The Characterization of Pigment Powders for Titanium Dioxide/Polymer Dispersions by the ‘Masterbatch’ Process

The Masterbatch process of mixing titanium dioxide pigment with low density polyethylene polymer powder has been investigated, with the aim of relating pigment properties to performance of the mixer. Five grades of TiO 2 were investigated. A series of lab-scale mixing trials were undertaken, and the peak torque from the mixer was correlated against a number of pigment characteristics, including: shear properties from a shearbox; compressibility from Unconfined Compression Tests; and the blade force required to move a blade over a bed of material. The blade force was calculated from a model based upon nip technology and not bulk mixing. The blade force gave a good correlation with peak torque for all 5 grades of pigment. The work indicates that solids properties predominate in the early parts of the mixing cycle, but models need to be developed to describe the whole of the mixing process.