FORMULATING FOR MILDNESS 83


soluble at a neutral pH. Regarding water solubility, it was recently found out that by adding a natural surfactant from the steviol glycoside type - a nonionic sugar-based surfactant - the apKA


of sodium oleate can be lowered more than one unit (‘new’ apKA :


About 7). As a result, 1% aqueous solutions of sodium oleate are clear at a neutral pH. This is the first example of a long-chain soap solution which is clear and stable at room temperature and a neutral pH.4 A completely different way is the modification of the architecture of soaps on a molecular level. The amino acid-based surfactant sodium N-acyl sarcosinate (Fig 7a), for instance, can be interpreted as an ‘interrupted soap’.11


The N-methyl amide


spacer significantly influences the properties of this molecule: The Krafft- temperature is so low that sodium lauroyl sarcosinate is soluble even in cold water. Acid-base titrations performed in our laboratory show that the apKA


is about 5.


So, sodium lauroyl sarcosinate is water- soluble even in slightly acidic solutions. Also, the sensitivity of lauroyl sarcosinates to water hardness in comparison to soaps is lower. By the way, for these properties the role played by the methyl-group at the nitrogen atom in lauroyl sarcosinates must not be underestimated. This has already been discussed in detail elsewhere.12,13 Zschimmer & Schwarz took advantage of the good water solubility of some amino acid-based surfactants and introduced Z 915 CS at in-cosmetics 2018 in Amsterdam. The well-balanced surfactants in this product are sodium coco sulfate and sodium cocoyl glutamate, an amino acid- based surfactant (Fig 7b). This surfactant has the same good solubility properties as sodium lauroyl sarcosinate. Acyl glutamates carry an additional carboxylic group. So, aqueous solutions of mono sodium cocoyl glutamate are even slightly acidic.14


Cocoyl


glutamate is a proven very mild surfactant6 and able to reduce the ‘harshness’ of coco sulfates. As well as the other ingredients in Z 915 CS, coco sulfate and cocoyl glutamate are completely based on renewable raw materials. Therefore, this product fulfils the requirements for a NATRUE certification.


A comeback of solid cleansing bars in Europe?


In the last decades in Central Europe - at least in public institutions - solid cleansing bars were replaced by liquid soaps or liquid syndets. For personal use at the moment there is a backward trend to solid cleansing bars and even a ‘new’ application area: solid shampoos. There are several reasons for the comeback: From an environmental point of view, solid wash pieces contain a very high active matter meaning small amounts of water, so water shipment is


September 2019


disodium lauryl sulfo succinate and sodium cocoyl isethionate.


Zetesap C 11, on the other hand, is a


mixture between soaps and a synthetic surfactant (sodium laureth sulfate). With this product attractive and high-performing transparent combo bars can be prepared. It can be handled easily by melting at about 70°C.


Besides hand and face washing the


Zetesap-Types were successfully tested as mild makeup remover. Zetesap-Types additionally can be used in technical applications like household cleaners.


Figure 8: Zetesap-Types: “Exceptionally creamy foam”.


reduced. The packing material can be made from renewable materials like paper. Plastic bottles are not needed. This is a contribution to the reduction of plastic materials. Another point is conveniency in travelling. There is no risk of product leakage in suitcases and solid cleansing products can be taken in the hand luggage without further precautions.


Conclusion In former times soaps were the only surfactants suitable for personal care applications. Some drawbacks of using soaps like the creation of an alkaline solution and the precipitation tendency led to the development of high-performing synthetic surfactants. Those surfactants overcome the drawbacks of soaps. So, in solid cleansing bars soaps first were replaced partly (combo bars) and later even completely (syndet bars). For the production of both types Zschimmer & Schwarz offers raw materials (Zetesap- Types). Via a unique manufacturing process this material is of premium quality. In the literature the following comment about one of the Zetesap-Types can be found:6


“The


solid emulsion system and the resulting liquid crystal structures of the syndet base, combined with the advanced formulation, are considered to give the ideal base with a smooth touch and an exceptionally creamy foam. Therefore, the consumer perception will evaluate dense cream foam as superior to bubbly foam ranking it as a more caring washing product” (Fig 8).


Zetesap 813 P and Zetesap 900 are syndet raw materials based on a combination of disodium lauryl sulfo succinate and sodium coco sulfate. In Zetesap 915 CS (surfactants: sodium coco sulfate and sodium cocoyl glutamate) all ingredients are completely based on renewable raw materials. This product, therefore, fulfils the requirements for a NATRUE-certification. The sulfate-free syndet raw material in our portfolio is Zetesap 5165. Here, the surfactants are


PC


References 1 Bertsch H. Soap Preparation, US Patent 2026816 (1936)


2 Klein R, Touraud D, Kunz W. Choline Carboxylate Surfactants: Biocompatible and highly soluble in water. Green Chem. 2008; 10: 433 - 435


3 Hall N. In: Soap manufacturing Technology 2016, Chapter 1: Implications of Soap Structure for Formulation and User Properties


4 Wolfrum S, Marcus J, Touraud D, Kunz W. A Renaissance of soaps? How to make clear and stable solutions at neutral pH and room temperature, Advances in Colloid and Interface Science 2016; 236: 28 - 42


5 Kanicky JR, Poniatowski AF, Mehta NR, Shah DO. Cooperativity among molecules at interfaces in relation to various technological processes, Langmuir 2000; 16: 172 - 177


6 Friedman M. In: Soap manufacturing Technology 2016, Chapter 4: Chemistry, Formulation and Performance of Syndet and Combo Bars


7 Wagner AT. Sulfate-free Surfactants: What about Sulfonates?, Personal Care Magazine 2018; 12(2): 61 - 65


8 Hollstein M, Spitz L. Manufacture and Properties of Synthetic Toilet Bars, Journal of Am. Oil Chem. Soc. 1982; 59 (10): 442 - 448


9 Murahata RI, Aronson MP, Sharko PT, Greene AP. In: Surfactants in Cosmetics, Surfactant Science Series Vol. 68 1997, Chapter 14: Cleansing Bars for Face and Body 10 Hill M, Moaddel T. In: Soap manufacturing Technology 2016, Chapter 2: Soap Structure and Phase Behaviour; Chapter 5: Transparent and Translucent Soaps


11 Thau P. In: Surfactants in Cosmetics, Surfactant Science Series Vol. 68 1997, Chapter 13: Surfactants for Skin Cleansers


12 Wagner AT. Powerful surfactants from renewable raw materials, Personal Care Magazine 2016; 9(2): 34 - 36


13 Raykundaliya N, Bordes R, Holmberg K, Wu J, Somasundaran P, Shah DO. The effect on solution properties of replacing a hydrogen atom with a methyl group in a surfactant. Tenside Surfactants Detergents 2015; 52 (5): 369 - 374.


14 Takehara M, Moriyuki H, Yoshimura I, Yoshida R. Surface Active N-Acylglutamate: Physicochemical Properties of Long Chain N- Acylglutamic Acids and Their Sodium Salts, Journal of Am. Oil Chem. Soc. 1972; 49: 143 – 150.


PERSONAL CARE ASIA PACIFIC


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