Soap and Cosmetics: A Comprehensive Overview

Soap in Cosmetics

Introduction

  • Soap is the oldest surfactant product, playing a major role in history.
  • The objective is to trace the development of soap from ancient times to modern formulations.
  • Soap is defined as a compound resulting from the reaction of insoluble fatty materials with a metal radical or organic base.
  • Soluble soaps are formed with sodium, potassium, or ammonium metal radicals.
  • Insoluble metal soaps are associated with heavy metals.
  • Other metallic soaps include zinc, lead, manganese, cobalt, or tin, requiring elevated temperatures or double decomposition.
  • Basic soap making reaction:
    Neutral Fat+Alkali→Soap+Glycerol\text{Neutral Fat} + \text{Alkali} \rightarrow \text{Soap} + \text{Glycerol}

Historical Background

  • Earliest soap-like material production: ancient Babylon, boiling fat with ashes.
  • Initially, soap was mainly used for washing garments.
  • The name "soap" may have originated from Mount Sapo, a site for animal sacrifice.
  • Melted animal fats and wood ashes washed down the mountain, forming crude soap along the riverbanks.
  • General use of soap as a washing medium dates back 1000 years in Mediterranean countries.
  • They produced soap using locally available fatty raw materials.
  • A breakthrough in the 19th century: the availability of cheap soda.
  • French chemist Leblanc developed a process to convert common salt into soda ash.
  • Belgian chemist Solvay further reduced soda costs with the ammonia process, improving quantity and quality.
  • The chemistry of soap making advanced in the 19th century with the discovery of fatty acids in neutral fats and oils.
  • This led to modern saponification processes using neutral fats or fatty acids with caustic materials.
  • Caustic soda produces harder sodium soap, while caustic potash yields softer potassium soap.
  • Master soap boilers underwent long apprenticeships to gain expertise.
  • Early soaps were crude; improvements resulted from better process understanding and higher quality raw materials.
  • In basic chemical terms, soap is the result of reacting fatty material and alkali.

Using Vegetable Materials

  • Early fatty materials: neutral animal fats (suet or tallow), vegetable oils (olive or rapeseed oil), and fish oils.
  • Early alkali sources: wood ash, possibly mixed with lime.
  • Modern practice: fats (animal or vegetable) blended with fatty acids and appropriate caustic alkali.
  • European preference: a blend of fat and fatty acids based on tallow or nut oil in a 4:1 ratio.
  • Bovine Spongiform Encephalopathy (BSE), or mad cow disease, is a progressive, fatal prion disease.
  • Tallow was derived from cattle, sheep, and goats.
  • Due to BSE concerns, there's a growing interest in vegetable-derived materials.
  • Secondary nut oil content is derived from coconut oil or palm kernel oil.
  • Producers improve fats and oils through bleaching and hydrogenation.
  • Fatty acid use can partially or totally substitute neutral fats.
  • Soap boilers need detailed knowledge of fatty feedstock chemistry to ensure complete saponification.

Soap Boiling

  • Soap production methods: kettle boiling, continuous process, and base using vegetable materials.
  • Kettle boiling: time-consuming, energy-intensive, with distinct stages.
  • Continuous process: quicker, less space, less energy.
  • Vegetable material base: widely used in Africa and Asia, reducing costs.
Kettle Boiling (Traditional Process)
  • Pan boiling in large open kettles involves distinct stages, starting with initial boiling or preliminary saponification.
  • After saponification, adding salt forms a soap layer.
  • The soap layer (neat soap) consists of ~65% real soap and ~35% water, containing traces of glycerin and salt.
  • Step 2: Boiling continues with caustic soda to remove excess fats and impurities.
  • Step 3: The pan stands to separate the soap layer from residual liquid.
  • Step 4: The soap is washed to remove excess salt and processed into bars, flakes, granules, or powder.
  • Glycerin, a valuable raw material, is recovered from the residual liquid after boiling.
  • Retaining a normal proportion of glycerin within the soap layer is essential for high-quality products.
Continuous Process
  • It is quicker and uses less space and energy, facilitating using fatty acids instead of neutral fats.
  • The resulting base soap may have different odor profiles.
  • Fats are converted into fatty acids and glycerin via high-pressure (5,000 degrees Celsius) fat splitting.
  • Specialized companies sell fatty acids and purified glycerin to soap base manufacturers.
Base Using Vegetable Materials
  • Vegetable-based products are widely used in Asia and Africa for cultural, religious, and economic reasons.
  • Increasing volumes of palm oil, kernel oil, and coconut oil have reduced costs.
  • Palm oil, fatty acids, and palm stearin replace tallow; coconut oil or palm kernel oil remain minor constituents.
  • Fatty acids replace neutral oils; palm oil's dark color may lead to a creamy yellow soap base.

Conversion to Finished Bars

  • Liquid soap is run into molds to solidify, then cut into blocks.
  • Bar soaps are still used for laundry and scrubbing.
  • Liquid soap (63% soap) is colored and perfumed, then run onto a chilling roller.
  • Semi-solid soap is scraped off as ribbons, passed to an extruder, and cut into bars.
  • Blocks pass through a conditioning tunnel before stamping and packaging.
Milling Process
  • Milling improves soap quality before extrusion.
  • Additives are introduced to a ribbon mixer along with pre-weighed soap base.
  • Typical additives: titanium dioxide (opacifier), perfume, pigments or dyes.
  • The soap mass is mixed and passed through a roll mill or extruder.
  • The process involves no external heat.
  • Modern processing evolves with greater speed and efficacy.

Fatty Fatty Oil Material

  • The scale of the perfumer is required to ensure that the final formulation will have excellent stability throughout the life of the bar
  • Soap is a relatively harsh chemical, requiring careful perfume selection for stability.
  • Pigment or dye selection requires care for adequate stability.
  • Adding other fatty oil materials creates super-fatted products with improved lathering properties and enhanced skin feel.
  • Typical Formulation:
    • Soap base
    • Titanium dioxide: 0.2 to 0.4%0.2 \text{ to } 0.4\%%
    • Perfume: 0.5 to 1%0.5 \text{ to } 1\%%
    • Color: as desired to obtain the total quantity.
  • Soaps with mild abrasives: pumice, oatmeal, maize meal, ground nut kernel, herbs, dried flowers, and seaweed.

Types of Soaps

  • Shaving, translucent, and transparent soaps.
Shaving Soap
  • Caustic potash is added to the saponification process for softer soap with enhanced lather.
  • Often, a free fatty acid finish minimizes irritation.
  • Specialized mixing equipment is essential for a good skin feel.
  • lather: stearic acid + coconut oil, saponified with caustic soda + caustic potash, and glycerin for texture and skin feel.
Translucent Soap
  • A relatively recent innovation involving adding glycerin and polyol with specific processing modifications.
  • Available in animal and vegetable-based variants.
  • Uses conventional equipment but special stamping tools made of alloy.
  • More difficult to mold due to surface texture and different shrinkage characteristics compared to opaque soaps.
Translucent Soap Base Formulation
  • Perfume or fragrance: 1 to 1.5%1 \text{ to } 1.5\%%
  • QS color: enhanced by adding mica-coated pigment for a pearl effect.
  • Solid natural particulate material (seaweed, loofah, poppy seeds).
Transparent Soap
  • Formulation and production methods vary considerably.
  • One method: dissolving good quality soap in alcohol with gentle heating to form a clear solution, then coloring and perfuming.
  • Most of the alcohol is removed by distillation, and the liquid soap is cast into blocks or molds and allowed to set.
  • The molded product is cut and pressed to its final shape.
  • Tablets are conditioned for up to three months, which can cause distortion.
  • Although the bars have excellent clarity, the process is labor-intensive and time-consuming.
  • The selection of fatty raw materials is similar to regular soap production.
  • The individual fats and oils or fatty acids directly affect the color of the finished product.
  • Castor oil aids product clarity but produces a yellow color.
Continuous Transparent Soap

  • Fats are premelted in one vessel.

  • In a second vessel, water, sugar, glycerol, and preservative are heated.

  • In a third vessel, an alcoholic solution of caustic soda is prepared.

  • The three phases are reacted to form the basic soap.

  • The soap mass is checked for setting characteristics and adjusted. Then transferred to a holding tank when the formulation, quantities of color and perfume are added.

  • The product is dosed into molds or cups and passed through a conditioning tunnel.

  • After cooling for 24 hours, they can be molded and film-wrapped.

  • Tablets have good clarity, but film wrapping is essential to prevent surface blooming.

  • A possible disadvantage is the presence of alcohol, necessitating control.

  • More recently, transparent soaps combine soap with detergent for excellent clarity and low odor.

  • It is essential to film-wrap the finished bar to avoid surface crystallization due to sugar deposits as the bar loses moisture.

  • Formulators adjust the proportion of propylene glycol, glycerol, and sugar to adjust the hardness of the final bar.

  • Using use of low color material results in base, which is most water white capable of accepting reasonably high level of fragrance, which is up to 5\%.

  • Select perfumes and additives to account for process conditions (up to two hours at 700 degrees Celsius).

  • Organic dye stuff colors best.

  • Light stability can be a problem; ultraviolet screens help minimize fading.

  • The tablet shape is restricted by the nature of the base material.

  • Translucent and transparent soap bars have consumer appeal because clarity connotes health, purity, mildness, and freshness.

Combination or Detergent
  • Although not strictly a soap, cream cleansing bars are a major category in the overall soap market.
  • Detergents mimic skin pH levels.
  • Raw materials are more expensive, resulting in higher market prices.
  • Many formulations are covered by patents.
  • Combinations use a soap-to-detergent ratio of around 50:50.
  • Less expensive raw materials, and pH union are only slightly reduced at around nine to 9.5.
  • Regular soap-making equipment is adapted for precise temperature control.
  • Extrusion equipment requires the correct compression for detergent materials.

Soap Liquids and Hand Washes

  • Traditional liquid soaps are saponified using oils and fats with high oleic acid content, with caustic potash and caustic soda.
  • Some liquid soaps contain a small proportion of true liquid soap as a detergent-based system.
  • The market is moving toward from only detergent based surfactant.
  • These products are enhanced with moisturizing raw materials to counteract their frequent use as handwashes.

Conclusion

  • A brief overview of soap making and guidance for future projects.