As shown in Fig. 6, the weight loss of modified PURFs at 800 °C was greatly affected by mass fractions of PEPA and CaCO3. When 4% mass fraction of PEPA was added, PEPA/CaCO3/PURFs with either 3% or 6% mass fraction of CaCO3 showed big weight loss peaks at 650 °C, and more CaCO3 resulted in bigger weight loss peak. However, the weight loss behavior of PEPA/CaCO3/PURFs with 6% mass fraction of PEPA was close to that of PEPA modified PU, with slightly weight loss at 650 °C.
We suppose that when 4% mass fraction of PEPA loaded in PEPA/CaCO3/PURFs, phosphorus acid generated by the decomposition of PEPA was more likely to react with CaCO3 than to catalyze the decomposition of PURF. Therefore the weight loss of this sample is nearly the same as that of pure PU. By contrast, when PEPA loaded 6% mass fraction and above, after phosphoric acid is consumed by CaCO3, there were still abundant of phosphorus acid left to accelerate the decomposition of PURF.
3.2.2. The degradation of PEPA/CaCO3/PURFs in N2 and air environment
The anti-oxidation effect of PEPA/CaCO3/PURF was studied by TGA in N2 and air environment, the results were given in Fig. 7. The formula of PEPA/CaCO3/PURF was 8 wt% PEPA and 6 wt% CaCO3 added to 100 wt% PU.