Study on the effect of urea-formaldehyde adhesive on the properties and microscopic characteristics of UF solidified foam

Urea-formaldehyde (UF) foam is extensively utilized in underground coal mine filling and sealing applications due to its low cost and exceptional internal flame retardant properties. However, its limited flexible functional groups result in poor toughness, a high pulverization rate, and low strength. For the above problems, this study employed urea formaldehyde adhesive as a binding agent to enhance the flexibility of UF resin and to improve the foaming process of UF foam. A novel type of UF solidified foam exhibiting superior toughness and a low pulverization rate was developed. The influence of the urea-formaldehyde adhesive on the UF solidified foam was assessed in terms of microstructure, pulverization rate, mechanical properties, and flame retardancy performance. The findings indicate that the urea formaldehyde adhesive completely melts within the UF system due to principles of similar miscibility, leading to an increase in system viscosity. This heightened viscosity restricts bubble growth, with some bubbles being inhibited during the nucleation stage, which subsequently results in a reduction in foam pore size and a decrease in the foaming ratio of the system. Additionally, the thickening of the bubble walls and the formation of crystals on these walls contribute to a decreased pulverization rate, alongside improvements in compressive strength and elastic modulus. The flammability tests indicate that the UF solidified foam incorporating urea-formaldehyde adhesive forms a dense carbon layer during combustion and releases inert gases such as CO2 and NH3, effectively inhibiting the progression of burning. The foam displays excellent flame retardant properties. When the urea formaldehyde addition is at 60 %, the overall performance is optimal, characterized by a more uniform pore size distribution, reduced pore diameter, and decreased porosity. The average pore diameter is 88.6 mu m, with a pulverization rate of 1.15 %. The compressive strength reaches 154 kPa, the elastic modulus is 1.77 MPa, the heat release rate is 10 kW/m2, and the total heat released upon flame extinction is 0.10 MJ/m2.