The effect of three flame retardants, K2CO3, Na2SiO3·9H2O, and Na2B4O7·10H2O on the process and composition of volatile products of the thermal degradation of wood has been investigated by the thermogravimetric (TG), differential thermogravimetry (DTG), differential thermal analysis (DTA), and the synchronous thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the ion current intensity and ion peak area of m/z = 18 and 44 MS signals were increased by the flame retardants but the ion peak area of m/z = 28 MS signal was decreased (except K2CO3) at the meantime. What's more, the ion current intensity and ion peak area of m/z = 60 and 68 MS signals were also decreased (except K2CO3), which mean that Na2B4O7 can significantly enhances the dehydration and inhibits the depolymerization of wood. Although K2CO3 accelerates the dehydration reaction, it cannot inhibit the depolymerization reaction effectively, so the flame retardant efficiency of K2CO3 is decreased with the higher concentration. The catalysis of dehydration reaction of Na2SiO3 is the worst one.
A flame-retardant wood was prepared using a series of insoluble molybdates through the double bath technique. The flame retardancy of the wood samples was studied with the limiting oxygen index (LOI) method. The relationships between the flame-retardant performance and the thermal property of wood were studied by the thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM), and the thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the insoluble molybdates, which were precipitated into the wood by the double bath technique, can obviously improve the flame retardancy of wood. Similarly, the transition metal molybdates showed higher flame-retardant efficiency than the main group metal molybdates do, which probably due to the thermal barrier effect that Fe2(MoO4)3 acts during the combustion of the samples. At the same time, Fe2(MoO4)3 catalyzed the dehydration and carbonization reactions of wood, and caused an increase in the amount of char produced, and an improvement of the stability of the char residue. Moreover, the mass spectrometry results indicated that the excess transition metal ions speed up the deep decomposition of the char residue, and resulting in the smoldering of wood.