Phosphorus/phosphorus-nitrogen flame retardants applied to polyurethane/rice husk eco-composites: thermal behavior, flame retardancy, and physico-mechanical properties

The objective of this work is to investigate the influence of two phosphorus/phosphorus-nitrogen flame retardants including diammonium hydrogen phosphate (DAP) and aluminum hydrogen phosphite (AHP) on the flame performance of polyurethane/rice husk (PUF-RH) eco-composites. The fire retardancy and thermal stability of the prepared composites were studied by UL-94, LOI, DSC, and TGA. The fire extinguished completely before reaching the 1-inch mark for PUF-RH containing 15 wt% DAP loading and thus the sample achieved the UL-94 HB. Meanwhile, PUR-RH and PUF-RH/AHP(15)completely burned and failed the UL-94 HB test. A UL-94 V-0 rating was obtained and LOI value significantly increased by 26.3% at 25 wt% loading of DAP for PUF-RH, which is consistent with enhanced thermal stability confirmed by TGA. DAP in PUF-RH mainly acts in fuel dilution and cooling effect, vapor phase, and condensed phase. Differences in experimental and calculated TG analyses strongly support an interaction between DAP and PUF-RH during their decomposition. The presence of DAP results in the composite with more regularity pore size and a higher density which could be reason for its improved compressive strength. DAP is a non-reactive additive in the polymer system; therefore, it does not influence theT(g)of PUF-RH.