The Optimisation of Masterbatch Formulations for Use in Single Screw Machines

Abstract

Abstract Previous work by Benkreira et al. [1] has shown that the critical stage in distribution of additives in single screw extruders is the zone where the polymer melts; the subsequent pumping of the melt makes little difference to the mixture quality. It is suggested that the ideal masterbatch melts before the host polymer and coats each granule, while remaining sufficiently viscous to promote the shear heating and melting of the polymer. In order to test this hypothesis and quantify the requirements in terms of relative melting points and melt viscosities, a set of model masterbatches was produced and used for injection moulding at 1 % addition in a variety of polypropylenes and polyethylenes, but always under the same moulding conditions. Image analysis and “experts” judgement was used to rate the performance of these master-batches. The conclusions drawn from this work are that the designer of a masterbatch must consider the melting ranges of the masterbatch and its host polymer, and their relative viscosities in the temperature range of the forming process, in order to optimise the ease of distribution of the masterbatch.