Catalyst-free construction of biomass-based robust and flame-retardant polyurethane foams

This study introduces a green synthesis method for the preparation of flame-retardant biobased polyurethane foams (PUFs) without the use of catalysts. The approach involves the design and utilization of two cardanolbased hydroxyalkyl benzoxazines (CHBzs) capable of self-catalytic foaming through the action of their oxazine rings. Additionally, tris(hydroxymethyl)phosphine oxide (THPO) is incorporated as both a crosslinking agent and a flame-retardant additive during the foaming process to enhance the physical properties and flame retardancy of the resulting PUFs. The thermodynamic performance, compressive strength, and flame-retardant properties of the synthesized foams are analyzed. Furthermore, the morphology of the combustion residues is investigated to understand the combustion process. The results demonstrate that the addition of THPO significantly improves the flame-retardant performance and thermal degradation characteristics of bio-based flame-retardant PUFs. This green synthesis approach offers a promising strategy for the development of sustainable and flame-retardant PUF materials.