Preparation and properties of rigid polyurethane foam containing inorganic halogen-free flame retardant

Rigid polyurethane foams modified by complete inorganic halogen-free flame retardants were prepared by using ammonium polyphosphate (APP) as main flame retardant, expandable graphite (EG) and bentonite as flame retardant and filler, respectively. Under the condition of fixing the amount of inorganic flame retardants and filler, the effects of the amount and ratio of bentonite and EG on the mechanical property, flame retardancy, cell structure, and thermal stability of the foams were evaluated. The results show that, with increasing the content of bentonite or EG, the compression strength of the foams increases at first and then decreases. The maximal compression strength can be obtained when the contents of bentonite and EG are 10% and 5%, respectively. The limiting oxygen index (LOI) values of the PU foams show good improvement of flame retardancy by adding EG, however the cell diameter of the foams will be increased at the same time. The bentonite as a nucleating agent can significantly reduce the cell diameter. The thermogravimetric analysis (TGA) illustrates that the thermal stability of foams containing bentonite or EG is significantly enhanced. The best balance among the flame retardancy, mechanical properties and the pore size can be achieved for the polyurethane foams prepared with 15% APP, 5% bentonite and 5% EG. Under the optimum condition, the compressive strength of the foams is 0.42 MPa, cell diameter is about 434 μm and LOI value is about 29%. ©, 2014, Zhejiang University. All right reserved.