Toughening of Polypropylene Highly Filled with Aluminum Hydroxide

The flame retardant and mechanical properties of polypropylene (PP), highly filled with aluminum hydroxide (Al(OH) ₃ ) and toughened with ethylene propylene diene monomer (EPDM) and zinc neutralized sulfated EPDM ionomer (Zn-S-EPDM), were studied along with their morphology. The PP matrix when highly filled with Al(OH) ₃ particles can achieve an adequate level of flame retardancy, but there is a decrease in the mechanical properties because of inadequate adhesion between the Al(OH) ₃ particles and the PP matrix and the strong tendency of the filler to agglomerate. The rubber incorporated in the PP/Al(OH) ₃ composites has two roles: as compatibilizer and toughening agent. Although ordinary EPDM significantly improves the Izod impact strength of the composites, the tensile properties are much worse because of the weak interfacial adhesion between the modifier and the matrix. Using Zn-S-EPDM instead EPDM, the tensile properties are much improved with only a slight decrease in toughness, because of improvements in the interfacial adhesion between modifier and matrix. SEM micrographs show that the rubber phase is dispersed in the continuous PP matrix and that most Al(OH) ₃ particles are uniformly distributed in the rubbery phase. Larger, obviously rubbery, domains can be seen in the PP/EPDM/Al(OH) ₃ ternary composites. Much finer rubbery domains were found in the PP/Zn-S-EPDM/Al(OH) ₃ composites.