PROCESS FOR MAKING POLYOLEFIN COMPOSITIONS

摘要

A process is disclosed of obtaining a thermoplastic composition formed from a polyolefin matrix comprising a polypropylene with a fluidity index of from 2 to 100 g/10 minutes when measured at 230°C under 2.16 kg, and a mineral lamellar filler which is talc with a median diameter D50 of at least 1 µm, as measured by Sedigraph, and a lamellarity index of at least 4 before introduction into the matrix and at least 3 when measured in the thermoplastic composition, by dispersing the lamellar talc in the polyolefin matrix in a viscoelastic state by means of at least on compounding extruder, which process comprises (a) the formation of a viscoelastic mixture of the polypropylene matrix and the lamellar mineral talc particles by heating and kneading the said composition at a temperature at least equal to the working temperature of the polypropylene, (b) the submission of the viscoelastic mixture to thermo-mechanical work, (c) the elimination of volatile components from the viscoelastic mixture, (d) the transformation of the viscoelastic mixture resulting from step (c) into an industrially usable granulated material, characterised in that, to obtain a controlled and homogenous dispersion and distribution of the lamellar mineral talc in the polypropylene matrix, while substantially retaining initial morphological characteristics of the lamellar mineral talc particles, the viscoelastic mixture is subjected during steps (a) and (b) to a weak and controlled rate of shearing of no more than 200s^-1 and the viscoelastic mixture is subjected in step (b) to at least one cycle of extension and relaxation in a dedicated zone which is at least 25% of the total length of the at least one screw of the compounding extruder. Also disclosed is the use of thermoplastic compositions obtained by such process in the manufacture of products for the automotive industry, domestic appliance industry, electronic industry, building industry, construction industry, internal design industry, sport and leisure industry, in packaging or in toys.