Latent Curing Agent of Epoxy Resin Based on Bio-Benzoxazine

A bio-based benzoxazine (V-fa) was synthesized from furfuramine, vanillin and paraformaldehyde. Its chemical structure was characterized by Fourier-transformed Infrared spectra (FT-IR) and ¹H-Nuclear Magnetic Resonance (¹H-NMR) spectra. Results show that this new benzoxazine monomer is synthesized successfully. Dicyclopentadiene-phenol epoxy resin (DCPD-ER) was selected as a research object. V-fa was added into DCPD-ER in different proportions as a latent curing agent. At the same time, a usual curing agent, diaminodiphenylmethane (DDM), was also used as a comparative study. The curing reaction of the resin system was studied by Differential Scanning Calorimetry (DSC) and FT-IR spectra. Compared with DCPD-ER/DDM, DCPD-ER/V-fa has a higher initial curing reaction temperature and curing reaction activation energy. DCPD-ER/V-fa can cure at a high temperature, which is attributed to the reaction between phenolic hydroxyl groups produced by ring-opening reaction of the benzoxazine and epoxy groups. In addition, the thermal properties of the cured products were investigated by Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). The addition of V-fa can improve the heat resistance and thermal stability of the resin system. The glass transition temperature (T_g), initial decomposition temperature and char yield under nitrogen at 800 ^oC (Y_c) of DCPD-ER/V-fa are higher than those of DCPD-ER/DDM, and the T_g and Y_c can reach as high as 192 ^oC and 44%, respectively. Moreover, the flame retardancy of DCPD-ER/V-fa was evaluated on the basis of the results from TGA measurements. The limiting oxygen index (LOI) of DCPD-ER/V-fa can reach as high as 35.1, suggesting that the addition of V-fa improves the flame retardancy of the epoxy resin.