Cyclodextrin nanosponges as novel green flame retardants for PP, LLDPE and PA6

Novel green flame retardant systems based on a complex of cyclodextrin nanosponges and phosphorus derivatives (namely, triethylphosphate and ammonium polyphosphate) have been prepared. The above additives have been subsequently melt compounded with polypropylene, linear low density polyethylene or polyamide 6 in order to improve the thermal stability of the latter polymers and their flame retardancy properties (assessed by combustion and flammability tests). The role of cyclodextrin nanosponges both as a carbon source and a foaming agent in such intumescent formulations has been demonstrated: indeed, the phosphorus derivatives are embedded and protected by the nanosponge architectures and thus are able to generate phosphoric acid directly in situ at high temperatures. As a consequence, cyclodextrin nanosponges dehydrate in presence of this acid source, giving rise to water vapour, favouring char formation and thus significantly enhancing the polymer resistance toward combustion.