25 March 2014
SIPERNAT silica particles for exfoliants as alternative to PE beads
SIPERNAT® hydrated silica particles can easily be incorporated in the formulation and are a suitable alternative to PE microspheres
Exfoliating body and face cleanser formulations often rely on polyethylene (PE) beads to help rejuvenate the skin by removing dead cells. Recent reports on plastic waste accumulating in the oceans and finding their way into the food chain have also raised concerns about the use of such microscopic PE particles in a variety of applications.
Hydrated silica, such as SIPERNAT® 22 and SIPERNAT® 2200, are suitable replacements which overcome some of the pressing environmental concerns of plastic spheres. These alternatives, while being effective cleaning agents, can offer additional advantages for formulators.
SIPERNAT® hydrated silica is available in different particle sizes applicable to the production of exfoliants. SIPERNAT® 22 (d50 particle size 120 µm) and SIPERNAT® 2200 (d50 particle size 320 µm) both feature a spherical particle shape. The particle size of both materials is shown in figure 1.
Figure 1: Particle size distribution of SIPERNAT 22 and SIPERNAT 2200 measured following ISO 13320-1 with a Coulter LS 230 instrument (Beckman Coulter, Brea (CA), USA)
Hydrated silica is a non-harmful material as has been shown in a number of high volume studies (1). Hydrated silica, an inorganic material, is not biodegradable in the ordinary sense. Biodegradation ultimately leads to mineralisation which is not possible for a material that does already have a mineral nature. With its chemical composition, SiO2 is closely related to the abundance of silicate forming the earth’s crust. This close relationship is also the reason why this material is listed as a nature-identical inorganic material that can be used in naturalcosmetic formulations certified by the NATRUE standard (2).
In contrast to hydrophobic PE spheres, the SIPERNAT® particles have a hydrophilic surface that make them easy to incorporate in aqueous solutions. As can be seen from figure 2, SIPERNAT® powder poured into pure water immediately mixes without any agitation being necessary.
In a comparative experiment under the same conditions, microspheres produced from polyethylene float on the surface of the water and require agitation and a surfactant to be wetted and dispersed in the liquid phase.
Figure 2: SIPERNAT 2200  readily mixes into the blue coloured water while PE microspheres (3)  remain on the surface of the liquid.
Hydrophilic nature - no floating on surface on washing off the exfoliant formulation
The most important advantage of the hydrophilic nature of the SIPERNAT® hydrated silica is, however, not the easy incorporation in the formulation but mainly the behaviour of the particles after their intended use as an abrasive exfoliant. When rinsing the exfoliant cleaner off the skin, the surfactant concentration is greatly reduced. To simulate this dilution, 5 g of an exfoliant formulation prepared according to the guide formulation given in table 1 containing either SIPERNAT® 2200 or PE spheres in identical concentration was poured in 10 fold of its volumewater. As can be seen from figure 3 after a standing time of approx. 30 min., the polyethylene particles have migrated to the surface while the silica particles of SIPERNAT® 22 or SIPERNAT® 2200 have settled out. This has dramatic consequences for the fate of the particles in water treatment plants. In contrast, the PE beads, once rinsed off the skin, SIPERNAT® behaves like sand in the sewage water system and remains later as an amorphous nature-identical material in the environment. No damage or pollution will be observed.
An additional advantage of SIPERNAT® 22 and SIPERNAT® 2200 is that the silica particles contribute to the viscosity build up which is achieved by the carbomer thickener, thus leading to a reduction of the necessary carbomer concentration to achieve the desired viscosity.
Figure 3: Formulation according to table 1 using either SIPERNAT 2200  or PE microspheres (3)  diluted with the 10 fold volume of pure water. While SIPERNAT 2200 settles out suspended, the PE microspheres start to float to the surface after standing for only approx. 5 min.
Table 1: Guide formulations for a face and a body scrub
PE spheres in personal cleaning products
The discussion about the role of micro plastic waste in aquatic environments has recently raised concerns about PE spheres, often used as abrasive particles in exfoliating personal cleaning products. Already at a UNESCO workshop in 2010 in Paris, effluents from waste water plants were listed as a source of microplastic contaminations in aquatic environments (4). Although PE beads in exfoliants are not the only origin of such contaminations, the growing debate has already led one important producer of personal care products to announce that they will phase out plastic spheres in their exfoliants by 2015 (5).
(1) See respective studies available at http://www.chem.unep.ch/irptc/sids/oecdsids/Silicated.pdf and by request from http://www.ecetoc.org/jacc-reports
(2) See flag “Annex 2 Nature identical” in www.natrue.org/fileadmin/nature/downloads/Annexes_V2_xls
(3) Microsrub 100PC of Micro Powders Inc., Tarrytown (NY), USA
(4) See proceedings of “Proceeding of the GESAMP International Workshop on microplastic particles as a vector in transporting persistent, bioaccumulation and toxic substances in the oceans”, available at http://www.gesamp.org/data/gesamp/files/media/Publications/Reports_and_studies_82/gallery_1510/objct_1670_large.pdf
(5) For more information see http://www. unilever.com/sustainableliving/Respondingtostakeholderconcerns/microplastics/index.aspx