Recycled paints: Are they as variable as they seem?

Several paint companies recently included a range of recycled paints among their proposed products. These are produced from recovered waste and mixed according to their main binders and colors to produce new batches of lower quality at lower cost. As they are relatively new to the market, no comparative study of their differentiation has yet been realized. We therefore collected different production batches of recycled paints of 7 different colors (white, off-white, blue, green, yellow, gray and brown). The paints were analyzed optically, by microscopy, infrared and raman spectroscopy and pyrolysis GC/MS. The intended goal was to verify if the common knowledge about paint frequencies and discriminating power of analytical techniques still apply to recycled paints. We have observed that microscopy (presence of colored spots) and Pyrolysis GC/MS (high discriminating power) were the recommended techniques to discriminate between production batches. These differences were less pronounced in Infrared and Raman analysis, which on the other hand represent an average spectrum of the most frequent compounds mixed together. While the composition of the main components is statistically stable and reflects the most common binders and extenders used in paint within a population, the minor components are much more variable and provide an almost unique signature to each of the recycled paints, better recognized by Pyrolysis GC/MS than Infrared and Raman spectroscopies.