Preparation and properties of a polyvinyl alcohol toughened urea-formaldehyde foam for thermal insulation applications

•PVA has a significant effect on improving the toughness of UF foam.•Cell shape was seen to be elongated in the rise direction with the addition of PVA.•Release of HCNO, CO2, NH3 was detected in the gaseous product of PVA modified UF foam during pyrolysis. Urea-formaldehyde (UF) foam exhibits excellent flame-retardant properties and low thermal conductivity. These properties make it suitable for thermal insulation in buildings. However, the brittleness of this material is its biggest disadvantage. In this study, polyvinyl alcohol (PVA) was used to improve the toughness of UF foam. The effect of the amount of PVA addition on the properties of the UF foam, such as the apparent densities, foaming ratio, compression strength, microstructure, fragility, limited oxygen index and thermal conductivity, were studied. The best performance was obtained for PVA modified UF foam with 1.5wt.% added PVA. The pyrolysis characteristics of the 1.5wt.% PVA modified UF foam were investigated using thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. Emissions of CO2, ammonia and isocyanic acid were identified during pyrolysis. By comparing the combustion and pyrolysis derivative thermogravimetry (DTG) curves, the effects of the presence of oxygen on the thermal decomposition were observed.