Recycling of TiO2 Pigments from Waste Paint: Process Development, Surface Analysis, and Characterization
Doctoral thesis, 2018
Typically, commercial grade pigments are not pure TiO2. Rather, they are surface treated in order to make the pigments more compatible with the paint matrix and to facilitate optimum dispersion. Waste paint feedstock for a recycling process will therefore contain TiO2 pigments having different chemistries due to the variety of surface coatings. In this research three pigments, coated with different combinations of aluminium, silicon, and zirconium oxides were investigated.
The TiO2 was recovered from paint in a three-step recycling process. First, the paint was pyrolysed at 500 °C in a nitrogen atmosphere to remove the volatile organic fraction. Next, the inorganic pyrolysed residues were oxidized in air at 500 °C to remove any residual organics and black carbon. After pyrolysis and oxidation the inorganic fraction was found to be contaminated with ionic salt residues from the decomposition of paint components during the recycling process. Therefore, the final step in the recycling process was to wash the residues in the presence of a mixture of ion exchangers yielding a pure secondary TiO2 product.
In order to clarify the extent to which the pigment was affected by the recycling process, the characteristics of the recycled pigments were studied using techniques such as powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and measurement of the dynamic electrophoretic mobility. Of the three pigments studied, it was shown that a pigment coated with a combination of silicon and aluminium oxides was more prone to degradation in the recycling process compared to pigments coated with a combination of aluminium and zirconium oxides or only aluminium oxide.
In addition, recycled pigment was used as a replacement for virgin pigment in a paint formulation. Results showed that the paint made from recycled TiO2 had a minor decrease in opacity, and that the effect on whiteness was insignificant when compared to a paint containing virgin pigment. However, surface defects due to poorly dispersed pigments decreased the gloss of the paint film. Even though the performance of the recycled pigment was lower than that of the virgin
Recycling
Recovery
Paint
Titanium dioxide
Waste.
Municipal solid waste handling
Pyrolysis
Pigment
Author
Mikael Karlsson
Chalmers, Chemistry and Chemical Engineering, Energy and Material
3 100 000 000 L dekorativ färg tillverkas globalt varje år. Ungefär 10 % av denna färg kommer aldrig till användning. Även i dagens samhälle där återvinning och resurseffektivisering är i fokus så saknas processer där färgavfall kan tas till vara på bästa sätt.
Det vita pigmentet titandioxid (TiO2) är i dagsläget det överlägset mest använda pigmentet i produkter såsom färg, plast och papper. Framställningen av TiO2 är dock energiintensiv och har en hög miljöbelastning. Därför söker färgindustrin efter alternativ till konventionellt framställd TiO2. I denna avhandling beskrivs hur TiO2 kan utvinnas från färgavfall med hjälp av en pyrolysprocess. Det återvunna pigmentet karakteriseras efter återvinningen och används sedan vid tillverkning av ny färg.
The white pigment titanium dioxide (TiO2) is currently the most widely used pigment in products such as paint, plastic and paper. However, the production of TiO2 is energy intensive and has a high environmental impact. Therefore, the paint industry is constantly looking for alternatives to conventionally produced TiO2. This thesis describes how TiO2 can be extracted from paint waste using a pyrolysis based process. The recycled pigment is characterized after recycling and is then used in the fabrication of new paint.
Driving Forces
Sustainable development
Areas of Advance
Building Futures (2010-2018)
Production
Materials Science
Subject Categories
Chemical Process Engineering
Materials Chemistry
Other Chemical Engineering
ISBN
978-91-7597-722-5
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4403
Publisher
Chalmers