The effect of zirconium incorporation on the thermal stability and carbonized product of phenol-formaldehyde resin

A kind of zirconium modified phenolic resin (Zr-PF) was prepared by using phenol, paraformaldehyde, ZrOCl2·8H2O, acetylacetone, ethanol and H2O2 as raw materials. The structure of the Zr-PF was characterized by Fourier transform infrared (FT-IR) spectra and solution 13C nuclear magnetic resonance (13C NMR) spectra. The viscosity and thermal degradation behaviors of the Zr-PF were studied by rotary viscometer and thermogravimetric analyzer-differential scanning calorimetry (TG-DSC), respectively. The carbonized products of ordinary phenolic resin (PF) and Zr-PF were further investigated by X-ray diffraction (XRD), laser Raman spectroscopy (Raman) and scanning electron microscopy (SEM). Results show that new chemical bonds are formed through coordination reactions between zirconium atoms in Zr-OH and oxygen atoms in the acetylacetone and hydroxymethyl phenols. Viscosity of the Zr-PF is higher than that of PF during 30-80 °C. Compared with PF, thermal stability of the Zr-PF is obviously improved and its char yield is 55% at 1200 °C, 8% higher than that of PF. The d002 value of carbonized Zr-PF decreases from 0.3470 nm (carbonized PF) to 0.3329 nm and its crystallite height increases from 23.89 nm (carbonized PF) to 29.21 nm due to zirconium incorporation. In addition, the ID/(ID + IG) value of carbonized Zr-PF decreases from 0.571 (carbonized PF) to 0.364 and the crystallite size of it increases from 29.90 nm (carbonized PF) to 44.79 nm. The results prove that the incorporation of zirconium exhibits obvious effects on promoting its graphite crystallite. What is more, the morphology of the carbonized Zr-PF changes from poor structure with many pore defects into dense and uniform matrix with uniformly dispersed ZrC particles.