Self-assembly of triazolyl-based cyclomatrix polyphosphazene and melamine cyanurate for flame-retardant, smoke-suppressing, and mechanically robust epoxy resin

Abstract

Epoxy resin (EP) is widely utilized in construction, rail transit, and structural engineering as coatings, adhesives, and resin matrices for fiber-reinforced composites, owing to its excellent processability, adhesion, thermal stability, and mechanical strength. However, its inherent high flammability significantly restricts its application in scenarios requiring stringent fire safety standards. Addressing this challenge, we developed a novel triazolyl-based cyclomatrix polyphosphazene (HTDA) that self-assembles with melamine cyanurate (MCA) through hydrogen bonding, forming a hybrid flame retardant (HTDA@MCA) with a distinctive lamellar structure. The impact of HTDA and HTDA@MCA on EP's thermal stability, fire resistance, and mechanical performance was systematically evaluated. Compared to HTDA alone, the HTDA@MCA hybrid demonstrated superior performance, significantly enhancing EP's elastic modulus, crosslink density, and glass transition temperature. At HTDA@MCA loadings of 7.5 % and 10 %, EP achieved a UL-94 V-0 rating and limiting oxygen index (LOI) values of 28.6 % and 29.4 %, respectively. Cone calorimeter and smoke density tests further revealed a 68 % reduction in peak heat release rate and a 54.8 % decrease in smoke production. The excellent dispersion and unique lamellar structure of HTDA@MCA contributed to significant improvements in EP's mechanical properties. This study proposes an innovative strategy for simultaneously improving the fire safety, thermal stability, and mechanical strength of EP, providing valuable guidance for the development of high-performance polymeric materials.