Flame-retardant coatings with ultraviolet resistance by doping KH-560 modified nano-silica into Na2SiO3/NaOH-activated copper tailings geopolymer

Abstract

Copper tailings (CTs) are the industrial waste that causes resource wastage and pollution issues; recycling approaches of CTs remain challenging and are worth exploring. Herein, the Na2SiO3/NaOH-activated CTs geopolymer coating is prepared by doping melamine polyphosphate (MPP), aluminum diethyl phosphate (ADP), and nano-silica modified by silane coupling agent KH-560 (KH-560@nano-silica). The flame retardancy and ultraviolet (UV) aging resistance of the coating are evaluated through various techniques. Cone calorimeter results indicate that 4 wt% KH-560@nano-silica reduces the peak heat release rate from 84.84 to 43.98 kW·m−2 and increases the flame retardancy index from 1.00 to 6.60. Moreover, 4 wt% KH-560@nano-silica diminishes the degree of decline in flame retardancy of the coating after UV aging by 63.02 %. Thermogravimetric analysis shows that 4 wt% KH-560@nano-silica increases the temperature of 5 % weight loss and 30 % weight loss of the coatings by 42.93 % and 60.99 %, respectively. Furthermore, microscopic analysis indicates that nano-silica and the catalytic charring of CTs and flame retardants contribute to forming dense and continuous residue. According to a three-dimensional diffusion model, the activation energy (Eα) increases from 154.69 to 171.94 kJ·mol−1 at 717 ∼ 987°C. Meanwhile, the coating exhibits a formaldehyde adsorption rate of 61.79 %. In conclusion, this study expands the application scope of inorganic geopolymers in the flame-retardant industry, offering a new strategy for the high-value recovery and utilization of CTs.