Preparation and thermal stability of heat-resistant phenolic resin system constructed by multiple heat-resistant compositions containing boron and silicon

This work reports a boron- and silicon-containing phenolic-formaldehyde (PF) resin exhibiting an extremely high thermal decomposition temperature and char yield and formed by copolymerizing phenol, formaldehyde, boric acid (BA), and phenyltriethoxysilane (PTES). The structure of BA and PTES-modified PF (BSPF) resin was characterized by Fourier transform infrared spectroscopy. Thermal stability of the investigated composites was estimated by means of thermogravimetric analysis (TGA). The results of TGA indicated that the modified resin exhibited excellent thermal stability. Specifically, the thermoset had a char yield of 77.0% when the boron and silicon contents were only 1.27 wt% and 1.7 wt%, respectively. Compared with the unmodified resin (PF), the temperature at the maximum decomposing rate of the BSPF increased by 84°C and its charring yield was enhanced by 15.0%. The cured products of PF and BSPF were further investigated by X-ray diffraction and Raman spectroscopy, respectively. The incorporation of boron and silicon into the carbon lattice results in a decrease of interlayer spacing, and Raman I D / I G values for PF and BSPF (2.63 and 1.32) show that the rearrangement of crystalline structure leads to an increase in graphite structure and a decrease in disordered structure upon the modification processes.