Preparation and performance of unidirectional moisture-wicking and flame-retardant cotton fabric

[Objective] Cotton fabric is one of the most widely used textile materials due to its skin-friendly softness, excellent moisture absorption, and breathability.However, its low limiting oxygen index(LOI)of only approximately 18% makes it highly flammable, posing a significant fire hazard.Additionally, cotton exhibits slow moisture release, which can leave the wearer with a clammy and cold sensation after sweating.To address the issues of flammability and slow moisture dissipation, this study focuses on developing flame-retardant cotton fabrics with unidirectional moisture transport, aiming to meet the dual requirements of fire safety and wearing comfort.[Methods] A flame-retardant coating was applied to the outer side of cotton fabric using a one-step blade coating method with a polyelectrolyte complex PPM formed from phosphorous acid(PA)-protonated hyperbranched polyethyleneimine(h-PEI)and montmorillonite(MMT).The inner side was printed with a hydrophobic paste via screen printing to achieve unidirectional moisture transport.The performance of the fabric was systematically investigated, with its wettability, moisture management, flame retardancy, and combustion behavior being evaluated using a contact angle meter, moisture management tester, vertical burning apparatus, and cone calorimeter, respectively.[Results] The test results indicated that a uniform flame-retardant coating was constructed on the outer side of the cotton fabric via a simple blade-coating method, while a hydrophobic layer was created on the inner side using screen printing.The evenly distributed small circular pores provided channels for moisture transport.The inner hydrophobic printed layer endowed the treated cotton fabric with an asymmetric wettability profile:hydrophilic on the outer side(initial contact angle of 63.0°)and hydrophobic on the inner side(initial contact angle of 96.0°).This asymmetric structure enabled the fabric to exhibit unidirectional moisture transport capability.When water droplets were applied to the hydrophobic inner surface, moisture was directionally transported to the outer side without back-permeation.Conversely, when water was applied to the hydrophilic outer surface, it spread on that side, keeping the inner surface dry.The hydrostatic pressure for water penetration from the inner side to the outer side was 23.5 mmH2O(1 mmH2O=9.81 Pa), whereas it was 103.0 mmH2O for the reverse direction.The treated cotton fabric exhibited a one-way transport index(OWTI)of 487.2 and a reverse transport index(RTTI)of -622.8.The outer flame-retardant PPM layer rendered the treated cotton fabric self-extinguishing upon removal from the flame, with a char length of 31 mm.Compared with the untreated cotton fabric, the time to ignition(TTI)of the treated cotton fabric was extended from 35 s to 45 s, providing more time for fire response and escape.The peak heat release rate(PHRR)and total heat release(THR)of the treated cotton fabric decreased by 12.1% and 6.4%, respectively.The residual char rate after combustion increased from 4.2% for the untreated cotton fabric to 16.0% for the treated cotton fabric.The fire growth rate index(FIGRA)of the untreated cotton fabric was 2.3 kW/(m2·s), which was reduced to 1.7 kW/(m2·s)for the treated cotton fabric.This significant reduction demonstrates the coating's effectiveness in suppressing flame spread during combustion and effectively mitigating the fire risk associated with cotton fabrics.[Conclusion] The results demonstrate that the hydrophobic printed layer imparts excellent unidirectional moisture transport functionality to the cotton fabric.This ensures that during perspiration, sweat is rapidly transferred to the fabric's outer layer, keeping the skin dry.Simultaneously, the PPM coating effectively suppresses heat release and catalyzes char formation, thereby imparting excellent flame retardancy to the treated cotton fabric.By utilizing this straightforward one-step blade-coating and screen-printing process, a cotton fabric integrating both fire safety and moisture comfort has been successfully produced.This fabric holds considerable promise for applications in industrial protective clothing, including firefighting apparel and thermal insulation textiles in industrial settings.