Investigation of the thermal ageing process and mechanism of benzoxazine/bismaleimide/cyanate ester copolymer

Fibre-reinforced polymer (FRP) composites with thermosetting resin matrices are widely used in civil engineering (e.g. pultruded FRP plates and bars), and their thermal ageing behaviour is a concern when they are subjected to elevated temperatures (e.g. FRP chimney). In the present article, the effects of thermal ageing at 200°C and 250°C in air for up to 1000 h on mechanical properties and mechanism of the benzoxazine (Boz), bisphenol A dicyanate cyanate ester (BADCy), and 4,4′-bismaleimidodiphenyl methane (BMI) have been investigated. The effect of time in thermal ageing on structural and mechanical properties of the Boz/BMI/BADCy resin was deeply studied. The moisture absorption increases linearly with the square root of ageing time and it follows Fick’s second law. There are two main categories of reactions in thermal ageing: the first one is the post-curing process, which leads to a larger crosslinking density and a reduced interior stress; while the other is the formation of microcracks and thermal oxidation at the surface of the Boz/BMI/BADCy resin. The combination of the above factors leads to an increase–decrease variation in the mechanical properties. This work is believed to benefit the wide and safe application of a certain Boz/BMI/BADCy resin system in engineering application.