Sichuan, China – While bio-based PU foam has environmental advantages, its inherent flammability limits its application in rigid foam insulation without incorporating flame retardant additives into the foam matrix. Now, scientists at Sichuan’s National Engineering Laboratory of Eco-Friendly Polymeric Materials have developed a way to make flame retardant eco-friendly PU foam without having to add a FR additive.
A green bio-based FR system was created by first reacting vanillin (which can be made from lignin) sequentially with ethanolamine and diethylphosphite. This phosphite-modified vanillin was then added to biomass-based polyols, along with expanded graphite obtained from natural graphite flakes as a synergistic filler. This graphite rapidly forms a protective char at high temperatures.
This mixture was then used to make biomass foam composites via the one-pot free foaming method, with the vanillin component conferring flame retardant properties.
The LOI value of this foam composite increased to 30.5 vol%, and a V-o rating was achieved in the UL-94 vertical burning test. Peak heat release rate and total smoke production were both down by about two thirds. Its flame retardant properties were retained after an accelerated thermal ageing test.
The team suggest that this could provide a way of conferring durable flame retardancy and long-term thermal insulation performance that would facilitate practical applications for bio-based foam composites.
The work has been published in the Journal of Materials Science and Technology.