Synthesis of Bio-based Epoxy Containing Phosphine Oxide as a Reactive Additive Toward Highly Toughened and Fire-retarded Epoxy Resins

Abstract

The integration of high mechanical toughness, impact strength as well as excellent flame-retardant properties toward epoxy resins (EPs) have always been a dilemma. The inadequate overall performance of EPs severely restricts their sustainable utilization in engineering aspects over long-term. Herein, a new bio-based agent (diglycidyl ether of magnolol phosphine oxide, referred as DGEMP) derived from magnolol (classified as lignan), extracted from natural plants Magnolia officinalis, was successfully synthesized and further employed as a flame-retardant reactive additive to diglycidyl ether of bisphenol A (DGEBA). As demonstration, the composite resin, DGEBA/15DGEMP (15 wt% DGEMP), achieved an Underwriters Laboratories-94 V-0 rating with a high limiting oxygen index (LOI) value (41.5%). In cone calorimeter tests, it showed that heat release and smoke production were effectively inhibited during combustion, wherein the peak heat release rate (PHRR) value of DGEBA/15DGEMP was reduced by 50% compared to neat DGEBA. Additionally, it exhibited a superior tensile strength (82.8 MPa), toughness (5.11 MJ/m³) and impact strength (36.5 kJ/m²), much higher than that of neat DGEBA (49.7 MPa, 2.05 MJ/m³ and 20.9 kJ/m²). Thus, it is highly anticipated that DGEMP imparts significantly improved mechanical and fire-retarded properties to conventional EPs, which holds a great potential to address the pressing challenges in EP thermosets industry.