PURF was prepared by mixing PAPI with polyols. After a few seconds the mixture foamed rapidly to form PURF. Then the foam was kept at 50 °C for 4 h.
PURFs modified with PEPA and/or CaCO3 were prepared as follows. First, PEPA and/or CaCO3 were dispersed in polyols by ultrasonication for 4 h, and then PAPI was added to the above mixture to form PURFs in a few seconds. Finally the as-formed modified PURFs were kept at 50 °C for 4 h.