Construction of durable flame-retardant and robust superhydrophobic coatings on cotton fabrics for water-oil separation application

A flame-retardant and superhydrophobic coating was deposited on cotton fabrics using a simple two-step spraying method. In detailed, the first step involved flame-retardant layer consisted of alkylammonium functional silsesquioxane (A-POSS)/phytic acid (PA) complex, while the second step generated superhydrophobic layer that was composed of hierarchical structured titanium oxide@polydimethylsiloxane (TiO₂@PDMS) composite. The influence of the components’ loading in the coating on flame-retardant, thermal and wetting properties of the coated cotton fabrics was investigated systematically. The optimized coated cotton sample denoted as C3-PDMS-TiO₂ was screened through limiting oxygen index (LOI), UL-94 flammability test, cone calorimetry measurement and water contact angle (WCA). Specifically, C3-PDMS-TiO₂ sample showed self-extinguishing behavior in the vertical burning test, as well as a significantly enhanced LOI to 29% from 18% for pristine cotton fabrics. Furthermore, the peak heat release rate (PHRR) and the total heat release (THR) values of C3-PDMS-TiO₂ were significantly declined by 70% and 41%, respectively, compared to those of pristine cotton fabrics. Additionally, C3-PDMS-TiO₂ exhibited super self-cleaning ability as a consequence of its superhydrophobic surface. Furthermore, C3-PDMS-TiO₂ was applied for water-oil separation, and exhibited robust ability even in strong acid- or alkali-oil mixtures. The C3-PDMS-TiO₂ fabrics also displayed super abrasion resistance (WCA > 139° after 50 abrasion cycles) and washing durability (self-extinguishing after 5 laundering cycles). This facile finishing technique has great potentials in application as multifunctional advanced textiles.