TEXTURES 77
Dynamic properties of amino acid based surfactants
n Dr Swetlana Scherbakow, Dr Martin Husmann, Dr Yana Bykov, Martina Spiegel - Schill+Seilacher GmbH, Germany
Personal hygiene regimes have become an important part of our everyday lives and this presents new challenges for the formulation of personal care products. Consumers increasingly demand not only excellent cleansing performance but also a continuing pleasing effect after rinse-off application. Furthermore, the products must meet the expectations created by increasing awareness of environmental concerns and be as near to natural as possible. The mildness of the formulations is essential and amino acid-based surfactants such as the salts of cocoyl glutamate and lauroyl sarcosinate have an increasingly important role to play in this developing market (Fig 1).
Both substances consist of the joining of a naturally occurring amino acid as a hydrophilic head to a long chain fatty acid as the hydrophobic tail. The ionic structure of the amino acid part has a high affinity to proteinaceous surfaces such as skin and
Sodium Cocoyl Glutamate (Perlastan SC 25 NKW) Sodium Lauroyl Sarcosinate (Perlastan L-30) Sodium Lauroyl Glutamate (Perlastan SL) Sodium Lauryl Sulphate (SLS)
80 70 60 50 40 30 20 10 0
0.001 0.010 CH3 R O N COONa Sodium N-Acyl Sarcosinate R – lauroyl, cocoyl, myristoyl, oleoyl or stearoyl R O H N * COONa Sodium N-Acyl L-Glutamate COOH Figure 1: Structure of the sodium salts of N-acyl sarcosinate and N-acyl L-glutamate.
hair. Studies have shown that these amino acid-based surfactants form a protective monolayer on the skin and this prevents drying out of the skin. This protective monolayer also keeps more aggressive primary or secondary surfactants that may be present away from the surface of the skin.1
A range of comparative testing of common anionic surfactants such as sodium
Coco Glucoside Sodium Laureth Sulphate (SLES) Cocamidopropyl Betaine (CAPB)
lauryl sulphate (SLS) and sodium laureth sulphate (SLES) against N-acyl glutamates and N-acyl sarcosinates show clear advantages of amino acid based surfactants in performance. A cytotoxicity test2
with cultured human
skin cells shows that the glutamates and sarcosinates are very mild to skin and eyes. This makes them a preferred component for maintaining a healthy skin condition in formulations for personal care applications.3 In stark contrast to standard surfactants such as SLS, SLES and cocamidopropyl betaine (CAPB), the N-acyl sarcosinates and N-acyl glutamates show a capability to buffer the pH of formulations in the area of 5.5. This buffer capacity allows the preparation of stable formulations without any negative effects on the healthy condition of the skin.4
N-acyl glutamates
such as Perlastan SC 25 NKW are well tolerated by the skin due to its low tendency to cause skin irritation (hypoallergenic) and absence of pore blocking (non-comedogenic) properties. The transepidermal water loss (TEWL) is
AIR WATER
a measure for the barrier stability of the epidermis and therefore an indicator for the irritant potential of substances. In a clinical study5
the TEWL of human skin was 0.100 1.000 Concentration (g/1000ml)
Figure 2: Static surface tension as a function of concentration. CMC of sodium cocoyl glutamate (Perlastan SC 25 NKW), sodium lauroyl glutamate (Perlastan SL), sodium lauroyl sarcosinate (Perlastan L-30) and other common surfactants.
September 2018 10.000 100.000
investigated after application of two rinse- off formulations based upon sodium cocoyl glutamate and sodium lauroyl sarcosinate as main components. No significant change in skin moisture of the subjects could be determined, which is to be interpreted as a positive result. Furthermore, the tested
PERSONAL CARE EUROPE
Surface Tension (mN/m)
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