Abstract:

Objective Lyocell fibers belong to regenerated cellulose fiber family with excellent comfort, breathability and biodegradability, which is widely used in clothing, bedding, furniture and other fields. However, the limiting oxygen index (LOI) of lyocell fiber is only 19%, indicating high flammability with a great threat to people's life and property safety. In addition, the hygroscopicity of lyocell fabrics provides suitable conditions for the propagation of microorganisms, which adversely influences human health. Therefore, the flame retardant and antibacterial modification for Lyocell fabrics is worthy of attention.

Method Aminoazole-based cyclotriphosphazene (HATA) is rich in phosphorus and nitrogen, which can achieve efficient flame retardant for fabrics. Besides, tannic acid (TA) belongs to biomass, which has a wide range of sources. Glycidyl trimethyl ammonium chloride (GTA) was utilized to improve the loading of tannic acid on the fabric, amnd triethoxyvinylsilane (VTEO) was selected to endow the fabric hydrophobicity. A multifunctional lyocell fabric was prepared by the dip-drying method, and the flame retardant, UV resistance, hydrophobicity and antibacterial properties were investigated by vertical flame tests (VFT), limiting oxygen index (LOI) evaluation, microscale combustion calorimetry (MCC), anti-UV performance test, contact angle test, and oscillating method of antimicrobial test.

Results In this study, control lyocell was burned out with little char residue during the VFT. However, treated Lyocell passed VFT with self-extinguish behavior and the char residue was only 5.5 cm. Besides, treated Lyocell after 5 laundering failed to pass VFT, but remained a little char residue. Compared with the control lyocell, the LOI value of treated Lyocell increased from 19.0% to 29.4%. MCC test showed that the peak heat release (PHRR) and total heat release (THR) of treated Lyocell decreased 74.9% and 65%, respectively. Moreover, TG resulted that the introduction of the coating reduced the maximum decomposition rate (R_max) and the temperature at the maximum decomposition rate (T_max) obviously, improving the char residue rate from 14.3% to 40.3%. The above results indicated that the coating played an important role in promote the formation of char layer to protect the fabrics. Meanwhile, through SEM, the micromorphology of control lyocell, treated lyocell, and the char residue of treated lyocell was examined. The char residue of treated Lyocell remained the original woven structure and had some noticeable bubbles. To detect the UV resistance of treated Lyocell, ultraviolet spectrophotometer was used to test the UV protection factor (UPF) of samples. The UPF value of treated lyocell increased from 7.69 to 64.04, which was over 40. According to the standard of GB/T 18830-2009, the treated lyocell can be defined as "anti-ultraviolet production". In addition, the water connect angle (WCA) of treated lyocell was 116°. When various liquids, such as coke, milk, juice, and tea, were applied on the surface of the treated lyocell, the droplets maintained stable spherical shape for an extended period. To evaluate the antibacterial property of treated lyocell against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), the shaking flask method was used to determine the antibacterial rate, the antimicrobial rates of the treated lyocell against S. aureus and E. coli reached 99.99% and 99.88%, respectively.

Conclusion A multifunctional coating, including the flame retardant, antibacterial, hydrophobic and anti-ultraviolet functions, was prepared by using the hydrogen bonding between HATA and TA, resulting in the formation of a water-insoluble precipitate. Furthermore, the introduction of VTEO provides hydrophobicity to the fabric. The treated Lyocell fabric passed VFT with self-extinguishing behavior, increasing the LOI value from 19.0% to 29.4% and the water contact angle to 116°. According to MCC test, the TA/HATA coating reduced the HRC, PHRR and THR values of lyocell fabrics. The TG results demonstrated that TA/HATA coating significantly improved the thermal stability and char residue rate of lyocell, and decreased the initial decomposition rate. Moreover, the coating endowed lyocell excellent antibacterial properties, hydrophobicity and UV resistance. This method provides a new strategy for constructing multifunctional fabrics.

Key words: Lyocell fabric, functional finish, flame retardant, antibacterial, hydrophobic, UV resistance, functional textile