A method for preparing flame-retardant cotton fabric based on chemical grafting

Abstract

This invention discloses a method for preparing flame-retardant cotton fabric based on chemical grafting. The method involves grafting chloroacetic acid onto the hydroxyl groups at the C6 position of cellulose to generate carboxymethyl cellulose. Sodium periodate is then used to oxidize the hydroxyl groups at the C2 and C3 positions of cellulose to dialdehyde cellulose, which undergoes a Schiff base reaction with glutamic acid, introducing a large amount of -COO- groups. Finally, the carboxyl groups undergo a complexation reaction with calcium ions to form a flame-retardant cotton fabric with an egg-like "egg-box" structure. The flame-retardant properties are significantly improved, with a limiting oxygen index of 33.6%. The modified cotton fabric of this invention maintains good levels of hydrophilicity, strength, and whiteness.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant cotton fabric technology, specifically relating to a method for preparing flame-retardant cotton fabric based on chemical grafting. Background Technology

[0002] Cotton fabrics are popular with consumers due to their softness, comfort, good moisture absorption, and high breathability. In fact, they are the most common natural cellulose textiles used in clothing, home décor, and industrial applications. However, cotton fabrics are highly flammable, with an oxygen limiting index (LOI) of 18% and an ignition temperature of only 350°C, far lower than many other commonly used textile materials. In the event of a fire, cotton fabrics easily ignite and burn rapidly, posing a significant safety threat and risk to human life and property. Therefore, adding flame retardants to cotton fabrics to improve their flame-retardant properties is essential.

[0003] Currently, various flame retardants are used in cotton fabrics, including halogen, phosphorus, nitrogen, silicon-based systems, boron-based flame retardants, metal compounds, and synergistic flame retardants. Among these options, phosphorus-containing flame retardants, such as... and Pyrovatex With dual functions—low toxicity, low smoke, halogen-free or low-halogen properties—and high thermal stability, phosphorus-containing flame retardants are widely used. However, these retardants block the hydroxyl groups in the cellulose macromolecules, significantly reducing other textile properties such as breathability, comfort, and flexural stiffness. Furthermore, the environmental pollution caused by excessive use of organophosphorus flame retardants and their potential threats to human health have recently drawn the attention of researchers.

[0004] Flame-retardant modified cotton fabrics are prone to decreased hydrophilicity, reduced whiteness, and significantly reduced mechanical strength, damaging the inherent properties of cotton fabrics and thus limiting their application. Therefore, developing a new method for manufacturing environmentally friendly flame-retardant cotton fabrics is imperative. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments.

[0006] As one aspect of the present invention, the present invention provides a method for preparing a flame-retardant cotton fabric based on chemical grafting, comprising,

[0007] (1) Preparation of COT-M cotton fabric by alkaline treatment of cotton fabric: The cotton fabric is soaked in sodium hydroxide solution, neutralized, washed and dried to obtain COT-M cotton fabric.

[0008] (2) Preparation of carboxymethyl fiber COT-CMC cotton fabric: The COT-M cotton fabric was soaked in chloroacetic acid solution to react, the cotton fabric was taken out, washed and dried to obtain COT-CMC cotton fabric.

[0009] (3) Preparation of COT-DCMC cotton fabric with dual aldehyde fiber: The COT-CMC cotton fabric is soaked in sodium periodate solution for reaction, the cotton fabric is taken out and soaked in glycerol solution, the cotton fabric is taken out, washed and dried to obtain COT-DCMC cotton fabric.

[0010] (4) Preparation of COT-Glu cotton fabric: The COT-DCMC cotton fabric is soaked in glutamic acid solution, shaken to react, the cotton fabric is taken out, washed and dried to obtain COT-Glu cotton fabric.

[0011] (5) Preparation of COT-Glu-Ca cotton fabric: The COT-Glu cotton fabric is soaked in calcium chloride solution, shaken to react, the cotton fabric is taken out, washed and dried to obtain COT-Glu-Ca cotton fabric.

[0012] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting described in this invention: in step (1), the concentration of sodium hydroxide solution is 24-25 wt%, and the soaking time is 10-20 min.

[0013] As a preferred embodiment of the method for preparing flame-retardant cotton fabric based on chemical grafting according to the present invention: in step (2), the concentration of chloroacetic acid solution is 25-30 wt%.

[0014] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting described in this invention: in step (2), the reaction temperature is 40-75℃ and the reaction time is 4-5 hours.

[0015] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting according to the present invention: in step (3), the concentration of sodium periodate solution is 0.2-0.4 mol / L; the reaction is carried out at a temperature of 40°C for 1-1.5 hours.

[0016] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting described in this invention: in step (3), the concentration of the glycerol solution is 0.1-0.2 mol / L, and the cotton fabric is soaked in the glycerol solution for 30-40 minutes.

[0017] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting described in this invention: in step (4), the concentration of glutamic acid solution is 50-100 mmol / L.

[0018] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting described in this invention: in step (4), the oscillation reaction is an oscillation reaction at a speed of 100-120 mm / s for 1-1.5 hours.

[0019] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting according to the present invention: in step (5), the concentration of the calcium chloride solution is 200-250 g / L, and the shaking reaction is a shaking reaction at a speed of 100-120 mm / s for 1-1.5 hours.

[0020] As a preferred embodiment of the preparation method of flame-retardant cotton fabric based on chemical grafting according to the present invention: in step (1), the washing is washing with water; the drying is drying at 55-60°C.

[0021] The beneficial effects of this invention are as follows: This invention modifies the C6 hydroxyl group of cellulose by grafting chloroacetic acid onto it to generate carboxymethyl cellulose. Then, sodium periodate is used to oxidize the C2 and C3 hydroxyl groups of cellulose to dialdehyde cellulose, which undergoes a Schiff base reaction with glutamic acid to form a flame-retardant cotton fabric with an egg-box structure. The flame retardancy of the carboxymethylated cotton fabric was tested using vertical burning and limiting oxygen index (LOI) measurements. It exhibits self-extinguishing capability and significantly improved flame retardancy, with an LIO of 33.6%. During combustion, a char layer is rapidly formed, isolating air and heat, confirming the successful modification of the cotton fabric. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analysis showed that chloroacetic acid, sodium periodate, and glutamic acid have minimal impact on the crystal structure of the cotton fabric. Chloroacetic acid and glutamic acid were successfully grafted onto the cotton fabric and complexed with calcium ions. Compared to raw cotton, the modified cotton fabric of this invention maintains good levels of hydrophilicity, strength, and whiteness, indicating successful modification. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0023] Figure 1 This is the FTIR spectrum of the sample.

[0024] Figure 2 This is an XPS full scan spectrum.

[0025] Figure 3 The XPS spectrum of N1s is deconvolutioned with Ca2p.

[0026] Figure 4 The image shows the XRD diffraction curve.

[0027] Figure 5 SEM images of cotton fabric grafting and chelation processes.

[0028] Figure 6 EDS analysis of cotton fabrics.

[0029] Figure 7 The TG and DTG curves are for the raw cotton sample and the final treated cotton fabric.

[0030] Figure 8 This is Example 1, a vertical combustion experiment.

[0031] Figure 9 For contact angle testing.

[0032] Figure 10 This is a schematic diagram of the flame-retardant cotton fabric modification process of the present invention.

[0033] Figure 11 This is a vertical combustion experiment for control example 1.

[0034] Figure 12 This is a vertical combustion experiment for control example 2. Detailed Implementation

[0035] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0036] Example 1:

[0037] (1) Preparation of COT-M by alkaline treatment of cotton fabric: 24g of sodium hydroxide was poured into 76ml of deionized water to prepare a 24% sodium hydroxide solution. A 300mm×89mm cotton fabric was soaked in the 24% sodium hydroxide solution for 10 minutes (liquor ratio 1:25); then the treated cotton fabric was soaked in a 24wt% acetic acid solution for 10 minutes to neutralize the excess sodium hydroxide. The treated cotton fabric was washed with deionized water to obtain COT-M cotton fabric, and then placed in a 60℃ forced-air drying oven to dry.

[0038] (2) Preparation of carboxymethyl fiber (COT-CMC): Weigh 25g of chloroacetic acid and pour it into 75ml of deionized water to prepare a 25% chloroacetic acid solution. Soak the COT-M cotton fabric in the chloroacetic acid solution and react at 40℃ for 4 hours. Take out the cotton fabric and wash it with deionized water to obtain COT-CMC cotton fabric. Then put it into a 60℃ forced-air drying oven to dry.

[0039] (3) Preparation of dialdehyde fiber (COT-DCMC): Weigh 4.28g of sodium periodate, pour it into a brown conical flask covered with tin foil and dissolve it in 100ml of deionized water to prepare a 0.2mol / L sodium periodate solution. Soak the COT-CMC cotton fabric in the sodium periodate solution and react at 40℃ for 1 hour. Take out the cotton fabric, weigh 0.46g of glycerol and mix it evenly with 50ml of deionized water to prepare a 0.1mol / L glycerol solution. Soak the cotton fabric in the 0.1mol / L glycerol solution for 30 minutes and wash it with deionized water to obtain the COT-DCMC cotton fabric. Place it in a 60℃ drying oven to dry.

[0040] (4) The reaction of dialdehyde fiber and L-glutamic acid to generate Schiff base (COT-Glu): Weigh 0.735g of glutamic acid and 100ml of deionized water into an Erlenmeyer flask and mix evenly to form a 50mmol / L glutamic acid solution. Soak the COT-DCMC cotton fabric in the solution and place it in a shaker at a speed of 120mm / s for 1 hour. Take out the cotton fabric and wash it with deionized water to obtain COT-Glu cotton fabric. Place it in a 60℃ forced-air drying oven to dry.

[0041] (5) Reaction of carboxyl group and calcium chloride (COT-Glu-Ca): Weigh 20g of calcium chloride and mix it evenly with 100ml of deionized water to form a calcium chloride solution of 200g / L. Put the COT-Glu cotton fabric into the calcium chloride solution and place it in a shaker at a speed of 120mm / s for 1 hour. Take out the cotton fabric and wash it with deionized water to obtain COT-Glu-Ca cotton fabric. Place it in a 60℃ drying oven to dry.

[0042] Vertical Burning Test: The flame retardant properties of the modified cotton fabrics were tested using a YG(B)815D-I vertical flame retardant performance tester, following GB / T5455-2014 "Test for Burning Performance of Textiles - Vertical Method". Sample Preparation: Five samples of approximately 300mm × 89mm were cut parallel to the warp direction and conditioned under standard atmospheric conditions for 24 hours. The samples were vertically fixed in the sample holder, and the fabric was ignited using an igniter. The flame height was controlled to be approximately 40±2mm. The burning time was 12 seconds, and the afterflame time was calculated. After the flame extinguished, the smoldering time of the sample was calculated. After the smoldering time ended, the burned sample was removed, the damaged length was measured, and photographs were taken.

[0043] Limiting oxygen index test: The flame retardant properties of the cotton fabric before and after modification were tested using an HC-2 oxygen index meter. Following the test method in GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method", the mixing ratio of O2 and N2 was arbitrarily adjusted to determine the minimum oxygen concentration required for the fabric to sustain combustion. A 0.2g sample and a support strip with a length of 200mm and a width of 20mm were prepared for the test.

[0044] Fourier transform infrared spectroscopy (FT-IR): The molecular structures of raw cotton fabrics, chloroacetic acid, periodic acid, glutamic acid, and calcium chloride-treated cotton fabrics were determined using a NEXUS-670 Fourier transform infrared spectrometer. The KBr pellet method was used for the tests, with wavenumbers ranging from 400 to 5000 cm⁻¹.

[0045] X-ray diffraction (XRD): Utilizing the X′Pert3 Powder, a commonly used structural characterization method, it can obtain material composition and perform phase analysis. The instrument used is an X′Pert3 power from the Dutch company PANalytical.

[0046] Scanning electron microscopy (SEM): A Nova Nano-450 scanning electron microscope was used to observe the changes in the morphology of raw cotton fabrics, cotton fabrics treated with chloroacetic acid, sodium periodate, glutamic acid, and calcium chloride, as well as the morphological characteristics of the carbon residue in the modified cotton fabrics. Before testing, the fabrics were cut into 0.5cm × 0.5cm pieces, adhered to a dedicated stage with conductive adhesive, and then sputter-coated with gold for 45 seconds.

[0047] Mechanical property testing: Five 5cm x 10cm samples were prepared and tested using a CMT4304 microcomputer-controlled electronic universal testing machine from Mester Industrial Systems (China) Co., Ltd. Testing environment: Temperature 20℃, relative humidity 65%. Sample testing parameters: Clamping length 5cm, tensile rate 25cm / min.

[0048] Contact angle test: The nanofiber membrane, along with the attached aluminum foil, was cut into 2cm × 2cm pieces, laid flat, and fixed on the worktable of a contact angle tester (JCY-2 type). The test results were then taken and read. Test parameters: Droplet volume 3μL, deionized water used. A JC2000D3 contact angle measuring instrument was used to test the moisture absorption of the fabric before and after modification.

[0049] Fabric whiteness test: Referring to GB / T 17644-2008 "Test Method for Whiteness of Textile Fibers", after zeroing and whiteness adjustment, the test sample is folded into 4 layers, and the whiteness of different parts of the fabric is measured with a WSD-3C fully automatic whiteness meter. The test is performed 3 times and the average value is taken.

[0050] FTIR spectral analysis: Figure 1 The following are the FTIR spectra of the samples from each step. Compared to the control cotton fabric, the stretching vibrations of the hydrogen bonds (-OH) in cellulose result in a wavelength of approximately 3336 cm⁻¹. -1 The broadening and intensification of the peak at this point indicates that the number of free hydroxyl groups on cotton cellulose gradually increases through chemical reactions with MCA and L-glutamic acid. The CH2 deformation vibration and CH bending vibration occur at approximately 1429 cm⁻¹. -1 1367cm -1 The peak value at that location changed significantly. Figure 1 Curve b) indicates that the crystallinity of cellulose decreases after treatment with sodium hydroxide. Simultaneously, the 1057 cm⁻¹ crystallinity caused by COC tensile vibration... -1 1107cm -1 The peak intensity of the carbon fiber was significantly weaker than that of the original cotton fabric, indicating that the carbon skeleton had been damaged to some extent. After reacting with MCA, the carbonyl group was at approximately 1726 cm⁻¹. -1 A new bond band corresponding to the C=O stretching vibration appeared, confirming that the MCA monomer was grafted onto the macromolecule of the cotton fabric. However, in the COT-DCMC spectrum, the intensity of this peak belonging to the aldehyde carbonyl group was significantly weakened. Figure 1 d), because at 896cm -1 The intensity of nearby wavelengths was assigned to hemiacetal and acetal bonds formed between the aldehyde group and the adjacent hydroxyl group. The results indicate that the aldehyde group was introduced into the structure via selective periodate oxidation. Figure 1 Compared to d, Figure 1 The characteristic peaks of the aldehyde group in e were significantly weakened, at 1643 cm⁻¹. -1 and 1427cm -1 The two nearby peaks belong to the asymmetric and symmetric stretching vibrations of the COO- group, respectively. Therefore, it can be inferred that the aldehyde group reacts with the amino group of L-glutamic acid, while the carboxyl group in COT-Glu exists as a carboxylate with stronger intensity. Furthermore, at 1645 cm⁻¹... -1 The peak value at 1645 cm⁻¹ also belongs to the amide I band (C=N stretching vibration), which overlaps with the asymmetric stretching vibration of the COO- group. -1 1427cm -1 and 1052cm -1 The absorption band intensity is significantly enhanced in this band (see...). Figure 1 f), and Figure 1 Compared to e, this further verifies that a large number of carboxyl groups are introduced into cotton fabrics and interact with calcium ions (Ca). 2+ A chelation reaction occurred.

[0051] XPS Analysis: Figure 2The images show XPS full-scan spectra: (a) COT-M, (b) COT-CMC, (c) COT-DCMC, (d) COT-Glu, and (e) COT-Glu-Ca. Further verification of the compositional mechanism of flame-retardant cotton fabrics and the role of Ca... 2+ The chelation effect with carboxyl groups in cellulose was investigated using XPS broadband spectroscopy to analyze the surface chemical composition of samples after each modification process and the final chelation. All five samples contained C and O (see...). Figure 2 Full-scan XPS spectra were used to observe new peaks for N1s and Ca 2p in the full-scan XPS spectra d, e, and e, respectively. The high-resolution C1s spectra of the five samples were then analyzed and characterized based on their shape signals.

[0052] For the COT-M sample, the three peaks at 284.6 eV, 286.4 eV, and 287.7 eV are attributed to the CC / CH, C-OH, and OCO bonds, respectively. However, the C1s peak shape of the COT-CMC sample ( Figure 2 b) Significantly different from the COT-M sample. A new peak was found at 288.9 eV, belonging to the ester bond (-COO-), with a higher and more prominent C-OH peak, indicating that more chloroacetic acid was grafted onto the alkali-treated cotton fabric. Furthermore, the proportion of C-OH in COT-DCMC was significantly lower than in COT-M and COT-CMC. After oxidation, the 287.1 eV peak corresponding to the carbon atoms in OCO or C=O shifted slightly to a lower bond energy (0.6 eV), indicating that the hydroxyl groups at the C2-C3 positions were oxidized by NaIO4 to form aldehyde groups. C=O and OCO coexisted, consistent with the FTIR spectrum. After L-glutamic acid grafting ( Figure 2 d) The two new peaks at 285.6 eV and 284.0 eV are correlated with the C=N peak of the C-N bond of L-glutamic acid and the Schiff base reaction between the amino group and the aldehyde group of L-glutamic acid, achieving the expected design. Considering calcium carboxylate (-COOCa 1 / 2 A network is formed on the surface of the cotton fabric, with Ca 2+ After combination, the peaks of C-OH, CN, and C=O / COC become significantly weaker, indicating that calcium carboxylate (-COOCa) 1 / 2 A network structure is formed on the surface of cotton fabric.

[0053] Figure 3 The XPS spectrum of N1s is deconvolved with Ca2p. In the N1s spectrum ( Figure 3 a) The peaks at 399.4 eV and 4000.4 eV were attributed to CN and C=N, respectively, while the -NH2 peak was not detected, indicating that the -NH2 group reacted with the -C=O group to form a new chemical bond and was completely consumed. 2+ After chelation (such as) Figure 3As shown in the N1s mode of a), the intensity and width of the peak near -CN increase slightly, while the center positions of the -CN and -C=N peaks do not shift significantly towards higher BE values, indicating that Ca 2+ Carboxyl groups were successfully adsorbed into the treated sample. Furthermore, analysis of the Ca 2p spectrum revealed a dual-state characteristic of the element: a first Ca 2p³ / ² band at 347.7 eV, and a second Ca 2p³ / ² band 3.6 eV higher than Ca 2p³ / ². XPS results indicate that -COO reacts with Ca atoms entering the cotton fabric surface via its carboxyl oxygen atom. 2 + ions successfully achieved strong coordination.

[0054] XRD analysis: Figure 4 XRD diffraction curves. (a) COT-M, (b) COT-CMC, (c) COT-DCMC, (d) COT-Glu, (e) COT-Glu-Ca. Figure 4 The diffraction peaks of cellulose in cotton were approximately located at 2θ = 14.8°, 16.2°, 22.6°, and 34.1°, corresponding to the reflection positions of the (1-10), (110), (002), and (040) crystal planes of cellulose I, respectively. After alkali treatment, the intensity of the characteristic peaks at 14.8° and 22.6° decreased significantly, and a new diffraction peak appeared at 20°, indicating that the 24wt% NaOH solution had a certain destructive effect on the crystal structure of cotton fabric, leading to partial conversion of cellulose I to cellulose II and an increase in reaction sites in the amorphous region. Figure 4 d shows that, with Figure 4 Compared to c, the peaks at 22.6° and 20° become wider and sharper, respectively, indicating that the periodate oxidation reaction occurs not only in the amorphous region of cellulose but also in the crystalline region. Figure 4 As shown in the figure, the diffraction peak at 22.6° shows a slight tilt after glutamic acid treatment. This indicates that the modifier affects the crystalline structure of the fabric. Furthermore, in Figure 4 In f, due to Ca 2+ The molecules enter the cellulose molecular chain and exhibit strong complexation with active groups, disrupting the original structure of cellulose and reducing its crystallinity. The crystallization peak drops sharply at 22.6°. These results further demonstrate the success of the cotton fabric modification.

[0055] SEM analysis: Figure 5SEM images of cotton fabrics during the grafting and chelation process. (a) COT; (b) COT-M; (c) COT-CMC; (d) COT-DCMC; (e) COT-Glu; (f) COT-Glu-Ca; (g) 500x magnification of the carbon layer in the COT-Glu-Ca fabric; (h) 5000x magnification of the residual carbon layer in the COT-Glu-Ca fabric. The morphology of cotton fibers was captured by SEM images, depicting the evolution from the initial morphology to the final residue, such as... Figure 5 As shown. The original cotton fabric surface was smooth and flat, with no other substances even detected. The cotton fabric fiber surface after alkali treatment was smooth and full. After grafting MCA and treating with NaIO4, the surface morphology of the cotton fibers changed slightly, forming a thin film. After treatment with L-glutamic acid and CaCl2, the surface of the cotton fabric became rough, with tiny white particles, indicating that L-glutamic acid was successfully grafted onto the cellulose macromolecules, and the CaCl2 on the surface of the cotton fabric... 2+ Effective adsorption was achieved. Combined XPS and FTIR analyses confirmed the modification and chelation of Ca in the cotton fabric. 2+ It was a success.

[0056] Figure 6 EDS analysis of cotton fabrics. a) COT (raw cotton fabric), b) COT-CMC, c) COT-DCMC, d) COT-Glu, e) COT-Glu-Ca, f) Carbon residue of COT-Glu-Ca. The chemical elemental composition of the cotton fabrics before and after treatment was analyzed using energy dispersive spectroscopy (EDS). The atomic weights of the cotton fabrics were determined by EDS. Figure 6 As shown, COT-CMC and COT-DCMC fabrics contained only C and O mainly from cotton fabric and chloroacetic acid, while the COT-Glu sample contained not only C and O from L-glutamic acid but also N from L-glutamic acid, confirming the successful grafting of L-glutamic acid onto the cotton fabric. Ca(II) was also detected on COT-Glu-Ca at a mass percentage of 10.14%, indicating that Ca... 2+ It is adsorbed onto the surface of cotton fabric. In the carbon layer, the atomic weight ratio of O decreases, while that of N and Ca increases. 2+ The increase in the atomic weight ratio indicates that Ca... 2+ It plays an important role in condensed-phase flame retardants. Calcium ions oxidize to form a protective film of calcium carbonate, which effectively isolates air, blocks heat, and facilitates mass transfer during combustion. The percentage of C and O atoms in the carbon layer decreases significantly after combustion due to the production of large amounts of non-combustible gases (H₂O, CO₂, etc.) during the process. The calcium content in the carbon layer... 2+ The increase in atomic percentage (from 0.51 wt% to 11.15 wt%) is also attributed to the enhanced flame-retardant effect of the condensed phase, which may be due to the calcium carboxylate (-COOCa) 1 / 2 Caused by the thermal decomposition products of ).

[0057] GT Analysis: Figure 7 TG and DTG curves for raw cotton samples (COT) and the final treated cotton fabric (COT-Glu-Ca): (a) TG in air, (b) TG in N2, (c) DTG in air, (d) DTG in N2. The TG and DTG curves of raw cotton and chemically modified cotton fabric in air and N2 are shown below. Figure 7 As shown in Table 1, the relevant data indicates that the final modified sample (COT-Glu-Ca) underwent three weight loss stages in air. The first stage of weight loss occurred within the temperature range of 43–167℃, with a weight loss rate of 8.7%, which is related to the evaporation of moisture absorbed by the cotton fabric. In the second stage, within the temperature range of 221.5–416.6℃, due to decarboxylation, dehydration, and glycosidic bond breakage of the modified cotton fabric, intermediate substances were formed, accompanied by the release of H2O and CO2. Rapid pyrolysis occurred at 291.3℃, with a maximum weight loss rate (Rmax) of 4.4%, while COT's maximum weight loss rate at 339.4℃ was 30.4%. The final step occurred between 416.6–567℃, where further decomposition of the intermediate substances formed calcium oxide and stable carbon, which adhered to the fabric surface as a protective layer. At 800℃, the residual carbon content was 5.6%, while COT's was almost zero. Clearly, the decomposition initiation temperature (Tonset) of COT-Glu-Ca is about 95°C lower than that of COT fabric. This is because calcium ions can catalyze the degradation of modified cotton fabric at lower temperatures (below 200°C). In N2, apart from the loss of adsorbed moisture, the thermal decomposition behavior of cotton fabric before and after flame retardant treatment only showed one large, rapid weight loss. The maximum decomposition temperature (Tmax) of COT-Glu-Ca is 270.5°C, far lower than that of COT (358.3°C). Furthermore, from (… Figure 7 As can be clearly seen from Table 2, under a nitrogen atmosphere, the residual carbon content of the COT-Glu-Ca sample was 28.2 wt%, which was 248.2% higher than that of the COT fabric (8.1 wt%). Simultaneously, the residual carbon content of the COT-Glu-Ca sample was significantly higher in N2 than in air, which is because N2 inhibits the thermal oxidation of cotton fabrics. In summary, the thermal decomposition properties of COT and COT-Glu-Ca differ significantly; COT-Glu-Ca has a lower thermal degradation temperature, a smaller maximum weight loss rate, and a higher residual carbon content. These phenomena demonstrate that introducing carboxyl groups and calcium ions into the cellulose molecules can catalyze the formation of more char layers, thereby inhibiting fiber combustion in the condensed phase. This significantly improves the thermal stability and flame retardancy of cotton fabrics.

[0058] Table 1. Thermogravimetric data of virgin cotton fabric (COT) and modified cotton fabric (COT-Glu-Ga) in air and N2.

[0059]

[0060] Figure 8 The image shows a vertical burning experiment. The top image is of the original cotton fabric, and the bottom image is of COT-Glu-Ca fabric. After a series of grafting and complexing treatments, the LOI value of the COT-Glu-Ca fabric reached 33.6%, which is 15.8% higher than that of the original cotton, indicating its excellent flame retardant properties. This is because Ca... 2+ It can catalyze the decarboxylation of fabrics and react with the released CO2 at high temperatures to generate CaCO3. CaCO3 ultimately coats the surface of the burning fabric, thus preventing heat and oxygen transfer and achieving flame retardancy. Furthermore, stronger bond energies generally result in better preservation of the molecular structure, leading to increased char formation. Carbon-nitrogen double bonds (C=N) are more conducive to char formation, improving the material's flame retardancy. The vertical burning process of cotton fabrics before and after modification is as follows: Figure 8 As shown in Table 2, the combustion characteristics of the two samples are significantly different. The control cotton fabric (COT) burns violently, rapidly, and completely, leaving a large amount of loose ash, while the modified fabric (COT-Glu-Ca) burns less noticeably, forming a very complete char layer after combustion. Therefore, it can be inferred that the modified cotton fabric burns through the interaction of a large amount of -COO- with Ca... 2+ The chelation of Ca2+ forms a special eggshell structure, acting as a protective layer to prevent heat from penetrating the fiber interior, thus giving the modified cotton fabric excellent flame retardancy. Compared with the original cotton fabric, the vertical burning effect of COT-Glu-Ca is significantly enhanced, which is also reflected in the difference in char layer images and the reduction in char length, smoldering time, and flame extension time. In other words, the prepared flame-retardant cotton fabric can undergo vertical burning tests. Furthermore, the char length is only 53 mm, and no large amount of smoke is produced, which further proves that the grafted cotton fabric with Ca2+ through a series of modifications and crosslinking has good flame retardant effects.

[0061] Table 2 Vertical Combustion Data

[0062]

[0063] Table 3 Whiteness and tensile properties test

[0064]

[0065]

[0066] The tensile properties of cotton fabrics were tested to investigate the effect of modification on their mechanical properties, as shown in Table 3. The breaking strength of the original cotton warp yarn was 368.4 N. After treatment with 24 wt% NaOH solution, the breaking strength increased by 17.59%. After grafting with chloroacetic acid, the tensile strength of the cotton warp yarn increased to 466.8 N. This is because the alkali treatment and chloroacetic acid grafting did not significantly damage the macromolecular structure of the cotton fibers, while the fabric density after alkali treatment was 20% higher than that of the original fabric, thus significantly improving the breaking strength. After treatment with sodium periodate, the tensile strength of the cotton fabric decreased by 36.1%. This is because the selective oxidation of sodium periodate led to the breakage of the C2-C3 bonds, causing some damage to the original macromolecular structure of the cotton fabric. The breaking strength of the fabric further decreased after treatment with L-glutamic acid, which is related to the acid resistance of the cotton fabric. For the COT-Glu-Ca fabric, due to the -COO and Ca... 2+ The formation of intramolecular and intermolecular network structures hinders the sliding of fiber macromolecular chains during stretching to some extent, thus slightly increasing the strength compared to COT-Glu. In summary, the mechanical properties of the fabric before and after modification do not change significantly, and it maintains good strength in practical use. The whiteness of the control cotton is 85.14%, and the whiteness of the modified cotton fabric is not significantly different from that of the original cotton, indicating that the whiteness of the modified cotton fabric is well maintained.

[0067] Figure 9 For contact angle testing, the left image shows the original cotton fabric, and the right image shows the modified cotton fabric COT-Glu-Ca. The contact angle test (see...) Figure 9 The results show that the hydrophilicity of the cotton fabric is 0°, consistent with the results of the modified cotton fabric (COT-Glu-Ca). This indicates that the series of modifications did not affect the hydrophilicity of the cotton fabric. These results further demonstrate that the chelation between calcium ions and -COO significantly enhances the flame retardancy of the fabric, while other excellent properties of the cotton fabric remain unaffected.

[0068] This invention successfully developed a novel flame-retardant cotton fabric that is green and formaldehyde-free during use and production. It can form a unique network skeleton structure on the surface and inside of cotton cellulose to enhance the connections between macromolecules. This modification strategy for cotton fabric can significantly improve the flame-retardant effect, even giving it self-extinguishing properties during combustion, with an LOI value as high as 33.6% after 12 seconds of burning and a carbon skeleton length of only 53 mm. (Chelated Ca) 2+ The reaction plays a crucial role in preventing the transfer of heat, flame, and oxygen from the thermal decomposition gases and inhibiting the thermal decomposition of internal fibers. These chemically modified cotton fabrics not only exhibit excellent flame retardancy but also maintain superior levels of whiteness, tensile strength, and moisture absorption. A novel approach to preparing halogen-free, phosphorus-free, and formaldehyde-free flame-retardant cotton fabrics without altering the inherent properties of the fabric is proposed.

[0069] Compare with Example 1:

[0070] (1) Preparation of COT-M by alkaline treatment of cotton fabric: 24g of sodium hydroxide was poured into 76ml of deionized water to prepare a 24% sodium hydroxide solution. A 300mm×89mm cotton fabric was soaked in the 24% sodium hydroxide solution for 10 minutes (liquor ratio 1:25); then the treated cotton fabric was soaked in a 24wt% acetic acid solution for 10 minutes to neutralize the excess sodium hydroxide. The treated cotton fabric was washed with deionized water to obtain COT-M cotton fabric, and then placed in a 60℃ forced-air drying oven to dry.

[0071] (2) Preparation of carboxymethyl fiber (COT-CMC): Weigh 25g of chloroacetic acid and pour it into 75ml of deionized water to prepare a 25% chloroacetic acid solution. Soak the COT-M cotton fabric in the chloroacetic acid solution and react at 40℃ for 4 hours. Take out the cotton fabric and wash it with deionized water to obtain COT-CMC cotton fabric. Then put it into a 60℃ forced-air drying oven to dry.

[0072] (3) Reaction of carboxyl group and calcium chloride: Weigh 20g of calcium chloride and mix it evenly with 100ml of deionized water to form a calcium chloride solution of 200g / L. Place the COT-CMC cotton fabric into the calcium chloride solution and place it in a shaker at a speed of 120mm / s for 1 hour. Take out the cotton fabric and wash it with deionized water to obtain the treated cotton fabric. Place it in a 60℃ forced-air drying oven to dry.

[0073] Carboxymethyl cellulose is produced by grafting chloroacetic acid onto the hydroxyl groups at the C6 position of cellulose. This carboxymethyl cellulose then undergoes chemical chelation with calcium ions in a CaCl2 aqueous solution, resulting in a flame-retardant cotton fabric that exhibits excellent vertical burning properties. Figure 11 As shown, flame-retardant cotton fabrics ignite immediately upon contact with a flame, burning intensely with almost no ash remaining. The combustion is relatively complete, with an afterflame time of 4.2 seconds, a smoldering time of 21.2 seconds, and a limiting oxygen index of 19.7%. This indicates that the method can improve the flame retardancy of cotton fabrics, but the effect is not ideal.

[0074] Compare with Example 2:

[0075] (1) Preparation of COT-M by alkaline treatment of cotton fabric: 24g of sodium hydroxide was poured into 76ml of deionized water to prepare a 24% sodium hydroxide solution. A 300mm×89mm cotton fabric was soaked in the 24% sodium hydroxide solution for 10 minutes (liquor ratio 1:25); then the treated cotton fabric was soaked in a 24wt% acetic acid solution for 10 minutes to neutralize the excess sodium hydroxide. The treated cotton fabric was washed with deionized water to obtain COT-M cotton fabric, and then placed in a 60℃ forced-air drying oven to dry.

[0076] (2) Preparation of dialdehyde fiber: Weigh 4.28g of sodium periodate, pour it into a brown conical flask covered with tin foil and dissolve it in 100ml of deionized water to prepare a 0.2mol / L sodium periodate solution. Soak the COT-M cotton fabric in the sodium periodate solution and react at 40℃ for 1 hour. Take out the cotton fabric, weigh 0.46g of glycerol and mix it evenly with 50ml of deionized water to prepare a 0.1mol / L glycerol solution. Soak the cotton fabric in the 0.1mol / L glycerol solution for 30 minutes and wash it with deionized water to obtain dialdehyde fiber cotton fabric. Place it in a 60℃ forced-air drying oven to dry.

[0077] (3) The reaction of dialdehyde fiber and L-glutamic acid to generate Schiff base: Weigh 0.735g of glutamic acid and 100ml of deionized water into an Erlenmeyer flask and mix evenly to form a 50mmol / L glutamic acid solution. Soak the dialdehyde fiber cotton fabric in it and place it in a shaker at a speed of 120mm / s for 1 hour. Take out the cotton fabric, wash it with deionized water, and put it into a 60℃ drying oven to dry.

[0078] (4) Reaction of carboxyl group and calcium chloride: Weigh 20g of calcium chloride and mix it evenly with 100ml of deionized water to form a calcium chloride solution of 200g / L. Put the cotton fabric obtained in step (3) into the calcium chloride solution and place it in a shaker with a speed of 120mm / s to shake for 1 hour. Take out the cotton fabric and wash it with deionized water to obtain the treated cotton fabric. Place it in a 60℃ drying oven to dry.

[0079] After raw cotton is treated with an alkaline solution, sodium periodate is used to oxidize the hydroxyl groups at the C2 and C3 positions of cellulose into dialdehyde cellulose, which then undergoes a Schiff base reaction with glutamic acid to form flame-retardant cotton fabric. The flame retardancy of the cotton fabric is tested using vertical burning and limiting oxygen index methods. Figure 12 As shown, compared with Control Example 1, the fabric burned slightly slower, the flame duration increased, less ash remained, and the combustion was more complete. The afterflame time was 9.5 s, the smoldering time was 33.8 s, and the limiting oxygen index was 21.2%, confirming that this method improved the flame retardancy of cotton fabrics, but the effect was still not good.

[0080] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing flame-retardant cotton fabric based on chemical grafting, characterized in that: Includes the following steps, (1) Preparation of COT-M cotton fabric by alkaline treatment of cotton fabric: The cotton fabric is soaked in sodium hydroxide solution, neutralized, washed and dried to obtain COT-M cotton fabric. (2) Preparation of carboxymethyl fiber COT-CMC cotton fabric: The COT-M cotton fabric was soaked in chloroacetic acid solution for reaction, the cotton fabric was taken out, washed and dried to obtain COT-CMC cotton fabric; (3) Preparation of COT-DCMC cotton fabric with dual aldehyde fiber: The COT-CMC cotton fabric is soaked in sodium periodate solution for reaction, the cotton fabric is taken out and soaked in glycerol solution, the cotton fabric is taken out, washed and dried to obtain COT-DCMC cotton fabric. (4) Preparation of COT-Glu cotton fabric: The COT-DCMC cotton fabric is soaked in glutamic acid solution, shaken to react, the cotton fabric is taken out, washed and dried to obtain COT-Glu cotton fabric. (5) Preparation of COT-Glu-Ca cotton fabric: The COT-Glu cotton fabric is soaked in calcium chloride solution, shaken to react, the cotton fabric is taken out, washed and dried to obtain COT-Glu-Ca cotton fabric. In step (1), the concentration of sodium hydroxide solution is 24~25wt%, and the soaking time is 10~20 min; In step (2), the concentration of the chloroacetic acid solution is 25-30 wt%; In step (2), the reaction temperature is 40~75℃ and the reaction time is 4~5 hours; In step (3), the concentration of the sodium periodate solution is 0.2~0.4 mol / L; the reaction is carried out at a temperature of 40℃ for 1~1.5 hours. In step (4), the concentration of the glutamic acid solution is 50~100 mmol / L; In step (5), the concentration of the calcium chloride solution is 200~250 g / L, and the shaking reaction is a shaking reaction at a speed of 100~120 mm / s for 1~1.5 hours.

2. The method for preparing flame-retardant cotton fabric based on chemical grafting according to claim 1, characterized in that: In step (3), the concentration of the glycerol solution is 0.1~0.2 mol / L, and the cotton fabric is soaked in the glycerol solution for 30~40 minutes.

3. The method for preparing flame-retardant cotton fabric based on chemical grafting according to claim 1, characterized in that: In step (4), the oscillation reaction is an oscillation reaction at a speed of 100~120 mm / s for 1~1.5 hours.

4. The method for preparing flame-retardant cotton fabric based on chemical grafting according to claim 1 or 2, characterized in that: In step (1), the washing is done with water; the drying is done at 55~60℃.

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