Tuning the functionalization chemistry of polypropylene for polypropylene/clay nanocomposites

New polypropylene (PP)-graft-maleic anhydride (PP-g-MA) samples have been successfully synthesized by adding N-bromosuccinimide (NBS) during the reactive extrusion process. These NBS-mediated PP-g-MAs possess higher graft content than classic PP-g-MAs (i.e. without NBS) while they keep acceptable molar masses. NBS-mediated PP-g-MAs were used as matrices in model PP-g-MA/organoclay nanocomposites and compared with commercial and home-made classic PP-g-MAs in order to evaluate their ability to disperse the clay. Significantly better degrees of clay delamination and dispersion were reached using NBS-mediated PP-g-MAs than with classic PP-g-MAs. As expected, PP-g-MAs having high graft content showed the best clay dispersion. Within the examined range of molar masses, the PP-g-MA molar mass had no influence on the clay dispersion. However PP-g-MAs exhibiting important reduction of crystallinity lead to poor clay dispersion whatever the graft content. The PP-g-MA/organoclay nanocomposite prepared using the selected “optimized” NBS-mediated PP-g-MA exhibited the best improvement of thermal properties and one of the best clay dispersions. PP/PP-g-MA blends were prepared to evaluate the miscibility between PP and selected PP-g-MAs. No problem of miscibility between the selected NBS-mediated PP-g-MA and PP was noticed. Finally the PP/organoclay prepared using the selected NBS-mediated PP-g-MA as compatibilizer showed much better clay dispersion and thermal stability than the one prepared with the corresponding classic PP-g-MA, thus establishing the interest to use such new NBS-mediated PP-g-MAs as compatibilizers.