Flame-retardant polyester fiber and preparation method thereof

Abstract

The invention provides a flame-retardant polyester fiber and a preparation method thereof, the flame-retardant polyester fiber is composed of a base material and a modification layer, the base material is polyester fiber, and the modification layer is mainly of a multi-layer structure formed by sequentially and alternately depositing chitosan, nano clay, chitosan and phytic acid or phytate on the base material through an electrostatic layer-by-layer self-assembly method. The positively charged chitosan, the negatively charged nano clay, the positively charged chitosan and the negatively charged phytic acid (or phytate) are alternately deposited on the surface of the polyester fiber to construct a multi-layer protection structure, so that not only is the positively charged chitosan, the negatively charged nano clay, the positively charged chitosan and the negatively charged phytic acid (or phytate) synergistically improve the flame retardance of the fiber, but also the direct contact between the phytic acid and the fiber can be effectively isolated; meanwhile, the acidity of the phytic acid can be neutralized by the chitosan and the nano clay, so that the corrosion of the phytic acid to the polyester fibers is greatly reduced, and the loss of the mechanical property of the polyester fibers is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester fibers, and particularly to a flame-retardant polyester fiber and a preparation method thereof. Background Art

[0002] Polyethylene terephthalate (PET) fiber, commonly known as polyester fiber, as a widely used synthetic fiber, is widely used in protective clothing, special work clothes, movie screens and various living materials due to its high output, good dimensional stability and wide application range. However, the limiting oxygen index (LOI) of polyester fiber is relatively low, only about 20%, and it is extremely easy to burn. Moreover, the molten droplets generated after combustion are likely to cause secondary combustion, which limits its wide application.

[0003] The flame-retardant function of fibers is mainly achieved through post-treatment. Currently, commercially available flame-retardant post-treatment agents can be divided into three categories: halogen-based, nitrogen-based and phosphorus-based. Among them, halogen-based flame retardants generate a large amount of toxic gases during combustion. Nitrogen-based flame retardants are easily decomposed under high-temperature conditions, reducing their flame-retardant performance and performing poorly in high-temperature environments. In contrast, phosphorus-based flame retardants have the advantages of high efficiency, smokelessness, low toxicity and pollution-free, and have good development prospects.

[0004] Phytic acid (PA) has a very rich source and has the characteristics of being renewable. Phytic acid itself contains 6 phosphate groups and shows a negatively charged property. When phytic acid is used as the acid source in intumescent flame retardants, a large number of phosphoric acid derivatives are generated during the pyrolysis of phytic acid, which can not only promote the dehydration and carbonization of the carbon source, but also capture free radicals, thereby improving the flame-retardant performance of the whole system. Therefore, phytic acid shows great flame-retardant potential in flame retardants. However, phytic acid has strong acidity. When used as a flame retardant for polyester fibers, it will penetrate into the fiber interior and induce the degradation of medium and high molecules, resulting in a significant reduction in the mechanical properties of the fiber. Therefore, the application of phytic acid in the flame-retardant modification of polyester fibers is limited, and how to optimize the application of phytic acid has become a research hotspot at present. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a flame-retardant polyester fiber to solve the problem that phytic acid will erode polyester fibers and reduce their mechanical properties in the prior art. At the same time, the present invention will also provide a preparation method of the flame-retardant polyester fiber.

[0006] To achieve the above object and other related objects, the present invention provides the following technical solutions: In the first aspect of the present invention, there is provided a flame-retardant polyester fiber, which is composed of a substrate and a modification layer. The substrate is a polyester fiber, and the modification layer is mainly a multi-layer structure formed by sequentially and alternately depositing chitosan, nanoclay, chitosan and phytic acid or phytic acid salts on the substrate through the electrostatic layer-by-layer self-assembly method.

[0007] In the present invention, a multi-layer protection structure is constructed on the surface of polyester fibers by alternately depositing positively charged chitosan, negatively charged nanoclay, positively charged chitosan, and negatively charged phytic acid (or phytate), effectively isolating the direct contact between phytic acid (or phytate) and the fibers; chitosan and nanoclay can also neutralize the acidity of phytic acid, significantly reducing the erosion of phytic acid on polyester fibers. Moreover, nanoclay can form a dense silicate carbon layer at high temperatures, which can cooperate with phytic acid to enhance the charring ability of the modified layer, form a more stable and denser carbon layer, block the transfer of heat and oxygen, improve the flame retardancy of polyester fibers, and form an efficient flame retardant barrier. In addition, nanoclay has a high specific surface area, can form more binding sites with chitosan in adjacent layers, improve the adhesion of the modified layer, and reduce the risk of the modified layer peeling off; hydrogen bonds can be formed between the hydroxyl groups on the surface of nanoclay and the amino or hydroxyl groups of chitosan, further enhancing the binding force. At the same time, the addition of nanoclay can improve the tensile strength of polyester fibers and offset the negative impact of phytic acid on the tensile strength of polyester fibers.

[0008] Further, the number of layers of the multi-layer structure is 5 to 25 layers; preferably 6 to 14 layers.

[0009] Further, the outermost layer of the modified layer is a chitosan layer or a nanoclay layer; preferably, the outermost layer of the modified layer is a nanoclay layer. Among them, the phytic acid layer has a high risk of peeling off due to acid erosion and a small molecular structure and is not suitable as the outermost layer; in contrast, the nanoclay layer is the least likely to peel off due to its lamellar structure, high specific surface area, and strong interaction with chitosan and is suitable as the outermost layer.

[0010] In an embodiment of the present invention, the phytate is selected from furfurylamine phytate. The furfurylamine phytate utilizes the amino group introduced by furfurylamine to play a synergistic flame retardant role with phytic acid; and the furan group introduced in furfurylamine is easy to crosslink and can form a stable crosslinking network during heating to further play a flame retardant role, and at the same time, this special structure can reduce the sacrifice of the mechanical properties of polyester by phytic acid.

[0011] Further, the furfurylamine phytate is obtained by the following preparation method: dissolve phytic acid in ethanol at room temperature, then slowly drop the phytic acid solution into pure furfurylamine, stir and react at 0 to 4 °C after dropping, and repeat centrifugation after the reaction ends, and obtain the furfurylamine phytate after vacuum drying.

[0012] Furthermore, the molar ratio of phytic acid to furfurylamine is 1:(2 to 15); preferably 1:(3 to 12).

[0013] Furthermore, the stirring rate is 400 to 600 revolutions per minute.

[0014] Furthermore, the reaction time is 2 to 6 hours.

[0015] In one embodiment of the present invention, a protective layer is coated outside the modification layer, and the protective layer is mainly composed of at least one of polyurethane, polyacrylic acid, and silane coupling agent.

[0016] By forming a protective coating on the surface of the modification layer, the overall stability and bonding strength of the modification layer can be enhanced in the present invention. Among them, the combined use of polyurethane and silane coupling agent can improve the flexibility and wear resistance of the fiber, and the compatibility of polyurethane and silane with nano-clay is very good. When the outermost layer of the modification layer is nano-clay, a strong chemical bond can be formed between the protective layer and the nano-clay layer, effectively protecting the modification layer and prolonging its service life. The combined use of acrylic acid and silane coupling agent can improve the hydrolysis resistance of the fiber, and the modification layer is not easy to fall off after multiple washes, and the flame retardant performance is persistent.

[0017] Further, the silane coupling agent is selected from vinylbenzylamine functional group silane coupling agent or methacryloxy silane coupling agent.

[0018] In the second aspect of the present invention, a method for preparing the above flame-retardant polyester fiber is provided, including the following steps: (1) Perform surface activation treatment on the polyester fiber; (2) Dissolve chitosan powder in acetic acid solution to prepare a chitosan solution; dissolve phytic acid or phytate in water to prepare a phytic acid or phytate solution; disperse nano-clay in water to prepare a nano-clay suspension; (3) Immerse the polyester fiber obtained in step (1) into the chitosan solution first, take it out, wash and dry it; then immerse it into the nano-clay suspension, take it out, wash and dry it; then immerse it into the chitosan solution, take it out, wash and dry it; finally immerse it into the phytic acid or phytate solution, take it out, wash and dry it; (4) Repeat step (3) to alternately deposit multiple layers of structure on the surface of the polyester fiber in sequence until the multiple layers of structure reach the target number of layers, and obtain a flame-retardant polyester fiber with a surface-coated modification layer.

[0019] Further, the surface activation treatment in step (1) includes: immersing the polyester fiber into a sodium hydroxide solution, taking it out, washing and drying it. The activation temperature is preferably 60-80 °C. The activation treatment can hydrolyze the surface of the polyester fiber to generate more active groups.

[0020] Further, the concentration of the chitosan solution in step (2) is 0.5-2 wt%; the concentration of the phytic acid or phytate solution is 1-10 wt%; the concentration of the nano-clay suspension is 1-2 wt%.

[0021] Further, the drying in step (3) is vacuum drying, and the drying temperature is 50-80 °C.

[0022] Further, the number of layers of the multi-layer structure in step (4) is 5 to 25 layers; preferably 6 to 14 layers.

[0023] In an embodiment of the present invention, it further includes step (5) of formulating a protective layer solution with a silane coupling agent and polyurethane or polyacrylic acid, immersing the flame-retardant polyester fiber obtained in step (4) into the protective layer solution, taking it out, washing, drying, and sintering it, so as to coat a protective layer on the surface of the modification layer.

[0024] As described above, a flame-retardant polyester fiber and a preparation method thereof according to the present invention have the following beneficial effects: 1. In the present invention, positively charged chitosan, negatively charged nanoclay, positively charged chitosan, and negatively charged phytic acid (or phytate) are alternately deposited on the surface of the polyester fiber to construct a multi-layer protection structure. Not only do the three work together to improve the flame retardancy of the fiber, but also effectively isolate the direct contact between phytic acid and the fiber. At the same time, chitosan and nanoclay can also neutralize the acidity of phytic acid, greatly reducing the erosion of phytic acid on the polyester fiber and reducing the loss of the mechanical properties of the polyester fiber.

[0025] 2. The present invention selects furfurylamine phytate to replace phytic acid. The introduction of furfurylamine can play a synergistic flame-retardant role with phytic acid; and the cross-linked network formed during the heating process can reduce the sacrifice of the mechanical properties of the polyester by phytic acid. The present invention also provides a method for efficiently preparing furfurylamine phytate, which has broad application prospects.

[0026] 3. The present invention forms a protective layer on the surface of the modification layer, which can enhance the overall stability and binding force of the modification layer; when the outermost layer of the modification layer is nanoclay, a strong chemical bond can be formed between the protective layer and the nanoclay layer, effectively protecting the modification layer, making the modification layer not easy to fall off, and improving the durability of the fiber. Specific embodiments

[0027] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0028] Example 1 A flame-retardant polyester fiber, which is composed of a base material and a modification layer. The base material is a polyester fiber, and the modification layer is mainly a multi-layer structure formed by alternately depositing chitosan, nanoclay, chitosan, and phytic acid on the base material in sequence through electrostatic layer-by-layer self-assembly method. The total number of layers of the multi-layer structure is 6 layers. The flame-retardant polyester fiber is prepared by the following steps: (1) Immerse the polyester fiber into a 2wt% sodium hydroxide solution for activation treatment at a temperature of 70°C for 30 minutes, then take out the fiber, wash it thoroughly with deionized water, and dry it at 60°C; (2) Dissolve chitosan powder in 1 wt% acetic acid solution to prepare a 1 wt% chitosan solution, and adjust the pH to 5 with hydrochloric acid and sodium hydroxide; dissolve phytic acid in deionized water to prepare a 2 wt% phytic acid solution; disperse nano-clay in deionized water to prepare a 1 wt% nano-clay suspension; (3) Immerse the polyester fiber obtained in step (1) in the chitosan solution at room temperature for 15 min, take it out, wash and dry it; then immerse it in the nano-clay suspension for 10 min, take it out, wash and dry it; then immerse it in the chitosan solution for 15 min, take it out, wash and dry it; immerse it in the phytic acid solution for 15 min, take it out, wash and dry it; immerse it in the chitosan solution for 15 min, take it out, wash and dry it; finally immerse it in the nano-clay suspension for 10 min, take it out, wash and dry it; to obtain flame-retardant polyester fiber with a modified layer of 6-layer structure.

[0029] After testing, the LOI value of the flame-retardant polyester fiber prepared in this example is 34.7%, the tensile strength is 34.5 MPa, and after 10 times of machine washing, the LOI value is still 34.1%, with a loss of 1.7%.

[0030] Example 2 A flame-retardant polyester fiber, which consists of a substrate and a modified layer. The substrate is polyester fiber, and the modified layer is mainly a multi-layer structure formed by alternately depositing chitosan, nano-clay, chitosan and furfurylamine phytate on the substrate by electrostatic layer-by-layer self-assembly method, and the total number of layers of the multi-layer structure is 6 layers.

[0031] The furfurylamine phytate is prepared by the following method: Add 0.02 mol of phytic acid to 100 mL of ethanol at room temperature, stir for 30 min to obtain a phytic acid solution; then, under the condition of magnetic stirring at 0 - 4 °C and 500 revolutions per minute, slowly drop the phytic acid solution into 0.12 mol of pure furfurylamine; after dropping, continue to keep the condition of magnetic stirring at 0 - 4 °C and 500 revolutions per minute for 4 hours; finally, after 3 times of repeated centrifugation and vacuum drying at 80 °C, the furfurylamine phytate is obtained.

[0032] The flame-retardant polyester fiber is prepared by the following steps: (1) Immerse the polyester fiber in 2 wt% sodium hydroxide solution for activation treatment at 70 °C for 30 minutes, then take out the fiber, wash it thoroughly with deionized water, and dry it at 60 °C; (2) Dissolve chitosan powder in 1 wt% acetic acid solution to prepare a 1 wt% chitosan solution, and adjust the pH to 5 with hydrochloric acid and sodium hydroxide; dissolve furfurylamine phytate in deionized water to prepare a 2 wt% furfurylamine phytate solution; disperse nano-clay in deionized water to prepare a 1 wt% nano-clay suspension; (3) Immerse the polyester fibers obtained in step (1) in a chitosan solution at room temperature for 15 min, take them out, wash and dry; then immerse them in a nano-clay suspension for 10 min, take them out, wash and dry; then immerse them in a chitosan solution for 15 min, take them out, wash and dry; immerse them in a furfurylamine phytate solution for 15 min, take them out, wash and dry; immerse them in a chitosan solution for 15 min, take them out, wash and dry; finally immerse them in a nano-clay suspension for 10 min, take them out, wash and dry; to obtain flame-retardant polyester fibers with a modified layer of 6-layer structure.

[0033] After testing, the LOI value of the flame-retardant polyester fibers prepared in this example is 35.8%, the tensile strength is 35.3 MPa, and after 10 machine washes, the LOI value is still 35.4%, with a loss of 1.1%.

[0034] Example 3 A kind of flame-retardant polyester fiber, the flame-retardant polyester fiber is composed of a substrate and a modified layer, the substrate is polyester fiber, the modified layer is mainly a multi-layer structure formed by sequentially and alternately depositing chitosan, nano-clay, chitosan and furfurylamine phytate on the substrate by electrostatic layer-by-layer self-assembly method, and the total number of layers of the multi-layer structure is 6 layers; a protective layer is also coated on the outer surface of the modified layer, and the protective layer includes polyacrylic acid and vinyl benzylamine functional group silane coupling agent.

[0035] The flame-retardant polyester fiber is prepared by the following steps: (1) Immerse the polyester fibers in a 2 wt% sodium hydroxide solution for activation treatment at 70 °C for 30 minutes, then take out the fibers, wash them thoroughly with deionized water, and dry them at 60 °C; (2) Dissolve chitosan powder in a 1 wt% acetic acid solution to prepare a 1 wt% chitosan solution, and adjust the pH to 5 with hydrochloric acid and sodium hydroxide; dissolve the furfurylamine phytate prepared in Example 2 in deionized water to prepare a 2 wt% furfurylamine phytate solution; disperse nano-clay in deionized water to prepare a 1 wt% nano-clay suspension; (3) Immerse the polyester fibers obtained in step (1) in a chitosan solution at room temperature for 15 min, take them out, wash and dry; then immerse them in a nano-clay suspension for 10 min, take them out, wash and dry; then immerse them in a chitosan solution for 15 min, take them out, wash and dry; immerse them in a furfurylamine phytate solution for 15 min, take them out, wash and dry; immerse them in a chitosan solution for 15 min, take them out, wash and dry; finally immerse them in a nano-clay suspension for 10 min, take them out, wash and dry; to form a modified layer with a total of 6 layers on the surface of the flame-retardant polyester fibers; (4) Prepare a protective layer solution containing 5% polyacrylic acid and 1% vinylbenzylamine functional group silane coupling agent. Immerse the polyester fibers from step (3) into the protective layer solution for 1 min, take them out, remove the excess solution with a squeezing roller, dry them, and sinter them at 120 °C for 3 min to obtain the flame-retardant polyester fibers.

[0036] After testing, the LOI value of the flame-retardant polyester fibers prepared in this example is 36.3%, the tensile strength is 36.1 MPa, and after 10 machine washes, the LOI value is still 36.1%, with a loss of 0.28%.

[0037] Comparative Example 1 A kind of flame-retardant polyester fiber, which is composed of a substrate and a modification layer. The substrate is polyester fiber, and the modification layer is mainly a multi-layer structure formed by alternately depositing chitosan and phytic acid on the substrate by electrostatic layer-by-layer self-assembly method. The total number of layers of the multi-layer structure is 6 layers. The flame-retardant polyester fiber is prepared by the following steps: (1) Immerse the polyester fibers in a 2 wt% sodium hydroxide solution for activation treatment at 70 °C for 30 minutes, then take out the fibers, wash them thoroughly with deionized water, and dry them at 60 °C; (2) Dissolve chitosan powder in a 1 wt% acetic acid solution to prepare a 1 wt% chitosan solution, and adjust the pH to 5 with hydrochloric acid and sodium hydroxide; dissolve phytic acid in deionized water to prepare a 2 wt% phytic acid solution; (3) First immerse the polyester fibers obtained in step (1) in the chitosan solution at room temperature for 15 min, take them out, wash and dry them; then immerse them in the phytic acid solution for 15 min, take them out, wash and dry them; repeat three times in total to obtain the flame-retardant polyester fiber with a 6-layer structure modification layer.

[0038] After testing, the LOI value of the flame-retardant polyester fibers prepared in the comparative example is 32.1%, the tensile strength is 29.0 MPa, and after 10 machine washes, the LOI value is only 29.2%, with a loss of 9.4%.

[0039] It can be seen from the comparison between Example 1 and Comparative Example 1 that only using the layer-by-layer self-assembly structure of phytic acid and chitosan, its flame-retardant effect mainly depends on the catalytic carbonization effect of phytic acid, lacking the physical barrier effect of nano-clay. Therefore, the flame-retardant performance of Comparative Example 1 is relatively weak; moreover, only using the layer-by-layer structure of phytic acid and chitosan has a poor bonding strength, is easy to fall off or be damaged during washing or friction, resulting in a significant decline in the flame-retardant performance. The addition of nano-clay can strengthen the bonding force between layers, improve the mechanical strength, toughness and wear resistance of the modification layer, reduce the risk of the modification layer falling off, and maintain the mechanical strength of the fibers.

[0040] In summary, the present invention alternately deposits positively charged chitosan, negatively charged nanoclay, positively charged chitosan, and negatively charged phytic acid (or phytate) on the surface of polyester fibers to construct a multi-layer protection structure. Not only do the three work together to enhance the flame retardancy of the fibers, but they can also effectively isolate the direct contact between phytic acid and the fibers. At the same time, chitosan and nanoclay can also neutralize the acidity of phytic acid, significantly reducing the erosion of phytic acid on polyester fibers. Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0041] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A flame retardant polyester fiber, characterized in that: The flame retardant polyester fiber consists of a substrate and a modified layer, wherein the substrate is polyester fiber, and the modified layer is mainly a multilayer structure of chitosan, nanoclay, chitosan and phytic acid or phytate which are alternately deposited on the substrate in sequence through an electrostatic layer-by-layer self-assembly method.

2. The flame-retardant polyester fiber according to claim 1, characterized in that: The number of layers of the multi-layer structure is 5 to 25.

3. The flame retardant polyester fiber according to claim 1, characterized in that: The phytate is selected from furfurylamine phytate.

4. The flame retardant polyester fiber according to claim 3, characterized in that: The furfurylamine phytate is obtained by the following preparation method: dissolving phytic acid in ethanol at room temperature, then slowly dropping the phytic acid solution into pure furfurylamine, stirring and reacting at 0-4°C after the dropwise addition is completed, repeating centrifugation after the reaction is completed, and obtaining the furfurylamine phytate after vacuum drying.

5. The flame retardant polyester fiber according to claim 4, characterized in that: The molar ratio of phytic acid to furfuralamine is 1:(2~15).

6. The flame retardant polyester fiber according to claim 1, characterized in that: The modified layer is coated with a protective layer, and the protective layer is mainly composed of at least one of polyurethane, polyacrylic acid and silane coupling agent.

7. A method for preparing the flame-retardant polyester fiber according to any one of claims 1 to 6, characterized in that: The steps include: (1) Surface activation treatment of polyester fibers; (2) dissolving chitosan powder in acetic acid solution to prepare chitosan solution; dissolving phytic acid or phytate in water to prepare phytic acid or phytate solution; dispersing nanoclay in water to prepare nanoclay suspension; (3) The polyester fiber obtained in step (1) is first immersed in a chitosan solution, taken out, washed and dried; then immersed in a nanoclay suspension, taken out, washed and dried; then immersed in a chitosan solution, taken out, washed and dried; finally immersed in a phytic acid or phytate solution, taken out, washed and dried; (4) Repeat step (3) to alternately deposit a multilayer structure on the surface of the polyester fiber until the multilayer structure reaches a target number of layers, thereby obtaining a flame-retardant polyester fiber with a surface-coated modified layer.

8. The preparation method according to claim 7, characterized in that: The surface activation treatment in step (1) comprises: immersing the polyester fiber in a sodium hydroxide solution, taking it out, washing it, and drying it.

9. The preparation method according to claim 7, characterized in that: In step (2), the concentration of the chitosan solution is 0.5-2 wt %; the concentration of the phytic acid or phytate solution is 1-10 wt %; and the concentration of the nanoclay suspension is 1-2 wt %.

10. The preparation method according to claim 7, characterized in that: The method further comprises step (5), wherein a silane coupling agent and polyurethane or polyacrylic acid are prepared into a protective layer solution, the flame-retardant polyester fiber obtained in step (4) is immersed in the protective layer solution, and the fiber is taken out and washed, dried and sintered to coat the surface of the modified layer with a protective layer.