Analysis of the flame retardant mechanism and method of fabrics

The flame retardant of textiles is roughly divided into two categories: flame retardant treatment of fibers and flame retardant finishing of fabrics according to the production process and the introduction method of flame retardants. 1. Flame retardant treatment of fibers 1. Flame retardant mechanism The flame retardant treatment of fibers is to add a certain flame retardant to some flammable raw silks such as polyester, nylon, acrylic, etc. to inhibit the free radicals or free radicals in the combustion process. It is to change the thermal decomposition process of the fiber and promote water carbonization; some make the flame retardant decompose and release non-combustible gas to cover the surface of the fiber to isolate the air. 2. Flame retardant treatment method ①. Improve the thermal stability of fiber-forming polymer. Introduce aromatic ring or aromatic heterocycle into the macromolecular chain of fiber-forming polymer to increase the rigidity of the molecular chain, the density of macromolecules and the cohesion. The high thermal stability polymer is then wet-spun into fibers; it becomes a three-dimensional cross-linked structure through the cross-linking reaction of linear macromolecular chains in the fiber, preventing the carbon chain from breaking, shrinking, and melting flame retardant. Sexual fibers; the fibers are kept in an air oxidation furnace at 200 to 300 ° C for tens of minutes or hours to carbonize the macromolecules of the fibers and become flame-retardant fibers. ②, flame retardant modified copolymerization method of raw silk: in the synthesis process of fiber-forming polymer, compounds containing phosphorus, halogen, sulfur and other flame retardant elements are introduced into macromolecules as comonomers (reactive flame retardants). In the chain, this flame-retardant substance is added to the fiber; the blending method: the same as the copolymerization method, it belongs to the modification of the precursor, which is a method of adding the flame retardant to the spinning melt or spinning the flame-retardant fiber; Grafting modification: The use of radiation heat, high-energy electron beam or chemical initiator to graft and copolymerize fibers or fabrics with ethylene flame retardant monomers is an effective and lasting flame retardant modification method. The flame retardancy of the grafted flame retardant modified fiber is related to the type of flame retardant elements in the graft monomer and the graft position. The order of the effect of the graft position on the flame retardant effect is: core grafting > uniform grafting > surface grafting branch. 2. Flame retardant finishing of fabrics 1. Flame retardant mechanism In the post-finishing process of textiles, the surface treatment of fabrics is carried out, so that the fabrics have flame retardant properties. ①. Covering layer theory The flame retardant can form a glass-like or stable foam covering layer at high temperature, which has the function of heat insulation and oxygen barrier, preventing flammable gas from escaping outward, and playing a flame retardant role. ②. Non-combustible gas theory The flame retardant is heated to decompose non-combustible gas, and the concentration of combustible gas decomposed from cellulose is diluted to below the lower limit of combustion. ③, Endothermic Theory Flame retardants undergo an endothermic reaction at high temperatures, reducing the temperature to prevent the spread of combustion. In addition, the fabric can quickly dissipate heat after finishing, so that the cellulose does not reach the temperature of fire. ④. The chemical reaction theory (catalytic dehydration theory) The flame retardant reacts with cellulose as a Lewis acid at high temperature, so that the fiber is catalytically dehydrated and carbonized, and the production of combustible gas is reduced. 3. Flame retardant finishing method 1. Padding baking method is the most widely used process in the flame retardant finishing process. The technological process is: padding—pre-bake—bake—post-processing. 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. Impregnation—The drying method, also known as the exhaust method, is to immerse the fabric in the flame retardant liquid for a certain period of time, and then dry and bake it so that the flame retardant liquid is absorbed by the fiber polymer. 3. Organic solvent method This method uses a water-insoluble flame retardant, which has the advantage of low energy consumption during flame retardant finishing. However, in actual operation, attention should be paid to the toxicity and flammability of the solvent. 4. Spraying method All products such as thick curtains and large carpets that cannot be processed by ordinary equipment can be finished by hand spraying in the last process. For fabrics with patterns, tufts and piles on the bulky surface, if the padding method is used, the surface fluff pattern will be damaged, so 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 difference of mechanical equipment, it is divided into blade coating method and casting coating method. At present, the flame retardant method widely used in the market is mainly to finish the finished product after the flame retardant, the process is simple, and the fiber used is relatively simple. Regardless of which method is used for flame retardant processing, the desired flame retardant properties must be achieved. The flame retardant performance of flame retardant fabrics is usually expressed by the limiting oxygen index LOI value, which indicates the minimum concentration of oxygen required for the sample to maintain combustion in a mixture of oxygen (O2) and nitrogen (N2). A high LOI value indicates that the fabric is less flammable because the fibers require more oxygen to maintain combustion; conversely, a lower LOI value means less oxygen is required for the fibers to burn, making it easier to maintain combustion. Table 1 shows the LOI values ​​of common fibers. Table 1 LOI value of common fibers Natural and conventional synthetic fibers LOI flame retardant, fireproof synthetic fibers LOI kapok, cellulose fibers 18-20 PVC 35-37 wool 24-25 aramid 25-37 nylon 20-22 PBI 30-43 poly In addition to considering flame retardancy, ester 20-22 phenolic 30-36 polyacrylonitrile 18-20 flame retardant fabrics should 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 molten material dripping after burning.