Preparation and application of epoxy resin derived from protocatechuic acid

The brittleness of epoxy resin needs toughening to meet the application requirements. Protocatechuic acid epoxy resin (PA-EP) was synthesized from protocatechuic acid (PA) and epichlorohydrin via two-step reaction, and used as special epoxy resin for the modification of bisphenol A epoxy resin. The structure and properties of the PA-EP were characterized by fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance spectroscopy (1HNMR), potentiometric titration and viscosity tester. FTIR, 1HNMR and viscosity analyses indicate that the target product was synthesized with epoxy value of 0.73 eq/100 g and viscosity of 43.2 Pa·s at 25℃. The mechanical properties show that the mechanical properties of PA-EP/E-51 thermosets are better than others when the mass ratio of PA-EP to E-51 is 10%. The tensile strength, flexural strength and impact strength are increased by 37.4%, 17.2% and 82.9% respectively. The scanning electron microscope (SEM) images of impact section show that PA-EP/E-51 thermosets exhibit ductile fracture characteristics. Dynamic mechanical analysis (DMA) and thermogravimetry (TG) results indicate that the glass transition temperature (Tg) increases from 116.0℃ (neat E-51) to 137.3℃ with 12.5% of PA-EP. The weight loss 10% and the maximum decomposition rate temperature are decreased slightly while the residue content of 800℃ increases from 5.9% (neat E-51) to 9.8% with 12.5% of PA-EP.