A novel, eco-friendly and durable flame-retardant cotton-based hyperbranched polyester derivative

A novel, formaldehyde-free, efficient and durable flame-retardant hyperbranched polyester derivative (HBPPN), containing nitrogen and phosphorus, was synthesized using a second-generation hyperbranched polyester, phosphorous acid and urea. The HBPPN was characterized by FT-IR and nuclear magnetic resonance spectroscopy. The FT-IR spectra indicated that the HBPPN may be grafted onto cotton by covalent bonds, modifying the degradation of the cotton. The flame-retardant properties of the HBPPN-treated cotton fabric were investigated based on vertical flammability, LOI, and cone calorimetry. The LOI value of 160 g/L HBPPN-treated cotton fabric was 39.6%, and the LOI value decreased to 27.3% after 50 laundering cycles, indicating the high durability of the cotton fabric treated with HBPPN. The vertical flammable tests showed that the cotton fabrics treated with HBPPN had short char lengths. The surface morphology of HBPPN-treated cotton fabrics was assessed using SEM. TGA demonstrated that the cotton fabrics treated with HBPPN easily formed char. Cone calorimetry indicated obviously lower values of PHRR and THR relative to those of the untreated cotton fabrics. XRD revealed that treatment with HBPPN did not substantially change the crystalline structure of the cotton. These results confirmed that HBPPN exhibited excellent flame retardancy and high durability. Graphic abstract