Crystallinity of Halogen-Free Flame-Retardant Polyolefin Compounds Loaded with Natural Magnesium Hydroxide

A typical halogen-free flame-retardant (HFFR) formulation for electric cables may contain polymers, various additives, and fire-retardant fillers. In this study, composites are prepared by mixing natural magnesium hydroxide (n-MDH) with linear low-density polyethylene (LLDPE) and a few types of ethylene–octene copolymers (C8-POE). Depending on the content of LLDPE and C8-POE, we obtained composites with different crystallinities that affected the final mechanical properties. The nucleation effect of the n-MDH and the variations in crystallinity caused by the blending of C8-POE/LLDPE/n-MDH were investigated. Notably, in the C8-POE/LLDPE blend, we found a decrease in the crystallization temperature of LLPDE compared to pure LLDPE and an increase in the crystallization temperature of C8-POE compared to pure C8-POE. On the contrary, the addition of n-MDH led to an increase in the crystallization temperature of LLDPE. As expected, the increase in the crystallinity of the polyolefin matrix of composites led to higher elastic modulus, higher tensile strength, and lower elongation at break. It has been observed that crystallinity also influences fire performance. Overall, these results show how to obtain the required mechanical features for halogen-free flame-retardant compounds for electric cable applications, depending on the quantities of the two miscible components in the final blend.