Analysis of the flame retardant principle of textiles

According to the production process and the method of introducing flame retardants, the flame retardant of textiles can be roughly divided into two types: flame retardant treatment of fibers and flame retardant finishing of fabrics. 1. Flame-retardant treatment of fiber 1. Flame-retardant mechanism The flame-retardant treatment of fiber is to add a certain flame retardant to some inherently combustible filaments, such as polyester, nylon, acrylic, etc., to inhibit free radicals or It is to change the thermal decomposition process of the fiber to promote water carbonization; some are to decompose the flame retardant and release incombustible gas to cover the surface of the fiber, which acts as a barrier to air. 2. Flame-retardant treatment method ①. Improve the thermal stability of the fiber-forming polymer. Introduce an aromatic ring or aromatic heterocycle into the macromolecular chain of the fiber-forming polymer to increase the rigidity of the molecular chain, the degree of density and cohesion of the large division. Then the high thermal stability high polymer is wet-spinned into fiber; through the cross-linking reaction between the linear macromolecular chains in the fiber, it becomes a three-dimensional cross-linked structure, which prevents the carbon chain from breaking without shrinking, and is flame retardant. Sexual fiber; the fiber stays in the air oxidation furnace at 200-300°C for tens of minutes or several hours to carbonize the fiber macromolecules and become flame-retardant fibers. ②. Raw silk flame-retardant modified copolymerization method: In the synthesis process of fiber-forming polymers, compounds containing phosphorus, halogen, sulfur and other flame-retardant elements are introduced as comonomers (reactive flame retardants) into the macromolecules In the chain, this highly flame-retardant substance is added to the fiber; blending method: It is the same as the copolymerization method to modify the original filament, which is a method of adding flame retardant to the spinning melt or spinning flame-retardant fiber; Graft modification: Use radiant heat, high-energy electron beams or chemical initiators to graft copolymerize fibers or fabrics with ethylene flame-retardant monomers, which is an effective and long-lasting flame-retardant modification method. The flame retardancy of grafted flame-retardant modified fiber is related to the types of flame-retardant elements in the grafting monomer and the grafting location. The order of the effect of the grafting location on the flame retardant effect is: core grafting>uniform grafting>surface grafting branch. 2. Flame-retardant finishing of fabrics 1. Flame-retardant mechanism. Surface treatment of fabrics during the finishing process of textiles makes the fabrics flame-retardant. ① Covering layer theory The flame retardant can form a glassy or stable foam cover layer at high temperature, which has the function of heat insulation and oxygen isolation, preventing combustible gas from escaping outward, and playing a flame retardant effect. ② Non-combustible gas theory The flame retardant decomposes non-combustible gas when heated, and dilutes the concentration of combustible gas from the decomposition of cellulose to below the lower combustion limit. ③, endothermic theory The flame retardant undergoes an endothermic reaction at high temperatures, reducing the temperature to prevent the spread of combustion. In addition, the heat can be quickly transferred out after the fabric is finished, so that the cellulose cannot reach the temperature of fire and combustion. ④. Chemical reaction theory (catalytic dehydration theory) The flame retardant acts as a Lewis acid to react with cellulose at high temperature to make the fiber catalytically dehydrated and carbonized, reducing the production of combustible gas. 3. Flame-retardant finishing method 1. The most widely used process in the flame-retardant finishing process of padding and baking method. The technological process is: padding-pre-baking-baking-post-treatment. The padding liquid is generally composed of flame retardant, catalyst, resin, wetting agent and softener, and is formulated into an aqueous solution or emulsion for finishing. 2. The impregnation-drying method is also known as the exhaustion method, which is to immerse the fabric in the flame retardant liquid for a certain period of time, and then dry and bake so that the flame retardant liquid is absorbed by the fiber polymer. 3. Organic solvent method This method uses non-water-soluble flame retardants, which has the advantage of low energy consumption during flame retardant finishing. But in actual operation, pay attention to the toxicity and flammability of the solvent. 4. Spray method. Any thick curtains, large carpets and other commodities that cannot be processed by ordinary equipment can be flame-retardant finishing by hand spray method in the last process. For fabrics with patterns, tufts, and piles on the bulky surface, if the padding method is used to damage the surface pile patterns, the continuous spray method is generally used. 5. The coating method mixes the flame retardant into the resin, and the flame retardant is fixed on the fabric by the adhesion of the resin. According to the different mechanical equipment, it is divided into knife coating method and casting coating method. At present, the flame retardant method widely used in the market is mainly based on the finishing treatment of the finished product with a flame retardant, the process is simple, and the use of fiber is relatively simple. No matter which method is used for flame-retardant processing, the expected flame-retardant performance must be achieved. The flame-retardant performance of flame-retardant fabrics is usually expressed by the limiting oxygen index LOI value, which represents the minimum concentration of oxygen required for the sample to maintain combustion in a mixed gas composed of oxygen (O2) and nitrogen (N2). A high LOI value indicates that the fabric is less flammable, because the fiber needs more oxygen to maintain combustion; on the contrary, the lower the LOI value, the less oxygen the fiber needs to burn, and the easier it is to maintain combustion. Table 1 shows the LOI values u200bu200bof common fibers. Table 1 LOI value of common fibers: natural and conventional synthetic fiber LOI flame retardant, fire-resistant synthetic fiber LOI kapok, cellulose fiber 18-20 polyvinyl chloride 35-37 wool 24-25 aramid 25-37 nylon 20-22 PBI 30-43 poly Ester 20-22 Phenolic 30-36 Polyacrylonitrile 18-20 In addition to considering flame retardancy, flame retardant fabrics must also consider the so-called second safety and third safety, that is, the toxicity and meltability of flame retardant products. Test the impact on the human body and the environment, and whether there is any molten material dripping after burning.