RD Titan Group Innovative TiO2 has shared some interesting news with the global digital magazine Compounding World | October 2018. Company co-founder and director Andriy Gonchar says that the most TiO2 grades for plastics are made hydrophobic by surface treatment of the particles using special organic additives. Such hydrophobic treatment provides improved wettability in melts of non-polar polymers, ensure their better dispersion and also provides the preparation of less viscous mixtures of the molten polymer and the pigment.
Substances used for titanium dioxide hydrophobisation can be divided into two types: additives that are physically adsorbed onto the particles surface (polydimethylsiloxanes, for example), or additives which chemically interact with the surface (such as egg, silane, phosphonic acids).
Additives of the first type have one common drawback - during the mixing of the pigment with the polymer melt, they tend to desorb from the surface of TiO2 particles and migrate, resulting in the effect of the "greasy" surface of the pigmented polymer material. In this regard, the use of the second type additives for titanium dioxide hydrophobisation is more preferable because they don’t desorb from the surface of TiO2 particles. Actually, most hydrophobic grades of the world's leading titanium dioxide producers are treated with additives of the second type.
Pigment manufacturers can use different methods of applying hydrophobic coatings. RD Titan Group Innovative TiO2 has developed a "dry" application technology for the production of Plastic Type 1 grades (designed for maximum processability). The latest development from the company, working with Swiss candle filter manufacturer Dr. Mueller, is a "wet" technology that allows treatment of the TiO2 in an aqueous suspension, after which (using a specially designed candle filter) the thermal exposure necessary for hydrophobisation and simultaneous drying of the pigment to a moisture content of less than 0.2% is performed.
This technology allows the effective process of hydrophobisation for the production of all three types of titanium dioxide grades for plastics. Conventional expensive equipment (filter presses and dryers) can be excluded, significantly reducing capital costs compared to the traditional techniques. The technology can be easily implemented at existing plants currently not producing hydrophobic TiO2 grades.