Formulations based on mineral fillers and polymeric matrices of different nature were studied to obtain halogen-free flame retardant compounds (HFFR) for cable applications. The work was carried out by comparing fire-retardant mineral fillers of natural origin with synthetic mineral ones available on the market. As a reference, a formulation based on micronized natural magnesium hydroxide (n-MDH, obtained from brucite) and an ethylene-vinyl acetate copolymer with 28% by weight (11% by moles) of vinyl acetate were selected, and the mechanical and flame retardant properties compared with formulations based on secondary polymers combined with EVA, metal hydroxides, and carbonates. Notably, we found a synergistic effect in the mechanical, rheological and flame retardant properties for the composite containing a mixture of n-MDH and boehmite in a 3:1 weight ratio. Overall, the present work provided a complete and optimized recipe for the formulation of polymer composites characterized by the required flame retardant and mechanical features in electric cables applications.

This study examines the preparation of several composites that are based on natural magnesium hydroxide (n-MDH) and various poly(ethylene-co-octene) polyolefin elastomers (POEs). Design of experiment (DoE) principles have been applied in order to optimize the mechanical, rheological, and flame-retardant properties of the final composites. DoE allows one to evaluate the influence of each variable on an experiment’s final properties. By increasing the density and crystallinity of the POE, a higher elastic modulus was obtained, which resulted in greater tensile strength and lower elongation at break. Improved flame retardant properties (as measured by the limiting oxygen index (LOI) and vertical burning tests) were obtained by increasing the amount of filler within the composite up to 65% and using a polymer with high crystallinity. More specifically, the best balance between mechanical, rheological, and flame retardant properties was provided by DoE using 63.75% n-MDH filler. The agreement between the predicted performance and the final properties of the composites has enabled the innovative use of DoE to provide reliable predictions about the final mechanical and flame retardant properties of the compounds that are used for low voltage electrical cable applications.

It was found that the use of natural magnesium hydroxide (n–MDH) as mineral filler in EVA based composites provided mechanical and rheological properties that did not completely comply with the halogen-free flame-retardant (HFFR) cables parameters. Moreover, the use of n–MDH mostly gave a rough grey surface in the compound extruded by rheometry capillary. In contrast, with the use of synthetic material (s–MDH), a combination of better outcomes was observed. Mechanical and rheological properties were more aligned with the application, and the aesthetics were also improved, i.e., the surface was smooth and whiter. Therefore, with the aim of obtaining good aesthetical quality on the extrudate, we studied formulations by varying the type of polymer matrix and using a mixture of the natural magnesium hydroxide combined with other kind of fillers (in a 3:1 ratio using as main filler n–MDH). On this account, we found a synergistic effect in the mechanical, rheological, and aesthetic properties for the filler blend system containing n–MDH in combination with s–MDH or Böhmite AlO(OH), or using a secondary polymer belonging to the polybutene family combined with EVA.