**1. Introduction**

Cotton is a natural fiber in which cellulose represents the major component of its chemical structure.

Nowadays, cotton fabrics are widely used in our daily lives due to their remarkable combination of properties: soft to the touch, good moisture vapor transmission and good moisture absorbency [1]. However, being organic in nature, cotton fabrics and other cellulose-based fabrics pose considerable fire risks [2]. Therefore, the flame-retardant finishing of cotton fabrics is important as it is strongly related to the protection of human beings and textile substrates from fire hazards.

In this context, the assessment of the flammability of cotton substrates has been approached by applying suitable flame-retardant finishes that are able to suppress or delay the appearance of a flame or reduce the flame-spread rate [3]. These finishes are applied to textiles by using a variety of agents, including borax and boric acid mixture, nitrogen- and phosphorus-based chemicals, antimony and halogen based chemicals [4].

Coating technology is regarded as the most practical method to impart functional agents to textile substrates [5]. Based on the chemicals used in the coating formulations and also on the desired performance of the coated surfaces, various types of coating techniques are used in textile functionalization, the main types including pad coating, direct or knife coating, sol gel coating, digital coating, electrospining coating and combined coating [6].

The current textile coating market is dominated by the use of binding agents or binders to fix the chemicals forming the coating layer, which have no affinity for fibers [7].

Numerous chemicals are used as binders. However, in most of them, formaldehyde is used as a crosslinker to apply the resistant coatings that are required by many advanced applications [8]. Formaldehyde is a toxic and carcinogenic chemical that has come under survey [9,10]. In addition, binders can contain solvents that are used as carriers during the manufacturing process. These solvents end up in the environment through waste water and air [11–13]. The major challenge facing textile manufacturers developing coated

**Citation:** Zouari, R.; Gargoubi, S. Enhancing Flame Resistance of Cellulosic Fibers Using an Ecofriendly Coating. *Coatings* **2021**, *11*, 179. https://doi.org/10.3390/ coatings11020179

Academic Editor: Philippe Evon Received: 31 December 2020 Accepted: 28 January 2021 Published: 3 February 2021

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textiles is how to rapidly switch to safer chemicals and processes. Recent research on functional coatings on textiles has focused on the use of environmentally friendly technologies and chemicals [6]. In this context, plasma technology was reported as an ecofriendly coating technique.

Plasma is a partially ionized gas composed of various species, such as electrons, negative and positive ions, radicals, excited molecules, neutrals, and UV photons. These different species are useful for textile surface modification. The plasma gas reacts with a small non-polymerizing molecule to achieve surface activation, cleaning, oxidation, modification in surface energy, an increase in surface roughness and etching. Similarly, plasma reacts with a bigger molecule to achieve plasma polymerization, coating, deposition, and creation of nanostructures [14]. These altogether improve the functional value of the textile materials. For fire-retardant coatings, plasma is applied either as a pretreatment, to increase the uptake of flame-retardant chemicals; for graft polymerization of these chemicals; or as a post-treatment to form strong bindings [4]. This technology also has other advantages, such as leaving the characteristics of the textile bulk unaffected, working in the gas phase without the need for water use, reducing processing time and achieving energy saving [15].

The aim of this study was to combine plasma pretreatment and acrylic acid grafting on cotton fabric to enhance the attachment of acrylate phosphate in order to obtain fireretardant cotton fabric. The acrylic acid finish on cotton highlights a formaldehyde-free route for achieving surface modification of cotton, with high scope for incorporation of much improved physical and mechanical properties [16]. The combination of physical and chemical surface treatments was expected to enhance cellulosic fibers functionality and to contribute to a green and safe production process and end product.

#### **2. Materials and Methods**
