Reutilization of melamine-formaldehyde foam wastes: Removing Sn2+ in simulated tin-containing wastewater to transform a fire hazard suppressant of flexible poly(vinyl chloride)

Melamine-formaldehyde (MF) foam has wide applications due to good flame retardancy, excellent sound absorption, and high thermal stability. However, the recycling of MF foam wastes remains a challenge due to its thermosetting nature. Here, we demonstrate a new strategy for discarded foams as solid adsorbents for removing tin ions in simulated tin-containing wastewater. Results showed that the removal rate of tin in simulated wastewater is as high as 99.996%. Moreover, after simple calcination, as-obtained products can be used as high-efficiency flame retardants for flexible poly(vinyl chloride) (PVC), reducing the peak of heat release rate and total smoke production of PVC by 51.8% and 45.8%, respectively, under the condition of 2.5 wt.% addition. In short, this strategy successfully converted MF foam and tin wastewater to valuable flame retardants, opening the way for the environmentally friendly recycling of MF waste and the simultaneous treatment of tin-containing wastewater.