1. A preparation method of PVA high solid content spinning solution is characterized by comprising the following steps: firstly adding PVA into a dissolving kettle containing DMF and water, raising the temperature in stages until the PVA swells, and then introducing CO into the dissolving kettle₂The gas forms a certain pressure until PVA is completely dissolved, and finally CO is discharged at a certain speed₂Gas is generated to obtain PVA high solid content spinning solution;

the PVA high-solid-content spinning solution has the solid content of 35-40 wt%.

2. The preparation method of the PVA high-solid-content spinning solution according to claim 1, wherein the mass ratio of DMF to water is 7-8: 2-3.

3. The method of claim 2, wherein the dissolution vessel further contains HfCl₄，HfCl₄The amount of the PVA, DMF and water accounts for 0.6-1.2 wt% of the total amount of the PVA, the DMF and the water.

4. The preparation method of the PVA high-solid-content spinning solution according to claim 1, wherein the degree of polymerization of PVA is 3600-3800, and the degree of alcoholysis is 98-99%.

5. The method for preparing the PVA high solid content spinning solution according to claim 1, wherein the step-by-step temperature rise refers to: the temperature is raised from room temperature to 35-40 ℃ and kept for 10-20 min, and then raised to 45-50 ℃ and kept for 20-30 min.

6. The method for preparing PVA high solid content spinning solution according to claim 1, wherein CO is introduced into the dissolving tank₂The pressure formed after the gas is 1.2-1.6 MPa.

7. The method of claim 1, wherein the PVA high solid content spinning solution is completely dissolved and CO is discharged₂Before the gas is generated, the dissolving kettle is stably placed for 50-80 min at the temperature of 50-60 ℃;

after PVA is completely dissolved, the viscosity of the spinning solution is 1800-200 Pa.s when the PVA is stably placed, and CO is completely discharged₂The viscosity of the gas-post spinning solution is 2000-2200 Pa · s.

8. The method of claim 7, wherein the CO is CO₂The gas discharge speed is 15-20L/min.

9. The application of the high-solid-content spinning solution prepared by the method of any one of claims 1 to 8, wherein the high-solid-content PVA spinning solution is subjected to dry-wet spinning to prepare high-strength coarse-denier PVA fibers;

the dry-wet spinning process comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters of the dry-wet spinning are as follows: the aperture of each spinneret orifice is 0.45-0.55 mm, and the extrusion rate of each spinneret orifice is 4.5-4.8 mL/min; the height of the air layer is 10-12 cm, the temperature of the coagulating bath is-5 to-3 ℃, and the curing time of the coagulating bath is 1.5-2.0 min; the multiple of primary stretching is 2.5-3.0 times; the temperature of the first extraction is 65-70 ℃, the time is 6-8 h, the temperature of the second extraction is 70-75 ℃, the time is 8-10 h, the temperature of the third extraction is 75-80 ℃, and the time is 10-12 h; the temperature of the first hot stretching is 195-200 ℃, the stretching ratio is 2.0-2.5 times, the temperature of the second hot stretching is 210-215 ℃, and the stretching ratio is 3.0-3.5 times.

10. The use according to claim 9, wherein the high-strength coarse-denier PVA fibers have a fineness of 29 to 38dtex, a breaking strength of 13.0 to 14.2cN/dtex, and an elastic modulus of 330 to 341 cN/dtex.

Background

The concrete has the advantages of high compressive strength, excellent durability, low cost, wide raw material source and the like, so the concrete is widely applied to the fields of highways, bridges, tunnels, airports, dams, wharfs, military industry and national defense and the like. However, the conventional concrete has the disadvantages of low breaking strength, poor crack resistance, high brittleness and the like, and the high-strength and high-modulus PVA fiber is often used for reinforcing the concrete due to the advantages of high breaking strength, strong adhesive force with cement-based concrete, good environmental resistance and the like. However, because the fineness of the conventional common high-strength high-modulus PVA fiber is small, the conventional high-strength high-modulus PVA fiber is easy to cohere in concrete, so that the maximum fiber mixing amount of each ton of concrete is only about 1.6 kg. The high-strength coarse-denier PVA fibers have larger titer and smaller specific surface area, can effectively reduce the entanglement among the fibers, and the maximum fiber mixing amount in each ton of concrete can reach about 25kg, so that a three-dimensional disorderly lapping and connecting system with uniform and dense distribution can be formed in the concrete, and the defects of poor crack resistance, large brittleness and the like of the concrete are effectively improved.

In patent CN2018112566827, a wet spinning method is adopted to prepare a high-strength high-modulus PVA fiber, but the concentration of a spinning solution in the wet spinning process is low, so that the titer of the prepared PVA fiber is small, which is about 2 dtex. In patent CN2012100796337, water is used as a plasticizer, and a melt spinning method is used to prepare a coarse denier PVA fiber, but because the strength and modulus are not high (the breaking strength is 1000-1700 MPa, and the elastic modulus is 25-32 GPa), and because the process parameters are complex, a high-strength coarse denier polyvinyl alcohol fiber cannot be prepared. The patent CN2009100573106 adopts a solid-phase alcoholysis method to prepare the coarse-denier PVA fiber, but the breaking strength is 600-1000 MPa, the elastic modulus is 25-40 GPa, the anti-cracking and reinforcing effects of concrete for civil engineering cannot be met, so that the high-strength coarse-denier PVA fiber is difficult to prepare, and the further application of the coarse-denier PVA fiber in the field of geotechnical construction is restricted to a great extent.

At present, fibers with large titer can be prepared by a melt spinning method, but the prepared fibers have low mechanical properties (breaking strength is less than 12.5cN/detx) on one hand, and the preparation process is complex and difficult to industrialize on the other hand. In general, the spinning solution concentration of wet spinning or dry and wet spinning is low, and the preparation of the coarse denier PVA fiber is difficult. If the solid content of the PVA spinning solution is too low, the concentration difference of double diffusion between the spinning solution trickle and the coagulating bath is large, holes can be generated in the prepared PVA fiber, and the high-strength coarse-denier PVA fiber is difficult to obtain. With the increase of the solid content of the spinning solution, the concentration difference action of double diffusion between the spinning solution trickle and the coagulating bath is weakened, the diffusion amount of the solvent is obviously reduced, the generation of holes in the fiber is effectively inhibited, the density of the obtained nascent fiber is increased, the structural uniformity is improved, and the preparation of the high-strength coarse-denier PVA fiber is facilitated. Therefore, the key factor for preparing the high-strength coarse denier PVA fiber needs to have a spinning solution with high concentration.

However, the prior art methods cannot produce a high concentration of the spinning dope.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a preparation method and application of a PVA high-solid-content spinning solution.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

PVA high solid contentA process for preparing spinning solution includes such steps as adding PVA to a dissolving kettle containing DMF and water, heating to swell PVA by stages (the PVA polymer is divided into crystal region and non-crystal region, the solvent is first in the non-crystal region, the solvent is then at a lower temp, the solvent gradually destroys crystal lattice and penetrates into crystal region, the temp is raised, and CO is then introduced into the dissolving kettle₂The gas forms a certain pressure until PVA is completely dissolved, and finally CO is discharged at a certain speed₂Gas (the dissolving kettle is provided with an air inlet valve and an air outlet valve, and CO can be discharged by opening the air outlet valve₂Gas) to obtain PVA high solid content spinning solution;

the solid content of the PVA high-solid-content spinning solution (namely the content of PVA in the spinning solution) is 35-40 wt%.

As a preferred technical scheme:

according to the preparation method of the PVA high-solid-content spinning solution, the mass ratio of DMF to water is 7-8: 2-3. According to the solubility parameter, the sum of the solubility parameters after the DMF and the water are mixed is close to the solubility parameter of the PVA, and the proportion setting of the invention is obtained by theoretical calculation.

In the preparation method of the PVA high-solid-content spinning solution, the dissolving kettle also contains HfCl₄，HfCl₄The amount of the solvent is 0.6-1.2 wt% of the total amount of PVA, DMF and water (the dissolving kettle contains HfCl)₄And carrying out ultrasonic treatment after adding PVA, wherein the ultrasonic treatment time is 30-60 min, and the ultrasonic treatment frequency is 33-45 kHz).

According to the preparation method of the PVA high-solid-content spinning solution, the polymerization degree of PVA is 3600-3800, and the alcoholysis degree is 98-99%.

In the preparation method of the PVA high solid content spinning solution, the staged temperature rise refers to that: the temperature is raised from room temperature (25 ℃) to 35-40 ℃ and kept for 10-20 min, and then raised to 45-50 ℃ and kept for 20-30 min.

In the preparation method of the PVA high-solid-content spinning solution, CO is introduced into a dissolving kettle₂The pressure formed after the gas is 1.2-1.6 MPa, and the collision and mutual interaction of the gas and the solvent can be influenced when the pressure is too lowThe generation of force is not beneficial to the dissolution of PVA, and in the range that the PVA can be dissolved, the time for forming and exhausting gas is prolonged when the pressure exceeds the required pressure, so that the production efficiency is reduced.

In the preparation method of the PVA high-solid-content spinning solution, after the PVA is completely dissolved, CO is discharged₂Before the gas, the dissolving kettle is placed stably for 50-80 min at the temperature of 50-60 ℃ (the gas escapes from the solvent when the temperature is too high, but the quality of the spinning solution is influenced when the temperature is too low, so that the temperature is controlled at 50-60 ℃);

after PVA is completely dissolved, the viscosity of the spinning solution is 1800-2000 Pa.s when the PVA is stably placed, and CO is completely discharged₂The viscosity of the gas-post spinning solution is 2000-2200 Pa · s.

The preparation method of the PVA high-solid-content spinning solution, CO₂The gas discharge speed is 15-20L/min, and the volume of the dissolving kettle is 100-150L.

The invention also provides application of the PVA high-solid-content spinning solution prepared by the method, and the PVA high-solid-content spinning solution is subjected to dry-wet spinning to prepare high-strength coarse-denier PVA fibers;

the dry-wet spinning process comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters of the dry-wet spinning are as follows: the aperture of each spinneret orifice is 0.45-0.55 mm, and the extrusion rate of each spinneret orifice is 4.5-4.8 mL/min; the height of the air layer is 10-12 cm, the temperature of the coagulating bath is-5 to-3 ℃, and the curing time of the coagulating bath is 1.5-2.0 min; the multiple of primary stretching is 2.5-3.0 times; the temperature of the first extraction is 65-70 ℃, the time is 6-8 h, the temperature of the second extraction is 70-75 ℃, the time is 8-10 h, the temperature of the third extraction is 75-80 ℃, and the time is 10-12 h; the temperature of the first hot stretching is 195-200 ℃, the stretching ratio is 2.0-2.5 times, the temperature of the second hot stretching is 210-215 ℃, and the stretching ratio is 3.0-3.5 times. Compared with polyvinyl alcohol with common titer, the coarse denier polyvinyl alcohol fiber has larger titer, so that the macromolecules on the inner layer and the outer layer of the fiber can form uniform folding chain crystals under the action of temperature and stress, the hot stretching temperature is slightly higher than that of the prior art, but the fiber is easy to melt due to overhigh temperature, thereby being not beneficial to the improvement of the subsequent stretching multiple; in a certain range, the higher the hot stretching temperature is, the higher the hot stretching multiple of the fiber is, the higher the total stretching multiple is, the larger the hot stretching temperature of the coarse denier fiber can be properly raised for the second time, but when the temperature is too high, the fiber can be fused, the continuous stretching cannot be performed, and the mechanical property of the fiber is further influenced; when the stretching multiple of one-time stretching is low, the pre-orientation degree of the fiber is insufficient, the crystal form is easy to become monoclinic crystal which is difficult to stretch, so that the hot stretching needs to be divided into two times of stretching during hot stretching, the total stretching multiple can be improved as much as possible, the second-time hot stretching multiple is the maximum stretching multiple which the fiber can bear at this time, and the total stretching multiple of the fiber is the product of three times of stretching multiples, most of the PVA fibers in the prior art are the first-time stretching multiple of 1.5-2 times, the first-time hot stretching multiple of 2.4-3.5 times and the second-time hot stretching multiple of 3.0-3.5, and the PVA fiber is prepared into coarse denier fiber, so that the stretching multiple is slightly lower than that in the prior art, and the mechanical property of the obtained fiber is basically the same as that in the prior art on the premise of ensuring that the fineness is greater than that in the prior art.

As a preferred technical scheme:

in the application, the fineness of the high-strength coarse-denier PVA fiber is 29-38 dtex (the fineness of the high-strength coarse-denier PVA fiber refers to the single-filament fineness), the breaking strength is 13.0-14.2 cN/dtex, the elastic modulus is 330-341 cN/dtex, and the breaking strength and the elastic modulus are measured according to GB/T14344-2008 chemical fiber filament tensile property test method.

The principle of the invention is as follows:

the fine denier fiber has larger specific surface area and is easy to adsorb and agglomerate in concrete. On the contrary, the large denier fiber is not easy to generate the phenomenon of agglomeration in concrete, however, the large denier fiber is generally difficult to prepare, and although the fiber with larger denier can be prepared by the melt spinning method at present, the prepared fiber has lower mechanical properties on one hand, and the preparation process is complex and difficult to industrialize on the other hand. In general, the spinning solution concentration of wet spinning or dry and wet spinning is low, and the preparation of the coarse denier PVA fiber is difficult. If the solid content of the PVA spinning solution is too low, the concentration difference of double diffusion between the spinning solution trickle and the coagulating bath is large, holes can be generated in the prepared PVA fiber, and the high-strength coarse-denier PVA fiber is difficult to obtain. With the increase of the solid content of the spinning solution, the concentration difference action of double diffusion between the spinning solution trickle and the coagulating bath is weakened, the diffusion amount of the solvent is obviously reduced, the generation of holes in the fiber is effectively inhibited, the density of the obtained nascent fiber is increased, the structural uniformity is improved, and the preparation of the high-strength coarse-denier PVA fiber is facilitated. Therefore, the key factor for preparing the high-strength coarse denier PVA fiber needs to have a spinning solution with high concentration.

The lower the viscosity of the isoviscous dope or the higher the concentration of the isoviscous dope, the better the solubility of the solvent, and it is a good solvent. Typically, a mixed solvent has a higher solvent capacity for the polymer than a single solvent. From the viewpoint of solubility parameters, it is more suitable to use as a mixed solvent than the commonly used solvents DMSO, DMF and water.

However, to obtain a high solids content PVA spinning solution, in addition to selecting a suitable solvent, the swelling to dissolution process of the PVA polymer is critical. The swelling process has important influence on the solvent of PVA, and for polar polymers, because the molecular weight of macromolecules is large, molecular chains are tangled, or the interaction between the molecular chains is large, a single long molecular chain is difficult to separate from the surface of a solid, the non-crosslinked polymer system dissolving process is that the micromolecular solvent firstly permeates between the molecular chains, the chain segment distance is enlarged, the system swells, the volume is larger along with the swelling, the molecular chains are finally separated by the solvent, and the system dissolves.

The adequacy of dissolution depends critically on whether or not it is sufficient to swell, which depends on the rate of solvent diffusion into the PVA. It is important to increase the relative content of the solvent, and when the content of the solvent is less than 78 wt%, the intermolecular entanglement density is high, the molecular chain is difficult to stretch, and at this time, the PVA polymer can only stay in the swelling process and can not be dissolved. With the decrease of the solvent content, the free volume of the macromolecules becomes smaller, and the resistance of the macromolecules to free movement through the interaction of hydrogen bonds and the macromolecule chains is increased. That is, when the concentration of the spinning solution is increased to 22 wt% or more, the viscosity of the spinning solution is greatly influenced even if the concentration of the spinning solution is increased to a small extent, so that the viscosity of the spinning solution is sharply increased with the increase of the concentration, which increases the difficulty of plasticizing PVA in a solvent, thereby affecting the sufficient dissolution of PVA.

Aiming at the problems that PVA has low solubility and spinning solution with high concentration is not easy to prepare in the prior art, the invention introduces CO₂The gas is formed into a certain pressure in the dissolving kettle to solve the problem, and the specific mechanism is as follows:

introducing CO₂Introducing into spinning solution, and increasing CO with the increase of pressure₂The internal energy of the polymer and DMF is greatly increased, DMF molecules and PVA polymer macromolecules can mutually permeate, the rotation of a macromolecular chain becomes easier, the flexibility is increased, and the movement of a molecular chain is more violent, so that the permeation speed of DMF to the PVA polymer is accelerated, and the full swelling is promoted;

CO₂dissolved in a solvent, which acts as a shear for the "screw", increasing the intermolecular spacing, CO₂The effective volume (i.e., the size of the actual volume) of the solvent can be promoted to increase from two aspects:

(1) CO compared to a gas that does not generate intermolecular forces with the solvent₂Van der Waals' force can be generated between molecules and DMF, the volume of DMF in the dissolving kettle can be increased, the dissolution of PVA is promoted, and CO₂And DMF, the structures due to the interaction are shown below.

(2) CO compared to a gas that does not generate intermolecular forces with the solvent₂And H₂Van der Waals' force is also generated between O, so that CO is introduced₂The effective volume of the post solution is increased, the intermolecular gap of the PVA polymer is also increased, and the solubility is further increased, so that the solid content of the spinning solution is continuously increased and the CO is further increased in a spinnable range₂And H₂The structure of O due to the interaction is shown below.

In addition, CO₂The actual dissolution in the solvent is also subject to the magnitude of pressure and CO₂Influence of the interaction between the molecule and the solution ions. CO with increasing pressure₂The collision of gas and solvent is intensified, and CO is actually₂And solvent molecules, but the collision frequency is increased, further promoting the swelling rate, with slowly increasing pressure, CO₂Further "running" into the interstices of the solvent creates some van der waals forces. CO 2₂And solvent molecules overcome the CO by van der Waals forces₂Kinetic energy of molecules, more CO per unit time₂The gas molecules are held by the liquid phase, which in turn increases the free volume of the solution, resulting in an increase in solubility and thus in an increase in the solids content of the spinning dope.

And (3) after the polyvinyl alcohol spinning solution is completely dissolved, slowly reducing the pressure from 1.2-1.6 MPa until no pressure exists, wherein although the viscosity of the spinning solution is slowly increased after the pressure is removed, the entanglement points of the disentangled PVA polymer macromolecular chains are not reconstructed in time after the entanglement points are disassembled, so that the PVA spinning solution still keeps the stability.

The preparation process of the high-strength coarse denier PVA fiber is a complex process, the larger the fiber number is, the larger the surface area is, the larger the probability of cracks and defects is, the crack area rapidly expands until the fiber breaks when external pressure is applied, and the high-strength coarse denier fiber has the following characteristics: (1) large titer, titer is more than 18 dtex; (2) high strength, breaking strength is more than or equal to 1600MPa (12.6 cN/dtex); (3) high modulus, elastic modulus is more than or equal to 40Gpa (315 cN/dtex).

The presence of hydrogen bonds between the PVA molecules increases the intermolecular interactions, and although it may reduce the entanglement itself, it makes the stretching of the PVA fiber difficult, particularly as: when the PVA fiber is stretched, the molecular chain can not be fully stretched, and the high molecular chain can not slide to improve the stretching multiple to obtain the high-strength PVA fiber. Therefore, the function of intermolecular hydrogen bonds needs to be weakened before stretching to achieve a high stretching ratio, thereby significantly improving the strength of the PVA fibers.

The invention adds the cross-linking agent into the coagulating bath to rapidly cross-link fiber molecules to form a net structure, thereby weakening the permeation of the coagulating agent to fibers, so that the fibers prepared by adopting the cross-linking agent and a dry-wet spinning process are not strongly dehydrated during coagulation forming, the cross-sectional area shape of the fibers is basically oval or even round, the skin-core structure is not obvious, the stretching multiple is favorably improved, and the mechanical property of the fibers is further improved. HfCl as with the usual boric acid crosslinking agent₄The PVA intermolecular hydrogen bond can be weakened, so that only a small amount of hydrogen bonds exist among PVA molecules, and at the moment, the entanglement of the PVA can be reduced, and the PVA fiber can be stretched. HfCl compared to conventional boric acid crosslinkers₄The particle size of the spinning solution is smaller, the spinning solution can be better dissolved in a solvent, and the spinning solution prepared by mixing the spinning solution with PVA is more uniform, so that the preparation of the primary yarn with uniform structure is facilitated. In addition, because the interaction force between boric acid and PVA is stronger, can not extract out completely in the extraction process of later stage, stay in the just raw silk and be unfavorable for the improvement of total stretch multiple, Hf and B are the elements of the same family, Hf is compared with the atomic number of B big, electron orbit radius is big, it is low to obtain electron ability, so lower with PVA intermolecular interaction force, it extracts out completely with it in the extraction process of later stage more easily, be favorable to later stage tensile, obtain high-strength PVA fibre.

HfCl₄The specific surface area of the fiber is large, the activity is high, after a part of solvent in spinning solution is removed in a coagulating bath, a network structure is formed with PVA molecules, the permeation of a coagulating agent to the fiber is weakened, and the nascent fiber with the cross section area close to a circle is obtained. Thus, the crosslinker HfCl₄The addition of the PVA fiber can ensure that the fiber has higher titer, simultaneously can weaken the hydrogen bond effect in PVA molecules and among molecules through the crosslinking effect, and improve the stretching multiple of the fiber, thereby obtaining the high-strength high-modulus PVA fiber with high orientation and high crystallization, and providing solid theoretical support for preparing the high-strength high-modulus PVA fiber.

Has the advantages that:

(1) the PVA high content of the inventionThe solid spinning solution is prepared by introducing CO into DMF and water as solvent through a dissolving kettle₂Gas, and forming a certain pressure in the dissolving kettle, CO₂Can be introduced into the reaction system with DMF or H₂O generates intermolecular acting force, so that the space distance between molecules and the effective volume of a solvent are increased, the solubility of PVA is further increased, and the PVA spinning solution with high solid content is prepared, wherein the solid content is 35-40 wt%; the viscosity is 1800 to 2000 pas.

(2) According to the PVA high-solid-content spinning solution and the preparation method thereof, the pressure in the de-spinning kettle is slowly reduced until no pressure exists, although the viscosity of the spinning solution is slowly increased after the pressure is removed, the entanglement points of the macromolecular chains of the PVA polymer which are subjected to de-entanglement at the moment are not reconstructed in time after the entanglement points are dispersed, so that the PVA spinning solution still keeps the stability, and the viscosity is recovered and stabilized to be 2000-2200 Pa & s.

(3) HfCl crosslinking agent used in the invention₄The particle size of the PVA fiber is small, and the PVA fiber is easy to be completely extracted in the extraction process, so that the later-stage stretching is facilitated, and the high-strength PVA fiber is obtained.

(4) The PVA high-solid-content spinning solution can be used for preparing high-strength coarse denier PVA fibers, and further can be applied to the fields of dam slope protection, bridge and tunnel construction, land reclamation from sea, airport runways and the like.

Detailed Description

The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

A preparation method of PVA high solid content spinning solution comprises the following steps:

(1) adding PVA into a dissolving kettle (the volume of the dissolving kettle is 100L) containing DMF and water, heating to 35 ℃ from room temperature and keeping for 20min, then heating to 45 ℃ and keeping for 30min until the PVA swells; wherein the polymerization degree of PVA is 3600, and the alcoholysis degree is 98%; the mass ratio of DMF to water is 7: 2;

(2) introducing CO into the dissolving kettle₂Forming the gas under the pressure of 1.2MPa until PVA is completely dissolved to obtain a solution with the viscosity of 1800 Pa.s, and then stably placing the dissolving kettle at the temperature of 50 ℃ for 80 min;

(3) CO is discharged at a rate of 15L/min₂Gas, to CO₂After the gas was completely discharged, a PVA high-solid-content spinning solution having a solid content of 35 wt% and a viscosity of 2000 pas was obtained.

Comparative example 1

A PVA spinning solution was prepared in the same manner as in example 1 except that argon was introduced into the dissolution vessel in the step (2) instead of CO₂The viscosity of the PVA dope obtained by completely dissolving PVA was 1850 pas, the viscosity of the PVA dope obtained by completely discharging argon gas was 2132 pas, and the solid content was 32 wt%.

As can be seen by comparing example 1 with comparative example 1, the spinning dope prepared in example 1 has a higher solid content and a slightly lower viscosity than comparative example 1 because the argon gas in comparative example 1 does not generate intermolecular force with the solvents DMF and water, and the CO in example 1 is compared with the argon gas which does not generate intermolecular force with the solvent₂And DMF and H₂The Van der Waals force is generated between O and CO is introduced₂The effective volume of the later solution is increased, the intermolecular gap of the PVA polymer is also increased, and the solubility is further increased, so that the solid content of the spinning solution is continuously increased within the spinnable range.

Example 2

A preparation method of PVA high solid content spinning solution comprises the following steps:

(1) adding PVA into a dissolving kettle (the volume of the dissolving kettle is 150L) containing DMF and water, heating to 36 ℃ from room temperature and keeping for 16min, then heating to 48 ℃ and keeping for 27min until the PVA swells; wherein the polymerization degree of PVA is 3600, and the alcoholysis degree is 98%; the mass ratio of DMF to water is 7: 3;

(2) introducing CO into the dissolving kettle₂The gas is brought to a pressure of 1.2MPa to PVACompletely dissolving to obtain a solution with the viscosity of 1820 Pa.s, and then stably placing the dissolving kettle at the temperature of 50 ℃ for 80 min;

(3) CO is discharged at a rate of 20L/min₂Gas, to CO₂After the gas was completely discharged, a PVA high-solid-content spinning solution having a solid content of 36 wt% and a viscosity of 2020 pas was obtained.

Example 3

A preparation method of PVA high solid content spinning solution comprises the following steps:

(1) to a solution containing DMF, water and HfCl₄Adding PVA into a dissolving kettle (the volume of the dissolving kettle is 100L), carrying out ultrasonic treatment (the ultrasonic treatment frequency is 33kHz) for 30min, heating to 36 ℃ from room temperature and keeping for 16min, then heating to 48 ℃ and keeping for 27min until the PVA swells; wherein, the polymerization degree of PVA is 3650, and the alcoholysis degree is 99%; mass ratio of DMF to water is 7:3, HfCl₄The amount of (B) was 0.6 wt% of the total amount of PVA, DMF and water;

(2) introducing CO into the dissolving kettle₂Forming the pressure of 1.4MPa by the gas until PVA is completely dissolved to obtain a solution with the viscosity of 1900 pas, and then stably placing the dissolving kettle at the temperature of 55 ℃ for 70 min;

(3) CO is discharged at a rate of 15L/min₂Gas, to CO₂After the gas was completely discharged, a PVA high-solid-content spinning solution having a solid content of 38 wt% and a viscosity of 2100 pas was obtained.

Example 4

A preparation method of PVA high solid content spinning solution comprises the following steps:

(1) to a solution containing DMF, water and HfCl₄Adding PVA into a dissolving kettle (the volume of the dissolving kettle is 150L), carrying out ultrasonic treatment (the ultrasonic treatment frequency is 40kHz) for 45min, heating to 36 ℃ from room temperature and keeping for 16min, then heating to 48 ℃ and keeping for 27min until the PVA swells; wherein, the polymerization degree of PVA is 3700, and the alcoholysis degree is 98%; mass ratio of DMF to water is 7:3, HfCl₄The amount of (B) was 0.8 wt% of the total amount of PVA, DMF and water;

(2) introducing CO into the dissolving kettle₂The gas was brought to a pressure of 1.5MPa until PVA was completely dissolved to give a solution having a viscosity of 1950 pas, after which the dissolution vessel was brought to 55 deg.CIs stably placed for 70min under the temperature condition;

(3) CO is discharged at a rate of 20L/min₂Gas, to CO₂After the gas was completely discharged, a PVA high-solid-content spinning solution having a solid content of 39 wt% and a viscosity of 2150 pas was obtained.

Example 5

A preparation method of PVA high solid content spinning solution comprises the following steps:

(1) to a solution containing DMF, water and HfCl₄Adding PVA into a dissolving kettle (the volume of the dissolving kettle is 120L), carrying out ultrasonic treatment (the ultrasonic treatment frequency is 5kHz) for 60min, heating to 40 ℃ from room temperature and keeping for 10min, then heating to 50 ℃ and keeping for 20min until the PVA swells; wherein, the polymerization degree of PVA is 3800, and the alcoholysis degree is 99%; mass ratio of DMF to water is 8:3, HfCl₄The amount of (b) was 1.2 wt% of the total amount of PVA, DMF and water;

(2) introducing CO into the dissolving kettle₂Forming the gas under the pressure of 1.6MPa until PVA is completely dissolved to obtain a solution with the viscosity of 2000Pa & s, and then stably placing the dissolving kettle at the temperature of 60 ℃ for 50 min;

(3) CO is discharged at a rate of 18L/min₂Gas, to CO₂After the gas was completely discharged, a PVA high-solid-content spinning solution having a solid content of 40 wt% and a viscosity of 2200 pas was obtained.

Example 6

The method for preparing the high-strength coarse denier PVA fiber by adopting the PVA high solid content spinning solution prepared in the embodiment 1 to carry out dry-wet spinning comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters are as follows: the aperture of each spinneret orifice is 0.45mm, and the extrusion rate of each spinneret orifice is 4.5 mL/min; the height of the air layer is 10cm, the temperature of the coagulating bath is-5 ℃, and the curing time of the coagulating bath is 1.5 min; the multiple of primary stretching is 2.5 times; the temperature of the first extraction is 65 ℃, the time is 8 hours, the temperature of the second extraction is 70 ℃, the time is 10 hours, the temperature of the third extraction is 75 ℃, and the time is 12 hours; the temperature of the first hot stretching is 195 ℃, the stretching ratio is 2 times, the temperature of the second hot stretching is 210 ℃, and the stretching ratio is 3 times.

The fineness of the finally prepared high-strength coarse-denier PVA fiber is 38dtex, the breaking strength is 13cN/dtex, and the elastic modulus is 330 cN/dtex.

Comparative example 2

A PVA fiber preparation method is basically the same as example 6, except that dry-wet spinning is carried out by using the PVA spinning solution prepared in comparative example 1, and the finally prepared PVA fiber has the fineness of 32dtex, the breaking strength of 12.6cN/dtex and the elastic modulus of 326 cN/dtex.

Comparing example 6 with comparative example 2, it can be seen that the mechanical properties of the fiber prepared in example 6 are slightly higher than those of comparative example 2, and the fineness is significantly larger than that of comparative example 2, because the solid content of the spinning solution of example 6 is larger than that of the spinning solution of comparative example 2, the high solid content spinning solution effectively inhibits the generation of holes in the fiber, and the linear density, fineness, structural uniformity and mechanical properties of the obtained fiber are increased.

Example 7

The method for preparing the high-strength coarse denier PVA fiber by adopting the PVA high solid content spinning solution prepared in the embodiment 2 to carry out dry-wet spinning comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters are as follows: the aperture of each spinneret orifice is 0.45mm, and the extrusion rate of each spinneret orifice is 4.5 mL/min; the height of the air layer is 10cm, the temperature of the coagulating bath is-5 ℃, and the curing time of the coagulating bath is 1.5 min; the multiple of primary stretching is 2.5 times; the temperature of the first extraction is 65 ℃, the time is 8 hours, the temperature of the second extraction is 70 ℃, the time is 10 hours, the temperature of the third extraction is 75 ℃, and the time is 12 hours; the temperature of the first hot stretching is 195 ℃, the stretching ratio is 2.2 times, the temperature of the second hot stretching is 210 ℃, and the stretching ratio is 3.1 times.

The fineness of the finally prepared high-strength coarse-denier PVA fiber is 36dtex, the breaking strength is 13.3cN/dtex, and the elastic modulus is 334 cN/dtex.

Example 8

The method for preparing the high-strength coarse denier PVA fiber by adopting the PVA high solid content spinning solution prepared in the embodiment 3 to carry out dry-wet spinning comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters are as follows: the aperture of each spinneret orifice is 0.48mm, and the extrusion rate of each spinneret orifice is 4.6 mL/min; the height of the air layer is 11cm, the temperature of the coagulating bath is-5 ℃, and the curing time of the coagulating bath is 1.8 min; the multiple of primary stretching is 2.6 times; the temperature of the first extraction is 68 ℃, the time is 7h, the temperature of the second extraction is 72 ℃, the time is 9h, the temperature of the third extraction is 78 ℃, and the time is 11 h; the temperature of the first hot stretching is 196 ℃, the stretching ratio is 2.4 times, the temperature of the second hot stretching is 212 ℃, and the stretching ratio is 3.2 times.

The fineness of the finally prepared high-strength coarse-denier PVA fiber is 35dtex, the breaking strength is 13.8cN/dtex, and the elastic modulus is 335 cN/dtex.

Example 9

The method for preparing the high-strength coarse denier PVA fiber by adopting the PVA high solid content spinning solution prepared in the embodiment 4 to carry out dry-wet spinning comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters are as follows: the aperture of each spinneret orifice is 0.5mm, and the extrusion rate of each spinneret orifice is 4.8 mL/min; the height of the air layer is 12cm, the temperature of the coagulating bath is-4 ℃, and the solidifying time of the coagulating bath is 2 min; the multiple of primary stretching is 2.8 times; the temperature of the first extraction is 68 ℃, the time is 7h, the temperature of the second extraction is 72 ℃, the time is 9h, the temperature of the third extraction is 78 ℃, and the time is 11 h; the temperature of the first hot stretching is 198 ℃, the stretching ratio is 2.5 times, the temperature of the second hot stretching is 215 ℃, and the stretching ratio is 3.5 times.

The fineness of the finally prepared high-strength coarse-denier PVA fiber is 32dtex, the breaking strength is 14cN/dtex, and the elastic modulus is 338 cN/dtex.

Example 10

The method for preparing the high-strength coarse denier PVA fiber by adopting the PVA high solid content spinning solution prepared in the embodiment 5 to carry out dry-wet spinning comprises the following steps: extruding PVA high solid content spinning solution through a spinneret orifice to form spinning trickle → leading the spinning trickle to enter a coagulating bath through an air layer → carrying out primary stretching → carrying out tertiary extraction → carrying out secondary hot stretching;

the technological parameters are as follows: the aperture of each spinneret orifice is 0.55mm, and the extrusion rate of each spinneret orifice is 4.8 mL/min; the height of the air layer is 12cm, the temperature of the coagulating bath is-3 ℃, and the solidifying time of the coagulating bath is 2 min; the multiple of primary stretching is 3 times; the temperature of the first extraction is 70 ℃, the time is 6 hours, the temperature of the second extraction is 75 ℃, the time is 8 hours, the temperature of the third extraction is 80 ℃, and the time is 10 hours; the temperature of the first hot stretching is 200 ℃, the stretching ratio is 2.5 times, the temperature of the second hot stretching is 215 ℃, and the stretching ratio is 3.5 times.

The fineness of the finally prepared high-strength coarse-denier PVA fiber is 29dtex, the breaking strength is 14.2cN/dtex, and the elastic modulus is 341 cN/dtex.