Ugo Zucchelli, Italmatch, presented inorganic phosphate salt PIN FRs (proprietary phosphinates) in polypropylene, polyethylene EVA. These PIN FRs act in both the solid phase (formation of protective char layer) and by releasing phosphorus radicals into the fire gases.
By including phosphorus in different oxidation states, faster char formation, improved intumescence and a better barrier to gas transfer through the char layer are achieved. UL94-V0 was achieved with glass fibre reinforced polypropylene, with unchanged colour and low corrosivity in processing (no release of acids). Challenges are the tendency of the inorganic salt to take up water, and so loss of fire safety or material mechanical properties.