I was talking to a customer recently who said “she didn’t want any paint containing plastics”. It’s a phrase I’ve heard before, often in reference to paints claiming to be eco-friendly or bio-renewable. However, it’s one I find confusing as the definition of plastic is:
“A material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be moulded into solid objects. The use of the term plastic instead of polymer is a source of confusion”
We’re all familiar with plastics but it’s polymers that bind paint together and are the film forming ingredient. These can be bio-renewable, naturally occurring polymers or products derived from petrochemicals. The vast majority of paints are made with the latter. Paints without any polymeric content would be whitewash – chalk (Calcium Carbonate) and possibly white pigment (Titanium Dioxide), suspended in water. Solvent based alkyd paints are usually made from bio-renewable resources, castor oil being a good example, but they contain solvents – white spirit in most decorative High Gloss or Eggshell paints for woodwork. If you want a paint that doesn’t contain petrochemical derived polymers, you’re limited to linseed oil paints or those held together with casein, starch or polysaccharide polymers. This really is “old technology” which was replaced in the 1950s by water based acrylic polymers.
Nowadays there’s far more polymers or water borne emulsion polymers to choose from. This is usually determined by cost or the application. You’d use different polymers in a water-based primer, an interior matt emulsion paint, a masonry paint or an exterior eggshell paint, for example, as the end use requires different properties. The latter two need excellent weatherability. Paints made from these types of polymers are sometimes
referred to as vinyls or latex paints but I feel these are very generic and slightly confusing terms. I always think of natural rubber or synthetic equivalents like SBR (Styrene Butadiene Rubber – think crepe soled desert boots which I lived in as a teenager) when I hear the term latex.
So, for a paint to be really eco-friendly, is it better to choose one that will last? If it’s based on a polymer derived from petrochemicals, the chances are that the performance and longevity will be superior. You’re repainting less often and therefore consuming less resources. If you insist on a cellulosic based paint manufactured in a country with a huge forestry industry or an emulsified linseed oil-based paint because it’s bio-renewable, it’s almost certainly imported and that raises the issue of the carbon footprint of shipping them.
Finally, it’s important to remember that once the paint’s dry, everything in it is trapped and not going to enter a water course and end up in the sea or soil!