Durable flame-retardant cellulose fiber, and yarns and fabric products thereof

A method for preparing a durable flame-retardant cellulose fiber, comprising:

• a. synthesis of a phosphorus-nitrogen composite flame retardant:
• mixing di-pentaerythritol (Di-PE) with an aqueous phosphoric acid solution and heating the mixture to 100-140 °C for 1-3 h, adding urea, further heating the mixture to 100-170 °C and stirring for 2-3 h, wherein a molar ratio of the Di-PE, the phosphoric acid, and the urea is 1:4:8, filtering a resulting precipitate, repeatedly washing the precipitate with anhydrous ethanol to remove impurities, drying the washed precipitate in an oven at 50-80 °C for 1-3 h, and pulverizing the dried precipitate to obtain a phosphorus-nitrogen composite flame retardant powder having a particle size of 300-1000 mesh;
• b. preparation of the durable flame-retardant cellulose fiber:
• dispersing the phosphorus-nitrogen composite flame retardant powder in distilled water to prepare a flame-retardant finishing solution having a solid content of 20-65%, adding dicyandiamide as a catalyst and urea as a promoter to the prepared solution, dissolving the mixture by heating in a water bath, wherein a weight of the dicyandiamide is 1-15% of an effective weight of the flame retardant, and a weight of the urea is 1-15% of the effective weight of the flame retardant, immersing cellulose fibers in the flame-retardant finishing solution for 1-30 min, removing excess solution using a nip roller to achieve a wet pickup of 50-150%, and baking the fibers at 120-200 °C for 1-15 min to obtain the durable flame-retardant cellulose fiber.