Preparation and Test of UV Resistant and Flame Retardant Cotton Fabric With Phytic Acid, Tannic Acid and Diethylenetriamine as Raw Materials

Although cotton fabric is widely used in various elds because of its unique advantages, it has the disadvantages of ammability and poor ultraviolet protection. By combining diethylenetriamine(DETA) (cid:0) phytic acid (PA) and tannic acid(TA) on cotton fabric, a chemical reaction intumescent ame retardant cotton fabric with anti-ultraviolet and anti-ame retardant was developed. The ame retardant and ultraviolet resistance of cotton fabric were characterized by limiting oxygen index (LOI) test, vertical combustion test, cone calorimetry test and ultraviolet resistance test. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and other tests were used to analyze the chemical composition, surface morphology and residual carbon after combustion of the cotton fabric, and it was conrmed that the modied cotton fabric has good ultraviolet resistance and ame retardant performance. In this study, an eco-friendly cotton fabric treatment method was proposed, which made cotton fabric have anti-ultraviolet and ame retardant properties, and a new application of tannic acid and phytic acid in ultraviolet protection and ame retardant of fabric was put forward.


Introduction
Characterized by great comfort, air permeability, hygroscopicity and tenderness, the cotton fabrics, which have an a nity for human skin, are widely used in clothes, decoration, technical fabrics and . What's more, compared to synthetic textiles, the cotton textiles have a poorer protection capacity against ultraviolet rays, and the UV protection factors of them are often lower than 15 (Kan et al.2014). Appropriate exposure to sunshine is favorable for health while inappropriate exposure to sun may do some harm to human body. According to different wave length, the UV radiation is divided into three types: UVA,UVB and UVC. Usually, the ultraviolet rays and the main part of the high energy ultraviolet from the sun will be absorbed by ozone layer. UVA and UVB, which have high energy and could penetrate deeply into dermis, are the two main ultraviolet rays that could reach the ground. Long-time exposure to ultraviolet rays will accelerate the skin aging of humanity, causing premature wrinkles (Kappes et al.2006;Choi et al.2010Honig et al.2018. And it will increase melanin and lead to various kinds of skin diseases and skin cancers. Presently, however, there are only few researches of modi cation that enable cotton textiles to have great fame retardation and UV resistance, most could only have one capacity. It is rarely reported that cotton fabric has ame retardancy and UV resistance at the same time. Therefore, it has become an important issue that how to empower ame retardation and UV resistance to cotton textiles. But in the past few decades,The most common and widely used productive method is to use re retardant that is based on halogen and includes methanal to make cotton textiles that have the capacity of ame retardation(Zheng et al.2019;Castellano et al.2019). Halogen-based ame retardants, which produce a large amount of harmful gases during combustion, are gradually replaced by phosphoruscontaining ame retardants (Shen et al.2013;Zhong et al.2007;Li et al.2019). In recent years, intumescent ame retardant system has attracted more and more attention because of its synergistic ame retardant.
Due to the synergistic effect of its three components, namely acid source, gas source and carbon source, it shows remarkable ame retardancy (Ge et al.2012;Fang et al.2015). In this paper, chemical reaction intumescent ame retardant cotton fabric was prepared with matrix cotton fabric as carbon source, diethylenetriamine as gas source and phytic acid as acid source. In order to improve the ame retardant effect and applicability of the intumescent ame retardant system, tannic acid was added as another carbon source. After tannic acid was added, the system also enjoyed the anti-ultraviolet performance.
As an environmental friendly, nontoxic biocompatible acid, phytic acid has been put into wide application (Jiang et al. 2012). Under thermal decomposition, it could induce cotton textiles to form coke by releasing carboxylic acid, phosphoric acid and sulfuric acid Cheng et al.2020). The more we add phosphorus to cotton textiles, the better is theirs ame retardation ability, and the molecular weight of P of phytic acid is around 28% (C. F. Cullis et al.1992;Zhou et al.2015). Besides, according to the mechanism of ame retardation, the synergistic effect of N and P performs better in ame retardation (Gaan et al.2008).
Tannic acid, featured with special characters such as antibacterial property, inoxidizability, the ability to precipitate protein, reducing capacity and UV resistance, is a natural phenolic compound found in many plants, and most can be found in the bark and performs well in re resistance (Baron et  So, through a low-cost, simplistic, e cient and chemically stable method, we take ecologically friendly and sustainable materials like phytic acid, Tannic acid and diethylenetriamine as our raw materials to produce chemical reaction intumescent ame retardant cotton fabric that have the capacity of ame retardation and UV resistance. The phytic acid, when used alone, can not have an ideal effect in the improvement of the ame retardation of cotton textiles and is unable to guard against ultraviolet rays. However, after adding adding tannic acid and diethylenetriamine can form intumescent ame retardant system, which can improve the ame retardant performance of cotton fabric and make it have the ability of anti ultraviolet at the same time. Phytic acid, tannic acid and diethylenetriamine are grafted onto cotton fabric by chemical reaction, so the adhesion is more reliable. This article dives into the chemical structure, ame retardation capacity and UV resistant ability of modi ed cotton textiles as well as the relevant mechanisms.

Preparation of Anti-ultraviolet and Flame Retardant Cotton Fabric
The rst is the preparation of aminated cotton fabric. 30 × 8 cm 2 cotton fabric was soaked in a beaker containing a mixed solution of 30ml N,N-dimethylformamide (DMF) and 20ml epichlorohydrin, and the beaker was placed in an oil bath with a water temperature of 85 ℃ to react for 1.5 h; Then, 1.5 ml of diethylenetriamine (DETA) was slowly dropped into a beaker, the solution was uniformly stirred, and the obtained cotton fabric was taken out after reacting for 1 h; The cotton fabric was washed several times with ethanol, and then the cotton fabric was repeatedly washed with distilled water to wash off the organic solvent on the surface of the cotton fabric; Finally, the sample was completely dried in an air drying oven at 70 ℃ to obtain ammoniated cotton fabric (CF-DETA).
Ammoniated cotton fabric was added into 100ml 0.01 mol/L tannic acid solution for 1h, and put into an air drying oven at 70 ℃ to completely dry, thus obtaining cotton fabric named CF-DETA-TA; 4ml of 50% phytic acid was add to 100ml of distilled water and stir evenly; Then, CF-DETA-TA was added into phytic acid solution, and the reaction was shaken in a shaking table for 2 hours; Finally, the cotton fabric was dried in an air drying oven at 70 ℃ to obtain ame retardant cotton fabric named CF-DETA-TA-PA.
In addition, the in uence of different concentrations of DETA-TA-PA (DTP) on the ame retardant properties of cotton fabrics was studied. The content of DTP was reduced to 25%, 50%, and 75% of the original, and the ame retardant cotton fabrics were prepared by the same preparation method.

Characterization and Performance Test of Modi ed Cotton Fabric
(1) Limiting oxygen index (LOI) test: LFY-606B oxygen index meter was used to check the LOI of cotton fabric and modi ed cotton fabric. The sample was cut to 150 × 58 mm 2 according to the standard GB/T5454-1997.
(2) Vertical combustion test: LFY-601A vertical combustion tester was used to carry out vertical combustion test on the sample. According to the standard GB/T5455-2014, the size of the tested cotton fabric is 300 × 80 mm 2 , and the ame length is 40mm.
(3) Cone calorimetry test: The combustion performance of raw cotton fabric and modi ed cotton fabric was measured by cone calorimeter, and the measured heat ux was 35 kW/m 2 . According to the standard ISO 5660-1, the size of the tested cotton fabric is 100 × 100 mm 2 , and each sample should be checked twice.
(4) Ultraviolet protection performance test: The Ultraviolet Protection Factor (UPF) of the sample was measured on the HD902C ultraviolet protection and sun protection test system, with a wavelength of 280-400 nm and an interval of 5 nm. (8) Thermogravimetric (TG) test: The thermal stability of the original and treated cotton fabrics was analyzed by Pyris 1 TG analyzer. Under nitrogen conditions, the heating rate was 20k/min and the temperature was 20-700℃.
(9) Mechanical properties test: The tensile strength of samples was studied by HD026PC multifunctional electronic fabric strength tester. According to standard GB/T 3923.1-2013, the size of each sample was prepared as 30 cm × 6 cm. One end of the sample was xed on the clamp, and the other end naturally fell on the next sample clamp for testing. Then the tensile strength and elongation at break of paper and paperboard at room temperature were tested at a speed of 25mm/min.

Analysis of Flame Retardant Performance
In order to visually show the ammability of modi ed cotton fabrics, LOI tests were carried out, and the results were summarized in Table 3.1. Compared with pure cotton fabric, the LOI value of modi ed cotton fabric is improved, which is as follows: the LOI value of unmodi ed cotton fabric was 16.5% (Zhang et al.2018); the ame retardant property of cotton fabric was slightly improved with the addition of DETA, and its LOI value was 20%; the LOI value of CF-DETA-TA was 25%, and that of CF-DETA-TA-PA was 34%.
The cotton fabric treated with DETA-TA-PA (DTP) can not burn in normal atmosphere, which reaches the LOI value of ame retardant standard cotton fabric (26.0%). Through the vertical combustion test, it can be seen from Table 3.1 that the cotton fabric burns rapidly within 12 s after being ignited as it is, and the after ame time and afterglow time are 12s and 14s respectively. The addition of DETA can improve the ame retardancy of cotton fabric, and the residual ame time and afterglow time are 10s and 10s, respectively, with burning time slightly shortened. Compared with the control sample, the ame retardancy of CF-DETA-TA is improved. Although CF-DETA-TA burns completely, the residual ame time is lower than the control sample, and the afterglow time is 0 s. As can be seen from Table 3.1, the damage length of CF-DETA-TA-PA is 75 mm respectively, and the after re and afterglow time are both 0 s, indicating that the ame can be extinguished immediately after leaving the re source. Therefore, the samples treated with DTP have excellent ame retardancy.
The LOI values of samples at different DTP concentrations were further studied, as shown in Table 3.2.
When the sample is treated with 50% DTP, the weight of cotton fabric increases by 7.30%, and the LOI value of cotton fabric is 27%, which is higher than the LOI value of ame retardant standard (26.0%). In addition, with the increase of DTP concentration, the LOI value of samples treated with DTP also increased. LOI test results show that the modi ed cotton fabric has excellent ame retardancy.

Cone Calorimetry Test
Cone calorimetry test is often used to evaluate the combustion behavior of different materials under speci c conditions and provide complete ame retardant characteristics (Zhang et al. 2021;Xu et al.2020), and the test results are shown in Table 3.3. Fig. 3.1 is a graph of heat release rate (HRR), total heat release (THR), total smoke production (TSP), smoke production rate (SPR), COP and CO 2 P of the sample.
As can be seen from Fig. 3.1, the HRR and THR values of the modi ed cotton fabric are lower than those of the raw cotton fabric. As can be seen from Table 3 Smoke intrusion is the main cause of death during re (Giebultowicz et al.2017). As can be seen from Fig. 3.1 (c) and (d), the smoke production rate of CF-DETA-TA-PA in the rst 50s is higher than that of the raw cotton fabric, but the SPR of the modi ed cotton fabric after 50s is very low, and the total smoke production is much lower than that of the control sample. In other words, CF-DETA-TA-PA not only has good ame retardancy, but also has low smoke exhaust amount, which may be due to the positive in uence of phosphoric acid or polyphosphoric acid generated during combustion on the pyrolysis of cellulose, resulting in early pyrolysis of cellulose. As can be seen from Fig. 3.1 (e) and (f), the COP value of the modi ed cotton fabric is higher, while the CO 2 P value is much lower than that of the control. The high COP value may be caused by incomplete combustion of coated cotton fabric, especially when phytic acid burns, phosphoric acid or polyphosphoric acid can be produced, which catalyzes cellulose to generate carbon residue, resulting in incomplete combustion of cotton ber. The above results prove that the modi ed cotton fabric has not only ame retardant performance, but also smoke suppression effect.

Analysis of Anti-UV Performance
According to Table 3 TA-PA is less than 2.32%. According to AS/NZS 4455 miniclip UPF classi cation system, CF-DETA-TA-PA is considered to have good UV protection performance. The results show that the modi ed cotton fabric not only has ame retardancy, but also has a good potential application prospect in ultraviolet protection materials (Pandiyarasan et al.2017). Fig. 3.2 is a SEM image of raw cotton fabric and modi ed cotton fabric. The raw cotton fabric showed a smooth surface, but after grafting DETA, it was found that the concavity and convexity of the surface increased after the graft copolymerization reaction, indicating that the organic monomer was grafted into the cellulose framework, as shown in Fig. 3.2 (b 1 , b 2 ). As shown in Fig. 2.2 (c 1 , c 2 ), after covering the tannin layer, the surface of cotton ber is rough, and the surface of CF-DETA-TA-PA is relatively smooth than that of CF-DETA-TA, but some cracks appear locally, which indicates that a layer of phytic acid is deposited on the surface of cotton fabric. The above results indicate that the coating was successfully   3.6 Analysis of FT-IR Spectra Fig. 3.5 is the FTIR spectra of raw cotton fabrics and modi ed cotton fabrics. The peak of raw cotton fabric at 3330cm -1 is attributed to the stretching vibration of hydroxyl groups in cotton ber, the peak at 2895cm -1 corresponds to the stretching vibration of C-C, the peak at 2876cm -1 corresponds to the stretching vibration of C-H, and the peaks at 1431 cm -1 and 1335 cm -1 correspond to the bending vibration of CH2 and CH on the main chain of cotton fabric, respectively, and the characteristic peak at originally existing in cotton fabric were weakened: the peak formed at 1626cm -1 corresponds to the stretching vibration of C-N, and the peak at 1261cm -1 proves the existence of N-H on cotton fabric. The peak at 2963cm -1 corresponds to the stretching vibration of the phenolic hydroxyl group after the addition of tannic acid, and the peak at 869cm -1 corresponds to the bending vibration of the benzene ring plane. In CF-DETA-TA-PA, the absorption peak at 1760cm -1 corresponds to the stretching vibration of P=O, and the peak at 1196cm -1 corresponds to the stretching vibration of P-O. The change of absorption peak position and intensity indicates that some substances are loaded on the surface of cotton fabric, which is consistent with the previously reported results (El-Shafei et al.2015).

TG Analysis
The thermal stability and thermal oxidation stability of control samples and treated samples were evaluated by N2 TG analysis. Fig. 3.6 is a TG and DTG diagram of the sample in N 2. Table 3.5 where the decomposition rate of the modi ed cotton fabric is lower than that of the control cotton fabric, and the carbon residues of the CF, CF-DETA, CF-DETA-TA, CF-DETA-TA-PA are 4.3%, 23.6%, 23.2%, and 43.0%, respectively. Phosphoric acid or polyphosphoric acid produced in the thermal degradation process of phytic acid is bene cial to the decomposition of cellulose into carbon slag, forming an insulating dense protective layer, which can prevent convection and conduction of heat and materials and reduce the decomposition temperature. The dense layer is also bene cial to increase the carbonization yield during combustion. The analysis results show that the decomposition rate of modi ed cotton fabric decreases obviously.
The maximum weight loss rate of the control sample at 353℃ is 25.7%/℃, and about 4.3% thermally stable carbon residue is formed at 700℃. The modi ed cotton fabric is still a one-step thermal degradation process, and CF-DETA and CF-DETA-TA almost show the same thermal behavior. It can be seen from the table that the decomposition temperatures of cotton fabrics treated by DETA, DETA-TA and DETA-TA-PA are 210℃, 223℃ and 208℃, respectively, which are signi cantly lower than those of control samples, indicating that ame retardants have signi cant in uence on the decomposition behavior of products, which is bene cial to preferential decomposition and charring. Similarly, the T max and T10% values of the treated cotton fabric are also low. In addition, the R max value of all coated cotton fabrics is low, which makes the modi ed cotton form more carbon residue than the control cotton, thus preventing the cotton fabric from further burning and releasing ammable volatile substances, and producing less volatile substances and combustible substances in the thermal degradation process. The data show that the modi ed cotton fabric has better thermal stability.  Fig. 3.7 (b 1 , b 2 ) shows the morphology of modi ed cotton fabric after combustion, that the shape of the sample remains intact and the residual carbon skeleton structure still exists clearly. There are many small bubbles on the surface of the carbon residue skeleton structure of CF-DETA-TA-PA, which is due to the decomposition of phytic acid to form phosphoric acid and pyrophosphate. (Tao et al. 2021) 3.9 Infrared Analysis of Combustion Samples

Summary
In this paper, a cotton fabric with anti-ultraviolet and ame retardant was prepared by grafting DETA, tannic acid and phytic acid on the surface of cotton fabric. The LOI value of unmodi ed cotton fabric is 16.5%, while that of treated cotton fabric can reach 34%, which meets the ame retardant standard of cotton fabric. TG test shows that at 700 ℃, the residual mass of treated cotton fabric is 43.0%, while that of raw cotton fabric is 4.3%. THR, PkHRR and TSP of treated cotton fabric are obviously lower than those of untreated cotton fabric, which indicates that modi ed cotton fabric can effectively inhibit cotton burning. The UPF value of modi ed cotton fabric is 131.8, and the ultraviolet transmittance is less than 2.32%. The tensile strength of the treated cotton fabric has no obvious change, but the elongation at break decreases. The morphology and structure of burned cotton fabric were analyzed by SEM and FTIR, and it was found that the modi ed cotton fabric could keep a more complete structure after burning.
Therefore, the improvement of ame retardancy and UV resistance of modi ed cotton fabric has broad application prospects.   3.9 Strain-stress curves of control and treated samples