Relationship between the distribution of organo-montmorillonite and the flammability of flame retardant polypropylene

This article studies the relationship between the distribution of organically modified montmorillonite (OMMT) and the flammability of flame retardant polypropylene which consists of polypropylene (PP), brominated epoxy resin-antimony oxide (BER-AO) and OMMT. Polypropylene-graft-maleic anhydride (PP-g-MAH) was used to increase the polarity of PP and aid the dispersion of OMMT. Two model systems, PP/BER-AO/OMMT and PP/PP-g-MAH/BER-AO/OMMT composites, have been prepared by melt blending. TEM studies reveal a significant change in the distribution of OMMT for these two systems. For the first composites, OMMT platelets are aggregated in the BER-AO domains, whereas for the second composites, OMMT platelets are dispersed in the PP matrix. The flame retardant properties of the second composite reflected by UL 94 vertical burning test and cone calorimetry are better than that of the first one. When OMMT platelets aggregate in BER-AO domains as in the first composite, the BER-AO associated with OMMT may agglomerate into long ribbon-like structures during burning, inducing uneven distribution of BER-AO. As a result, loose and uneven residues are formed at the end of combustion. In comparison, OMMT platelets dispersed in polymer matrix are more efficient at stabilizing the polymer and preventing aggregation of BER-AO during burning, which induce thick and uniform char layers at the end of combustion. POLYM. ENG. SCI., 2012. (C) 2011 Society of Plastics Engineers