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Comparison of Aluminium Hydroxide and Magnesium Hydroxide as Flame Retardants in Sebs-Based Composites

The flame retardancy and mechanical properties of styrene-ethylene/butylene-styrene block copolymer (SEBS) based composites, containing paraffinic hydrocarbon extender oil filled SEBS (O-SEBS), blended with copolymer polypropylene (PP), and flame-retardant filler aluminium hydroxide (ATH) or magnesium hydroxide (MH) were investigated. Limiting Oxygen Index (LOI) values of both ATH and MH filled composites increased substantially as the amount of ATH and MH increased, respectively. Furthermore, the LOI values of the ATH system are higher than those of MH for the same addition level. When MH is introduced, progressively, into ATH-filled composites, and for a constant combined filler loading of 65 wt.%, LOI only decreases, when the ratio of MH to ATH exceeds 40%. Combining the two retardants, in the composites, may have a synergistic effect with respect to fire retardance. Tensile strength, up to 50 wt.% filler, and elongation at break of the composites decrease as the amount of filler increases. However, the elongation at break of the composites filled with MH is a little higher than that with ATH, but for tensile strength there is little difference between them. At filler loading greater than 50 wt.%, the tensile strength levels off but the% elongation is dramatically reduced. Introduction of MH in ATH filled composites leads to some variation in the mechanical properties of the composites. For a combined filler loading of 65 wt.%, the elongation at break increases from around 180 to 200% for a progressive increase in the ratio of MH to ATH up to 40% and there is a large increase in% elongation to around 300% when MH ratio reaches 55–60%, thereafter the% elongation falls. This effect may be linked to particle size distribution of the respective MH and ATH fillers. In contrast, there is little effect on the tensile strength. The thermogravimetric analysis (TGA) and differential TG (DTG) data show that ATH and MH increase the thermal stability of the SEBS-based composites.