Characterization of waxes as possible coating material for organic aerogels
Aerogels require nontoxic coatings which are good barriers to the environment and do not affect the fragile porous network. There is a wide range of coating materials available for a variety of applications and functionalities. Waxes, for example, are good moisture barrier candidates and do not require additional solvents during processing. Hence, in this work four different natural waxes were tested concerning their application as coating material for porous aerogels. Therefore, beeswax, candelilla wax, rice bran wax and sunflower wax were investigated regarding their thermic properties, moisture barrier properties and wettability. Beeswax and rice wax proved favourable for coating aerogels. Beeswax shows low water vapour permeability, low minimum film forming temperature and forms continuous films. The water vapour permeability of rice wax is higher compared to beeswax, but there is no minimum film forming temperature in the temperature range of 20 °C–80 °C and the appearance of the rice wax films is homogeneous. Candelilla wax and sunflower wax are not suitable for coating of aerogels. Candelilla wax forms discontinuous films which diminish its water barrier properties. Sunflower wax has the highest water vapour permeability, forms porous films and forms cracks on the surface of the film during solidification below 62 °C.