Heating De-fluorination derived radicals promoted interfacial grafting and enhanced Kevlar/Bismaleimide composites

Lack of stable, active reacting centers of fiber with bismaleimide (BMI) resin severely limited interfacial properties of composites. In this article, we found defluorination derived radicals under high temperature was able to participate into BMI resin curing reaction. X-ray Photoelectron Spectroscopy (XPS), In-situ Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis-Fourier Transform Infrared Spectroscopy-Gas Chromatography/Mass (TGA-GC/MS) Spectrometry hyphenated testing results of model molecules revealed decomposition process of fluorinated layer, and in-situ Electron Paramagnetic Resonance (EPR) captured alkyl radicals from defluorination. According to Differential Scanning Calorimeter results, above radicals were able to promote curing of BMI resin via radical coupling, which meant definite covalent combination between fluorinated aramid fiber and BMI matrix. Therefore, composite interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) simultaneously enhanced by 41.93% and 31.44% at maximum, respectively. Consequently, flexural properties of laminates also increased where flexural strength and flexural modulus respectively improved by 26.29% and 35.24%.