New modification strategy for thermoplastic polyurethane with high hygrothermal ageing resistance and flame retardancy

Thermoplastic polyurethane (TPU) has been extensively used in many industrial communities, such as aerospace, electronics, and automotive manufacturing due to its remarkable mechanical strength, elasticity, and excellent chemical resistance. However, flammability and performance deterioration under high-temperature and high-humidity of TPU greatly limit its wider application. Herein, TPU composites with high hygrothermal ageing resistance and flame retardancy are prepared by introducing a molecularly engineered fluorinated thermoplastic polyurethane (FTPU) and synergistic flame retardant. The results show that the presence of FTPU greatly enhances the hydrophobicity of the matrix, impeding the diffusion of the water molecules into the composite, and alleviating the decrease of glass transition temperature and the rise of loss factor resulted from water plasticization effect. As a result, the TPU/FTPU composite shows a much higher mechanical property retention rate after immersing in water of 80 °C for 7 days, as compared to the pristine TPU. In addition, FTPU also exhibits synergistic effect with aluminum diethylphosphinate (ADP) and melamine cyanurate (MCA). The composite containing FTPU, ADP, and MCA (8 %, 4.5 %, and 4.5 %, respectively) can meet UL94 V-0 flame-retardant standard while the counterpart without FTPU shows UL94 V-2 flame retardancy. At the same time, such composite still exhibits tensile strength retention rate of 84.3 % after hygrothermal ageing treatment. This work provides a new modification strategy to simultaneously improve the hygrothermal ageing resistance and flame retardancy of TPU, which also can hopefully inspire the design of other polymers for high performance purpose.