• Brucite
• capillary rheometer
• eva
• Flame retardants
• highly filled polyolefin compounds
• Rheology
• Surface properties

In this master's thesis work, the rheological and surface properties of highly filled polyolefin compounds for the production of low flammability and fire retardant cables have been studied.
One of the aims of the following work was to study the dependence of the properties of the final compound on the variation of the properties of the ingredients used. Specifically, different formulations in terms of both the mineral filler and the polymeric composition were selected and tested in order to obtain ultimate composite properties possibly to those suggested by the sector regulations and the current production processes.
Another object was to develop a new method for assessing the surface quality of the extrudate through the use of a capillary rheometer, a laboratory-scale method capable of giving indications and predictions on the surface quality of the materials once processed in industrial-scale cable extrusion lines.
This point is very important as at present there is no laboratory test that can give information on the surface quality of a compound for cables without the use of an extruder, which however requires the use of larger quantities of material.
The tests were carried out by comparing the new products (based on ground mineral fillers of natural origin) with synthetic mineral fillers obtained by precipitation which are commercially available, and which are widely used industrially as flame retardants.
The reference formulation studied was based on micronized natural magnesium hydroxide, obtained starting from brucite (mineral widely used in the flame retardant sector) and of ethylene-vinyl acetate copolymer with 28% of comonomer (EVA28) as the main polymer.
The variables taken into consideration for the mineral fillers were the type of mineral, the type (synthetic or natural), any surface treatment and their combination.
The variables taken into consideration for the polymers were the chemical composition (copolymers of ethylene, 1-butene, hexene and octene), crystallinity, molecular weight, the distribution of the molecular weights (function of the type of catalysis used for the production of the polymer).
The compounds were prepared with a roller mixer. Crystallinity was characterized by DSC, mechanical properties were measured with a dynamometer, while rheological and surface properties were studied with Melt Flow Index (MFI) and capillary rheometer.
Capillary rheometer analyses were conducted with the aim of reproducing the extrusion conditions, in order to also have an indication of the surface quality of the extruded material, which represents one of the critical parameters with the use of natural mineral fillers.