Enhancing mechanical, thermal property and flame retardancy of optical polythiourethane with self-assembly phosphazene nanoparticles

Polythiourethane (PTU) has attracted considerable attention in engineering building materials. Here, based on phosphazene nanoparticles (PZS-1 and PZS-2) prepared by water-triggered and ultrasonic self-assembly method, phosphazene/polythiourethane (PZS/PTU) composites with excellent mechanical strength, high flame retardancy and good transparency was obtained. Then, the comprehensive properties of both composites were evaluated, where PZS-2 endowed PTU with better overall performance. Due to the good dispersibility of PZS and its strengthed interfacial interaction with PTU matrix, both PZS significantly enhanced mechanical and thermal property of PTU, where the tensile strength and glass transition temperature of PZS/PTU composites reached to 84.34 MPa and 59.94 degrees C respectively. More importantly, compared to pure PTU, the values of peak heat release rate (HRR), total heat release rate (THR), smoke production rate (SPR), and total smoke production (TSP) of composites were decreased by 10.5%, 13.3%, 30.6% and 18.0%, respectively. The limiting oxygen index of composites was improved to 21.39% due to the catalytic carbonization of PZS, the expanded carbon layer and the incombustible gases released during combustion. Meanwhile, the PZS/PTU composite exhibited the high refractive index of 1.6580 and good transparency (not less than 85% at 500 nm). The PZS/PTU composite was promising candidates for optical flame retardant coatings and engineering building materials.