Water-resistant, hydrophobic UVB-shielding films from water-borne nanostructured latexes

Hydrophobic structured latexes prepared by multi-step emulsion polymerization provide the means for the preparation of films with good mechanical properties without the use of coalescing aids. We demonstrate using the UVB-filter 2-ethylhexyl-4-methoxycinnamate (EMC) that a lipophilic substance can be entrapped in the core-shell latexes during their synthesis. Three VOC-free latexes were prepared using the amino acid based surfactant sodium lauroylsarcosinate as an emulsifier containing 0.7, 1.4, 1.9% w/w EMC corresponding to 2.0, 3.6, 4.9% w/w of the UVB-filter in the cast films. The non-loaded latex and its respective film were also prepared without using any coalescing agent. EMC was found to be stable under the polymerization conditions. All the latexes presented similar hydrodynamic diameters regardless of their cargo content. Dynamic mechanical analysis evidenced the compartmentalized structure of the films and a decrease of the glass transition temperatures corresponding to each compartment with increasing the EMC content. Tensile strength experiments manifested smaller stress at break and enlarged strain at break values for increasing the EMC content. All the films loaded with the UVB-filter were found to completely block UVB radiation even after a one month-long soaking in water and a four day long sun exposure. This opens a novel way of skin and wound protection against UVB radiation.