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

Abstract

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.

Effects of aging process and testing temperature on the open-hole compressive properties of a carbon fiber composite

“…Using the artificial accelerated thermal-oxidative aging test method according to the T g of the unaged specimens, determined as described in “Dynamic mechanical analysis” section, 27,28 thermal-oxidative aging was conducted in a DHG-9140A electrothermal constant temperature blast drying oven (Shanghai Linpin Instrument Stock Co., Ltd, Shanghai, China) at 190°C for 40 days. The change in mass was determined by weighing every day with the ALC-210.4 analytical balance of Sartorius Scientific Instruments Co., Ltd (Beijing, China), and the mass-loss rate was then calculated by…”

Effects of hygrothermal and thermal-oxidative ageing on the open-hole properties of T800/high-temperature epoxy resin composites with different hole shapes

“…The substrate was oxidized to produce chemical ageing, and a large number of cracks were generated at the interface between the fibre and the matrix. 25 Oxygen entered the interior of the material through these cracks, which increased the contact area and accelerated the rate of thermal-oxidative ageing. 26…”

Effects of thermal–oxidative aging on the mechanical properties of open-hole T800 carbon fiber/high-temperature epoxy composites

“…23,28 At the aging temperature of 190°C, the interfacial debonding deteriorates with increasing aging time, voids appear between the fibers and matrix, and matrix cracking becomes extensive. 18,22,23 This may be because aging at 190°C has little effect on the fibers but leads to the matrix shrinkage; the variation of thermal expansion coefficients leads to shrinkage stress and interfacial damage. 29,30…”

“…The properties of composites subjected to thermal–oxidative aging have been studied extensively. Wang et al 18 investigated the properties of the benzoxazine/bismaleimide/cyanate ester copolymer subjected to thermal aging at 200°C and 250°C for 1000 h. They found that thermal oxidation and surface microcrack formation were the main results of thermal aging. Akay et al 19 studied the thermal aging of carbon fiber composites for 2000 h at temperatures of 210°C, 230°C, and 250°C.…”