Organopalygorskite and Molybdenum Sulfide Combinations to Produce Mechanical and Processing Enhanced Flame-Retardant PE/EVA Blend Composites with Low Magnesium Hydroxide Loading

The effect of organopalygorskite (OPGS), molybdenum sulfide (MoS2), and magnesium hydroxide (MH) combinations on fire retardant and flammability characteristics of low-density polyethylene/ethylene vinyl acetate (LDPE/EVA) blends was investigated using the limited oxygen index (LOI), horizontal burning test (UL-94), and cone calorimeter measurements. The combination of OPGS with exfoliated MoS2 nanosheets is employed to reduce the conventional hydroxide content and enhance the PE/EVA blend flame-retardant properties with a notable improvement in mechanical and processing characteristics. The flame-retardant properties of the composites were compared with a reference PE/EVA sample with 55 wt% of MH, which is commonly used for wire coating. The effect of each additive and the use of a maleated polyethylene (PEgMA) as a compatibilizing agent on PE/EVA flame-retardant properties were analyzed. The results of the LOI and UL-94 tests confirmed that the addition of OPGS combined with MoS2 substantially increases the LOI value (26%) and reduces the burning rate (66%) and the pHRR (83%) compared with neat polymer blend and passes V-0 rating during UL-94 vertical test, which were very similar to the values obtained for the reference sample with higher MH content. In addition, the results indicate that the addition of these additives simultaneously increases the tensile modulus with mechanical properties even higher than the reference sample. Most important, the results indicated that these additive combination allows to reduce the total MH filler content to achieve the flame-retardant requirements and with enhanced mechanical properties and with higher melt flow rates and lower viscosities facilitating the processing of the polymer composites at lower pressure in the processing extruder. Therefore, this additives combination provides a favorable way to obtain efficient flame-retardant materials with halogen-free, low smoke, and easy processing characteristics. J. VINYL ADDIT. TECHNOL., 2020. (c) 2020 Society of Plastics Engineers