Introduction to the flame retardant finishing process of polybenzene cotton
1. Foreword
The Proban method fire protection technology originated from the British Aowei Company. The main ingredients are low molecular precondensates of tetrahydroxymethylphosphorus chloride (THPC) and amide. After the fabric is padded with Proban fire retardant, the preshrunk formed by THPC and amide penetrates into the amorphous area and gaps of the fiber. Subsequently, during ammonia fumigation, NH3 cross-links with the hydroxymethyl group in the preshrunk body, forming a fireproof polymer inside the fiber and then oxidized to stabilize it. Therefore, the fabric treated by the Proban method has a soft feel and little strength loss, and basically maintains the comfort and durability of the fabric. It is suitable for making various types of protective clothing, bedding, decorative items and children’s fireproof pajamas. It is currently an important method for fireproof finishing of durable cotton fabrics.
2. Principles of fire prevention
Phosphorus-containing compounds cause cellulose fibers to undergo a dehydration reaction during the thermal process. 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 cellulose to carbonize the fiber. During the ammonia fumigation process of fabrics padded with Proban fire retardant, 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 strengthens the reaction performance of the phosphorus compound and -OH, thus producing efficient and durable fire protection properties.
3. Process flow
Padding fireproof finishing solution (room temperature) → pre-drying (100~120℃) → ammonia fumigation → oxidation water washing → drying (130~140℃) → pre-shrinking → finished product.
4. Discussion on process conditions
1. Determination of the concentration of fire retardant: In the process of formulating the process, it should be determined according to the thickness of the fabric and the liquid removal rate:
①. Determination of liquid rolling rate:
A. The liquid rolling rate is calculated according to the following formula
In the formula: I: liquid squeeze rate (%); M: dry weight of fabric (g);
N: Fabric weight after padding (g)
B. Selection of liquid mangle rate:
Based on the performance of the fabric itself and the bearing capacity of the roller, generally 70~75% is selected for pure cotton yarn card, and 80~85% is selected for pure cotton canvas.
Determination of padding fluid concentration: Calculate according to the following formula
C=B/A
In the formula, C: padding liquid concentration (%); B: fire retardant dosage (relative cloth weight %)
A: liquid squeeze rate
Principles for selecting the amount of fire retardant agent (B):
Generally for thin fabrics, the amount of Proban on the fabric should be more than 40% of the weight of the fabric, and for medium-thick fabrics it can be 35~40%. Then, according to the selection principle of liquid removal rate, substitute it into the above formula to get the optimal concentration. .
2. The size of the moisture content:
After the fabric is dried by padding with fire retardant, it must have a certain humidity to facilitate the cross-linking reaction between NH3 and the fire retardant on the fabric during ammonia fumigation, thereby achieving a fire retardant effect and being washable. Generally, the moisture content should be controlled between 12 and 16%, and the moisture content error of the left, middle and right should not 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. , too little moisture content will lead to insufficient cross-linking, and the fire retardant effect will not be washable. Too much moisture content will lead to excessive cross-linking, a hard feel, and large color changes.
3. Determination of ammonia flow rate:
From the previous reaction equation, 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. Usually the ammonia gas flow rate is controlled at 350~500L/min. If the flow rate is too small, the cross-linking will be insufficient, and the fire retardant effect will be poor and the washability is poor; if the flow rate is too large, it will cause waste and ammonia gas will leak out, resulting in a harsh working environment. 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.
4. Concentration of oxidizing agent
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 fire retardant. Depends on the size. The usual dosage is 30~35% concentration. The speed of the padding oxidation solution should not be too fast to ensure that enough H2O2 remains on the fabric, and then neutralized and soaped off after ventilation and oxidation. The oxidation time should not be too long, otherwise the strength of the fabric will be reduced.
5. Conclusion
The pure cotton fire-retardant fabrics finished with propylbenzene have excellent fire-retardant effect and meet the international GB-8965-98 “Fire-retardant protective clothing” requirements, and also meet the EU “EN470, EN470-1, EN533, EN531, BS5852″ ” and other standards, it has passed the first-class fire-retardant fabric test of the European Community, the United States, and the United Kingdom. It is low-toxic, environmentally friendly, safe and reliable for the human body, breathable, breathable, soft to the touch and comfortable to wear. It has been accepted by countries around the world.
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