Sustainable and efficient metal hydroxides as halogen-free flame-retardant additives in polyolefin-based composites for cable sheathing applications

This study investigates sustainable strategies for large-scale industrial production in the cable industry ( e.g. sheathing applications), focusing on halogen-free flame-retardant (HFFR) additives in polyolefin composites. Three metal hydroxides are evaluated: precipitated aluminium hydroxide (p-ATH), precipitated magnesium hydroxide (p-MDH), and naturally milled magnesium hydroxide (nm-MDH). While p-ATH and p-MDH are chemically processed and carbon-intensive, nm-MDH is derived from untreated minerals, offering a lower environmental impact. All hydroxides were characterised using XRD, TGA, morphological, and spectroscopic analyses. p-ATH and p-MDH show gibbsite and brucite structures, respectively, while nm-MDH features a brucite structure with minor dolomite content, enhancing flame resistance due to higher decomposition temperatures and inert gas release. Flame-retardant polymer composites (FRPCs) were produced by melt-mixing 60 %wt. metal hydroxides into a polyolefin-based ( i.e. EVA/LLDPE/MA-g-LLDPE) matrix. Rheological tests show that p-ATH-based FRPCs maintain liquid-like behaviour, while p-MDH and nm-MDH composites exhibit solid-like properties. Morphological analysis reveals better polymer-filler interaction in p-MDH and nm-MDH composites, supported by reactions with MA-g-LLDPE. All FRPCs demonstrated excellent flame and thermal resistance. Additionally, metal hydroxides reduced oxidative degradation under UV-B exposure, suggesting improved weatherability.