Rigid polyurethane foam (RPUF) composites with triphenyl phosphate (TPhP), aluminum trihydrate (ATH), and zinc borate (ZnB) alone, as well as their binary blends, were prepared via a one-shot process. The amount of flame retardant (FR) or FR blend was varied from 10 to 50% by polyol weight percentage, and the weight fraction of the blends was also fixed at 40%. The effects of additives on thermal insulation, mechanical, and flame retardancy properties of the composites were investigated. Thermal conductivity of the neat foam (RPUF) decreased from 22.53 to 21.04-21.58 mW m −1 K −1 . The compressive strength of foams displayed an increase with increasing the amount of TPhP, ATH, and ZnB till 40% by weight. The limited oxygen index values of all foams increased and the flame spread rates of all foams significantly decreased. It was also observed that the flame was self-extinguished in some cases. The cone calorimeter test results indicated that the FR additives improved the flame retardancy of the RPUF. INDTRODUCTIONRigid polyurethane foams (RPUFs) are one of the most consumed polymeric materials to a great extent. They have wide range applications in insulation, transportation, building construction, domestic appliance, automobile industry, and many others because of their high closed-cell content, low thermal conductivity, high strength with low weight, good shock absorption, and so on. 1-3 Nowadays, humanity is under threat because of limited energy resources in the world. In that case, RPUFs possessing low thermal conductivity values come into prominence because RPUFs are one of the unique materials for thermal insulation. RPUFs predominantly contain closed-cell structures, and in the closed-cell structures of foams, a blowing agent constituting the gas is trapped during production. The thermal conductivity of an RPUF is strongly affected by this blowing agent. The lower thermal conductivity of the blowing agent causes the lower thermal conductivity of RPUF. 4,5 When RPUFs compare with the conventional thermal insulating materials such as brick, concrete, wood, glass fiber, and so on, the conventional materials need to be used at much higher thickness in an attempt to match the insulation performance of 50 mm RPUF, for instance, ranging from 1720 mm for brick, 200 mm for wood, and 80 mm for polystyrene. The excellent thermal insulation property of RPUFs is not the only parameter making RPUFs one of the most used engineering materials but also their high mechanical strength with low weight and their easy processability make it as an interesting material. 6,7 For example, RPUF is one of the most important structural element of the refrigerators' skeleton besides providing high insulation for home refrigerators.However, as in the case of a majority of polymeric materials, RPUF is also easily combustible. As a matter of fact that, it is more combustible than other materials because of its rigid cellular and organic structure, additionally, it contains flammable, explosive gases in its closed cells. During the burnin...

The use of flame retardants (FRs) to improve the flame retardancy but also having good insulation and mechanical properties of rigid polyurethane foam (RPUF) has become significant due to the increasing demand in both the industry and academia. In the present study, a series of RPUF composites containing expandable graphite (EG), ammonium pentaborate (APB) octahydrate, and their binary blends were prepared with one‐shot and free‐rise methods. The effects of FRs on the FR and physical‐mechanical properties of RPUFs were investigated. The results show that both EG and APB could improve the flame retardancy of RPUFs and reduced the smoke production. The FR effect of EG was better than APB and more importantly, synergistic effect was found between EG and APB. The best results were obtained by the foam in the composition of 15E and 5A. The cone calorimeter test results showed that the peak heat release rate (pHRR) and total smoke release (THR) of 15E/5A foam were lower than the foams of 20E and 20A. The pHRR and THR values of 15E/5A foam decreased about 57.5% and 42.8% compared to the neat RPUF, respectively. Total smoke production (m2) also reduced about 77.0% by 20E and 83.6% by 15E/5A foams. Thermogravimetric analysis indicates that the char residue of 15E/5A foam increased to 39.5%, which provided better flame retardancy. The foam composites have high compressive strength (105‐150 kPa) and low thermal conductivity values (19.9‐21.3 mW/mK). While the thermal conductivity of 15E/5A foam increased by 0.5%, its compressive strength increased by 6.1%.

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