Preparation method of high-strength and high-modulus polyester fiber and polyester fiber

Abstract

The invention relates to the technical field of polyester fibers, and discloses a preparation method of a high-strength and high-modulus polyester fiber and the polyester fiber, and the preparation method comprises the following steps: (1) mixing 4, 4 '-diphenyldicarboxylic acid, 1, 3-propylene glycol, a catalyst and a heat stabilizer, and carrying out esterification reaction; (2) after esterification is completed, performing a first-stage polycondensation reaction, then performing a second-stage polycondensation reaction, and removing small molecules and water while reacting to obtain a polymer; and (3) carrying out melt spinning on the polymer, and sequentially carrying out first-stage side blowing, second-stage side blowing and post-stretching to obtain the polyester fiber. The PET melt is prepared from the 4, 4 '-biphenyldicarboxylic acid monomer and the 1, 3-propylene glycol monomer through esterification and condensation polymerization, the relative molecular mass can be improved, the stereoregularity of macromolecular chains can be increased, and finally the polyester fiber with high breaking strength, elasticity modulus and melting point can be prepared through melt spinning.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester fibers, and particularly to a preparation method of high-strength and high-modulus polyester fibers and polyester fibers. Background Art

[0002] Currently, the preparation of high-strength and high-modulus polyester (PET) fibers mainly uses terephthalic acid (PTA) and ethylene glycol (EG) as monomers and adopts the direct esterification method for polymerization. First, polyester esterification product (BHET) is generated, then polycondensation is carried out under certain conditions to produce polyester chips, and finally, spinning is carried out by the melt spinning method. However, the breaking strength of the polyester fibers prepared by this traditional method is generally 4 - 6 cN / dtex, the elastic modulus is generally 60 - 100 cN / dtex, and the melting point is generally 255 - 263 °C. It is difficult to meet the special requirements of the industrial field for mechanical properties. How to improve the strength and modulus of polyester fibers to prepare high-strength and high-modulus polyester fibers is a research topic worthy of study.

[0003] The main reason for the insufficient strength and modulus of the polyester fibers prepared by the traditional method is that the molecular weight of the PTA monomer is relatively low and the reaction activity is relatively high. Therefore, the molecular weight of the polyester prepared after polycondensation is not high enough. This first affects the improvement of the melt viscosity, and then leads to easy breakage during spinning. The fibers cannot withstand high multiples of stretching, and finally the mechanical properties of the fibers are not high. At the same time, since the PTA monomer only contains one benzene ring structure, the synthesized polyester macromolecules have insufficient rigidity, resulting in a low melting point of the fibers.

[0004] The invention patent with the publication number of CN114000226A discloses a cationic dyeable and flame-retardant high-strength polyester fiber. First, oligomer A, oligomer B, and BHET are mixed and then subjected to a polycondensation reaction to prepare a cationic dyeable and flame-retardant polyester masterbatch, and then it is mixed with polyester chips in a certain proportion and subjected to melt spinning. The breaking strength of the polyester fibers prepared by this method is only up to 4.8 cN / dtex at most, and the preparation process is complex. The invention patent with the publication number of CN106397749A discloses a synthesis method of high-strength and high-modulus polyester. First, a composite alcohol solution and a composite accelerator are prepared, and high-strength and high-modulus polyester is prepared by controlling their different proportions for polycondensation. However, it does not carry out spinning and research on the mechanical properties of the fibers. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for preparing a high-strength and high-modulus polyester fiber and the polyester fiber. By using 4,4'-biphenyldicarboxylic acid (BBA) monomer to replace the traditional terephthalic acid (PTA) monomer, and using 1,3-propanediol (PDO) monomer to replace the traditional ethylene glycol (EG) monomer, these two monomers are successively subjected to esterification and polycondensation reactions to prepare a PET melt, and then the polyester fiber is obtained by melt spinning. This not only gives a higher relative molecular mass to the macromolecular chain, increases the rigid structure of the molecular chain, but also increases the stereoregularity of the macromolecular chain, and finally prepares a polyester fiber with high breaking strength, elastic modulus and melting point.

[0006] The object of the present invention is achieved by the following technical solutions: In the first aspect, the present invention provides a method for preparing a high-strength and high-modulus polyester fiber, comprising the following steps: (1) Mix 4,4'-biphenyldicarboxylic acid, 1,3-propanediol, a catalyst and a heat stabilizer, and carry out an esterification reaction; (2) After the esterification is completed, first carry out a first-stage polycondensation reaction, and then carry out a second-stage polycondensation reaction, while removing small molecules and water during the reaction to obtain a polymer; The reaction equation of the polycondensation reaction is as follows: (3) Melt-spin the polymer, and then successively pass through the first-stage side blowing, the second-stage side blowing and post-drawing to obtain the polyester fiber.

[0007] The present invention uses 4,4'-biphenyldicarboxylic acid (BBA) monomer to replace the traditional terephthalic acid (PTA) monomer, and uses 1,3-propanediol (PDO) monomer to replace the traditional ethylene glycol (EG) monomer. These two monomers are successively subjected to esterification and polycondensation reactions to prepare a PET melt. Compared with the prior art in which PTA and EG monomers are used for esterification and polycondensation to prepare a PET melt, since the molecular weights of the new monomers are both larger and the reaction activities are respectively lower than those of PTA and EG, it is easier to obtain a PET macromolecule with a higher molecular weight. The BBA monomer also has a special structure with two benzene rings, and during polymerization, it can increase the proportion of the rigid structure in the PET macromolecule, thereby being beneficial to increasing the melting temperature of the PET fiber.

[0008] In addition, if only PTA is replaced with BBA monomer and the EG monomer remains unchanged, although the PET macromolecules can obtain more rigid structures after polycondensation, the excessive rigidity and insufficient flexibility of the macromolecular chains will be disadvantageous for spinning. After replacing the EG monomer with PDO monomer, since the carbon chain link in the PDO monomer is longer, the movement ability of the macromolecular chain segments will increase, and different stereoregularities can be presented through the internal rotation of the carbon-carbon bonds on the molecular chain. At the same time, due to the larger steric hindrance effect of the biphenyl structure compared to the single benzene ring structure, it is also more conducive to improving the stereoregularity of the PET molecular chain, and ultimately conducive to the close aggregation of macromolecules and the improvement of crystallization performance.

[0009] Therefore, the present invention introduces BBA and PDO monomers to replace the original two monomers, which not only endows the macromolecular chains with higher relative molecular weights, increases the rigid structures of the molecular chains, but also increases the stereoregularity of the macromolecular chains, and is conducive to preparing polyester fibers with better mechanical properties and thermal stability.

[0010] Preferably, the molar ratio of 4,4'-biphenyldicarboxylic acid to 1,3-propanediol is 1:1.1 - 1.4.

[0011] Preferably, the dosage of the catalyst is 0.04 - 0.1% of the mass of 4,4'-biphenyldicarboxylic acid; the catalyst is Sb 2 O 3 or GeO 2 。

[0012] Preferably, the dosage of the heat stabilizer is 0.02 - 0.1% of the mass of 4,4'-biphenyldicarboxylic acid; the heat stabilizer is triphenyl phosphite.

[0013] Preferably, the temperature of the esterification reaction is 280 - 310 °C, the pressure is 100 - 120 kPa, and the reaction time is 2 - 4 h.

[0014] Preferably, the temperature of the first-stage polycondensation reaction is 260 - 270 °C, the pressure is 5 - 7 kPa, and the polycondensation time is 2 - 3 h.

[0015] Preferably, the temperature of the second-stage polycondensation reaction is 270 - 290 °C, the pressure is 50 - 90 Pa, and the polycondensation time is 2 - 3 h.

[0016] Preferably, the relative molecular weight of the polymer is not less than 23,000; more preferably, the relative molecular weight of the polymer is not less than 24,000.

[0017] Preferably, the temperature of the melt spinning is 265 - 290 °C, the pressure is 40 - 60 MPa; the spinning speed of the melt spinning is 2500 - 2800 m / min.

[0018] The present invention adopts a high-pressure melt spinning process, including a step-by-step heating and preheating process in the feeding stage, a high-pressure compression, exhaust and gradual melting process in the spinning box.

[0019] Preferably, the blowing temperature of the first-stage side blowing is 8-15°C, the relative humidity is 70-90%, and the wind speed is 0.2-0.4 m / s.

[0020] The temperature of the first-stage side blowing device is relatively low because the macromolecular chains of the filaments extruded from the spinneret holes are affected by the shear force of the spinneret holes and a large temperature difference (the temperature difference between the spinning solution in the spinneret holes and the first-stage side blowing), which rapidly reduces the thermal motion of the macromolecular chains, and the fibers are rapidly solidified, enabling the straightened state of the macromolecules to be maintained.

[0021] Preferably, the blowing temperature of the second-stage side blowing is 50-70°C, the relative humidity is 50-60%, and the wind speed is 0.3-0.6 m / s.

[0022] The temperature of the second-stage side blowing device is relatively high because after the fibers enter the high-temperature area, the macromolecular chains will relax due to the action of temperature. At this time, under the action of a certain multiple of winding tension, the macromolecules can be kept in a straightened chain structure, which is ultimately beneficial to the improvement of the draw ratio, and the crystallinity and orientation degree of the fibers will also increase accordingly, thus being beneficial to the improvement of the breaking strength, elastic modulus and melting point.

[0023] Preferably, the draw ratio of the post-drawing is not less than 4.0.

[0024] In a second aspect, the present invention also provides a high-strength and high-modulus polyester fiber prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) By introducing 4,4'-biphenyldicarboxylic acid (BBA) monomer and 1,3-propanediol (PDO) monomer to replace the original two monomers respectively, the present invention not only endows the macromolecular chains with higher molecular weight, increases the rigid structure of the molecular chains, but also increases the stereoregularity of the macromolecular chains, which is beneficial to preparing polyester fibers with better mechanical properties and thermal stability.

[0026] (2) The existing synthesis process mainly first adopts a multi-stage esterification method to generate polyester ester (BHET), and then conducts a multi-step polycondensation reaction under certain conditions to generate PET chips. This method has the disadvantages of long polymerization process, low efficiency and high energy consumption. However, the present invention adopts a direct esterification method and conducts a polycondensation reaction in the same reaction kettle, which can greatly shorten the reaction process and save energy consumption.

[0027] (3) The preparation process of the present invention is simple and no three wastes are generated. Detailed implementation manners

[0028] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0029] The preparation of the high-strength and high-modulus polyester fiber in the present invention includes the following steps: (1) First, displace the air in the polymerization kettle with nitrogen, and then fully mix and stir 4,4'-biphenyldicarboxylic acid (BBA), 1,3-propanediol (PDO), a catalyst and a heat stabilizer evenly and then add them to the reaction kettle. Among them, the molar ratio of 4,4'-biphenyldicarboxylic acid to 1,3-propanediol is 1:1.1 - 1.4, the dosage of the catalyst is 0.04 - 0.1% of the mass of 4,4'-biphenyldicarboxylic acid, and the dosage of the heat stabilizer is 0.02 - 0.1% of the mass of 4,4'-biphenyldicarboxylic acid; carry out an esterification reaction, the temperature in the reaction kettle is 280 - 310 °C, the pressure is 100 - 120 kPa, and the reaction time is 2 - 4 h to prepare BHET; (2) After the esterification is completed, adjust the temperature in the reaction kettle to 260 - 270 °C, the pressure to 5 - 7 kPa, and the polycondensation time to 2 - 3 h to carry out the first-stage polycondensation reaction; then adjust the temperature in the reaction kettle to 270 - 290 °C, the pressure to 50 - 90 Pa, and the polycondensation time to 2 - 3 h to carry out the second-stage polycondensation reaction. During the polycondensation reaction, use pure recycled N 2 Carry the generated PDO and water out of the system, and remove PDO and water in the recycled nitrogen through an adsorption tower equipped with artificial molecular sieve. After polycondensation, a polymer with a higher molecular weight is obtained, and then PET chips are prepared; (3) After drying the PET chips, carry out melt spinning. In the spinning box, it is compressed, exhausted and melted under high pressure to extrude filaments. The pressure of the high-pressure spinning is 40 - 60 MPa, the spinning temperature is 265 - 290 °C, and the spinning speed is 2500 - 2800 m / min; the spun filament bundle passes through two-stage side blowing devices in sequence. The distance between the first-stage side blowing device and the spinneret is 10 - 20 cm, the blowing temperature is 8 - 15 °C, the relative humidity is 70 - 90%, and the wind speed is 0.2 - 0.4 m / s. The blowing temperature in the second-stage side blowing device is 50 - 70 °C, the relative humidity is 50 - 60%, and the wind speed is 0.3 - 0.6 m / s; then carry out post-drawing to obtain polyester fibers.

[0030] In the specific embodiment of the present invention, the catalyst is Sb 2 O 3 or GeO 2 .

[0031] In the specific embodiment of the present invention, the heat stabilizer is triphenyl phosphite.

[0032] In a specific embodiment of the present invention, the main component of the adsorbent in the adsorption tower filled with artificial molecular sieve is a sodium aluminosilicate hydroxide compound.

[0033] In a specific embodiment of the present invention, the temperature during the drying of PET chips is 100 - 150 °C, and the drying time is 3 - 8 h.

[0034] Example 1 (1) First, use N 2 to displace the air in the polymerization kettle, and then fully stir and mix BBA and PDO monomers (molar ratio of 1:1.2), Sb 2 O 3 catalyst (0.04% of the mass of BBA) and triphenyl phosphite (0.02% of the mass of BBA), and then add them to the reaction kettle. The temperature in the reaction kettle is controlled at 295 °C, and the reaction is carried out under a pressure of 110 kPa for 3.5 h; (2) After the esterification is completed, adjust the temperature in the reaction kettle to 260 °C, and the pressure in the reaction kettle is 6 kPa, and carry out the first-stage polycondensation reaction for 2.0 h; then adjust the temperature in the reaction kettle to 275 °C again, and the pressure in the reaction kettle is 50 Pa, and carry out the second-stage polycondensation reaction for 2.5 h. During the reaction process, pure circulating nitrogen is used to carry the generated PDO and water out of the system, and the PDO and water in the circulating nitrogen are removed through an adsorption tower filled with a sodium aluminosilicate hydroxide compound. Finally, a PET polymer with a relative molecular mass of 25650 is obtained, and then PET chips are prepared.

[0035] Example 2 (1) First, use N 2 to displace the air in the polymerization kettle, and then fully stir and mix BBA and PDO monomers (molar ratio of 1:1.1), Sb 2 O 3 catalyst (0.06% of the mass of BBA) and triphenyl phosphite (0.05% of the mass of BBA), and then add them to the reaction kettle. The temperature in the reaction kettle is controlled at 310 °C, and the reaction is carried out under a pressure of 110 kPa for 3.5 h; (2) After the esterification is completed, adjust the temperature in the reaction kettle to 270 °C, and the pressure in the reaction kettle is 6 kPa, and carry out the first-stage polycondensation reaction for 2.0 h; then adjust the temperature in the reaction kettle to 290 °C again, and the pressure in the reaction kettle is 50 Pa, and carry out the second-stage polycondensation reaction for 2.5 h. During the reaction process, pure circulating nitrogen is used to carry the generated PDO and water out of the system, and the PDO and water in the circulating nitrogen are removed through an adsorption tower filled with a sodium aluminosilicate hydroxide compound. Finally, a PET polymer with a relative molecular mass of 23240 is obtained, and then PET chips are prepared.

[0036] Example 3 (1) First, use N 2 to displace the air in the polymerization kettle, and then add BBA and PDO monomers (molar ratio 1:1.4), Sb 2 O 3 catalyst (0.1% of the mass of BBA) and triphenyl phosphite (0.06% of the mass of BBA) into the reaction kettle after fully stirring and mixing them evenly. Control the temperature in the reaction kettle at 290 °C and react under a pressure of 110 kPa for 3.5 h; (2) After the esterification is completed, adjust the temperature in the reaction kettle to 265 °C and the pressure in the reaction kettle to 6 kPa for the first-stage polycondensation reaction, and the polycondensation time is 2.0 h; adjust the temperature in the reaction kettle to 285 °C and the pressure in the reaction kettle to 50 Pa again for the second-stage polycondensation reaction, and the polycondensation time is 2.5 h. During the reaction process, use pure recycled nitrogen to carry the generated PDO and water out of the system, and remove the PDO and water in the recycled nitrogen through an adsorption tower filled with sodium aluminate silicate hydroxide. Finally, obtain a PET polymer with a relative molecular mass of 24073, and then prepare PET chips.

[0037] Example 4 (1) First, use N 2 to displace the air in the polymerization kettle, and then add BBA and PDO monomers (molar ratio 1:1.3), Sb 2 O 3 catalyst (0.08% of the mass of BBA) and triphenyl phosphite (0.08% of the mass of BBA) into the reaction kettle after fully stirring and mixing them evenly. Control the temperature in the reaction kettle at 285 °C and react under a pressure of 110 kPa for 3.5 h; (2) After the esterification is completed, adjust the temperature in the reaction kettle to 260 °C and the pressure in the reaction kettle to 6 kPa for the first-stage polycondensation reaction, and the polycondensation time is 2.0 h; adjust the temperature in the reaction kettle to 270 °C and the pressure in the reaction kettle to 50 Pa again for the second-stage polycondensation reaction, and the polycondensation time is 2.5 h. During the reaction process, use pure recycled nitrogen to carry the generated PDO and water out of the system, and remove the PDO and water in the recycled nitrogen through an adsorption tower filled with sodium aluminate silicate hydroxide. Finally, obtain a PET polymer with a relative molecular mass of 28762, and then prepare PET chips.

[0038] Example 5 (1) Transfer the PET chips prepared in Example 1 to a vacuum drum dryer for drying. The drying temperature is 120 °C and the drying time is 5 h.

[0039] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating section of the feeding stage gradually rises from 50°C to 265°C, and then in the spinning box at 290°C, it is compressed under high pressure in the compression section, exhausted, gradually melted, and extruded into filaments. When spinning, the pore diameter of the spinneret is 0.20 mm, the pressure is 45 MPa, and the spinning speed is 2500 m / min.

[0040] (3) The fibers extruded from the spinneret enter a two-stage side-blowing device at different temperatures for cooling. The distance between the first-stage side-blowing device and the spinneret is 10 cm, the blowing temperature is 10°C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The blowing temperature in the second-stage side-blowing device is 60°C, the relative humidity is 60%, and the wind speed is 0.4 m / s. The post-drawing multiple of the final fibers reaches 4.3 times, and high-strength and high-modulus polyester fibers are finally prepared, with a breaking strength of 8.6 cN / dtex, an elastic modulus of 112 cN / dtex, and a melting point of 266°C.

[0041] Example 6 (1) Transfer the PET chips prepared in Example 2 to a vacuum rotary drum dryer for drying. The drying temperature is 120°C, and the drying time is 5 h.

[0042] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating section of the feeding stage gradually rises from 50°C to 265°C, and then in the spinning box at 290°C, it is compressed under high pressure in the compression section, exhausted, gradually melted, and extruded into filaments. When spinning, the pore diameter of the spinneret is 0.20 mm, the pressure is 45 MPa, and the spinning speed is 2500 m / min.

[0043] (3) The fibers extruded from the spinneret enter a two-stage side-blowing device at different temperatures for cooling. The distance between the first-stage side-blowing device and the spinneret is 10 cm, the blowing temperature is 10°C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The blowing temperature in the second-stage side-blowing device is 60°C, the relative humidity is 60%, and the wind speed is 0.4 m / s. The post-drawing multiple of the final fibers reaches 4.1 times, and high-strength and high-modulus polyester fibers are finally prepared, with a breaking strength of 7.4 cN / dtex, an elastic modulus of 97 cN / dtex, and a melting point of 264°C.

[0044] Example 7 (1) Transfer the PET chips prepared in Example 3 to a vacuum rotary drum dryer for drying. The drying temperature is 120°C, and the drying time is 5 h.

[0045] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating section of the feeding stage gradually rises from 50 °C to 265 °C, and then in the spinning box at 290 °C, it is compressed under high pressure in the compression section, exhausted, gradually melted, and extruded into filaments. When spinning, the aperture of the spinneret is 0.20 mm, the pressure is 45 MPa, and the spinning speed is 2500 m / min.

[0046] (3) The fibers extruded from the spinneret enter a two-stage side air-blowing device at different temperatures for cooling. The distance between the first-stage side air-blowing device and the spinneret is 10 cm, the air-blowing temperature is 10 °C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The air-blowing temperature in the second-stage side air-blowing device is 60 °C, the relative humidity is 60%, and the wind speed is 0.4 m / s. The post-drawing multiple of the final fibers reaches 4.2 times, and high-strength and high-modulus polyester fibers are finally prepared, with a breaking strength of 7.9 cN / dtex, an elastic modulus of 106 cN / dtex, and a melting point of 265 °C.

[0047] Example 8 (1) Transfer the PET chips prepared in Example 4 to a vacuum rotary drum dryer for drying. The drying temperature is 120 °C, and the drying time is 5 h.

[0048] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating section of the feeding stage gradually rises from 50 °C to 265 °C, and then in the spinning box at 290 °C, it is compressed under high pressure in the compression section, exhausted, gradually melted, and extruded into filaments. When spinning, the aperture of the spinneret is 0.20 mm, the pressure is 45 MPa, and the spinning speed is 2500 m / min.

[0049] (3) The fibers extruded from the spinneret enter a two-stage side air-blowing device at different temperatures for cooling. The distance between the first-stage side air-blowing device and the spinneret is 10 cm, the air-blowing temperature is 10 °C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The air-blowing temperature in the second-stage side air-blowing device is 60 °C, the relative humidity is 60%, and the wind speed is 0.4 m / s. The post-drawing multiple of the final fibers reaches 4.6 times, and high-strength and high-modulus polyester fibers are finally prepared, with a breaking strength of 9.2 cN / dtex, an elastic modulus of 129 cN / dtex, and a melting point of 270 °C.

[0050] Comparative Example 1 (The difference from Example 1 is that only PTA is replaced by BBA monomer, and the EG monomer remains unchanged) (1) First, use N 2 to displace the air in the polymerization kettle, and then add PTA and PDO monomers (molar ratio 1:1.2), Sb 2 O 3The catalyst (0.04% of the mass of PTA) and triphenyl phosphite (0.02% of the mass of PTA) were thoroughly stirred and then added to the reaction kettle. The temperature inside the reaction kettle was controlled at 295 °C, and the reaction was carried out at a pressure of 110 kPa for 3.5 h; (2) After the esterification was completed, the temperature inside the reaction kettle was adjusted to 260 °C, and the pressure inside the reaction kettle was 6 kPa. The first-stage polycondensation reaction was carried out for 2.0 h. The temperature inside the reaction kettle was adjusted again to 275 °C, and the pressure inside the reaction kettle was 50 Pa. The second-stage polycondensation reaction was carried out for 2.5 h. During the reaction process, pure circulating nitrogen was used to carry the generated PDO and water out of the system, and the PDO and water in the circulating nitrogen were removed through an adsorption tower filled with sodium aluminate silicate hydroxide. Finally, a PET polymer with a relative molecular mass of 21370 was obtained, and then PET chips were prepared.

[0051] Comparative Example 2 (different from Example 5 in that: the PET chips prepared in Comparative Example 1 were used instead) (1) The PET chips prepared in Comparative Example 1 were transferred to a vacuum rotary drum dryer for drying. The drying temperature was 120 °C, and the drying time was 5 h.

[0052] (2) The dried PET chips were added to the spinning barrel. The temperature in the preheating section of the feeding stage gradually increased from 50 °C to 265 °C, and then in the spinning box at a temperature of 290 °C, it was compressed, exhausted, gradually melted and extruded through a spinneret. The aperture of the spinneret during spinning was 0.20 mm, the pressure was 45 MPa, and the spinning speed was 2500 m / min.

[0053] (3) The fibers extruded from the spinneret entered a two-stage side-blowing device at different temperatures for cooling. The distance between the first-stage side-blowing device and the spinneret was 10 cm, the blowing temperature was 10 °C, the relative humidity was 80%, and the wind speed was 0.3 m / s. The blowing temperature in the second-stage side-blowing device was 60 °C, the relative humidity was 60%, and the wind speed was 0.4 m / s. Finally, the post-drawing multiple of the fibers reached 3.9 times, and high-strength and high-modulus polyester fibers were finally prepared. The breaking strength was 5.6 cN / dtex, the elastic modulus was 92 cN / dtex, and the melting point was 261 °C.

[0054] Comparative Example 3 (different from Example 5 in that: the spinning pressure was too low) (1) The PET chips prepared in Comparative Example 1 were transferred to a vacuum rotary drum dryer for drying. The drying temperature was 120 °C, and the drying time was 5 h.

[0055] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating zone of the feeding stage gradually rises from 50°C to 265°C, and then in the spinning box at 290°C, it is compressed under high pressure in the compression section, exhausted, gradually melted and extruded. When spinning, the aperture of the spinneret is 0.20 mm, the pressure is 35 MPa, and the spinning speed is 2500 m / min.

[0056] (3) The fibers extruded from the spinneret enter the two-stage side blowing device at different temperatures for cooling. The distance between the first-stage side blowing device and the spinneret is 10 cm, the blowing temperature is 10°C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The blowing temperature in the second-stage side blowing device is 60°C, the relative humidity is 60%, and the wind speed is 0.4 m / s. The post-drawing multiple of the final fiber reaches 4.1 times, and finally high-strength and high-modulus polyester fiber is prepared, with a breaking strength of 6.8 cN / dtex, an elastic modulus of 97 cN / dtex, and a melting point of 263°C.

[0057] Comparative Example 4 (the difference from Example 5 is that only the first-stage side blowing is carried out) (1) Transfer the PET chips prepared in Example 1 to a vacuum rotary drum dryer for drying. The drying temperature is 120°C and the drying time is 5 h.

[0058] (2) Add the dried PET chips into the spinning barrel. The temperature in the preheating zone of the feeding stage gradually rises from 50°C to 265°C, and then in the spinning box at 290°C, it is compressed under high pressure in the compression section, exhausted, gradually melted and extruded. When spinning, the aperture of the spinneret is 0.20 mm, the pressure is 45 MPa, and the spinning speed is 2500 m / min.

[0059] (3) The fibers extruded from the spinneret enter the single-stage side blowing device for cooling. The distance between the side blowing device and the spinneret is 10 cm, the blowing temperature is 10°C, the relative humidity is 80%, and the wind speed is 0.3 m / s. The post-drawing multiple of the final fiber reaches 4.2 times, and finally high-strength and high-modulus polyester fiber is prepared, with a breaking strength of 8.3 cN / dtex, an elastic modulus of 105 cN / dtex, and a melting point of 264°C.

[0060] Table 1 Relative molecular weights of the PET polymers prepared in Examples 1-4 and Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Relative molecular mass 25650 23240 24073 28762 21370 Table 2 Mechanical properties and melting points of the PET fibers prepared in Examples 5-8 and Comparative Examples 2-4 As shown in Table 1, in Comparative Example 1, since only PTA was replaced with BBA monomer and the EG monomer remained unchanged, the relative molecular mass of the polymer prepared from BBA monomer and EG monomer was significantly lower than that of Example 1, and it was not conducive to spinning due to the excessive rigidity and insufficient flexibility of the macromolecular chain. In Comparative Example 2, since the PET chips in Comparative Example 1 were used for spinning, the spinning effect was poor, and the breaking strength, elastic modulus and melting point of the prepared PET fibers were all reduced.

[0061] As shown in Table 2, compared with the traditional method of esterifying and polycondensing PTA and EG monomers to prepare PET melt, the relative molecular mass of the PET melt prepared from BBA and PDO monomers is higher. This is because the new monomers have larger molecular weights and lower reaction activities than PTA and EG respectively, so it is easier to obtain PET macromolecules with higher molecular weights. When the PET melt prepared from BBA and PDO monomers is spun, it is easier to obtain polyester fibers with high strength, high modulus and high melting point. This is mainly because the PET melt with high molecular weight has higher viscosity, and the stretching ratio that the fiber can withstand is higher. Moreover, the rigid structure accounts for a relatively high proportion in the PET macromolecules prepared by this method, which is conducive to the crystallization of macromolecules inside the fiber and has higher heat resistance.

[0062] In addition, since the PET melt prepared by the present invention from BBA and PDO monomers has a higher relative molecular mass and greater viscosity, pressure needs to be applied during melt spinning. Only by controlling the pressure and temperature within a suitable range during spinning can the subsequent spinning effect of the PET melt be better. In Comparative Example 3, since the pressure during pressure melt spinning was set too low, the breaking strength and elastic modulus of the obtained PET fibers were both lower than those of Example 5. Moreover, after the fibers are obtained by pressure melt spinning, a two-stage side air blowing device needs to be used for air blowing and cooling, which is more suitable for the internal structure of the PET polymer in the present invention. After entering the regions with different temperature gradients, the macromolecular chains will be relaxed due to the action of temperature, which can not only keep the macromolecules in a straight chain structure, conducive to stretching at a higher post-drawing ratio, but also increase the crystallinity and orientation degree of the fiber, which is beneficial to improving the mechanical properties of the PET fiber and enhancing the breaking strength, elastic modulus and melting point of the final PET fiber. Therefore, in Comparative Example 4, since only the first-stage side air blowing was used, the breaking strength, elastic modulus and melting point of the prepared PET fibers were all reduced compared with those of Example 5.

[0063] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-strength and high-modulus polyester fiber, characterized in that: The steps include: (1) mixing 4,4'-biphenyldicarboxylic acid, 1,3-propylene glycol, a catalyst and a heat stabilizer to carry out an esterification reaction; (2) After the esterification is completed, the first stage polycondensation reaction is carried out first, and then the second stage polycondensation reaction is carried out. The reaction removes small molecules and water at the same time to obtain a polymer; (3) The polymer is melt-spun, and then sequentially subjected to first-stage side blowing, second-stage side blowing and post-stretching to obtain polyester fiber.

2. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, characterized in that: The molar ratio of the 4,4'-biphenyldicarboxylic acid to 1,3-propylene glycol is 1:1.1-1.

4.

3. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, characterized in that: The amount of the catalyst used is 0.04-0.1% of the mass of 4,4'-biphenyldicarboxylic acid; the amount of the heat stabilizer used is 0.02-0.1% of the mass of 4,4'-biphenyldicarboxylic acid.

4. The method for preparing high-strength and high-modulus polyester fiber according to any one of claims 1 to 3, characterized in that: The temperature of the esterification reaction is 280-310° C., the pressure is 100-120 kPa, and the reaction time is 2-4 h.

5. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, characterized in that: The temperature of the first stage polycondensation reaction is 260-270°C, the pressure is 5-7 kPa, and the polycondensation time is 2-3 h.

6. The method for preparing high-strength and high-modulus polyester fiber according to claim 1 or 5, characterized in that: The temperature of the second stage polycondensation reaction is 270-290°C, the pressure is 50-90 Pa, and the polycondensation time is 2-3 h.

7. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, characterized in that: The temperature of the melt spinning is 265-290° C., and the pressure is 40-60 MPa; the spinning speed of the melt spinning is 2500-2800 m / min.

8. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, characterized in that: The first-stage side blowing has a blowing temperature of 8-15°C, a relative humidity of 70-90%, and a wind speed of 0.2-0.4 m / s.

9. The method for preparing high-strength and high-modulus polyester fiber according to claim 1, 7 or 8, characterized in that: The second-stage side blowing has a blowing temperature of 50-70°C, a relative humidity of 50-60%, and a wind speed of 0.3-0.6 m / s.

10. A high-strength and high-modulus polyester fiber prepared by the preparation method according to any one of claims 1 to 9.

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