MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF TERNARY PHASE POLYPROPYLENE ELASTOMER/MAGNESIUM HYDROXIDE FIRE-RETARDANT COMPOSITIONS/

Fire-retardant polypropylene (PP) composites were prepared by combinin g this polymer with uncoated and surface treated forms of magnesium hy droxide filler and various elastomeric modifiers, with and without mal eic anhydride functionalization. Mechanical properties of binary and t ernary phase compositions differed significantly and are discussed in terms of their microstructures (determined principally by SEM and FTIR ) and the relative interaction of the components. Impact strength, in particular, was strongly influenced by the presence of filler surface treatment and the degree of rubbery phase dispersion. FTIR showed that functionalized ethylene-propylene rubber (F-EPR) reacted with the sur face of uncoated magnesium hydroxide leading to extensive rubber encap sulation and an improvement in toughness relative to unmodified EPR, w hich was present in the matrix only as phase dispersed droplets. Howev er, by blending F-EPR with filler surface treated with magnesium stear ate, encapsulation was inhibited and the rubber was preferentially dis persed in the PP matrix. This formulation resulted in both improved fi ller-matrix interaction and enhanced matrix toughening leading to a fu rther increase in impact strength. The effects of material composition on melt flow behavior and UL94 flammability rating, are also reported . (C) 1996 John Wiley & Sons, Inc.