The synthesis and characterization of a novel flame retardant containing rigid polyurethane foam

Abstract

Rigid polyurethane foams are one of the most preferred thermal insulation materials due to their excellent thermal insulation properties, mechanical strength, lightness, and applicability. They are used in various fields from household appliances to pipes, cladding, and insulated panels, and are commonly encountered in daily life. However, these materials pose a risk to human life and health due to their weak characteristic of being easily flammable and capable of intensifying fires. This risk has created a need for flame retardant materials. Flame retardants are added to polyurethane to prevent the flames from rapidly intensifying in the event of a fire, providing people with an escape time. Traditional flame retardants contained halogens such as bromine and chlorine, but their use has been restricted due to the release of toxic gases during a fire. As a result, there has been a need for alternative flame retardants with different chemical structures. Currently, commonly used flame retardants include phosphorus-based compounds such as tris(2-chloroethyl) phosphate and triphenyl phosphate; phosphonates such as dimethyl propyl phosphonate; ammonium polyphosphate (APP) and DOPO derivatives like phosphaphenanthrene oxide; nitrogen-based compounds such as melamine, melamine cyanurate, and melamine polyphosphate; polymeric silicone derivatives; and inorganic flame retardants like magnesium hydroxide and aluminum trihydroxide. This thesis was carried out in two stages: the synthesis of a flame retardant containing fluorine and nitrogen, and the addition of the flame retardant to rigid polyurethane foam. The synthesis process was carried out in three stages, successfully synthesizing a fluorine-containing, hydroxyl-terminated compound with a triazole structure through a copper-catalyzed azide-alkyne cycloaddition reaction, an example of click chemistry. Techniques such as fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies were used to elucidate the structural properties of the resulting compound. The flame retardant, incorporated into the rigid polyurethane formulation by mechanically mixing in various percentages, was aimed to react with isocyanates, through its OH groups as a polyol, which are the components of polyurethane, thus exhibiting chemical flame retardant functionality. Consequently, the structural properties of the RPUF samples were examined using techniques such as FTIR, thermal and flammability properties with cone calorimeter, limiting oxygen index (LOI), thermogravimetric analysis (TGA), and thermal conductivity meter, and morphological properties with scanning electron microscopy (SEM). The impact of the flame retardant on the mechanical properties was investigated through compression testing and foam density measurements of the RPUF samples. The hydrophobic contribution of the flame retardant to the foam samples due to its fluorine content was measured with a contact angle meter. All analyses were carried out on foam samples containing no flame retardant and those containing 5%, 10%, and 15% flame retardant. Test results show significant improvement in the flame retardancy of rigid polyurethane foam with enhanced LOI values and reduced peak heat release rates. Additionally, it was observed that the flame retardant successfully bonded chemically to the foam structure, did not deteriorate its mechanical properties and cell structure, maintained excellent thermal insulation, and increased contact angle values imparted hydrophobicity due to its fluorine content. This thesis demonstrates the potential of nitrogen and fluorine-containing flame retardants for providing superior fire protection, indicating that they are promising candidates for future applications in fire-resistant materials.