Testing the Biodegradation and Styling Performance of Polyurethane Film Formers.
Film-forming polymers are used in diverse cosmetic formulations, such as for hairstyling, hair conditioning or sun care. Like other cosmetic ingredients, polymers end their lives in water; either in domestic wastewater or directly in environmental water. In order to address the rising awareness of the environmental fate of products, the cosmetic industry constantly seeks new solutions to reduce the environmental impact by careful ingredient selection. However, in applications with high performance requirements, such as hairstyling, the change toward more sustainable ingredients is especially challenging.
Furthermore, and in the particular case of polymers, there is a lack of clear and relevant information regarding their environmental fate. The majority of currently used synthetic film-forming polymers, such as acrylates or vinyl pyrrolidones (VP), do not biodegrade well and present the risk of persisting in the environment. This is attributed to the fact that such polymers, obtained by the radical polymerization of vinyl monomers, possess a backbone composed of carboncarbon linkages that cannot be easily cleaved by enzymes. On the other hand, natural polymers are assumed by consumers to biodegrade better. However, just as for synthetic substances, the level and kinetics of biodegradation may strongly vary depending on the chemical structure of the polymer. Furthermore, natural polymers are often modified for the purposes of the application, which may significantly impair their biodegradability. This is sometimes the case with cellulose, which, when modified into carboxymethyl cellulose or hydroxyethyl cellulose, loses its ability to biodegrade with increasing degree of modification.2 It also is known that synthetic polymers with heteroatoms in their backbone, such as some polyesters or polyurethanes, can be easily degraded by microorganisms.3 Nevertheless, the biodegradation ability and kinetics will strongly depend on the specific molecular structure and accessibility of the cleavable sites by enzymes. It is therefore necessary to investigate the biodegradability of each particular substance.
It is known that synthetic polymers with heteroatoms in their backbone, such as some polyesters or polyurethanes, can be easily degraded by microorganisms.
The biodegradability of materials can be determined according to various standardized methods, e.g., ASTM, ISO and OECD, depending on the environment—soft water, sea water, compost, etc.—and physical state of the sample. For polymers dissolved or dispersed in water, the OECD 301 and 302 methods are recognized standards.1 These test methods were initially developed for small organic molecules that typically biodegrade quickly, which explains the relatively short, approx. 28-day test duration; although high molecular weight polymers may take longer to degrade.