Grafted-IPN epoxy/polyurethane prepolymer; synthesis, morphological, mechanical, and thermal properties investigation of cured networks

Abstract

Epoxy resins (EP), known for their intriguing properties suffer from their inherent brittleness, resulting from a highly cross-linked structure. A NCO-terminated polyurethane prepolymer resin (PPU) synthesized and grafted onto EP to increase its mechanical and toughness properties. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the formation of EP/PPU grafted interpenetrating polymer network (g-IPN). Thermogravimetric Analysis (TGA), Dynamic Mechanical Thermal Analysis (DMTA), bending, and fracture tests were used to examine the sample's mechanical characteristics and thermal stability. The TGA test results showed that the presence of the PPU more than 10 phr resulted in only a slight reduction in initial thermal stability. The EP/PPU20 sample exhibits a slightly lower initial degradation temperature (T_d 10 % = 333 °C) than neat EP (T_d 10 % = 339 °C). Furthermore, EP/PPU samples exhibited lower glass transition temperature (T_g) than neat EP. When the PPU content was increased to 20 phr, fracture toughness improved by 138 % over neat EP. The composite morphology was also investigated using Scanning Electron Microscopy (SEM). The addition of PPU enhanced surface roughness in the EP/PPU samples, owing to the formation of the g-IPN. Notably, the EP/PPU10 sample had a slightly higher lap shear strength compared to the samples evaluated.