Abstract:

Objective Cotton fabrics are one of the most important textiles; they are widely used in clothing, furniture, and decoration. However, cotton fabrics have a low limiting oxygen index (LOI) of only 17%, and they are highly flammable, which is easy to cause fire accidents. Meanwhile, the most widely used existing halogen-containing flame retardants are facing many restrictions due to the generation of halogenated hydrocarbons during burning. In addition, cotton fabrics have poor anti-ultraviolet (UV) properties and cannot protect the skin from UV damage. Therefore, it is necessary to design an additive to improve the flame retardancy of cotton fabrics with the anti-UV properties.
Method Tea polyphenols (TP), phenyl phosphonic acid (PPOA) and iron (Ⅲ) sulfate hydrate(Fe(SO₄)₃) were selected to prepare tea polyphenols-iron-phenyl phosphonic acid complex (named TP-Fe-PPOA). Phosphoric acid or polyphosphoric acid produced by the thermal degradation of PPOA are known to be able to promote char formation of materials, and TP generates free radicals and slows down burning. The benzene ring absorbs UV light and improves the anti-UV properties of fabrics. Flame retardant cotton fabrics were prepared by the dip-coating technology, and the flame retardant, anti-UV and mechanical properties were investigated by limiting oxygen index evaluation, vertical flame tests (VFT), cone calorimetry test (CCT), anti-UV performance test and universal testing machine.
Results Test results show that TP-Fe-PPOA was evenly adhered to the surface of cotton fabrics (Fig. 1). There is a synergistic effect between TP-Fe and PPOA. Cotton/TP-Fe cannot achieve self-extinguishing(as shown in Fig. 5 and Tab. 3). There is a serious phenomenon of negative burning, and the cotton fabrics are completely destroyed in VFT. Cotton/PPOA slows down the flame spread significantly compared with cotton fabrics. However, the LOI value of Cotton/PPOA is still only 21.9%. When they were treated with TP-Fe-PPOA, cotton fabrics became self-extinguishing, the damage length was only 6.7 cm in VFT, and the LOI increased from 17.6% to 24.7%. Meanwhile, the peak heat release rate value of Cotton/TP-Fe-PPOA was 11.8% lower than that of cotton fabrics(Fig. 6 and Tab. 4). The results indicated that after the flame retardant treatment, smoke release was effectively mitigated. The smoke production rate value of flame retardant fabrics was smaller than that of cotton fabrics, and the total smoke production value was also significantly reduced, which can greatly reduce the probability of death by asphyxiation in a fire. Moreover, the cotton fabrics left almost no char residues after CCT, while Cotton/TP-Fe-PPOA left more compact char residues(Fig. 8). These char residues act as a barrier to slow down the transfer of heat, oxygen, combustible gases and smoke, protecting the underlying fabrics. Fortunately, while achieving the flame retardant and anti-UV properties, the air permeability of Cotton/TP-Fe-PPOA was decreased by only 13.1% (Fig. 9). However, the mechanical properties of the flame retardant cotton fabrics were deteriorated severely due to the acidity of PPOA (Tab. 5). The elongation at break of Cotton/TP-Fe-PPOA in both warp and weft directions was decreased by about 28.8% and 12.6% compared to that of cotton fabrics. In addition, anti-UV was also greatly improved (Tab. 6). The UV protection factor (UPF) of Cotton/ TP-FE-PPOA increased from 7.47±0.19 to 37.85±2.34, which is close to the standard of UPF≥40 for sun protection products.
Conclusion The above results show that TP-Fe-PPOA can make cotton fabrics with better flame retardant effect and better anti-UV properties at the same time. These flame retardant cotton fabrics with anti-UV properties are suitable for use as curtains, which not only meet the needs of flame retardant, but can also block UV light, slow down the aging process of indoor fabrics and protect people from UV light. Unfortunately, the mechanical properties of these flame retardant cotton fabrics are severely lost, especially the loss of tensile strength. Therefore, it is necessary to consider the use of neutral or alkaline additives to reduce the acid brittleness of cotton fabrics in order to retain the original mechanical properties of the fabrics in the future research. Considering that Cotton/PPOA performs well in VFT and LOI, it can be concluded that phosphorus-containing flame retardants have good effects on improving the flame retardant properties of cotton fabrics. Therefore, PPOA can be replaced with less acidic phosphorus-containing flame retardants or the acidity of PPOA can be reduced through the reaction to achieve the purpose of reducing the loss of mechanical properties of flame retardant fabrics.

Key words: flame retardant, anti-ultraviolet property, cotton fabric, tea polyphenols-iron-phenyl phosphonic acid complex, dip-coating technology