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 relatin g pigment properties to performance of the mixer. Five grades of TiO2 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 chara cteristics, including: shear properties from a shearbox; compressibility fr om Unconfined Compression Tests; and the blade force required to move a bla de over a bed of material. The blade force was calculated from a model base d upon nip technology and not bulk mixing. The blade force gave a good corr elation with peak torque for all 5 grades of pigment. The work indicates th at solids properties predominate in the early parts of the mixing cycle, bu t models need to be developed to describe the whole of the mixing process.