METHOD FOR PREPARING CATIONIC DYEABLE FLAME-RETARDANT HIGH-STRENGTH POLYESTER FIBER

TECHNICAL FIELD

The present invention belongs to the technical field of polymer materials, and more particularly, relates to a method for preparing a cationic dyeable flame-retardant high-strength polyester fiber.

BACKGROUND

Polyester has many excellent properties and is a high molecular polymer material widely used in various fields. However, due to its chemical structure and combustion characteristics, polyester fiber has a low limiting oxygen index (LOI), which is only about 21%, and its ignition temperature is very close to its decomposition temperature, making it very easy to burn. At the same time, the heat generated by PET fiber during combustion is much greater than its own melting heat, so the matrix is very easy to soften and form molten droplets. The molten droplets not only cause burns, but also easily cause secondary combustion, causing secondary damage to people. In addition, PET has a regular molecular structure, is easy to crystallize and has no dyeable functional groups, although it can be dyed with disperse dyes under high temperature and high pressure, the production conditions are harsh, the production cost is high, and the product color is not ideal.

Regarding the flame retardancy of polyester fibers, flame retardant modification is an important method to solve the flame retardancy of polyester non-intrinsic flame retardant polymer materials. With the in-depth research on flame retardants and flame retardant methods, various flame retardants and related flame retardant modification methods have developed rapidly. Currently, the flame-retardant polyester fiber is mainly prepared by the following methods:

- the first method is to treat the surface of fibers and products with flame retardants; the second is to use flame-retardant materials during the spinning process; the third is to use flame-retardant materials for copolymerization. The first method has the problem of flame retardant effect and washability, as the number of washing times increases, the flame retardant on the surface of fiber products is significantly lost; the second method is generally to introduce nano-sized inorganic materials into the polymer to improve the flame retardant properties, which only be effective when the addition ratio is very high, while the high specific surface area of inorganic materials is difficult to disperse in high-viscosity polymer systems, resulting in a decrease in the spinnability of the polymer. The first two methods mainly suffer from poor dispersion of the flame retardant, and the third method can overcome the shortcomings of the first two methods and is therefore widely used.

There is a lot of public technical information on the dyeing of polyester fibers, and the dyeing performance of polyester fibers is generally improved by introducing components containing sulfonate groups for copolymerization at the stage of polyester synthesis, and the components containing sulfonate groups include sodium isophthalate sulfonate and its esterified substances.

The prior art prepares the polyester or the polyester fiber with both flame-retardant effect and dyeing effect by simultaneously introducing flame retardant and components containing sulfonate groups into polyester. Patent CN1359962A uses terephthalic acid and ethylene glycol as the first monomer and the second monomer, and uses reactive the phosphorus flame retardant and isophthalate containing sulfonate groups as the third monomer and the fourth monomer to obtain flame-retardant cationic dyeable polyester copolymer, and then spins polyester fiber with excellent flame retardancy and cationic dyeability; CN101864612A2 first reacts carboxyethyl hypophosphite (CEPPA) with sodium isophthalate sulfonate to generate flame-retardant cationic dyeable auxiliary agent, and then reacts with terephthalic acid (PTA) and ethylene glycol (EG) to obtain cationic dyeable halogen-free flame-retardant polyester, and further obtains cationic dyeable halogen-free flame retardant polyester fiber; CN103739832 discloses a method for preparing a cationic dye-dyable flame-retardant polyester resin, including the steps of subjecting a halogen-free copolymerized phosphorus-based flame retardant, ethylene glycol and a composite catalyst to an esterification reaction to obtain an esterified liquid of the halogen-free copolymerized flame retardant; subjecting sulfonic acid dimethyl isophthalate and ethylene glycol to an ester exchange reaction to obtain a sulfonate-based dihydroxyethyl isophthalate solution; subjecting terephthalic acid (or dimethyl terephthalate), ethylene glycol and an auxiliary agent to an esterification reaction, and then adding a catalyst, a stabilizer, an auxiliary agent, a phosphorus-based flame retardant esterified liquid (or a phosphorus-based flame retardant prepolymer liquid) and a sulfonic acid-based dihydroxyethyl isophthalate solution to a condensation reaction.

However, since flame retardants and cationic dyeable components are introduced into polyester based on copolymerization reactions, the regularity of the polyester is reduced, resulting in a decrease in the original orientation and crystallinity of the polyester, and lower strength of the final polyester fiber, which affects applicability.

SUMMARY

The purpose of the invention is to solve the above problems existing in the prior art, and to provide a method for preparing a cationic dyeable flame-retardant high-strength polyester fiber.

To this end, the technical schemes of the invention are as follows:

A method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, after mixing oligomer A, oligomer B, and ethylene terephthalate and carrying out a polycondensation reaction to obtain a cationic dyeable flame-retardant polyester masterbatch, adding the dried cationic dyeable flame-retardant polyester masterbatch (with a moisture content of less than 30 ppm) to polyester chips according to a certain ratio for melt spinning, to prepare the cationic dyeable flame-retardant high-strength polyester fiber;

- wherein oligomer A is prepared by the esterification reaction of a phosphorus flame retardant and a diol; oligomer B is prepared by the esterification reaction of sodium isophthalate sulfonate and a diol;
- wherein the degree of polymerization of oligomer A is 3-7; the degree of polymerization of oligomer B is 2-6; the invention must control the degree of polymerization of oligomer A and oligomer B, because the prepared masterbatch is a block copolymer, if the polymerization of oligomer A and oligomer B is too high or too low, it will lead to changes in the properties of the prepared masterbatch; when the polymerization of oligomer A and oligomer B is too high, it causes a decrease in the number of segments in the masterbatch, in which the proportion of ethylene terephthalate hard segments increases, and the fluidity of the masterbatch decreases significantly; when the polymerization of oligomer A and oligomer B is too low, it causes an increase in the number of segments in the masterbatch, in which the proportion of ethylene terephthalate hard segments decreases, and the crystallizability of the masterbatch decreases;
- wherein a ratio of the sum of the molar weight of oligomer A and oligomer B to the molar weight of ethylene terephthalate is 3:7-6:4; wherein the modified component composed of oligomer A and oligomer B must reach a certain proportion to achieve a modification effect; if the sum of the molar ratio of oligomer A and oligomer B is less than 30%, the content of the modified component composed of oligomer A and oligomer B in the prepared masterbatch is too low, and the amount of application must be very high to achieve the expected flame-retardant and dyeing effects, but it will have an adverse effect on the spinnability of the fiber; if the sum of the molar ratio of oligomer A and oligomer B is higher than 60%, the content of the modified component composed of oligomer A and oligomer B in the prepared masterbatch is too high, resulting in a low proportion of ethylene terephthalate hard segments in the prepared masterbatch, and a decrease in the crystallizability of the masterbatch, occurring bonding problems during the drying process of the masterbatch to affect the application. Therefore, the ratio of the sum of the molar weight of oligomer A and oligomer B to the molar weight of ethylene terephthalate must be strictly controlled.

The following preferred technology program is presented to give a detailed description for this invention:

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein a molar ratio of the phosphorus flame retardant to sodium isophthalate sulfonate is 2:8-8:2; the sulfonate component and the phosphorus flame retardant in the masterbatch of the invention can produce a synergistic flame retardant effect, wherein the ratio of the phosphorus flame retardant to sodium isophthalate sulfonate must be within a specific range to achieve the synergistic flame retardancy; the ratio of molar amounts of the phosphorus flame retardant to sodium isophthalate sulfonate is within this range, which can avoid the problem of low fluidity of the prepared masterbatch due to the high content of sodium isophthalate sulfonate in the masterbatch (correspondingly, the low content of the phosphorus flame retardant), the decrease in melt fluidity due to the large ionic bond force of sodium isophthalate sulfonate, and the problem that the limiting oxygen index of the prepared masterbatch does not meet the design requirements; it can also avoid the problem of low carbonization and anti-melting droplet performance of the prepared masterbatch due to the low content of sodium isophthalate sulfonate in the masterbatch.

In addition, the phosphorus flame retardant form a sticky film of phosphoric acid and polyphosphoric acid on the surface of the polymer through thermal decomposition, making the polymer flame-retardant. Free radicals such as PO· and HPO· are generated during the combustion process, capturing active H· or OH· in the gas phase and achieve gas-phase flame retardant effect through the combination of free radicals, which can reduce the rate of thermal degradation rate of polymers. The ionic monomers of the sulfonate structure in the flame retardant system can form ion clusters in the molecular chain of the ionomer, forming a stable physical cross-linking network. After introducing, it can increase the melt strength of the ionomer, and at the same time cooperate with the phosphorus flame retardant to quickly form a stable and dense carbon layer to suppress the droplet phenomenon. The composite ratio of the phosphorus flame retardant and sodium isophthalate sulfonate must be controlled within a certain range. When the molar ratio of the phosphorus flame retardant to sodium isophthalate sulfonate is lower than 2:8, the low content of the phosphorus flame retardant in the flame retardant system will lead to a decrease in the ability to capture free radicals during combustion, showing a decrease in the limiting oxygen index; when the molar ratio of the phosphorus flame retardant to sodium isophthalate sulfonate is higher than 8:2, the high content of the phosphorus flame retardant in the flame retardant system will lead to an enhanced ability to capture free radicals during combustion, showing an increase in the limiting oxygen index, but a stable physical cross-linked network structure cannot be formed during combustion and a molten droplet problem is created.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein a preparation process of oligomer A or oligomer B is as follows: after mixing X, the diol and a catalyst, carrying out the esterification reaction under the protection of protective gas (nitrogen, etc.) to obtain oligomer A or oligomer B, X is the phosphorus flame retardant or sodium isophthalate sulfonate; the temperature of the esterification reaction is 140-220° C., the pressure is 0.01-0.5 MPa, and the time is 3-6 h; the temperature, pressure and time of the esterification reaction are set in such way to avoid the problem of insufficient reaction to reach the specified degree of polymerization, i.e., low molecular weight, due to their low values; it can also avoid the problem of too high values, which leads to too sufficient reaction and too high molecular weight of the synthesized product.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the molar ratio of X to the diol is 1:1.15-1:1.5, and the mass of the catalyst is 0.001-0.05% of the mass of X; X is a bifunctional group, the diol is also a bifunctional group, the molar ratio of X to the diol is within this range, which can realize the full reaction of X and enhance the reaction rate, avoiding the slow reaction rate due to the amount of the diol is too small, the reaction rate decreases and affects the efficiency of the problem, especially when the amount of the diol is lower than X, which can not realize the full reaction of X; it also avoids the problem of a significant increase in the content of by-products due to the self-condensation reaction that occurs when there is too much diol in excess due to a high amount of diol.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the phosphorus flame retardant is more than one selected from CEPPA (2-carboxyethylphenyl hypophosphite), DDP ([(6-oxo-6H-dibenzo [c,e][1,2]oxaphosphorin-6-yl) methyl]succinic acid) and BCPPO (bis(p-carboxyphenyl)phenylphosphine oxide), and the purity reaches more than 99%; wherein the diol is ethylene glycol, propylene glycol, butylene glycol or pentanediol; and the catalyst is ethylene glycol antimony or ethylene glycol titanium.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the temperature of the polycondensation reaction is 220-280° C., an absolute pressure is below 100 Pa (absolute pressure is a technical term, gauge pressure=absolute pressure-atmospheric pressure), and the time is 3-5 h; the number average molecular weight of the cationic dyeable flame-retardant polyester masterbatch is 15000-25000 g/mol, the melt index is 30-90 g/10 min, the semi-crystallization time t12 (test method is DSC non-isothermal crystallization method) is 3-15 min, and the crystallinity (test method is XRD method) is 20-40%. It can be seen that the cationic dyeable flame-retardant polyester masterbatch has good crystallinity and fluidity, the good crystallization performance of the masterbatch ensures that the masterbatch can be fully dried before spinning, and will not be unusable due to poor crystallization performance that leads to adhesion in the drying process; the good fluidity can make the masterbatch easy to disperse in the outer layer of the melt, that is, the surface of the fiber when blended with polyester, so that the flame-retardant functional components can be distributed on the surface as much as possible to achieve the maximum modification effect.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the mass ratio of the cationic dyeable flame-retardant polyester masterbatch to the polyester chip is 4:96-12:88; an intrinsic viscosity of the polyester chip is 0.60-1.10 dL/g, and the melt index is 15-30 g/10 min.

- wherein spinning process parameters of the POY fiber are: a spinning box temperature of 250-300° C.; a cooling and blowing temperature of 10-50° C., a wind speed of 0.1-1.5 m/s, a relative humidity of 55-95%; a first godet wheel speed of 2500-3500 m/min, a second godet wheel speed of 2500-3500 m/min, and a winding speed of 2500-3500 m/min;
- wherein a preparation process of the DTY fiber includes: feeding the POY fiber into the first roller, and the DTY fiber is obtained through a yarn guide porcelain, a hot box, another yarn guide porcelain, a false twister, a second roller, an interlacing device, a third roller, a tanker, a winding roller and a wound DTY spindle.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the cationic dyeable flame-retardant high-strength polyester fiber is a fully drawn yarn (FDY) fiber, and spinning process parameters are: a spinning box temperature of 250-300° C.; a cooling and blowing temperature of 10-50° C., a wind speed of 0.1-1.5 m/s, a relative humidity of 55-95%; a roller speed of a first godet roller of 2500-3000 m/min, a roller speed of a second godet roller of 3000-4500 m/min, and a winding speed of 3000-4500 m/min.

The said method for preparing a cationic dyeable flame-retardant high-strength polyester fiber, wherein the cationic dyeable flame-retardant high-strength polyester fiber has an orientation degree (test method is microscope direct observation calculation method) ≥0.90, a tensile breaking strength ≥4.5 cN/dtex, a cationic dye uptake rate of more than 95%, and a limiting oxygen index (LOI) ≥30%. The cationic dyeable flame-retardant polyester fiber in the prior art has an orientation degree <0.9, a tensile breaking strength ≥2.5cN/dtex, a cationic dye uptake of 90˜95%, and the LOI ≥30%.

The principle of the present invention is as follows:

The prior art forms flame-retardant easy-to-dye copolyester chips, and the core of the present invention is to form a high-proportion copolymerized cationic dyeable flame-retardant polyester masterbatch. The invention is to react the flame retardant and the cationic dyeable component with the diol to generate oligomer A and oligomer B respectively, and then mix the oligomer A and oligomer B with ethylene terephthalate at the same time, and remove the small molecule diol through transesterification to form a copolymer product (cationic dyeable flame-retardant polyester masterbatch). Both oligomer A and oligomer B are controlled to have a certain molecular weight in the invention, and are capped with excessive diols, and have high transesterification reaction activity, by adjusting the addition ratio and reaction parameters, the formed product has a block structure. The block copolymer has the characteristics of general block polymers: a controllable molecular weight, a narrow molecular weight distribution, and a designable molecular structure and composition, wherein oligomer A and oligomer B are soft segments, and ethylene terephthalate is a hard segment.

Although there are publicly reported products obtained by esterification reaction of the phosphorus flame retardant, sodium isophthalate sulfonate and the diol in the prior art, the invention emphasizes that the phosphorus flame retardant, sodium isophthalate sulfonate and the diol are esterified step by step to prepare oligomers and then copolymerize, so that the sequence structure of the prepared cationic dyeable flame-retardant polyester masterbatch can be controlled, rather than a random structure, wherein the hard segment of the cationic dyeable flame-retardant polyester masterbatch is a part with good crystallizability, and by changing the ratio of the components of the soft segment and the hard segment, the crystallizability of the masterbatch can be regulated, ensuring that the masterbatch has practical application value. In addition, the fluidity of the masterbatch is greatly different from that of conventional polyester, and by adjusting the soft and hard ratio, the masterbatch can be realized to have a higher fluidity, so that the difference in fluidity between the masterbatch and the polyester will form a blending effect of a microphase separation structure, so that the masterbatch is easier to disperse on the surface of the fiber after blending with the polyester, so that the cationic dyeable component and the flame retardant component can play a greater role.

At present, the preparation of functional copolyesters, including the preparation of flame-retardant cationic dyeable copolyesters, is an important aspect, but the more important aspect is how to ensure the spinnability of functional copolyesters and the strength of fibers. The good mechanical properties of polyester fibers themselves are an important reason for their wide application, but after the copolymer components are introduced into the prior art, the original polyester spinnability and the mechanical properties of the fibers are significantly reduced, which is because the introduction of functional components into the polyester destroys the original regularity and reduces the strength of the fibers. Introducing functional masterbatches into polyester melts for spinning by blending and modification has little effect on the regularity of polyester and the orientation of the fibers, therefore, the mechanical strength of the fibers is not significantly affected, while achieving cationic dyeability and flame retardant functions, the original mechanical strength of the fibers is maintained.

Benefits:

- (4) The cationic dyeable flame-retardant high-strength polyester fiber prepared by the cationic dyeable flame-retardant polyester masterbatch of the invention, the fiber has a limiting oxygen index of more than 30 and has good flame retardant performance. When the masterbatch undergoes high-temperature melting during the combustion process, the ionic groups in the PET molecular chains of the melt drive the molecular chains to aggregate, and the high-density molecular chains promote the formation of a carbon layer on the surface of the polyester combustion and increase the viscosity of the melt after high-temperature melting, thereby improving the flame retardant and anti-melting droplet properties of PET, which belongs to the condensed phase flame retardant and has the characteristics of good flame retardant effect, long-lasting flame retardant performance, anti-melting droplet, halogen-free, low toxicity and good safety;
- (5) the cationic dyeable flame-retardant polyester masterbatch prepared by the invention is a macromolecular polymer, adding the masterbatch to the polyester in a certain proportion slightly affects the spinnability of the polyester; the macromolecular masterbatch and the polyester are blended to ensure the blending compatibility while not affecting the original tensile orientation of the polyester, thereby achieving compatibility between function and mechanical strength;
- (6) the cationic dyeable flame-retardant high-strength polyester fiber prepared by the cationic dyeable flame-retardant polyester masterbatch of the invention, can be used in automobiles, ships, the interior decoration of high-class hotels, national defense and military industry, and special labor protection equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE is a SEM image of a cross section of the cationic dyeable flame-retardant high-strength polyester fiber prepared by the cationic dyeable flame-retardant polyester masterbatch of Example 6

DETAILED DESCRIPTION OF THE EMBODIMENTS

Based on above mentioned method, the following embodiments are carried out for further demonstration in the present invention. It is to be understood that these embodiments are only intended to illustrate the invention and are not intended to limit the scope of the invention. In addition, it should be understood that after reading the contents described in the present invention, those technical personnel in this field can make various changes or modifications to the invention, and these equivalent forms also fall within the scope of the claims attached to the application.

Example 1