Bio-based phytic acid and urea interfacial layer by layer assembly for flame-retardant cotton

In this work, LBL technology is applied to prepare a bio-based flame- retardant coating (U@PA-Na) by a sequential assembly of positively charged urea (U) and negatively charged sodium phytate (PA-Na) solution in water medium. The U@PA-Na system possess the characters of safety, non-toxic, and high efficiency in flame retardant. The flame retardancy of U@PA-Na is evaluated by the cotton coated with U@PA-Na coatings (COT/ U@PA-Na) before and after washing treatment. The limiting oxygen index (LOI), vertical flame test (UL-94), and cone calorimeter test (CCT) composites are measured to evaluate the flame retardancy of COT/U@PA-Na. The LOI value of the COT/U@PA-Na3 composite after washing treatment can still reach 34.6% and pass UL-94 B1 grade, accompanied by damage length less than 150 mm and burning time less than 5s. It shows that U@PA-Na has excellent flame retardancy and water resistance. Cone calorimeter (CCT) measurements show that the peak heat release rate (PHRR) and total heat release (THR) of COT/U@PA-Na3 decreas by about 61% and 74% compared with untreated fabrics. The thermal decomposition time of the treated cotton fabric is significantly delayed, and the peak decomposition temperature (T1max) is reduced by about 62 degrees C, while the average residue is improved to about 21% at 650 degrees C. The image of the cone calorimetric burnt carbon slag shows that the carbon layer of cotton fabric treated by U@PA-Na is very dense, indicating that the synergistic effect of PA and U can promote the formation of a high-quality carbon layer which plays a "barrier effect" to protect the substrate and delay the combustion process. The flammability and forced combustion tests show that the bio-based U@PA-Na flame-retardant system with good washing resistance can significantly improve the flame retardancy of cotton fabric, greatly reducing the fire risk.