Thermal degradation pathways in multi-component epoxy composites

In this study, the thermal degradation behavior of epoxy composites formulates with a bisphenol A (BPA) and bisphenol F (BPF) resin blend, a reactive alkyl glycidyl ether diluent, and quartz filler, cured with a cycloaliphatic amine hardener was investigated. Thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (py-GC-MS) were employed to explore the degradation pathways and identify the key pyrolyzates. The results revealed that BPA and BPF degrade through distinct but interrelated mechanisms, producing major pyrolyzates such as phenol, BPA, and xanthene. The reactive diluent significantly influenced the pyrolysis profile by introducing unique long-chain hydrocarbons, alcohols, and ethers because of its incomplete incorporation into the polymer matrix. Despite its inert nature, the quartz filler reduced the abundance of pyrolyzates and increased the residual mass, improving the thermal stability of the composite without altering the degradation pathways. This study highlights the complex interplay between resin chemistry, reactive diluents, and fillers in determining thermal behavior. These insights are essential for optimising epoxy composite formulations to enhance their thermal stability and durability for high-performance applications. • Thermal degradation products of epoxy composites are determined by Py-GC-MS. • BPA and phenolic compounds are pyrolysis products derived from epoxy resin. • C6-C16 hydrocarbons and alcohols are pyrolysis products from reactive diluent. • Quartz sand increased thermal stability and reduced pyrolyzates formation.