Synthesis of biobased phosphorus-containing flame retardants for epoxy thermosets comparison of additive and reactive approaches

This study presents a two-steps synthesis of novel additive or reactive phosphorus-and-sulfur-containing flame retardants (P-FR) for epoxy thermosets. The first step consists in totally epoxydizing the phloroglucinol. Then, the epoxy functions grafted are partially or totally open by a thiol bearing a phosphonate group to obtain a reactive P-FR and an additive P-FR respectively. The two synthesized P-FR are then incorporated into a DGEBA-IPDA matrix according to an appropriate approach. The impact of these P-FR on glass transition temperature (Tg) is assessed by DSC. Tg values exhibit the plasticizing effect of the additive P-FR and the loss of epoxy functionality due to the incorporation of the reactive P-FR. The thermal properties of the prepared thermosets are characterized by TGA, showing the more efficient action of the reactive P-FR in condensed phase (charring). TGA-FTIR coupling show the presence of phosphorus-containing gases released during the thermal degradation but these P-containing gases have no radical scavenging action in the gas phase. PCFC analyses prove the similar flame retardant properties of the two P-FR by reducing significantly the pHRR, the THR and the EHC. The cone calorimeter tests exhibit a strong intumescent effect of the residue brought by the two P-FR, leading to insulating expanded residue. (C) 2015 Elsevier Ltd. All rights reserved.