Research and discussion on flame retardant finishing technology of cotton fabrics
According to data, fires caused by burning mattresses or bedding in the United States claim an average of 330 lives, cause 2,070 injuries, and cause $300 million in economic losses every year. It can be seen that cotton fire-resistant fabrics play a certain role in reducing the frequency of fires.
With the progress of the fabric industry and the improvement of people’s living standards, consumers are not only satisfied with the beauty and comfort of work clothes, but also require environmentally friendly work clothes. Therefore, fire-resistant fabrics must not only achieve the purpose of fire protection, but also make them The formaldehyde content meets the national requirements.
1. Principles of fire prevention
After the fabric is padded with fire-retardant liquid, the pre-shrink formed by the fire-retardant agent and amide penetrates into the amorphous area and gaps of the fiber, and is subsequently NH during ammonia fumigation. It is cross-linked with the hydroxymethyl group in the preshrunk body to form a fireproof polymer inside the fiber and then oxidized to stabilize it. Phosphorus-containing compounds dehydrate the fibers during pyrolysis. The phosphorus-containing fire retardant first decomposes into non-volatile phosphoric acid or polyphosphoric anhydride within the fiber pyrolysis temperature range and undergoes a dehydration reaction with the hydroxyl group (-OH) of the fiber to carbonize the fiber. During the ammonia fumigation process of fabrics padded with fire retardants, a highly cross-linked polymer of phosphorus dichloride/nitrogen is formed inside the cellulose, resulting in a P-N synergistic effect. The performance (polarity) of the P-N bond is higher than that of the P-O bond, which enhances the reaction performance of the phosphorus compound and -0H, thus producing fire resistance.
The so-called “fireproof” is not fireproof. It does not mean that the fabric will not be burned by fire after being treated with fireproofing. It means that the fabric will reduce its flammability under flame, reduce the area of the burning part and reduce its burning. speed. It will stop burning after the flame leaves and has self-extinguishing properties.
2. Process test results and discussions
1. Test samples and chemicals
Sample: Certain length of cotton fabric.
Agent; fire retardant – THPC (factory number FR1), buffer – TEA, penetrant – NT, ammonia, oxalic acid, non-ionic softener – AC, hydrogen peroxide (50%), liquid alkali, heavy sulfide sodium.
2. Test method
This test adopted the vertical burning method. Take 5 pieces of fabrics that have been finished with the fireproofing process in the warp and weft directions (horizontal and longitudinal directions), each piece is 8.9 cm × 25.4 cm, and fix the sample on the vertical combustion testing machine. The distance between the high points is 1.7 cm. The sample holder must be vertical to the top or bottom of the box. Adjust the flame height to 40 mm. Move the fire source to the bottom of the sample and burn for 3 seconds before taking the sample out of the test box.
Measurement of char length: Fold the sample in half along its length at the highest burning point, hang a weight on the carbonized side of the cloth sample at a distance of 6.4 cm from the bottom and the collar edge, and hold the other side of the cloth sample with your hands. On one side, slowly lift the weight so that it is suspended in the air. Use a ruler to measure the burnt length of the cloth sample and record it to the nearest 0.1 cm.
Formaldehyde and pH value testing can be carried out according to the test standards in Table 1. The various test standards for our factory’s fireproof cloth are as shown in Table 1:
The basic safety technical requirements for fabrics are shown in Table 2.
3. Fire protection process conditions and process flow
1. Fire protection process conditions
(1) The influence of pH value on finishing effect
The fire retardant agent is used at 350~450 g/L, and the dosage of other additives remains unchanged. The impact of the pH value of the solution during padding on the post-fire retardant finishing effect is shown in Table 3. It can be seen from Table 1 that after finishing in weak acid conditions, the fire resistance of the fabric is better. So the pH is taken as 5.6. The pH value of the solution during padding in our factory is generally 5.6 to 6.0.
(2) Effect of pre-baking temperature on finishing effect
The fire retardant agent is used at 350~450 g/L, and the amounts of other additives remain unchanged. See Table 4 for the effect of pre-baking temperature on the fire retardant effect. It can be seen from Table 2 that the fire protection effect is better at 110℃, so 110℃ is used.
(3) Effect of fire retardant dosage on fire performance
With the dosage of other additives unchanged, the fabric was padded in different concentrations of fire retardants for testing. The results are shown in Table 5. It can be seen from Table 3 that increasing the amount of fire retardant will improve the fire retardant performance. However, excessive use will affect the feel of the fabric and increase the cost. Considering various factors, the appropriate concentration of fire retardant is 350~450 g/L.
2. Fire prevention process
Padding fire-proof finishing liquid – pre-drying (80~110℃) – ammonia fumigation – oxidation washing water – drying (130℃ ~ 140℃) – soft shaping – finished product
(1) Pad rolling on the shaping machine
Fire retardant working fluid formula: FR1 is 350~450 g/L, NT is 1~2 g/L, TEA is 14~18 g/L, and the pH value of the adjusted solution is 5.6~6.0.
Determination of pressure water rate: I=(N—M)/M ×100%, where: I: pressure water rate (%); M: dry weight of fabric (g); N: weight of fabric after padding (g) During padding, the pressure of the rolling wheel on the setting machine is 0.15MPa, which is adjusted depending on the thickness of the cloth.
After the cloth surface is padded, cut a piece of wet cloth and weigh it to 18.29 g. After drying, it is 10.6 g, and the moisture content is 72.5%. (Based on the performance of the fabric itself and the rolling wheel For affordability, choose pure cotton (70% to 75%). The adjusted wind speed is 800 ~ 1000 m/min, the machine speed is 18 ~ 20 m/min, and the baking humidity is 80 ~ 10℃. The above three values are adjusted according to the thickness of the cloth. The purpose of adjusting this value is to ensure that the baked cloth has a certain humidity, which facilitates the production of NH3 and the fire retardant on the fabric during ammonia fumigation.Chain reaction, fire prevention effect. Generally, the moisture content is controlled between 14% and 18%, and the moisture content of the left, middle and right cannot exceed 2%, otherwise it is easy to produce color differences between the left, middle and right. Therefore, the moisture content should be monitored at any time during the production process and adjusted at any time. If the ratio is too small, it will lead to insufficient cross-linking, unsatisfactory fire protection effect, excessive moisture content, hard feel, and large color changes.
(2) Ammonia fumigation
The amount of ammonia consumed per kilogram of fire retardant is theoretically certain, but in the actual production process it should be slightly excessive to ensure sufficient cross-linking. Generally, the ammonia gas flow rate is controlled at 35 to 45 m. /min, the flow rate is too small, cross-linking is insufficient, the fire protection effect is not ideal, and the wash resistance is poor; the flow rate is too large, causing waste and ammonia leakage, resulting in a harsh working environment and affecting personal safety. In practical applications, the flow rate of ammonia gas should also be adjusted according to the thickness of the fabric and the amount of fire retardant agent to achieve the best fire retardant effect.
To achieve sufficient ammonia fumigation, the machine speed must be adjusted to about 8-15 m/min, and the temperature must be controlled at about 28-32°C. During the ammonia fumigation process, oxalic acid is also added, which is used to neutralize and dilute the exhaust gas.
(3) Washing water in the water washing machine (formaldehyde washing)
In order to make the fire retardant more stable after being cured by ammonia fumigation, P+3 must be oxidized to P+5. This is usually achieved by padding H2O2. The amount of H2O2 should be based on the thickness of the fabric and the amount of the fire retardant. It depends on the dosage. Our factory adjusts the concentration of H2O2 to 27% ~ 3O%. The speed of padding oxidation solution should not be too fast to ensure that enough H2O2 remains on the fabric. Generally, the machine speed is adjusted to 15~20 m/min. After being ventilated and oxidized, it is then neutralized and washed away with soap. The oxidation time should not be too long, otherwise the strength of the fabric will be reduced.
Our factory uses Na2C02 and NaOH for neutralization. In addition to neutralizing the pH of the cloth surface, they can also adjust the pH value of the solution; sodium bisulfite is mainly responsible for the formaldehyde content of the washed cloth surface, because after the fabric is padded, the cloth surface The formaldehyde content contained is as high as 2000 ppM, which is far beyond the scope stipulated by the country and is harmful to the human body. Urea has been used to remove formaldehyde, but the effect was not obvious. After washing, the formaldehyde and pH content and fire protection function should be tested. If it is satisfactory, it can be softened; if the fire protection test fails, the fire protection treatment must be redone; if the formaldehyde content is higher than the standard, formaldehyde washing must be arranged again. The dosage of each agent for washing formaldehyde, the pH value and temperature of the solution are shown in Table 6 (adjust the dosage of the agent appropriately according to the quantity of cloth).
(4) Soft shaping on the shaping machine
Because fabrics generally have unsatisfactory hand feel after being treated with fire retardants, they need to be softened to restore the hand feel. But if it is a printed fabric, it does not have to be soft, because the soft and set shape of the printed fabric will change its pattern. Non-ionic softeners should be used for fire-retardant cloth, because ionic softeners contain silicone oil, which acts as a combustion-supporting agent and is extremely detrimental to fire-retardant cloth. Our factory has used weak positive softening leavening agent for softening treatment. After treatment, the cloth surface is smoother and the hand feel is softer than using non-ionic softening agent. However, it affects the fireproof effect and is not adopted for the time being. The dosage of AC is generally 40~60 g/L. The temperature is controlled at around 130℃.
4. Conclusion
1. The amount of fire retardant agent has an impact on the fire retardant performance. The best fire retardant concentration is 35O~450 g/L.
2. The pH value of the fire retardant agent has an impact on the fire retardant performance. The appropriate pH value range is 5.6 ~ 6.0.
3. The baking temperature of the fire retardant agent has a certain impact on the fire retardant performance. The suitable temperature is 8O~120℃.
Fabrics treated above can generally achieve fire-retardant effects. They are low-toxic, environmentally friendly, and safe and reliable for the human body. Breathable, breathable, soft to the touch and comfortable to wear.
AAAGFHTRYKUYIU7OUP
Extendedreading:https://www.tpu-ptfe.com/post/7720.html
