Synthesis and properties of a new halogen-free flame-retardant epoxy resin curing agent

Abstract

A novel intumescent flame-retardant curing agent, poly-( meta-xylylenediamine spirocyclic pentaerythritol bisphosphonate) (PMXSPB), was synthesized and subsequently characterized using Fourier transform infrared, proton nuclear magnetic resonance, and mass spectroscopies. PMXSPB was used as a flame-retardant and curing agent for preparing halogen-free flame-retarded epoxy (EP) resins. The thermal stability, mechanical properties, flame resistance, and morphology of the char layer of flame-retarded EP resins were investigated using thermogravimetric analysis, tensile and Charpy impact tests, limiting oxygen index (LOI), the UL94 test, and scanning electron microscopy, respectively. The results demonstrated that the addition of PMXSPB improved the flame resistance of EP resin composites, and the residual char ratio at 600°C was significantly increased. The flame-retarded composites filling with 3.01% phosphorus content (EP 100 g and PMXSPB 35 g) exhibited the best combination of properties, including a higher glass transition temperature (147°C), good thermal stability, an initial weight loss temperature of 269°C, and an LOI of 31.2. The vertical burning test reached the UL94 V-0 level, and the tensile and impact strengths were 51 MPa and 4.8 kJ m−2, respectively.