Control of aroma permeability in latex coatings by altering the vinyl acid content and the temperature around Tg

The mass transport of four different aroma compounds (ethyl butyrate, 1-hexanol, heptanal and limonene) through styrene-acrylate latex dispersion coatings with different amounts of vinyl acid groups has been studied using a permeation cell. The permeation test was studied above and below the glass transition temperature of the styrene-acrylate latex films in order to study the influence of changes in free volume and polymer rigidity on the aroma permeation induced by glassy-rubbery transition. An increase in the carboxylic acid content of the latices reduced the diffusivity. The solubility of all the aroma compounds tended to increase with increasing carboxylic acid groups content in the latex films, including the non-polar limonene. Other factors than polarity and chemical attraction forces including volatility and molar volume of the aroma compounds thus affected the mass transfer. Since solubility and diffusion oppose each other, the differences in permeability towards aroma compounds between the latex films were small. Below the glass transition temperature, the free volume is less, resulting in a lower mobility of the permeants and, therefore, a lower diffusivity than above the glass transition. A small increase in solubility was seen at the lower temperature, probably due to the lower volatility of the aroma compounds.