Comparative study of the synergistic effect of binary and ternary LDH with intumescent flame retardant on the properties of polypropylene composites†
Organo-modified binary (MgAl-) and ternary (MgZnAl-) layered double hydroxides (LDHs) were synthesized via a co-precipitation method, and subsequently dispersed into polypropylene (PP) in combination with an intumescent flame retardant (IFR) by a melt blending process. A comparative study on the effect of binary and ternary LDHs on the mechanical, thermal properties and flammability of flame retardant PP composites was undertaken. The incorporation of either binary or ternary LDH resulted in a slightly decreased tensile strength compared to neat PP matrix; however, the Young's modulus of PP/IFR/LDH composites was improved. The synergism between either binary or ternary LDH and IFR occurred during the combustion, but the ternary LDH showed superior char-formation ability and smoke suppression over the binary one due to the presence of the element zinc. In contrast to the binary LDH, the ternary LDH produced better quality char that effectively suppressed the spread of the flame and finally extinguished the fire.