Thomas G. O’Lenick, PhD - SurfaTech Corporation, US SUN CARE
Improving sunscreen performance
a
Hydrophilic portion Hydrophobic portion
In a polar solvent b c Core
Hydrophilic group Hydrophobic group
In a non-polar solvent Figure 1: a) Behaviour of sorbeth hexaoleate in different solvents, with b) above critical concentration of entanglement (c*), and c) below c*.
Recently, there has been growing interest in sunscreen performance. This interest includes not only making more efficient formulations but also more effective formulations. There are many factors that need to be considered when determining the efficiency of sunscreen formulations, including: desired SPF,1
wavelength shift, and photostablity,3 name a few.
UVA/UVB coverage,2 just to
The quest for complete protection from the sun has led to numerous research efforts that are aimed not only effective sunscreens, but also products that efficiently use sunscreens, minimising the concentration of filters. A product that protects over a wide variety of ultraviolet (UV) spectrum and is effective has become a priority. This quest has led to a new series of amphiphilic polymers that have been developed to help improve the efficiency of sunscreens. These amphiphilic polymers have a polar core surrounded by a fatty oil soluble group. This series of polymers can provide not only a shift in wavelength, but also boost the SPF of the sunscreen formulation. These new polymers have been coined ‘Spider Esters’.
Spider esters
Spider esters were specifically designed4–8 to have a hydrophilic core surrounded by a hydrophobic periphery. This produces an amphilphilic polymer. The term, amphiphilic polymer, means that the polymer contains two distinct regions that have different polarities covalently bonded together. This amphiphilic nature makes spider
D
esters very attractive because of their unique solubilites. Amphiphilic polymers are covalently bonded together and do not have the same inherent stability issues that emulsions suffer from. Oil-in-water emulsions have pockets of hydrophobic oil contained in the core of micelles surrounded by an aqueous environment. When hydrophobic organic sunscreens are added into the emulsion, they migrate into
Table 1: Formulations 1 and 2. Part Ingredient
A Water
B C
Acrylates/C10-30 Alkyl Acrylate Crosspolymer DiSodium EDTA Triethanolamine Octocrylene Octisalate
Oxybenzone Avobenzone Stearic Acid
Glyceryl Monostearate SE Benzyl Alcohol Dimethicone
C12-15 Alcohols Benzoate
Sorbeth 2 Hexaoleate (Spider Ester ESO) Octyldodecyl Citrate Crosspolymer Octocrylene
Parabens/Phenoxyethanol
the hydrophobic micelle cores and remain suspended in a unified matrix. When the spider ester is introduced into a polar solvent, the hydrophobic periphery will collapse upon itself to minimise its contact with the solvent environment (see Fig. 1). Figure 1 allows for a simple breakdown of how these spider esters behave in solvent. Please note that this is not an actual representation, just a simple way to
% w/w
Formulation 1 Formulation 2 74.20
0.25 0.05 1.00 3.00 3.00 2.00 1.00 2.00 3.00 1.00 0.50 8.00 – –
3.00 1.00
67.20 0.25 0.05 1.00 3.00 3.00 2.00 1.00 2.00 3.00 1.00 0.50 8.00 5.00 2.00 3.00 1.00
A typical preparation procedure: Disperse part A. Add part B while heating to 80˚C stir until clear. Add part C to combined part AB while mixing. Cool with stirring to 50˚C and add part D. Continue cooling, QS and mix.
April 2012 PERSONAL CARE 101
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