Abstract:

Objective Viscose fabrics, known for their breathability, dyeability, and comfort as renewable cellulose-based textiles, have found widespread use in daily life. However, viscose fabrics retain the flammable nature of cellulose-based materials, with a limiting oxygen index (LOI) of only about 18.5%. As their usage grows, so does the potential fire hazard they pose. Therefore, the flame-retardant finishing of viscose fabrics is crucial to safeguard human lives and property. Furthermore, viscose fabrics often have lower tensile strength, and most flame retardants are acidic, potentially compromising the fabric's strength during finishing. Hence, achieving flame retardancy while maintaining mechanical properties is a highly significant challenge.

Method Phytic acid (PA) and maltitol were mixed in a three-necked flask with specific molar ratios i.e., 1∶1, 1∶2, 1∶3, 1∶4, and 1∶5, and reacted under magnetic stirring at 130 ℃ for 3 h to produce the flame retardant, named PAMAab (ab presents the molar ratio of PA to maltitol). PAMA was dissolved in water to prepare aqueous solutions of 100 g/L and 200 g/L, respectively. Then, viscose fabrics were soaked in the flame-retardant solution with a bath ratio of 1∶20, and 5% sodium hypophosphite was added as a stabilizer. The flame retardant was applied to viscose fabrics using a pad-dry-curing method, in which the viscose fabrics were immersed into the solution at 70 ℃ for 20 min, then pre-dried at 80 ℃ for 3 min, followed by curing at 170 ℃ for 3 min to obtain the flame retardant treated viscose fabrics.

Results To prepare the flame-retardant treated viscose fabrics with better flame retardancy and mechanical properties, the effect of different molar ratios of PA to maltitol on the flame retardancy and mechanical properties of treated viscose fabrics was investigated in detail. The results indicated that the flame-retardant treated viscose fabrics achieved an improved balanced combination of the flame retardancy and mechanical properties when the molar ratio of PA to maltitol was 1∶3. Scanning electron microscope results showed that the flame retardant and PAMA successfully covered the surface of the fibers without noticeably blocking the orifices between them. With a flame-retardant concentration of 100 g/L, LOI value of the PAMA13-100 treated viscose fabric increased from 18.5% to 30.1%, enabling self-extinguishing with no after-flame or after-glow time. Thermal stability analysis revealed that PAMA13-100 exhibited reduced thermal stability in the low-temperature range but improved thermal stability in higher temperature zones, with a significant increase in char residues at 700 ℃. The peak heat release rate and total heat release of PAMA13-100 were decreased by 83% and 51%, respectively, and total smoke production was decreased from 3.3 m² to 0.2 m². PAMA13-100 demonstrated denser and more stable residual chars after cone calorimeter test, effectively preventing further flame spread and greatly enhancing the fire safety of finished viscose fabrics. Additionally, it is noteworthy that the tensile strength retention in warp direction of PAMA13-100 approached 100%, nearly 400% higher compared with that of fabrics treated with pure PA, and the tensile strength in weft direction arrived at 114%, ensuring the secured subsequent processing and use of finished viscose fabrics. This system enabled the finished viscose fabrics to achieve a UPF value of over 40, meeting the requirements for ultraviolet protection textiles and demonstrating potential as a multifunctional product.

Conclusion In conclusion, the flame retardant, PAMA, enhanced the flame retardancy and tensile strength retention of viscose fabrics treated with PA-based flame retardants through the pad-dry-curing finishing process. This system exhibited self-extinguishing properties without after-glow or after-flame time when the weight gain was 10.1%, and it effectively reduced smoke release. It can be applied to carpets, curtains, and other textiles. In subsequent research, efforts will focus on optimizing and improving its washing durability to achieve higher practical value.

Key words: viscose fabric, bio-based flame retardant, flame retardancy, tensile strength, phytic acid, maltitol, functional textile