Improvements in the flame retardancy, smoke suppression, mechanical strength and thermal insulating properties of rigid polyurethane foams modified with DOPO-grafted cyclosiloxane and diatomite

With the continuous growth in demand for flame-retardant materials in the construction and insulation industries, flame-retardant modification of rigid polyurethane foam (RPUFs) has become critical for their safe application in scenarios such as building energy conservation, cold chain refrigeration, and pipeline insulation. However, the high loading levels of traditional flame retardants often result in reduced mechanical strength and/or increased thermal conductivity of RPUFs. To address this issue, this study aims to enhance the flame retardancy, smoke suppression performance, mechanical strength, and thermal insulation properties of RPUFs by synthesizing an organic flame retardant additive containing phosphorus and silicon (PSiFR) and blending it with diatomaceous earth into RPUFs, leveraging the synergistic effects of the two materials. The optimal formulation is RPUFs containing 9.6 wt% PSiFR and 0.4 wt% diatomaceous earth (RPUF-3). Specifically, the peak heat release rate, total heat release, and total smoke generation of RPUF-3 are 47.2 %, 40.6 %, and 27.0 % lower than those of unmodified RPUFs, respectively. Compared with the compressive strength of unmodified RPUF (6.12kN·m/kg), the compressive strength of RPUF-3 is increased to 6.72 kN·m/kg. And also, its thermal conductivity (0.044 W/(m·K)) shows a downward trend compared with that of unmodified RPUF (0.044 W/(m·K)). The synergistic addition of PSiFR and diatomite successfully achieved simultaneous improvements in the flame retardancy, smoke suppression capability, mechanical strength, and thermal insulation performance of RPUF. This method provides an efficient and feasible modification strategy for fields such as building energy conservation and cold chain refrigeration.