Bio-Based Rigid Polyurethane Foams Made Flame-Retardant after Addition of Aluminum Hypophosphite

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Spring 2021


Olefins present unsaturations that can be chemically modified to introduce hydroxyl groups. This process was performed on carvone, an essential oil extracted from bay leaf, that reacted with 2-mercaptoethanol (2ME) through a UV catalyzed reaction at room temperature and solventless process named as thiol-ene click chemistry. The novel carvone-derived polyol was characterized through hydroxyl number, viscosity, IR spectroscopy, and size exclusion chromatography. Then it was used to make flame-retardant polyurethane foams, at which a synthesized inorganic compound named aluminum hypophosphite (AHP) was blended into the mixture. Separately, aluminum trihydroxide (ATH) was also added for comparison. Both sets of foam were analyzed in terms of density, closed-cell content, compressive strength, thermostability, burning test, and weight loss percentage. The foams had 95% of closed cell content. Weight loss went from 45 to 3.06% (8.9 wt.% AHP) in comparison to 12.23% (15.43 wt.% ATH). Also, burning time dropped from 98 to 5.2s (8.9 wt.% AHP) and 58s (15.43 wt.% ATH). The difference was addressed to AHP’s action for the formation of a char layer promoted by phosphorus that dehydrated the polyurethane’s surface, leading to a denser carbonaceous layer. On top of that, it released radical species that captured reactive radical fragments, effectively preventing fire from spreading. Simultaneously, aluminum promoted an endothermic decomposition that released water and formed a diffused alumina layer. The combination of these two fire mechanisms occurring at the same time surpassed the fire quenching performance of foams blended with commercial ATH. Thus, satisfactory flame-retardancy properties were achieved.


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