The improvements in flame retardance and mechanical properties of polypropylene FR blends by acrylic acid graft copolymerization

Acrylic acid (AAc) was grafted onto a polypropylene (PP) backbone by a mechanochemical graft copolymerization reaction initiated by benzoyl peroxide (BPO) in a twin screw extruder. The modified PP was then blended together with the flame-retardant additive (FR), tris(2,3-dibromopropyl) isocyanurate for flammability reduction. Antimony (III) trioxide was selected as a synergistic agent. The flammability of the blends, according to the limiting oxygen index (LOI), mechanical properties, and thermal degradation of these materials were all investigated with various amounts of AAc and FR. Although the flammability of the PP/FR blends was reduced by the addition of the FR, the tensile strength and impact strength were also decreased. A characteristic of FR as a plasticizer was found by measuring the variation of Izod impact strength vs FR content, and a phenomenon of antiplastization appeared. For PP-g-AAc/FR blends, the LOI, T-pi, tensile strength, impact strength, and Young's modulus all increased because of the AAc grafting modification.