Better Formulations for Today's Bar Soaps.

Formulation changes, superior manufacturing methods and vegetable blends are changing the look, feel and performance of today's bar cleansers and answering consumer demand for more skin-friendly products.

DURING THE PAST decade, washing agents have all but replaced conventional toilet soaps in promotions and development within the personal care industry. Although generally acknowledged as being the most widely used personal washing medium, toilet soap has more recently been labeled outmoded, detrimental, harsh and unsuitable for cleaning human skin. Many soap manufacturers have jumped on the bandwagon and helped usher in the use of non-soap alternatives in response to public demand.

Like many other personal cleansing products, toilet soaps do indeed have some disadvantages, such as poor performance in hard water, an alkaline reaction in solution and poor solubility and rinsability of certain compositions. But soap is also a fairly tolerant material which can accommodate various beneficial skin care ingredients. However, there are limitations to these additions, the principal problem being an interference with the ability to produce high quality finished bars when processed at high speeds using fully automated extrusion, stamping and packaging equipment. In order to maintain public interest in personal cleansing products, soap manufacturers have consistently brought out new products on an almost annual basis.

Superfatted Soaps

Superfatted or cosmetic soap is a conventional soap formulation which combines an effective skin-substantive

emollient with a neutralizing agent to eliminate the residual free alkali. A wide variety of superfatting agents, including lanolin, mineral oil, petroleum jelly, fatty esters, fatty alcohols and plant extracts, have been used for this purpose. Inorganic acids such as phosphoric acid which are added to the liquid soap during processing or immediately before drying are often used as neutralizing agents. In Europe, distilled hydrogenated coconut fatty acid is perhaps the most widely used superfatting material, since it neutralizes the free alkali while acting as an effective skin emollient. This method does have its disadvantages, however, the primary problem being cost.

The addition of 5-8% of superfatting material to a conventional toilet soap composition significantly affects the volume and nature of its lather or generated foam. To compensate for this, a formulation change from the traditional 80/20 tallow/coconut blend to one of 60/40 or even 50/50 is necessary to obtain a desirable dense, cosmetic-type lather which leaves the skin soft and smooth after washing. An increased public preference for the use of renewable and vegetable-based raw materials has further fostered a changeover from tallow-based soaps to those made from palm and palm kernel/ coconut oils.

Syndets and Combo Bars

Synthetic or soapless bars have also appeared, with their undisputed claims of mildness and skin friendly compositions, particularly the highly successful combination, or "combo," bar. Combo bars incorporate small quantities of soap as a processing aid and not as the primary surfactant. The product is equally effective in all kinds of water and, in some countries, its use has already surpassed that of traditional soaps.

Environmental concern has again led to the widespread development and use of vegetable-based surfactants, most of which are now based on palm kernel or coconut fatty acids. A further significant change in personal washing habits is the extensive use of products such as non-soap liquid cleansing agents, hair shampoos, shower and bathing liquids and gels, all of which have caused an inevitable decline in the general use of traditional toilet soap in many developed countries.

Translucent and Transparent Soaps

Translucent/transparent soaps have become more popular in recent years, especially among consumers who prefer natural products. The earliest representative of this class was a Pears soap made more than 200 years ago by Lever Brothers, England. Remarkably, this soap is still available today, though its composition and method of manufacture has evolved greatly. Transparent toilet soaps and those with a limited degree of transparency, the so-called translucent soaps, have long been popular with certain segments of the population. Both show an improved transparency during use and consumers relate this appearance with a concept of purity and lack of adulteration. The idea is that if one can see through the product, it must be pure and free of harmful ingredients. In addition, the modern emphasis on environmental care and the use of natural and renewable raw materials has also contributed to the interest in these specialty soaps, since they are mainly, though not exclusively, made from vegetable-based fatty materials. The soaps are pleasant to use, readily soluble and lather freely with an easy rinsibility, an important requirement for manufacturers' claims of mildness.

The essential difference between transparent and translucent soaps is, of course, bar clarity. A translucent bar will allow the passage of some light, but due to dispersion of the light, an object behind it can not be clearly distinguished. A transparent bar does not exhibit the same degree of light dispersion, so an object placed behind the bar is readily discernable. Originally this formed the basis for the old definition of a transparent soap, through which a boldface type of 14 print size had to be easily read by an individual with normal vision. Instrumental methods are now available for this purpose but are still based upon light transmission through soap bars of a known thickness.

Manufacturing Methods

There are two basic manufacturing routes for producing translucent/transparent soaps. In both cases, a special blend of oils and fats/fatty acids is reacted with a strong alkali, typically caustic soda (though a proportion of potassium hydroxide or an organic base may be used) in the presence of crystal inhibitors and solvents, to produce a clear liquid or isotropic soap. For a transparent soap, the clear hot liquid soap is poured into individual molds to cool and solidify. This is the so-named pourable or pourable cast melt bar soap. In the second method a similar reaction procedure is followed but with a different soap and additive composition. The resulting liquid soap is then directly cooled to 35-40 [degrees] C and partially dried in a conventional vacuum soap drier. The cooled soap is then converted into a noodle form which, after maturing for several days, is extruded and stamped from a solid translucent bar using a conventional toilet soap finishing line.

Because washing operations are not involved in either method, any liberated glycerin is retained in the soap. All reactants must also be reasonably pure and not produce any insoluble impurities or discoloration after saponification. Softened or deionized water must also be used throughout the process. Common fatty materials include glycerides or fatty acids of tallow, coconut/palm kernel oils, palm oil, castor oil and rapeseed oil--all of which must be free of large amounts of unsaponifiable matter. Castor oil tends to be heat-sensitive, causing a brownish discoloration. Therefore it is usually added to the main fat blend immediately prior to the addition of the alkali. The latter is added as a cold solution to the fat blend maintained at 60-70 [degrees] C, since higher temperatures can cause discoloration and unwanted exothermic heat.

Pourable Transparent Soaps

Pourable transparent soaps are similarly prepared in a heated reactor, fitted with a variable-speed stirrer and water cooling facilities. A low titre, fatty acid blend is normally used together with a variety of crystal inhibiting ingredients and preservatives. These soaps can be a valuable addition to the product range of a small cosmetics manufacturer which does not own an expensive toilet soap finishing line. This enables the company to produce good quality, modern soaps by purchasing a ready-made transparent soap base in block or pellet form from any specialist supplier. The soap can be easily melted in small quantities at 40-60 [degrees] C using a water bath or other temperature controlled vessel and then poured into individual molds to slowly cool and solidify at room temperatures.

Individual perfumes, color, emollients and other additives can be added to the liquid soap before cooling, although care must be taken not to add materials that could interfere with the final transparency. Soap blanks may also be prepared in this way and subsequently stamped out in the usual manner. Finished soap bars are usually shrink-wrapped in plastic film to maintain product quality and retain water content. It is sometimes advisable to allow stamped bars to air dry for 24 hours to prevent condensation within the sealed wrapper.

Producers of personal washing bars are constantly seeking new ways to produce milder formulations with enhanced skin care properties. One of the best ways to achieve this goal is to incorporate relatively high levels of an effective skin-substantive emollient. With ordinary extrusion technology for both soap and syndet bars, there are limitations to the amount of additives that can be used. These limits can be overcome by using the cast bar pouring method, but care must be taken to maintain good bar clarity with a minimum degree of stickiness and good pourability. Excessive mush formation during use must be avoided as well. Such requirements are often achieved by replacing the soap (or some component) with a suitable blend of surfactants such as sodium lauryl sulfate, sodium lauryl ether sulfate, sodium cocoyl isethionate or cocoamidopropyl betaine together with fatty acids, polyethylene glycols, parafin wax and silicones. With suitable formulations, it is also possible to reduce the water content to [is less than] 10% while still maintaining a clear and pourable isotropic transparent soap.

A typical European poured bar soap would include the following ingredients, in descending order: water, propylene glycol, sodium stearate, sodium lauryl sulfate, glycerin, sucrose, sodium cocoate, sodium xylene sulfate, sodium lauryl sulfate, stearic acid, fragrance, methyl gluceth-3, isopropyl myristate, benzophenone-3, EDTA [Na.sub.4] salt, BHT and methylparaben.

GEORGE R. WHALEY, soaps and detergents industry veteran, is consulting from his headquarters at 8 Albany Road, Bury Lancs BL9 9RD, England. Phone and fax: [phone].