Abstract:

Objective Owing to its excellent biocompatibility, dyeing, softness, thermal and wet comfort, cotton fiber has been widely used in various fields, such as home textiles, clothing and industrial textiles. However, the limiting oxygen index of cotton fiber is about 18 and thus it is a combustible and flammable fiber. Doping flame-retardant in cotton fiber can improve its flame retardance. Treating cotton fabrics with nitrogen series, phosphorus series, boron series or silicon series alone would improve the flame resistance, but its effect is not satisfactory, and the cost is high. This research aims to achieve synergistic improvement in flame retardance by treating the cotton fabric with these flame retardants together.

Method Polyethyleneimine (PEI), phytic acid (PA) and nano-silica (SiO₂) were used as raw materials to construct a P/N/Si-modified composite for synergistic improvement in the flame retardancy. The surface morphology, thermal stability, heat release property, flame retardant property and flame-retardant mechanism of the treated cotton fabric were analyzed by scanning electron microscopy (SEM), vertical combustion test, limiting oxygen index test, thermogravimetric analysis, microcalorimetry and smoke density.

Results According to the FT-IR spectra and SEM image, N, P and Si elements exist on the fiber surface of PEI/PA/SiO₂-modified cotton fabric. The initial degradation temperature (T_5%) of PEI/PA/SiO₂-modified cotton fabric was 97 ℃, and the decomposition rate reached a maximum at 288 ℃. Compared with raw cotton fabric, the initial degradation temperature was significantly reduced, and the char residue content increased to 38.54%, indicating that the composite flame retardant can successfully slow down the thermal decomposition of cotton fabric. The subsequent burning time, smoldering time and damage length of PEI/PA/SiO₂-modified cotton fibers were significantly reduced, and the LOI values reached 30.3%. This indicates that the synergistic flame retardancy of PEI, PA and SiO₂, in which the respective attributes are integrated, can improve the flame retardancy of the fabric. The prepared fabric satisfied the related standard. Compared with pure cotton fabric, peak heat release rate (pHRR), heat release capacity (HRC) and total heat release (THR) of PEI/PA/SiO₂-modified cotton fabric decreased by 84.2%, 85.0% and 83.3%, respectively, indicating it has high carbon formation efficiency and low the volume of gas generation in the thermal decomposition process. The smoke production of PEI/PA/SiO₂-modified cotton fiber was decreased and stable, which can effectively reduce the possibility of suffocation death in the fire. The smoke release of PEI/PA/SiO₂-modified cotton fabric was the least and the most stable among all samples, which indicates that PEI/PA/SiO₂-modified cotton fabric can not only effectively improve the flame-retardant performance of cotton fabric, but also reduce the release rate and release amount of smoke during the combustion process. Compared with the raw cotton fiber, the warp breaking strength and weft breaking strength of PEI/PA/SiO₂-modified cotton fabric decreased by 14.8% and 14.1%, respectively.

Conclusion The results showed that PEI/PA/SiO₂-modified cotton fabric can promote the catalytic carbon formation of cotton fiber at low temperature, reduce the amount of smoke release, and form a highly graphitized carbon layer on the fiber surface to isolate the contact between combustible gas and fiber, and thus achieve satisfactory flame retardant effect. PEI/PA/SiO₂-modified cotton fabric shows significantly better flame retardance performance than PEI, PA or PEI/PA-modified samples and meets the standard of decorative fabric flame retardant B1 requirements. Besides, PEI/PA/SiO₂-modified cotton fabric also improves the mechanical properties of cotton fabric by decreasing the damage of strong acidity from PA.

Key words: cotton fabric, flame retardancy, spraying method, composite synergistic effect, carbonization at low temperature, flame retardant mechanism