A research paper tests calcium hypophosphite (CaPi) and magnesium hypophosphite (MgPi) as PIN FRs for cotton fabrics, also with nano-particles of a clay and a silsesquioxane as synergists (sodium montmorillonite, octa-ammonium polyhedral oligomeric silsesquioxane POSS). CaPi showed slightly better flame retardant effectiveness (LOI 23 at 15% weight loading CaPi on cotton, compared to 21 with 14% MgPi and 18 for untreated cotton fabric). FR effectiveness was only very slightly further improved by replacing 10% of the CaPi by clay or POSS. The lowest heat release was 43% that of untreated cotton with 15% loading of 95% calcium hypophosphite / 5% POSS. FR effect is identified as resulting from char formation. The different PIN products used are water soluble, so wash durability would need to be addressed for these treatments to be useful.
“Thermal stability and flame retardant properties of calcium and magnesium-hypophosphite-finished cotton fabrics and the evaluation of interaction with clay and POSS nanoparticles”, S. Furtana et al., Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-019-08751-2