چكيده به لاتين
Thermoplastic Polyurethane (TPU) is an efficient engineering plastic in various industries with excellent properties, such as abrasion resistance, aging and chemical resistance, high tensile strength, high compressive resistance, and good processability. However, its high flammblity with producing large amounts of heat, smoke and toxic gases and high melt dripping during combustion, limits its many applications. Therefore, improving the fire performance of TPU by flame retardants, while maintaining its good properties, is one of the research topics especially in the last two decades. Previous studies have confirmed the high efficiency of phosphorus-containing intumescent flame retardants (IFR) in TPU. Despite this, it has been stated that high loadings of IFR needed to achieve good flame retardancy, can decrease the flame retardant efficiency or thermo-mechanical properties. In addition, the preparation of flame retardant TPU with reduced heat and toxic smoke during combustion and simultaneously anti-dripping, while maintaining thermo-mechanical properties, remains a challenge in the field of fire safety of TPU. On the other hand, some flame retardant materials require complex and expensive synthesis methods. According to the above, in this research, with the aim of achieving excellent flame retardant properties, suppressing the smoke-toxicity, and anti-dripping during TPU burning, in the first stage, TPU composites, by adding three-component IFR system, including ammonium polyphosphate (APP), melamine polyphosphate (MPP), and pentaerythritol (PER) with different components ratios were prepared by melt mixing and their fire performance was evaluated by flammability and cone calorimeter tests to achieve the highest flame retardant efficiency. In the second step, TPU nanocomposites were prepared by adding three nanostructures, namely nanosilica, graphene and molybdenum disulfide in very low loadings (up to 1 wt.%) to the TPU/IFR composites, and their fire performance was evaluated to investigating the synergistic effects of IFR/Nanoadditives on the fire reaction properties of TPU. The influence of these flame retardants on the thermal stability and mechanical properties of TPU were analyzed. In order to predict the flame retardancy mechanism, the structure of the char after combustion and elemental analysis were investigated using a scanning electron microscope (SEM) and EDS. The results showed that the used IFR system, in addition to the high flame retardant efficiency, showed excellent smoke and toxic gas suppression, retarded dripping and improved thermal stability, by creating an intumescent char. Adding nanomaterial showed a good synergy with the IFR and efficient flame retardancy. Besides, excellent smoke-toxicity suppression and anti-dripping were achieved by the compact char formation as an effective protective layer to prevent the heat and oxygen penetration into the underlying polymer. According to the EDS analysis, the flame retardant mechanism in most TPU composites primarily took place in the condensed phase. However, in the case of TPU/IFR/0.5%Graphene, it occurred in both the gas and condensed phases. The flame retardants had varying effects on the mechanical properties of TPU composites, with certain nanocomposites showing an increase in ductility compared to the neat TPU. The employed IFR system and the nanostructures mentioned in this study, which improved the fire performance of TPU, had not been investigated before. These findings can serve as a useful reference for the development of flame retardant TPU composites, aiming to enhancing the fire safety of TPU and broadening its applications.
