Abstract:

Objective Fibers and textiles are essential materials used across many application fields, but most of them present significant fire hazards due to their inherent flammability. Although surface treatments can impart flame retardancy, the limited durability of most coatings restricts their practical utility. This study aims to develop a highly durable flame-retardant coating for cotton fabrics by leveraging strong cation-π interactions to enhance the adhesion between the coating and the substrate. Through this strategy, the coating is designed to provide not only effective flame retardancy but also long-lasting protection capable of withstanding mechanical abrasion.

Method In this study, a UV-initiated polymerization strategy was employed to synthesize poly(acryloyloxyethyl dimethyl benzyl ammonium chloride) (PADBAC) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). Vinyl phosphonic acid (VA) was further incorporated to formulate a composite flame-retardant coating (PA₆PM/VA_6%). Within the coating matrix, the benzene rings of PADBAC interact with the quaternary ammonium cations of PMPC through cation-π interactions, thereby enhancing adhesion strength and interfacial adhesion. The coating was then applied to cotton fabrics, followed by characterization of adhesion strength, flame retardancy, and mechanical stability.

Results Cotton fabric characterization showed that the PA₆PM/VA_6% coating exhibited good adhesion, flame retardancy, and durability. First, benefiting from the designed cation-π interactions between the benzene rings in PADBAC and the quaternary ammonium cations in PMPC, the coating demonstrated strong interfacial adhesion, achieving an adhesion strength of 2.35 MPa. These interactions effectively enhanced both the adhesion strength of the coating and its adhesion to the fiber substrate, while further enabling reliable adhesion to a broad range of surface types. The PA₆PM/VA_6% coating also demonstrated good flame-retardancy in vertical burning tests. Upon removal of the ignition source, the coated fabric self-extinguished, exhibiting a damage length of only 7.5 cm, and showed a high limiting oxygen index (LOI) value of 35%. Thermogravimetric analysis revealed a synergistic mechanism during thermal exposure, which is that VA and PMPC can enhance char formation, promoting the development of a dense and expanded char layer. This char served as an effective physical barrier, insulating the underlying polymer from heat and oxygen, thereby reinforcing the flame-retardant effect. Most importantly, the PA₆PM/VA_6%coating demonstrated remarkable mechanical stability. Even after 1 000 standard rubbing cycles, the coated fabric retained its self-extinguishing performance, with the LOI value remaining above 28.0%. These results indicate excellent wear resistance and highlight the coating's promising potential for practical applications in protective clothing, rail transit and outdoor tents.

Conclusion This study developed a highly durable phosphorus-nitrogen synergistic flame-retardant protective coating based on cation-π interactions. PADBAC and PMPC were synthesized by UV-initiated polymerization, and VA was incorporated to formulate a flame-retardant composite coating (PA₆PM/VA_6%). Within this coating matrix, the benzene rings in PADBAC were pound to engage in cation-π interactions with the quaternary ammonium cations of the PMPC segments, effectively reinforcing both adhesions strength of the coating and its adhesion to the fiber surface, resulting in an adhesion strength of 2.35 MPa. Cotton fabrics modified with this coating exhibited self-extinguishing behavior upon flame removal in vertical burning tests, with a damaged char length of only 7.5 cm, and demonstrated a high LOI value of 35%. During burning, VA and PMPC synergistically promoted char formation, generating a dense and expanded carbonaceous layer that further enhanced flame retardancy. Moreover, after 1 000 rubbing cycles, the treated fabric maintained an LOI value above 28.0%, indicating excellent abrasion resistance and durable flame-retardant performance. This coating shows promising potential for practical applications in protective clothing, rail transit, construction, and public safety.

Key words: cation-π interaction, flame-retardant coating, flame-retardant fabric, strong adhesion, cotton fabric, durability, phosphorus-nitrogen synergistic flame retardation, functional textiles