Facile preparation of magnolol-based epoxy resin with intrinsic flame retardancy, high rigidity and hydrophobicity

During this research, a magnolol-based epoxy monomer (MDE) is successfully synthesized by a facile two-step method containing methodnucleophilic substitution reaction and Prilezhaev epoxidationa at 20–30 °C fro m magnolol extracted from magnolia officinalis (Magnolia officinalis Rehd.Et Wils). Subsequently, MDE and bisphenol A diglycidyl ether (trade name E44) are cured with 4,4′-methylenedianiline (DDM), respectively. The cured MDE (MDE/DDM) self-extinguishes within 1 s after each ignition for 10 s and easily passes a V-0 rating of UL-94 and possesses a value of limiting oxygen index (LOI) reaching 44.9%. Compared with E44/DDM, the peak heat release rate (pHRR) and total heat release (THR) of MDE/DDM decrease by 65.4% and 59.2%, respectively. Storage modulus (E′) of MDE/DDM are 43.9% higher than that of the cured E44 (E44/DDM). The characterization of epoxy resins, such as thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), thermogravimetric/infrared spectrometry (TG-IR), raman spectra, and scanning electron microscope (SEM) indicates that rich biphenyl structure and phosphorus-containing group play a crucial part in promoting the formation of char layers, NH3, and H2O, which help flame retardancy and hydrophobicity. This work provides a thought to develop a new type, sustainable, flame retardant, and hydrophobic bio-based epoxy resin.