The process and modification methods of flame retardant polyester fibers


1. The process of flame retardancy of polyester fibers
The flame retardancy of polyester fibers is usually divided into two main processes. Firstly, selecting and developing flame retardants with good performance, and then adding them to the fiber spinning raw materials through physical or chemical methods to achieve a firm and uniform distribution of flame retardants in the fibers. Moreover, the introduction of flame retardants has minimal impact on the physical and mechanical properties of the fibers.
2. Methods of fiber modification
There are currently four main methods for modifying flame retardant fibers:
2.1 Copolymerization flame retardant modification
Small molecule flame retardants containing flame retardant elements, mainly phosphorus, halogens (I, Br, Cl, F), sulfur, etc., are used as co monomers to participate in the polymerization process of fiber polymers, allowing the flame retardant to bind to the polymer's macromolecular chains and achieve long-term flame retardant effects. Copolymer flame retardants must be suitable for high temperature conditions of polymerization, have good stability, do not decompose, and have no side reactions.
2.2 Blending flame retardant modification
The method of spinning flame-retardant fibers by adding flame retardants to spinning melt or solution. The flame retardants used include low molecular weight compounds, high molecular weight compounds, or inorganic compounds and their mixtures. For blending with the melt, it is required that the flame retardants can withstand high temperature spinning and have good compatibility with the main polymer, without affecting the post-processing of spinning, and have no significant impact on the physical and mechanical properties of the fibers. The flame retardant performance has good durability.
2.3 Graft flame retardant modification
Fiber grafting copolymerization is an effective and durable flame retardant modification method, such as using high-energy radiation for grafting flame retardant modification.
2.4 Flame retardant finishing
A modification method that involves soaking fibers or fabrics in a solution of water or other solvents containing flame retardants, followed by pressing, drying, and other processes to give fibers or fabrics flame retardant properties.
3. List the production methods of flame retardant polyester filament
3.1 Slice drying
The melting point and maximum crystallization temperature of flame retardant polyester chips are lower than those of ordinary polyester chips, but the apparent viscosity is higher than that of ordinary polyester chips. If ordinary polyester chip drying process is used, flame retardant chips are prone to adhesion, clumping, yellowing, and cannot be produced normally. Therefore, the drying process for flame retardant chips should control the temperature lower, duration longer, and air volume higher. At the same time, increasing the vibration intensity enables flame retardant chips to have a good boiling effect on the boiling bed, in order to disperse adhesive particles. Actual process control: pre crystallization temperature of 148 ℃, drying temperature of 155 ℃, air flow of 8.5 m3/h, drying time of more than 12 hours, good drying effect of flame retardant chips, viscosity of 0.621, and moisture content of 1.8 × 10-5. During production, attention should also be paid to: during the initial feeding, the pre crystallization temperature should be controlled to be lower than 140 ℃, and attention should be paid to observing the boiling situation of the chips inside the pre crystallization, adjusting the reasonable amount, strictly controlling the heating rate, and reducing chip agglomeration.
3.2 Spinning temperature
The melting point of flame retardant chips is lower than that of ordinary polyester chips, so the spinning temperature control should also be lower than PET. However, due to the addition of flame retardants, flame retardant chips weaken the activity of large molecular chains and increase the apparent viscosity of the melt, resulting in poor melt fluidity. A low spinning temperature can easily cause the spinneret component to withstand excessive melt pressure, but a high temperature can cause rapid thermal degradation of flame retardant polyester with poor heat resistance.
3.3 Cooling forming
Compared with ordinary fibers, the addition of flame retardants significantly accelerates the crystallization rate of flame retardant fibers. Therefore, it is necessary to strengthen the cooling conditions appropriately, which is conducive to improving the mechanical properties of flame-retardant fibers. However, the wind speed should not be too high, as excessive wind speed can cause oscillation in the filament and increase the unevenness of the filament.
4、 The development trend of flame retardant polyester fibers
1. Functional compounding
Functional composite is a new trend in the development of functional fibers today, aimed at expanding the application fields of existing single functional fibers, increasing product added value, and enhancing product market competitiveness. Its varieties include flame retardant+cation, flame retardant+antibacterial, flame retardant+moisture absorption, etc.
2. High Tech
Flame retardant polyester/inorganic nanocomposites can not only meet the flame retardant levels required by many usage scenarios, but also maintain or even improve the original excellent properties of polyester, making this composite flame retardant polyester and fiber have broad and attractive development prospects.
3. Greenization
The greening of flame retardant fibers refers to reducing the toxic effects of the production process on the environment and operators, and preventing the fibers from having adverse effects on the wearer. Because flame retardants used in flame-retardant fibers generally contain elements such as halogens, phosphorus, sulfur, etc., most of which have significant toxicity. When a fire occurs, there will be no secondary toxicity. At present, the production processes of flame retardant fibers that are beneficial to the environment and daily use include skin core composite spinning method and flame retardant microcapsule method.