Posted in | Plastics and Polymers

Benefits of Using Polyurethane Raw Material in Sunscreens

At the In-Cosmetics 2010 trade show in Paris from April 13 to 15 Bayer MaterialScience will be presenting new and extensive test results giving proof of the benefits of the polyurethane raw material Baycusan C 1000 also for sunscreen formulations. Although it contains no UV-absorbing components, the film-forming polymer raises the sun protection factor (SPF) of sample formulations. In other words, it acts as an SPF booster.

It also makes sunscreen products extremely waterproof. "We developed and tested a whole series of possible formulations, varying the UV-A and UV-B filters, both inorganic and organic, while doing so. In our suggested formulations, we also took into account the fact that people in various countries around the world have very different ideas about the ideal skin feeling," explains Dr. Sophie Viala, Head of Cosmetics Application Engineering at Bayer MaterialScience.

Baycusan C 1000 acts as SPF booster
To provide protection across the entire relevant wavelength of the sun's spectrum, sunscreen products almost always include several UV filters. Viala and her team worked with cosmetic testing institutes to measure how the addition of up to ten percent Baycusan C 1000 influences the sun protection factor of various sample formulations. Both in-vitro and in-vivo procedures that meet the guidelines of the European Cosmetics Association Colipa were used. The results showed that this solvent-free polyurethane dispersion increases the SPF significantly - from 30 to 50, for example. The level of increase depends on the UV filters used and the precise formulation.

"Baycusan C 1000 offers the perfect solution to a well-known dilemma: How to respond to the trend towards ever-higher protection factors without compromising on the pleasant skin feeling provided by products with lower SPF values," says Viala. Without boosters, the SPF can only be increased by using higher concentrations of UV filters, and this change in formulation usually feels wax-like, greasy or sticky on the skin. In contrast, Baycusan C 1000 forms elastic films that feel very pleasant on the skin. As new tests confirm, they support a high level of water-vapor transmission and allow the skin to breathe.

Baycusan C 1000 makes sunscreen waterproof
A proportion of just five percent Baycusan C 1000 can be enough to make sunscreen waterproof in line with Colipa specifications. "We have developed numerous sample formulations for sunscreens based on our polyurethane that pass the water-resistance test," confirms Viala. These also include formulations that exhibit a lower than usual proportion of emulsifiers, so that on contact with water they are much less likely to re-emulsify and thus reduce the level of protection provided. Such formulations outside the standard are possible because Baycusan C 1000 has a stabilizing effect and thus acts as a co-emulsifier.

Two other properties of the polymer have a positive impact on water resistance. First, it forms a very even and uninterrupted film on the skin, which provides the mechanical influences of the water with few points of attack. And second, it boasts excellent compatibility with all the usual UV filters, including inorganic filters such as coated zinc oxide or titanium dioxide particles. Poor compatibility would result in the emulsion rejecting the particles so that they could be easily washed away by water. In addition, the polymer from Bayer MaterialScience also helps fix the UV filter on the skin by preventing its migration, an effect that is seen in some formulations even when not exposed to water.

A favorite among processors
"In sunscreen formulations, Baycusan C 1000 not only provides consumers with safe, pleasant and largely invisible protection, but also makes the life of the formulator much easier," explains Viala. The polyurethane dispersion has a low viscosity, which means it is easy to integrate into the formulation. Other established film formers, such as vinylpyrrolidone co-polymers, have to be melted before they are ready for processing. Like all other Baycusan C products, Baycusan C 1000 is also free of co-solvents and preservatives, thus providing the cosmetics industry with maximum freedom as regards the formulation.

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