Alexandra G. McMahon, B.S., Research & Development Chemist, Koster Kuenen, Inc.
Belen M. Lemieux, M.S., Research & Development Laboratory Manager, Koster Keunen, Inc., lemieux@kosterkeunen.com

Humans have been manufacturing soap since at least 2800 B.C., modifying and perfecting their recipes over the centuries. Today’s traditional soap bars are made via saponification of triglycerides: the alkaline hydrolysis of fatty ester bonds, leading to mainly C16-C18 fatty acid soaps and glycerol. In this paper, we explore the use of Natural Waxes from Koster Keunen, Inc. as starting raw materials in soap formulations, both alone and as additives to traditional triglycerides. Twelve Natural Waxes were blended with olive oil at 50/50 ratios, each blend was fully saponified, and the reaction products were evaluated for different properties and compared to a standard olive oil soap bar. It was determined through experimentation that each Saponified Natural Wax or Saponified Natural Wax Blend made a chemically complex finished soap, with different properties from the control and from each other. Some of the benefits encountered included improved bar hardness, a longer lifespan, more hydrophobicity, and innovative INCI declarations. 

Few personal care products can have their history traced as far back as soap. While the historical accounts on soap and soapmaking are rife with legend, experts agree that the earliest evidence dates back to 2800 BC in Ancient Babylon, when a soap-like substance was discovered during an archaeological dig¹.

Other records show ancient Egyptians, Greeks and Romans also made and used soap for thousands of years, perfecting the technique over time. By 1100 AD, soap making was an established practice in Mediterranean countries with easy access to olive oil, a key ingredient in Castille Soap, which was widely traded at the time².

Soap was introduced to the Americas in the 17^th century, when soap makers arrived in Jamestown, VA¹. Over the next 200 years, as the United States industrialized, soapmaking evolved into one of the fastest growing businesses, with P&G’s Ivory being one of the first to gain national distribution³. However, food and fat shortages during World War I led German engineers to introduce synthetic replacements for soap, now known as detergents⁴. American consumers quickly embraced detergents due to their efficiency, availability, and low price; moving traditional soaps over time to niche market segments, particularly “Indie” brands, artisanal soap makers, and crafters⁵.

In recent years, and specifically at the onset of the COVID-19 Pandemic, the demand for hand soap has escalated. In fact, the global hand soap market is forecasted to grow by 6.7% from 2020 to 2030, with the household segment accounting for over 70% of the market share⁶. Although it is not clear what percentage of said growth refers to traditional soap bars (versus “syndet” bars or liquid detergents), current consumer trends, such as natural ingredient demand, small business support, and plastic reduction seem to support the persistence of traditional soaps^{7, 8}.

All soaps have in common one core recipe: Lipid + Alkali = Soap + By-product. 

The chemical reaction that takes place is called saponification and can be defined as the alkaline hydrolysis of fatty ester bonds, resulting in fatty acid salts -the soaps- and a by-product (typically glycerol)⁹. 

Most commercial soaps (and also DIY versions) are variations of “tried and true” recipes, based on well-known saponification reactions of well-known lipids, like tallow or palm oil¹⁰, with the only variations being in fragrance, color, and claim ingredients. This work is meant to encourage chemists and soap makers looking for innovation to vary the lipid source. This can be done by trying new ingredients, trying new combinations of known ingredients, or varying the ratios of these combinations. This will lead to new and innovative soap products, as well as by-products (often overlooked but important as well), which will affect the product performance, sensory aspects, and ingredient listing. 

Lipids are a diverse group of organic compounds, characterized by their hydrophobicity and their biological importance. They present either as linear alkyl chains, saturated or with unsaturations, or as isoprene units in varying structures. These molecules may contain oxygenated substituents, such as carboxylic acids or hydroxyl groups¹¹.  

Traditional soapmaking would not be possible without a specific class of lipids, known as fatty acids. Fatty acids are linear alkyl chains, typically C12 – C22, saturated or with unsaturations, and a terminal carboxyl group¹². In nature, fatty acids are typically found linked by ester bonds to glycerol, called triacylglycerols or triglycerides¹¹ Due to this richness in fatty acids and widespread availability, triglycerides are the most prevalent starting raw materials in soapmaking. Some examples of lipid sources rich in triglycerides are tallow, palm oil, or olive oil¹³.

Waxes are a class of lipids with varying definitions and classification options. In a strict sense, waxes are comprised of long chain monoesters: long chain fatty acids esterified onto long chain alcohols with similar chain lengths, mainly saturated. A more practical description of waxes should include that they are blends of many components, including monoesters, hydrocarbons, sterol esters, and fatty alcohols¹⁴. 

 Many natural waxes are biosynthesized by living organisms to provide a protective barrier against environmental stresses. Due to their protective nature, waxes are widely used in personal care and OTC drugs to provide a barrier to human skin, and are staple ingredients in lip balms, hand salves, and body creams¹⁵. In this paper, we explore the use of natural waxes as starting materials for traditional soaps.  

Traditional lipid sources used in soap making, like animal fats (very high triglyceride content, usually centered around C16 – C18 saturated fatty acids) or plant oils (very high triglyceride content, usually centered around C18 unsaturated fatty acids)¹³, will yield almost exclusively combinations of saturated and unsaturated C16 –C18 fatty acid soaps, and glycerol as a by-product. While these small differences in carbon number and degree of unsaturation can translate to subtle differences in a finished soap bar, the chemical richness and complexity of each natural wax will create soap bars with vastly different chemical compositions.  

In addition to the C16-C18 soaps and glycerol described above, waxes can also yield very high molecular weight soaps (from C24 up to C38) and a broad molecular weight range of fatty alcohols as reaction by-products, while keeping their unsaponifiable materials intact. These higher molecular weight soaps are more hydrophobic than their traditional counterparts, resulting in harder finished bars with a longer lifespan. In addition, both the newly generated higher molecular weight fatty alcohols, as well as the existing unsaponifiables will also contribute to the overall hydrophobicity of the soap bar, improving the film –forming and skin protecting qualities of the bar¹⁵.

The reaction products obtained from the saponification of each major natural wax component are summarized in Table 1.

Table 1. Saponifiable Materials Found in Natural Waxes.

Table 2. Chemical and Physical Properties of Natural Waxes.

• Saponification values for each Natural Wax in Table 2 were either obtained from the specification sheet provided by Koster Keunen, Inc. or calculated using the USP 401 Method¹⁶. The saponification values were then used to determine the amount of the 30% sodium hydroxide solution required for each saponification reaction. 
• The saponification reactions were carried out as follows:
  • Each Wax or Wax/olive oil blend was heated to approximately 80°C as Phase A and allowed to cool below 60°C. 
  • The appropriate amount of 30% Sodium hydroxide solution was also heated to 60°C as Phase B.  
  • Phase B was added to Phase A with sufficient mixing using a propeller mixer, while maintaining the temperature at 60 °C for approximately 25 minutes. The saponified blend was then immediately poured into a silicone mold and allowed to cure for 48 hours.  
  • After the 48-hour cure time, a pH testing at or below 10 confirmed the reaction was complete. 

Each Natural Wax, as well as the olive oil control, was saponified individually (100%) and the reaction products were evaluated. In some cases, Natural Waxes did not make a commercially acceptable soap at 100% usage, as the bars were composed of a high level of unsaponifiables. To continue the experiment, each Natural Wax was blended with olive oil at 50% ratios, saponified, and the reaction products were evaluated and compared to 100% olive oil (control). We will refer to these blends as “saponified blends” for the remainder of this paper, and each one was evaluated within the following categories: 

Quantitative Evaluation: Effect on Bar Rigidity.

Penetration values were measured on a Koehler K19500 penetrometer. The penetration of 100% saponified olive oil was recorded at 57 dmm (needle, 50g). The saponified blends measuring below 57 dmm proved to harden the bar, increasing bar rigidity, while the saponified blends measuring above 57 dmm proved to soften the bar, decreasing bar rigidity.  

Tactile Evaluation: Effect on Bar Cleansing Properties and Lather 

In a sensory panel performed internally (N=20); individuals were given specific hand washing instructions and asked to evaluate both the lather on the hands and the cleansing properties of each saponified blend against the olive oil control. Panelists rated each saponified blend as “increases,” “decreases,” or “no change.”  

Sensory Evaluation: Effect on Bar Color and Odor 

The same sensory panel was asked to describe the finished bar colors and odor. These subjective observations were determined by comparing each saponified blend to the olive oil control. 

Practical Evaluations: Trace Level, Recommended Use Level, Recommended Applications 

Trace Level was determined by a skilled soap maker based on how fast/slow each saponification reaction took place. The Recommended Use Level and Recommended Applications for commercial soapmaking were also determined for each Natural Wax.  

All results are presented in Table 3. 

Table 3. Properties of Saponified Natural Wax/Olive Oil blends. 50% of Each Natural Wax was saponified with 50% Olive Oil and evaluated.

The results in Table 3 indicate each Natural Wax tested brought forth very distinct characteristics and attributes in traditional soapmaking. It was also determined that certain waxes are not always a suitable addition to these traditional techniques. Specifically, Natural Waxes with high melt points, higher molecular weight components or hydrogenated triglycerides can pose some challenges in processing techniques and are therefore recommended as hardening additives at ≤ 15% use level. Despite these few specific challenges, we were able to conclude that the following Natural Waxes offer numerous advantages in soap making, whether at 100% usage or as an addition to traditional triglyceride formulations.  

Although there is minimal information in current literature regarding the use and effects of Natural Waxes in soapmaking, possibly due to a very triglyceride-focused soap industry, the results of these experiments indicate the beginning of a relationship between the two. The uniqueness of each Natural Wax can be leveraged to create improvements in appearance, performance, and stability, setting the soap maker apart from the competition. In conclusion, incorporating Natural Waxes into traditional soap recipes allows for new formulas and more creativity, while keeping in alignment with a sustainable, natural future.