet mildness with relatively good processability—the latter is a significant limitation of most syndets, which do not possess the excellent phase structuring behavior of soaps.
Other commonly used syndet ingredients include sodium lauryl (ether) sulfate, alkyl polyglucosides, sarcosinates, and coco betaines. Lever Fabergé’s ‘Dove’ moisturizing bar is the market-leading syndet worldwide and uses sodium cocoyl isethionate as the principal surfactant.What are Combars?
Combars (combination bars) are, as their name implies, mixtures of synthetic actives and soap. They attempt to combine the economy and processability of soap with the mildness and other benefits of syndets.
To facilitate the production of combars on standard finishing lines, 25% or less of the syndet component is typically added, although higher levels are technically feasible. "Lever 2000, made by Unilever in the US, is the leading combar product. The syndet coactive is sodium cocoyl isethionate.