Design lignin doped with nitrogen and phosphorus for flame retardant phenolic foam materials

Developing lignin-based flame retardants for phenolic foam with exceptional flame retardancy and mechanical performances remains a huge challenge due to complicated chemical structure and unstable chemical activity of lignin. In this study, nitrogen-phosphorus doped lignin flame retardant (NP-LMDL) was prepared by modifying reactive lignin with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and triethylenetetramine (TETA), which was utilized to partially replace phenol to prepare flame retardant phenolic foams (NP-LMDLPFx). The results showed that nitrogen-phosphorus doped lignin enhanced the flame retardant performance and compressive strength of the foam. The limiting oxygen index (LOI) and compressive strength of NP-LMDLPF15 increased by 33.3% and 43.7% comparing with pure phenolic foam (PF). The peak heat release rate (pHRR) and peak smoke release rate (pRSR) decreased by 48.0% and 53.2%. Moreover, the structure and elemental constitution of char residues were analyzed to discuss the flame retardant mechanism of nitrogen and phos-phorus in foam. Nitrogen and phosphorus in NP-LMDLPFx worked together to promote polymers carbonization and generate rich nitrogen and phosphorus char residue layer, insulate heat and oxygen to play the role of flame retardant.

Automated summary

In this study, a nitrogen-phosphorus doped lignin flame retardant (NP-LMDL) was prepared and used to partially replace phenol in phenolic foam to prepare flame retardant phenolic foams (NP-LMDLPFx). The nitrogen-phosphorus doped lignin enhanced the flame retardant performance and compressive strength of the foam.