A flame-retardant polyester fiber and its preparation method

Abstract

The present invention relates to a flame-retardant polyester fiber and a preparation method thereof. After uniformly mixing a flame-retardant masterbatch with polyester, melt spinning is carried out to obtain the flame-retardant polyester fiber. The matrix of the flame-retardant masterbatch is polypropylene, and polymeric carbodiimide and a phosphorus-based flame retardant are uniformly dispersed in the polypropylene; the melt spinning process parameters include: a spinning temperature of 270 to 300 °C; on the cross-section of the flame-retardant polyester fiber, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer. In the preparation method of the present invention, the polymeric carbodiimide and the phosphorus-based flame retardant are blended with polypropylene, and the polypropylene melt with smaller shear and tensile viscosities flows towards the high-shear and high-tensile stress regions in the complex flow field during the spinning process, realizing the migration of the flame-retardant components to the fiber surface layer and enhancing the flame-retardant effect; the flame-retardant polyester fiber prepared by the present invention has good flame-retardant performance and washing resistance.

Description

Technical Field

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

[0002] Polyethylene terephthalate (PET, hereinafter referred to as polyester) is one of the most commonly used thermoplastic polymers at present. Due to its excellent chemical corrosion resistance, high mechanical strength, and wear resistance, polyester is widely used in textiles, food packaging, decoration, and other fields. However, since polyester itself does not contain flame-retardant elements, it is prone to combustion during application, forming a large amount of molten droplets and smoke, which endangers people's lives and property safety. In order to be safely used in the environment, the flame-retardant modification of polyester fibers has attracted the attention of many researchers.

[0003] At present, the methods for flame-retardant modification of polyester fibers include copolymerization, blending, and post-treatment methods. Among them:

[0004] The copolymerization method embeds flame-retardant functional monomers into the molecular main chain, which has the advantages of long-lasting modification effect and less loss of modified components. However, due to the introduction of functional monomers, the structural regularity of the molecular main chain is damaged, resulting in a decrease in the mechanical properties of the modified polyester fiber, and at the same time, the production cost is relatively high;

[0005] In contrast, the blending method has the advantages of simple processing and low cost, but also faces problems such as a large amount of flame retardant added or loss of modified components during use. If the amount of flame retardant added is too large, it will affect the mechanical properties of the modified fiber. At the same time, due to the catalytic effect of excessive flame retardant addition on the thermal degradation during the hot processing of polyester, it will affect the processing performance of the modified fiber. For example, the patent application CN111118651B discloses a preparation method of a flame-retardant polyester fiber, in which a nano-scale metal oxide is constructed on the surface of nano-inorganic particles to reduce the agglomeration between inorganic nano-particles, and at the same time, an alkyl phosphinate metal salt is added as a flame retardant during the polymerization stage, and the flame-retardant polyester fiber is prepared by melt spinning. This method modifies the surface of nano-inorganic particles and has the characteristics of catalyzing the polycondensation reaction. However, the phosphorus-based flame retardant itself has a certain characteristic of catalyzing the thermal degradation reaction, and the amount of flame retardant added is relatively high, with an addition weight ratio of 6-8 wt%, which may have an adverse effect on the subsequent melt spinning process;

[0006] The post-treatment method is a method for flame-retardant treatment on the surface of fibers or fabrics. It concentrates the flame-retardant components on the burning surface, forming a more effective flame-retardant protection. However, due to factors such as weak binding force with the fabric surface, the flame-retardant effect of the samples prepared by the post-treatment method decreases significantly after a certain period of use or multiple washings. For example, Patent Application CN116289216B discloses a preparation method of a halogen-free and phosphorus-free flame-retardant and anti-melting-drop polyester fabric. The cationic polyacrylamide, oxidized sodium alginate, and p-hydroxybenzaldehyde are deposited on the surface of the polyester fabric by the layer-by-layer self-assembly method, forming a good charring and anti-melting-drop effect. However, since there is no chemical bond connection between the modified layer and the surface of the polyester fiber, the modified coating is still faced with the problem of poor washability of the modified fabric due to environmental factors such as friction during the subsequent washing process.

[0007] Therefore, it is of great significance to study a flame-retardant polyester fiber with excellent mechanical properties, low flame-retardant content, excellent flame-retardant performance, and excellent water-wash resistance and its preparation method. Summary of the Invention

[0008] The purpose of the present invention is to solve the problems existing in the prior art and provide a flame-retardant polyester fiber and its preparation method.

[0009] To achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0010] A preparation method of a flame-retardant polyester fiber, after uniformly mixing a flame-retardant masterbatch with polyester, melt spinning is carried out to obtain the flame-retardant polyester fiber. The matrix of the flame-retardant masterbatch is polypropylene, and the polymeric carbodiimide and the phosphorus-based flame retardant are uniformly dispersed in the polypropylene;

[0011] The melt spinning process parameters include: the spinning temperature is 270 - 300 °C;

[0012] The melting point of polypropylene is 165 - 170 °C, and the melt index at a weight of 2.16 kg of the weight and a temperature of 230 °C is 45 - 60 g / 10 min; the melt index of polyester at a weight of 2.16 kg of the weight and a temperature of 270 - 300 °C is 30 - 45 g / 10 min;

[0013] The test temperatures of polypropylene and polyester are different. The main reason is that the melting points of the two polymers are different. Polypropylene has good fluidity at 230 °C, but this temperature is still lower than the melting point of the polyester polymer. At a temperature of about 290 °C, the polyester polymer has good fluidity, but at this temperature, the melt viscosity of polypropylene is low and the fluidity is excellent, which cannot meet the test requirements. Therefore, the test melt index temperatures of the two components are different;

[0014] The content of the phosphorus-based flame retardant in the flame-retardant polyester fiber does not exceed 2.5 wt%.

[0015] The flame retardant polyester fiber of the present invention has a low flame retardant content and excellent flame retardant performance, because: (1) During the spinning process, the flame retardant masterbatch migrates directionally and concentrates on the fiber surface layer, increasing the content of flame retardant elements on the surface layer and enhancing the flame retardant effect. The specific principle is as follows: There is an uneven shear stress field in the spinning box. Since the spinning temperature is 270-300°C, which is much higher than the melting point of polypropylene (165-170°C), and the melt index of polypropylene is 45-60 g / 10 min at a weight of 2.16 kg and a temperature of 230°C, while the melt index of polyester is 30-45 g / 10 min at a weight of 2.16 kg and a temperature of 270-300°C, the shear viscosity of polypropylene in the present invention is significantly lower than that of polyester at this processing temperature, and it migrates to the surface layer; (2) The flame retardant polyester masterbatch contains polymeric carbodiimide, which can have a synergistic effect with the phosphorus-based flame retardant. The specific principle is as follows: In the initial stage of combustion, since the ignition point temperature of polypropylene is lower than that of the polyester polymer when polypropylene and polyester burn, the polypropylene concentrated on the fiber surface layer burns first (i.e., polypropylene undergoes thermal degradation reaction first), thereby triggering the flame retardant effect of the phosphorus-based flame retardant in advance to form a carbon layer and reducing the combustion degree of the modified polyester; at the same time, in the flame retardant masterbatch, the carbodiimide that is not reacted with the end groups and coated in polypropylene reacts with the end groups formed in the initial stage of polyester thermal degradation to form a cross-linked network structure, increasing the melt viscosity, inhibiting the formation of molten droplets, and further delaying the combustion process and combustion degree of polyester; when the polyester melt further undergoes a combustion reaction, the nitrogen element in the polymeric carbodiimide -N=C=N- structure forms non-combustible gases during the combustion process, which plays a role in diluting the concentration of combustible gases and oxygen concentration on the combustion surface, and synergizes with the reaction of the phosphorus element in the phosphorus-containing flame retardant copolyester to capture free radicals to form an excellent flame retardant effect in the gas-phase flame retardant process; in the condensed-phase flame retardant process, the aromatic structure in the molecular structure of polymeric carbodiimide synergizes with the char-forming performance of the phosphorus-based flame retardant (the carbodiimide component plays a role in diluting combustion gases and accelerating the formation of a carbon layer in the gas-phase and condensed-phase flame retardant processes respectively).

[0016] The flame-retardant polyester fiber of the present invention has excellent mechanical properties because: (1) the blending method is adopted in the present invention; (2) the content of the phosphorus-based flame retardant in the flame-retardant polyester fiber is relatively low; (3) the flame-retardant masterbatch contains polymeric carbodiimide, which can have a synergistic effect with polyester. The specific principle is as follows: during the spinning process, polypropylene, which is the matrix of the flame-retardant masterbatch, and polyester are heated and mixed by a screw. Under the action of the screw shear force, the flame-retardant masterbatch is dispersed in the polyester matrix. The polymeric carbodiimide in the masterbatch can react with the terminal carboxyl groups generated by the thermal degradation of polyester at the two-phase interface between the polypropylene melt and the polyester melt, solving the problem of reduced processing performance due to the decrease in intrinsic viscosity during the spinning process of polyester; and in this process, the ester bonds in the polyester molecular chain break randomly, so molecular chain segments with carboxyl groups at the end and different molecular weights are formed. The terminal carboxyl groups of the molecular chains with different chain lengths react with polymeric carbodiimide and are connected by urea bonds, so that the flame-retardant polyester fiber not only retains the high strength of the long molecular chain segments, but also has a high elongation rate achieved by the intermittently connected long molecular chains; in addition, after the terminal carboxyl groups of the molecular chains with different chain lengths react with polymeric carbodiimide and are connected by urea bonds, a branched structure with different branch lengths is formed. The branched molecular chains are more likely to entangle with each other, forming a physical crosslinking network and improving the mechanical properties.

[0017] The flame-retardant polyester fiber of the present invention has excellent washability because: (1) the matrix of the flame-retardant masterbatch concentrated on the fiber surface is polypropylene, which can endow the fiber surface with certain hydrophobic properties, has wash resistance during subsequent washing, and has a long-lasting flame-retardant effect; (2) in the prior art post-treatment method, during the flame-retardant modification process, it is necessary to connect the modifying substance and the matrix to be modified by means such as physical coating or chemical grafting, so there is a problem of weak binding force with the fabric surface. However, in the present invention, polypropylene and polyester are melt-blended and then extruded for spinning, and after the fiber is cooled and solidified, polypropylene and polyester are in a "frozen" state, and the molecular chains or components cannot move or migrate and lose. Therefore, during use, there is no loss or reduction of the modified components due to the strength of the binding force, thus achieving the effect of wash resistance.

[0018] In the prior art, polymeric carbodiimide is added to prepare flame-retardant materials. However, its purpose is to improve the hydrolysis resistance of polymers during processing or use, or to improve the compatibility between flame retardants and polymers. For example, Patent Application CN102056992B adds polycarbodiimide during the preparation of thermoplastic flame-retardant resin to improve the hydrolysis resistance of the flame-retardant material during use. Patent Application CN102834458B adds aliphatic and aromatic carbodiimides during the preparation of flame-retardant polylactic acid materials to improve the hydrolysis resistance of the polymer during processing and at the same time improve the compatibility between the flame retardant and the polymer. Patent Application CN102612540B adds carbodiimide compounds during the preparation of polybutylene terephthalate to improve the hydrolysis resistance. According to the above description, the function of polymeric carbodiimide in the present invention is not only to improve the hydrolysis resistance of polymers during processing or use and to improve the compatibility between flame retardants and polymers, and these functions are difficult to be anticipated based on the prior art.

[0019] As a preferred technical solution:

[0020] For the preparation method of a flame-retardant polyester fiber as described above, the phosphorus-based flame retardant is one or more of diethyl phosphinate flame retardants, polyphosphate ester flame retardants or ammonium polyphosphate flame retardants; the limiting oxygen index value of the flame-retardant polyester fiber or the fabric woven from the flame-retardant polyester fiber is 30% - 35%, and the limiting oxygen index value is 28% - 32% after 50 times of washing; the present invention can obtain excellent flame-retardant effects by using ordinary phosphorus-based flame retardants with a relatively small addition amount; polypropylene has the characteristics of regular structure and high crystallization, so the glass transition temperature of polypropylene is usually between 135 and 150 °C, and the glass transition temperature of polyester is usually between 60 and 75 °C. Selecting polypropylene as the matrix of the flame-retardant masterbatch, during the subsequent treatment and use of the flame-retardant polyester fiber, it is difficult for the polymeric carbodiimide and the phosphorus-based flame retardant to migrate and lose from the polypropylene. At the same time, polypropylene has a certain hydrophobic effect, and since it is mostly distributed on the surface layer of the polyester, it improves the hydrophobic property of the flame-retardant polyester fiber to a certain extent, thereby improving the washing resistance effect.

[0021] For the preparation method of a flame-retardant polyester fiber as described above, the mass of the flame-retardant masterbatch is 6 - 10 wt% of the total mass of the flame-retardant masterbatch and polyester, and the content of the phosphorus-based flame retardant in the flame-retardant masterbatch is 15 - 25 wt%. These two parameters cooperate with each other to determine the content of the phosphorus-based flame retardant in the flame-retardant polyester fiber.

[0022] A method for preparing a flame-retardant polyester fiber as described above, wherein the content of polypropylene in the flame-retardant masterbatch is 40-70 wt%; since the melt viscosity of the polypropylene is relatively low at the spinning temperature and it is incompatible with the polyester polymer, if the addition amount of the polypropylene is too high, during the spinning process, it will lead to a decrease in the melt stability during the processing of the mixed polymer melt, and at the same time, it will cause poor processing phenomena such as broken filaments, hairy filaments, and floating filaments after extrusion from the spinneret; if the content of polypropylene is too low, it cannot achieve good blending of the phosphorus-based flame retardant and the polymeric carbodiimide, resulting in uneven distribution of the contents of the phosphorus-based flame retardant and the polymeric carbodiimide during the processing of the flame-retardant masterbatch. While affecting the processing and pelletizing of the masterbatch, subsequent addition of the flame-retardant masterbatch for spinning will also lead to uneven distribution of the phosphorus-based flame retardant and the polymeric carbodiimide in the fiber, thus affecting the modification and use effects; when the content of polypropylene in the flame-retardant masterbatch is 40-70 wt%, after the preparation of the flame-retardant masterbatch, the three components of the flame retardant, carbodiimide, and polypropylene are already in a well-mixed state, and the content concentrations of the surface modification components inside and on the surface of the masterbatch are the same. During the spinning process, the melt of the flame-retardant masterbatch and the melt of the polyester are mixed under the action of a screw, but due to the low compatibility between the matrix components, a small amount of the flame retardant diffuses into the polyester at the two-phase interface, which will not affect the migration effect.

[0023] A method for preparing a flame-retardant polyester fiber as described above, wherein the content of the polymeric carbodiimide in the flame-retardant polyester fiber is 0.3-4.5 wt%.

[0024] A method for preparing a flame-retardant polyester fiber as described above, wherein the polymeric carbodiimide is an aromatic polycarbodiimide, the number average molecular weight is 1000-8000 g / mol, the appearance is in powder form, and the screening particle size is 100-500 mesh; the phosphorus-based flame retardant is in powder form, and the screening particle size is 100-500 mesh; the polypropylene is isotactic polypropylene, and the isotactic polypropylene is suitable for spinning, and the appearance is in powder form, and the screening particle size is 100-500 mesh; wherein, the range of the powder particle size is defined to ensure that the modified components and the polypropylene powder can be mixed evenly, avoiding the situation of uneven component content during the preparation of the masterbatch due to too large a difference in particle size between the components; the polyester is one or more of virgin polyester or recycled polyester, the chemical composition of the virgin polyester is polyester, and the intrinsic viscosity range is 0.6-1.0 dL / g, and the recycled polyester is obtained by treating, drying, and melting and reprocessing waste polyester, and the intrinsic viscosity range is 0.6-0.8 dL / g.

[0025] A method for preparing a flame-retardant polyester fiber as described above, wherein the preparation process of the flame-retardant masterbatch is: after mixing each component evenly according to the ratio, melt-blending and extruding through a twin-screw extrusion device to obtain the flame-retardant masterbatch.

[0026] A method for preparing a flame-retardant polyester fiber as described above, before mixing, the flame-retardant masterbatch and the polyester need to be dried separately using a vacuum rotary drum drying oven; the drying temperature of the polyester is 135 - 165 °C, the drying time is 12 - 24 hours, and the vacuum degree of the vacuum rotary drum drying oven is less than 100 Pa; the drying temperature of the flame-retardant masterbatch is 95 - 105 °C, the drying time is 8 - 16 hours, and the vacuum degree of the vacuum rotary drum drying oven is less than 100 Pa.

[0027] A method for preparing a flame-retardant polyester fiber as described above, the melt spinning process parameters also include: the drawing temperature is 65 - 170 °C, the heat setting temperature is 65 - 170 °C, the spinning speed (the spinning speed refers to the rotational speed of the friction roller in the spinning process) is 800 - 3000 m / min, the rotational speed of the first winding roller (the rotational speed of the first winding roller is the rotational speed of the fiber passing through the first winding roller) is 50 - 200 m / min, the aspect ratio of the spinneret hole is 3 - 4.5:1, and the side blowing temperature is 5 - 15 °C; among them, the rotational speed of the first winding roller controls the stretching process from when the melt is extruded from the spinneret to the fiber solidification point. This process can further promote the migration of the flame-retardant masterbatch to the fiber surface layer because there is an uneven stretching stress field during the extrusion and stretching process. Since the melt is still in a molten state after being extruded from the spinneret and during the fiber stretching process, before the solidification point in the spinning process, the temperature of the fiber core layer is higher and the temperature of the fiber surface layer is lower, resulting in an uneven distribution of the radial stretching stress in the fiber cross-section. Therefore, the low stretching viscosity component migrates to the high stretching stress region (fiber surface layer).

[0028] The present invention also provides a flame-retardant polyester fiber prepared by using the method for preparing a flame-retardant polyester fiber described in any one of the above. In the cross-section, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer.

[0029] As a preferred technical solution:

[0030] A flame-retardant polyester fiber as described above, the breaking strength of the flame-retardant polyester fiber ≥ 4.5 cN / dtex, and the elongation at break is 30% - 40%.

[0031] Beneficial effects:

[0032] (1) In the method for preparing a flame-retardant polyester fiber of the present invention, the polymeric carbodiimide and the phosphorus-based flame retardant are blended with polypropylene. Since a multiphase system is formed after the polypropylene and the polyester matrix are melt-mixed, the polypropylene melt with a smaller shear and stretching viscosity flows into the high shear and high stretching stress regions in the complex flow field during the spinning process, realizing the directional migration of the prepared flame-retardant masterbatch, forming a gradient distribution of the prepared flame-retardant masterbatch in the fiber cross-section, making the prepared flame-retardant masterbatch more concentrated on the fiber surface layer, increasing the content of the flame-retardant elements on the surface layer, and enhancing the flame-retardant effect;

[0033] (2) In the preparation method of a flame-retardant polyester fiber of the present invention, the polymeric carbodiimide exhibits a synergistic effect with the polyester and the phosphorus-based flame retardant respectively. Not only does it increase the spinnability and improve the mechanical properties of the product during the spinning process, but it also enhances the flame retardancy during the combustion process.

[0034] (3) The flame-retardant polyester fiber prepared by the present invention has good flame retardancy and washability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Photographs showing the precipitation after dropping methanol into solutions of the flame-retardant polyester fibers of Example 1 and Comparative Example 2 dissolved in hexafluoroisopropanol. The left photograph shows the flame-retardant polyester fiber of Comparative Example 2, and the right photograph shows the flame-retardant polyester fiber of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0037] The test methods for the performance indicators involved in the present invention are as follows:

[0038] Limiting oxygen index: According to GB / T 5454-1997 "Textiles - Burning performance - Determination of oxygen index", the limiting oxygen index of the flame-retardant polyester fiber is evaluated.

[0039] Limiting oxygen index after 50 washes: The washing test is carried out with reference to "GB / T 8629-2017 Textiles - Domestic washing and drying procedures for testing", and then according to GB / T 5454-1997 "Textiles - Burning performance - Determination of oxygen index", the limiting oxygen index of the flame-retardant polyester fiber after 50 washes is evaluated.

[0040] Breaking strength: According to GB / T 14344-2022 "Test method for tensile properties of chemical fiber filaments", the tensile breaking strength performance of the flame-retardant polyester fiber is evaluated by the breaking strength.

[0041] Elongation at break: According to GB / T 14344-2022 "Test method for tensile properties of chemical fiber filaments", the tensile elongation at break performance of the flame-retardant polyester fiber is evaluated by the elongation at break.

[0042] Intrinsic viscosity: According to GB / T 14190-2017 "Test methods for fiber-grade polyester (PET) chips", the intrinsic viscosity of the polyester is evaluated.

[0043] Example 1

[0044] A preparation method of flame-retardant polyester fiber, the specific steps are as follows:

[0045] (1) Preparation of raw materials:

[0046] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Material Technology Co., Ltd., grade 210-1000), number average molecular weight is 1000 g / mol, average particle size is 100 mesh;

[0047] Phosphorus-based flame retardant: Diethyl phosphinate flame retardant (manufacturer: Clariant (China) Co., Ltd., grade: OP950), average particle size is 100 mesh;

[0048] Polypropylene: Isotactic polypropylene, average particle size is 100 mesh, melting point is 165 °C, melt index is 60 g / 10 min at a weight of 2.16 kg and a temperature of 230 °C;

[0049] Polyester: Virgin polyester, intrinsic viscosity is 1 dL / g, melt index is 30 g / 10 min at a weight of 2.16 kg and a temperature of 270 °C;

[0050] (2) After mixing the polymeric carbodiimide, phosphorus-based flame retardant and polypropylene evenly, melt-blend and extrude through a twin-screw extrusion device to obtain a flame-retardant masterbatch;

[0051] The content of the phosphorus-based flame retardant in the flame-retardant masterbatch is 15 wt%, and the content of polypropylene is 40 wt%;

[0052] (3) The flame-retardant masterbatch is dried for 16 hours at a temperature of 95 °C and a vacuum degree of 99 Pa using a vacuum rotary drum drying oven;

[0053] (4) The polyester is dried for 24 hours at a temperature of 135 °C and a vacuum degree of 99 Pa using a vacuum rotary drum drying oven;

[0054] (5) After mixing the dried flame-retardant masterbatch and polyester evenly, melt spinning is carried out to obtain flame-retardant polyester fiber; the mass of the flame-retardant masterbatch is 10 wt% of the total mass of the flame-retardant masterbatch and polyester;

[0055] The process parameters of melt spinning are: spinning temperature 270 °C, drawing temperature 65 °C, heat setting temperature 65 °C, spinning speed 800 m / min, the rotation speed of the first winding roller 50 m / min, the aspect ratio of the spinneret hole 4.5:1, and the side blowing temperature 5 °C.

[0056] On the cross-section of the finally obtained flame-retardant polyester fiber, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer; the breaking strength of the flame-retardant polyester fiber is 5.5 cN / dtex, and the elongation at break is 30%; the limiting oxygen index value of the flame-retardant polyester fiber is 35%, and the limiting oxygen index value is 32% after 50 times of washing.

[0057] Comparative Example 1

[0058] A preparation method of a flame-retardant polyester fiber is basically the same as that of Example 1, except that: in step (2), the polymeric carbodiimide is replaced with a phosphorus-based flame retardant with the same mass fraction (the same as in Example 1).

[0059] The breaking strength of the finally obtained flame-retardant polyester fiber is 4.7 cN / dtex, and the elongation at break is 30%; the limiting oxygen index value of the flame-retardant polyester fiber is 32%.

[0060] Comparing Comparative Example 1 with Example 1, it can be found that the breaking strength is reduced. This is because after increasing the content of the phosphorus-based flame retardant, the regularity between the polyester molecular chains is affected, resulting in a decrease in the fiber breaking strength; at the same time, without the polymeric carbodiimide, the polymer degradation process during hot processing and post-treatment cannot be effectively inhibited, further leading to a decrease in the fiber breaking strength; during the combustion process, after replacing the polymeric carbodiimide with the same mass fraction of the flame retardant, a flame-retardant synergistic effect cannot be formed, and the limiting oxygen index is slightly lower than the flame-retardant effect in Example 1. At the same time, the phosphorus-based flame retardant forms a catalytic thermal degradation effect on the polymer matrix during combustion, and the melt viscosity of the polymer in the combustion part drops sharply and forms molten drops.

[0061] Comparative Example 2

[0062] A preparation method of a flame-retardant polyester fiber is basically the same as that of Example 1, except that: during the preparation process of the flame-retardant masterbatch, the polymeric carbodiimide is not added, the addition amounts of the phosphorus-based flame retardant and polypropylene change, and the addition amount of the flame-retardant masterbatch during the melt spinning process changes.

[0063] The contents of the phosphorus-based flame retardant and polypropylene in the finally obtained flame-retardant polyester fiber are the same as those in Example 1.

[0064] The breaking strength of the finally obtained flame-retardant polyester fiber is 4.7 cN / dtex, and the elongation at break is 26%.

[0065] Comparing Example 1 with Comparative Example 2, it can be seen that the mechanical properties of the flame-retardant polyester fiber in Comparative Example 2 are significantly lower than those in Example 1. This is because the flame-retardant masterbatch in Comparative Example 2 does not contain polymeric carbodiimide, and it is impossible to increase the spinnability and improve the mechanical properties of the product during the spinning process.

[0066] Such as Figure 1As shown, the flame-retardant polyester fibers of Example 1 and Comparative Example 2 were respectively dissolved in hexafluoroisopropanol. After adding methanol dropwise, the precipitation diagrams of the Comparative Examples were obtained; the left figure is the flame-retardant polyester fiber of Comparative Example 2, and the right figure is the flame-retardant polyester fiber of Example 1; as can be seen from the figure, the right figure forms a gel state after dissolution and precipitation. This is because during the preparation of the flame-retardant polyester fiber of Example 1, the terminal carboxyl groups of the molecular chains with different chain lengths react with the polymeric carbodiimide and form acylurea bonds to connect, forming a branched structure with different branch lengths. After branching, the molecular chains are more likely to entangle with each other to form a physical cross-linking network, thus forming a gel state after dissolution and precipitation.

[0067] Example 2

[0068] A preparation method of a flame-retardant polyester fiber comprises the following specific steps:

[0069] (1) Preparation of raw materials:

[0070] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Material Technology Co., Ltd., grade: 210-2500), number-average molecular weight is 2500 g / mol, and average particle size is 200 mesh;

[0071] Phosphorus-based flame retardant: Polyphosphate flame retardant (manufacturer: Suzhou Baolidi Material Technology Co., Ltd., grade: TA9011), average particle size is 200 mesh;

[0072] Polypropylene: Isotactic polypropylene, average particle size is 200 mesh, melting point is 166 °C, and melt index at a weight of 2.16 kg and a temperature of 230 °C is 58 g / 10 min;

[0073] Polyester: Recycled polyester, intrinsic viscosity is 0.8 dL / g; melt index at a weight of 2.16 kg and a temperature of 275 °C is 33 g / 10 min;

[0074] (2) After uniformly mixing the polymeric carbodiimide, the phosphorus-based flame retardant and polypropylene, melt-blending and extruding through a twin-screw extrusion device to obtain a flame-retardant masterbatch;

[0075] The content of the phosphorus-based flame retardant in the flame-retardant masterbatch is 16 wt%, and the content of polypropylene is 48 wt%;

[0076] (3) The flame-retardant masterbatch is dried in a vacuum rotary drum drying oven at a temperature of 98 °C and a vacuum degree of 98 Pa for 15 hours;

[0077] (4) The polyester is dried in a vacuum rotary drum drying oven at a temperature of 140 °C and a vacuum degree of 98 Pa for 22 hours;

[0078] (5) After uniformly mixing the dried flame retardant masterbatch with polyester, melt spinning is carried out to obtain flame retardant polyester fibers; the mass of the flame retardant masterbatch is 9 wt% of the total mass of the flame retardant masterbatch and polyester.

[0079] The process parameters of melt spinning are as follows: spinning temperature 275 °C, drawing temperature 70 °C, heat setting temperature 70 °C, spinning speed 100 m / min, rotational speed of the first winding roller 80 m / min, aspect ratio of the spinneret hole 4:1, side blowing temperature 8 °C.

[0080] On the cross-section of the finally obtained flame retardant polyester fibers, the contents of polymeric carbodiimide and phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer; the breaking strength of the flame retardant polyester fibers is 5.3 cN / dtex, and the breaking elongation is 32%; the limiting oxygen index value of the fabric woven from the flame retardant polyester fibers is 33%, and the limiting oxygen index value is 31% after 50 times of washing.

[0081] Example 3

[0082] A preparation method of flame retardant polyester fibers, the specific steps are as follows:

[0083] (1) Preparation of raw materials:

[0084] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Material Technology Co., Ltd., brand: 210-3500), number average molecular weight is 3500 g / mol, average particle size is 250 mesh;

[0085] Phosphorus-based flame retardant: Ammonium polyphosphate flame retardant (manufacturer: Shifang Changfeng Chemical Co., Ltd., brand: Ammonium polyphosphate type I), average particle size is 250 mesh;

[0086] Polypropylene: Isotactic polypropylene, average particle size is 260 mesh, melting point is 167 °C, melt index is 56 g / 10 min at a weight of 2.16 kg and a temperature of 230 °C;

[0087] Polyester: Virgin polyester, intrinsic viscosity is 0.85 dL / g, melt index is 36 g / 10 min at a weight of 2.16 kg and a temperature of 280 °C;

[0088] (2) After uniformly mixing the polymeric carbodiimide, phosphorus-based flame retardant and polypropylene, melt blending and extrusion are carried out through a twin-screw extrusion device to obtain a flame retardant masterbatch;

[0089] The content of the phosphorus-based flame retardant in the flame retardant masterbatch is 18 wt%, and the content of polypropylene is 55 wt%;

[0090] (3) The flame retardant masterbatch is dried for 14 hours at a temperature of 100 °C and a vacuum degree of 96 Pa using a vacuum rotary drum drying oven;

[0091] (4) The polyester is dried for 20 hours in a vacuum rotary drum drying oven at a temperature of 145 °C and a vacuum degree of 96 Pa;

[0092] (5) After the dried flame retardant masterbatch is uniformly mixed with the polyester, it is melt spun to obtain flame retardant polyester fibers; the mass of the flame retardant masterbatch is 8.5 wt% of the total mass of the flame retardant masterbatch and the polyester;

[0093] The process parameters of melt spinning are as follows: spinning temperature 280 °C, drawing temperature 100 °C, heat setting temperature 100 °C, spinning speed 1500 m / min, rotational speed of the first winding roller 100 m / min, aspect ratio of the spinneret hole 3.5:1, side blowing temperature 10 °C.

[0094] On the cross-section of the finally obtained flame retardant polyester fibers, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer; the breaking strength of the flame retardant polyester fibers is 5.1 cN / dtex, and the elongation at break is 35%; the limiting oxygen index value of the flame retardant polyester fibers is 32%, and the limiting oxygen index value is 30% after 50 times of washing.

[0095] Example 4

[0096] A method for preparing flame retardant polyester fibers, the specific steps are as follows:

[0097] (1) Preparation of raw materials:

[0098] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Material Technology Co., Ltd., grade: 210 - 4500), number average molecular weight is 4500 g / mol, average particle size is 300 mesh;

[0099] Phosphorus-based flame retardant: Diethyl phosphinate flame retardant (manufacturer: Clariant (China) Co., Ltd., grade: OP950), average particle size is 300 mesh;

[0100] Polypropylene: Isotactic polypropylene, average particle size is 300 mesh, melting point is 168 °C, and melt index is 52 g / 10 min at a weight of 2.16 kg and a temperature of 230 °C;

[0101] Polyester: Recycled polyester, intrinsic viscosity is 0.6 dL / g; melt index is 40 g / 10 min at a weight of 2.16 kg and a temperature of 285 °C;

[0102] (2) After the polymeric carbodiimide, the phosphorus-based flame retardant and the polypropylene are uniformly mixed, they are melt blended and extruded through a twin-screw extrusion device to obtain a flame retardant masterbatch;

[0103] The content of the phosphorus-based flame retardant in the flame retardant masterbatch is 20 wt%, and the content of the polypropylene is 60 wt%;

[0104] (3) The flame retardant masterbatch is dried in a vacuum rotary drum drying oven at a temperature of 102 °C and a vacuum degree of 95 Pa for 12 hours;

[0105] (4) The polyester is dried in a vacuum rotary drum drying oven at a temperature of 150 °C and a vacuum degree of 95 Pa for 18 hours;

[0106] (5) After the dried flame retardant masterbatch and polyester are mixed evenly, they are melt-spun to obtain flame retardant polyester fibers; the mass of the flame retardant masterbatch is 7 wt% of the total mass of the flame retardant masterbatch and polyester;

[0107] The process parameters of melt spinning are as follows: spinning temperature 285 °C, drawing temperature 120 °C, heat setting temperature 120 °C, spinning speed 2000 m / min, rotational speed of the first winding roll 150 m / min, aspect ratio of the spinneret hole 3:1, side blowing temperature 12 °C.

[0108] On the cross-section of the finally obtained flame retardant polyester fibers, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer; the breaking strength of the flame retardant polyester fibers is 5.0 cN / dtex, and the elongation at break is 37%; the limiting oxygen index value of the fabric woven from the flame retardant polyester fibers is 31.50%, and the limiting oxygen index value is 29.50% after 50 times of washing.

[0109] Example 5

[0110] A method for preparing flame retardant polyester fibers, the specific steps are as follows:

[0111] (1) Preparation of raw materials:

[0112] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Material Technology Co., Ltd., grade: 210 - 6500), number average molecular weight is 6500 g / mol, average particle size is 400 mesh;

[0113] Phosphorus-based flame retardant: Polyphosphate flame retardant (manufacturer: Suzhou Baolidi Material Technology Co., Ltd., grade: TA9011), average particle size is 400 mesh;

[0114] Polypropylene: Isotactic polypropylene, average particle size is 400 mesh, melting point is 169 °C, and melt index is 50 g / 10 min at a weight of 2.16 kg and a temperature of 230 °C;

[0115] Polyester: Virgin polyester, intrinsic viscosity is 0.6 dL / g, and melt index is 42 g / 10 min at a weight of 2.16 kg and a temperature of 290 °C;

[0116] (2) Mix the polymeric carbodiimide, phosphorus-based flame retardant, and polypropylene evenly, and then melt blend and extrude them through a twin-screw extrusion device to obtain a flame retardant masterbatch;

[0117] The content of the phosphorus-based flame retardant in the flame retardant masterbatch is 22 wt%, and the content of polypropylene is 65 wt%;

[0118] (3) Dry the flame retardant masterbatch in a vacuum rotary drum drying oven at a temperature of 104 °C and a vacuum degree of 92 Pa for 10 hours;

[0119] (4) Dry the polyester in a vacuum rotary drum drying oven at a temperature of 155 °C and a vacuum degree of 93 Pa for 16 hours;

[0120] (5) Mix the dried flame retardant masterbatch and polyester evenly, and then melt spin to obtain flame retardant polyester fibers; the mass of the flame retardant masterbatch is 6.5 wt% of the total mass of the flame retardant masterbatch and polyester;

[0121] The process parameters of melt spinning are as follows: spinning temperature 290 °C, drawing temperature 150 °C, heat setting temperature 150 °C, spinning speed 2500 m / min, rotational speed of the first winding roller 180 m / min, aspect ratio of the spinneret hole 3.5:1, and side blowing temperature 14 °C.

[0122] On the cross-section of the finally obtained flame retardant polyester fibers, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer; the breaking strength of the flame retardant polyester fibers is 4.8 cN / dtex, and the breaking elongation is 39%; the limiting oxygen index value of the flame retardant polyester fibers is 31%, and the limiting oxygen index value is 29% after 50 washes.

[0123] Example 6

[0124] A method for preparing flame retardant polyester fibers, the specific steps are as follows:

[0125] (1) Preparation of raw materials:

[0126] Polymeric carbodiimide: Aromatic polycarbodiimide (manufacturer: Shanghai Langyi New Materials Technology Co., Ltd., grade: 210 - 8000), number average molecular weight is 8000 g / mol, and average particle size is 500 mesh;

[0127] Phosphorus-based flame retardant: A mixture of a phosphoric acid ester-based flame retardant (manufacturer: Suzhou Baolidi Material Technology Co., Ltd., grade: TA9011) and an ammonium polyphosphate-based flame retardant (manufacturer: Shifang Changfeng Chemical Co., Ltd., grade: ammonium polyphosphate type I) with a mass ratio of 1:1, and average particle size is 500 mesh;

[0128] Polypropylene: Isotactic polypropylene, with an average particle size of 500 mesh, a melting point of 170 °C, and a melt index of 45 g / 10 min at a weight of 2.16 kg and a temperature of 230 °C;

[0129] Polyester: A mixture of virgin polyester and recycled polyester with a mass ratio of 1:1. The intrinsic viscosity of the virgin polyester is 0.8 dL / g, and the intrinsic viscosity of the recycled polyester is 0.75 dL / g. The melt indices of the virgin polyester and recycled polyester are 43 and 45 g / 10 min respectively at a weight of 2.16 kg and a temperature of 300 °C;

[0130] (2) Mix the polymeric carbodiimide, phosphorus-based flame retardant, and polypropylene evenly, and then melt-blend and extrude through a twin-screw extrusion device to obtain a flame retardant masterbatch;

[0131] The content of the phosphorus-based flame retardant in the flame retardant masterbatch is 25 wt%, and the content of polypropylene is 70 wt%;

[0132] (3) Dry the flame retardant masterbatch in a vacuum rotary drum drying oven at a temperature of 105 °C and a vacuum degree of 90 Pa for 8 hours;

[0133] (4) Dry the polyester in a vacuum rotary drum drying oven at a temperature of 165 °C and a vacuum degree of 90 Pa for 12 hours;

[0134] (5) Mix the dried flame retardant masterbatch and polyester evenly, and then melt-spin to obtain flame retardant polyester fibers. The mass of the flame retardant masterbatch is 6 wt% of the total mass of the flame retardant masterbatch and polyester;

[0135] The process parameters of melt spinning are as follows: spinning temperature 300 °C, drawing temperature 170 °C, heat setting temperature 170 °C, spinning speed 3000 m / min, the rotational speed of the first winding roller 200 m / min, the aspect ratio of the spinneret hole 3:1, and the side blowing temperature 15 °C.

[0136] In the cross-section of the finally obtained flame retardant polyester fibers, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer. The breaking strength of the flame retardant polyester fibers is 4.5 cN / dtex, and the breaking elongation is 40%. The limiting oxygen index value of the fabric woven from the flame retardant polyester fibers is 30%, and the limiting oxygen index value is 28% after 50 times of washing.

Claims

1. A preparation method of flame-retardant polyester fiber, which comprises melt-spinning after uniformly mixing a flame-retardant masterbatch and polyester to obtain the flame-retardant polyester fiber, characterized in that, The matrix of the flame retardant masterbatch is polypropylene, and polymeric carbodiimide and a phosphorus-based flame retardant are uniformly dispersed in the polypropylene; The polymeric carbodiimide is aromatic polycarbodiimide; The content of polypropylene in the flame retardant masterbatch is 40-70 wt%; The melt spinning process parameters include: a spinning temperature of 270-300 °C; The melting point of polypropylene is 165-170 °C, and its melt index at a weight of 2.16 kg of the weight and a temperature of 230 °C is 45-60 g / 10 min; the melt index of the polyester at a weight of 2.16 kg of the weight and a temperature of 270-300 °C is 30-45 g / 10 min; The content of the phosphorus-based flame retardant in the flame retardant polyester fiber does not exceed 2.5 wt%.

2. The preparation method of a flame-retardant polyester fiber according to claim 1, characterized in that, The phosphorus-based flame retardant is one or more of diethyl phosphinate flame retardants, polyphosphate ester flame retardants or ammonium polyphosphate flame retardants; the limiting oxygen index value of the flame retardant polyester fiber or the fabric woven from the flame retardant polyester fiber is 30%-35%, and the limiting oxygen index value is 28%-32% after 50 times of washing.

3. The preparation method of a flame-retardant polyester fiber according to claim 2, characterized in that, The mass of the flame retardant masterbatch is 6-10 wt% of the total mass of the flame retardant masterbatch and the polyester, and the content of the phosphorus-based flame retardant in the flame retardant masterbatch is 15-25 wt%.

4. The preparation method of a flame-retardant polyester fiber according to claim 1, characterized in that, The content of polymeric carbodiimide in the flame retardant polyester fiber is 0.3-4.5 wt%.

5. The preparation method of a flame-retardant polyester fiber according to claim 1, characterized in that The number average molecular weight of the aromatic polycarbodiimide is 1000-8000 g / mol, and the particle size is 100-500 mesh; the particle size of the phosphorus-based flame retardant is 100-500 mesh; the polypropylene is isotactic polypropylene, and the particle size is 100-500 mesh; the polyester is one or more of virgin polyester or recycled polyester, the intrinsic viscosity range of the virgin polyester is 0.6-1.0 dL / g, and the intrinsic viscosity range of the recycled polyester is 0.6-0.8 dL / g.

6. The preparation method of a flame-retardant polyester fiber according to claim 1, characterized in that, The preparation process of the flame retardant masterbatch is: after mixing each component evenly, melt-blending and extruding through a twin-screw extrusion device to obtain the flame retardant masterbatch.

7. The preparation method of a flame-retardant polyester fiber according to claim 1, characterized in that, The melt spinning process parameters also include: a drawing temperature of 65-170 °C, a heat setting temperature of 65-170 °C, a spinning speed of 800-3000 m / min, a rotational speed of the first winding roll of 50-200 m / min, an aspect ratio of the spinneret hole of 3-4.5:1, and a side blowing temperature of 5-15 °C.

8. A flame-retardant polyester fiber prepared by the preparation method of a flame-retardant polyester fiber according to any one of claims 1 to 7, characterized in that, In the cross-section, the contents of the polymeric carbodiimide and the phosphorus-based flame retardant show a decreasing trend from the outer layer to the inner layer.

9. A flame-retardant polyester fiber according to claim 8, characterized in that, The breaking strength of the flame retardant polyester fiber ≥4.5 cN / dtex, and the breaking elongation is 30%-40%.

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