Abstract:

Objective As the most commonly used natural fiber textile, cotton fabrics are widely applied for various end uses because of their biodegradability, moisture absorption and breathability, softness and wide range of sources. However, cotton fabrics also display extremely flammable, hydrophilic and easily contaminated. In order to solve these problems and further improve the applicability of cotton fabrics in daily life, a simple two-step impregnation method is proposed in this paper to add flame retardancy and hydrophobicity to cotton fabrics.
Method Firstly, eugenol and phenyl dichlorophosphate were used to synthesize the bio-based flame retardant (DEP) by substitution reaction to prepare flame-retardant cotton fabrics. The phosphorus-containing substances in flame retardant can be decomposed in advance, catalyzing the dehydration of cotton fabrics into carbon and improve the thermal stability of cotton fabrics. Subsequently, zirconium based organometallic framework UiO-66 particles were modified with methyltrimethoxysilane to prepare the hydrophobic agent by simple surface modification, used for hydrophobic finishing of flame-retardant cotton fabrics. Low surface energy substances and micro-nano materials are combined on the surface of the fabrics to construct a micro-nano hydrophobic coating.
Results The structure, thermal stability, flame retardancy, hydrophobic capacity and antifouling property of the obtained flame retardant and hydrophobic cotton fabrics were characterized by scanning electron micro-scope (SEM), thermogravimetric analysis (TGA), vertical burning test, water contact angle (WCA) and droplet diagram, respectively. Furthermore, the flame retardant mechanism and hydrophobic mechanism were further investigated. The chemical structure of the product in the FT-IR spectra (Fig. 2) and ¹H NMR spectra (Fig. 3) both conform to the chemical structure of the flame retardant, demonstrating the successful synthesis of the flame retardant. The surface morphology of the treated cotton fabric and hydrophobic particles was observed by SEM, and the results showed that the flame retardant and hydrophobic agent were successfully and uniformly attached to the cotton fabric without destroying the original structure of the fabric and not affecting the normal morphology of the cotton fabric (Fig. 4). That the residual char content at 800 ℃ ranges from 1.7% of the raw cotton fabric to 8.6% of DEP3-UiO-66/MTM with an obvious char layer (Fig. 5), indicating that the thermal stability of the treated cotton fabric has been improved, which also reflect the enhancement of flame retardancy of the treated cotton fabric. This is mainly attributed to the flame retardant role played by phosphorus-containing flame retardants in the condensed phase. The LOI of pure cotton and DEP3 were 18.5% and and 26.5% (Tab. 2), respectively. The treated cotton fabric presented good char-forming ability after combustion (Fig. 6), and the introduction of DEP flame retardant coating effectively improves the flame retardancy of cotton fabric. In addition, the treated fabrics show good hydrophobicity. Among them, the WCA of DEP3-UiO-66/MTM is as high as 139° and the slide angle is 28° (Fig. 7). As can be seen from the droplet diagram of the treated cotton fabrics (Fig. 8), DEP3-UiO-66/MTM can withstand a variety of common stains in life such as ink, mud, coffee, milk, tea, acid (hydrochloric acid dyed with methyl red), alkali (sodium hydroxide solution dyed with thymolphthalein) and water droplets, and remain rounded on the surface of the treated cotton fabrics, showing excellent anti-fouling performance. The whiteness and bending length of the flame retardant hydrophobic fabrics were 83.89% and 21.0 cm (Tab. 3), respectively, which were not much different from those of pure cotton fabrics.
Conclusion The results confirm that the modified cotton fabric has good flame-retardant, hydrophobic and antifouling properties. The flame retardant hydrophobic composite coating is constructed via a simple, efficient, eco-friendly way using biomass as the raw material, which is green, environment-friendly and easy to operate. The prepared flame retardant hydrophobic multifunctional fabrics have broad application prospects in protective clothing, medical equipment, clothing, decoration and industrial buildings.

Key words: eugenol, flame retardant, hydrophobic, bio-based flame retardant agent, phosphorus-containing compound, cotton fabric, functional textile