CN116084034A - Solidification forming method for improving homogenization and crystallinity of polyacrylonitrile nascent fiber - Google Patents

Abstract

The invention discloses a coagulation molding method for improving the homogenization and crystallinity of polyacrylonitrile primary fibers, which comprises the following steps: the polyacrylonitrile stock solution obtained by copolymerizing acrylonitrile and a comonomer enters a coagulation bath after spinning, And carry out drafting, obtain as-spun fiber; Described coagulation bath comprises coagulant and solvent, and described coagulant is diethylene glycol, and solvent is selected from dimethylsulfoxide, dimethylformamide, dimethylacetamide, acetone , NaSCN aqueous solution or ZnCl _aqueous solution, in the coagulation bath, the mass percentage of coagulant is 20%-80%; The comonomer is selected from itaconic acid, sodium propylene sulfonate, sodium methacrylate, methyl acrylate , methyl methacrylate, methacrylic acid or acrylamide.

Description

A solidification molding method for improving the homogenization and crystallinity of polyacrylonitrile primary fibers

technical field

The invention belongs to the technical field of high-performance carbon fiber precursor preparation, and specifically relates to a solidification molding method for improving the homogenization and crystallinity of polyacrylonitrile nascent fibers, and is used for preparing high-performance carbon fiber PAN precursors.

Background technique

The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

Carbon fiber has the advantages of high specific strength, high specific modulus, heat conduction, heat resistance, and self-lubrication. As an indispensable material, carbon fiber is widely used in automobiles, aerospace, biomedicine, renewable energy, building materials and other fields.

In the wet spinning process, the fine flow of polyacrylonitrile enters the coagulation bath through the spinneret hole, and then the solvent in the stock solution diffuses to the coagulation bath due to the concentration difference, and the coagulant in the coagulation bath diffuses to the stock solution. Double diffusion, finally The trickle of stock solution reaches the critical concentration and the primary fibers are precipitated. This process determines the degree of homogeneity of the as-spun fibers. The faster the double diffusion speed, the stronger the force between the coagulant and the polyacrylonitrile chain, the easier it is to quickly form a dense structure in the cortex of the primary fiber, which increases the resistance of the coagulant to the interior of the primary fiber, resulting in loose internal structure of the primary fiber And the skin-core structure is serious and inherits the structure to carbon fiber. Moreover, the stronger the interaction between the coagulant and the polyacrylonitrile chain, the more the polyacrylonitrile chain is bound, so it cannot freely move and arrange to participate in the formation of crystallization, resulting in lower crystallinity of the as-spun fiber.

The current common technology is to use water as a coagulant, but due to the strong polarity of water, it binds the polyacrylonitrile chain strongly, resulting in severe phase separation, so the as-spun fibers are prone to produce holes and have uneven texture. However, increasing the solvent concentration to alleviate the degree of interaction between water and polyacrylonitrile chains in the coagulation bath will lead to insufficient diffusion dynamics, resulting in swelling and adhesion of the primary fibers, and the overall structure is loose. In addition, considering the price of the solvent in the coagulation bath, increasing the proportion of the solvent in the coagulation bath will often increase the production cost.

Contents of the invention

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a coagulation molding method for improving the homogenization and crystallinity of polyacrylonitrile primary fibers, which can effectively slow down double diffusion and reduce the consumption of solvents, thereby obtaining high-performance polyacrylonitrile Acrylonitrile raw silk and carbon fiber. In the wet spinning process, a reasonable choice of coagulant can reduce the consumption of solvent, slow down the severe phase separation caused by double diffusion, and improve the crystallinity of the as-spun fiber, so that homogeneous and high-quality fiber can be prepared. Raw silk for mechanical strength.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

A coagulation molding method for improving the homogenization and crystallinity of polyacrylonitrile primary fibers, comprising the steps of:

The polyacrylonitrile stock solution obtained by copolymerizing acrylonitrile and comonomer enters the coagulation bath after spinning, and is drawn to obtain primary fibers;

Described coagulation bath comprises coagulant and solvent, and described coagulant is diethylene glycol, and solvent is selected from dimethyl sulfoxide, dimethylformamide, dimethylacetamide, acetone, NaSCN aqueous solution or ZnCl _aqueous solution, solidifies In the bath, the mass percentage of coagulant is 20%-80%;

The above solvents are used to produce polyacrylonitrile precursors, and the solvents in the coagulation bath should match them.

The comonomer is selected from itaconic acid, sodium propylene sulfonate, sodium methacrylate sulfonate, methyl acrylate, methyl methacrylate, methacrylic acid or acrylamide.

The above comonomers have the advantage of larger steric volume, so they can reduce the interaction between polyacrylonitrile molecular chains, thereby improving the elasticity of polyacrylonitrile fibers. In addition, the above comonomers can increase the degree of cyclization of polyacrylonitrile fibers, thereby making the fibers denser.

In the coagulation bath, the solvent in the polyacrylonitrile stock solution stream diffuses into the coagulation bath, and the coagulant in the coagulation bath diffuses into the stock solution stream. When the double diffusion reaches equilibrium, the stock solution stream reaches a critical concentration and precipitates.

In some embodiments, the temperature of the coagulation bath is 20-70°C. With this coagulation temperature a uniform coagulation of the fibers can be obtained.

In some embodiments, the comonomer is itaconic acid. The reactive nature of itaconic acid is active, which is beneficial to the cyclization process of polyacrylonitrile precursor during preoxidation.

In some embodiments, the solvent of the coagulation bath is dimethyl sulfoxide. Dimethyl sulfoxide has low toxicity.

In some embodiments, the polyacrylonitrile stock solution is sprayed at a linear speed of 5-50 m/min after spinning.

In some embodiments, the draft ratio is -10% to -100%.

The beneficial effects obtained by one or more embodiments of the present invention are as follows:

The present invention replaces the coagulant water in the traditional coagulation bath with diethylene glycol, which reduces the interaction between the coagulant and the polyacrylonitrile chain molecules, so that the polyacrylonitrile molecular chains can freely stack and participate in crystallization to a large extent, thereby Increased crystallinity of the as-spun fibers. At the same time, the weak force between the coagulant and the polyacrylonitrile chain weakens the degree of phase separation, inhibits the formation of a dense skin structure, reduces the diffusion resistance of the coagulant in the thin stream, and ensures that the obtained nascent fiber is from the inside to the outside. The structure is uniform, and the skin-core structure is improved, so as to improve the mechanical properties of the polyacrylonitrile precursor.

In the coagulation bath, diethylene glycol enters into the thin stream of stock solution from the coagulation bath through double diffusion to regulate the precipitation rate of polyacrylonitrile. Compared with the commonly used coagulation bath with water as the coagulant, the polyacrylonitrile-disolvent-diethylene glycol ternary phase diagram has a larger metastable region. Since diethylene glycol is less polar than water, the diethylene glycol/polyacrylonitrile interaction parameter is smaller than the water/polyacrylonitrile interaction parameter.

Therefore, compared with water as a coagulant, diethylene glycol has less restraint on the polyacrylonitrile chain. On the one hand, it slows down the rapid solidification and precipitation on the surface of the stock solution stream, and helps the coagulant to diffuse into the stock solution stream, thereby facilitating uniformity. On the other hand, the interaction between diethylene glycol and polyacrylonitrile molecular chains is relatively weak, so that the entanglement between polyacrylonitrile molecules is small, which is conducive to the orderly movement of molecular chains to participate in crystal growth.

When the mass percentage of diethylene glycol in the coagulation bath is 20-80%, the homogenization degree of the fiber can be better improved, and at the same time, the looseness of the overall structure of the fiber caused by insufficient double diffusion power is avoided.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention.

Fig. 1 is a schematic diagram of wet spinning for preparing as-spun fibers with high homogeneity and high crystallinity according to an embodiment of the present invention.

Among them, 1. spinneret; 2. coagulation bath; 3. primary fiber; 4. godet.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The present invention will be further described below in conjunction with embodiment.

Example 1

A solidification molding method for improving homogenization and crystallinity of polyacrylonitrile primary fibers, the preparation steps of which are as follows:

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, comonomer ratio is 99:1. After 12 hours of de-singling and degassing, wet spinning can be carried out.

The linear speed of the polymer in the spinneret hole is 20m/min, the coagulation bath adopts the mixed solution of dimethyl sulfoxide and diethylene glycol (mass ratio is 3:7), the drafting of the coagulation bath is -25%, and the as-spun fibers are coagulated The residence time in the bath was 7s, and the temperature of the coagulation bath was kept at 30°C.

The as-spun fibers are washed with water, drawn, and dried to obtain polyacrylonitrile precursors. The tensile strength of the obtained precursor was 6.4 cN/Dtex. Cut the dried primary fiber into powder, and use D/max-rc X-ray diffraction to analyze and test the powder. The scanning range is 5-50°, the scanning rate is 4°/min, and the Hinrichen method is used to calculate Crystallinity C, the formula C=Ac/Ac+Aa, where Ac is the area of the diffraction peak of the crystalline region at 2θ≈17°, Aa is the area of the diffraction peak of the amorphous region, and the calculated crystallinity is 42.31%.

Example 2

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

Adjust metering pump rotating speed, the polymer linear velocity of spinneret hole is 25m/min, all the other process parameters and steps are with embodiment 1, calculate and obtain precursor tensile strength and be 7.3cN/Dtex, the crystallinity of the as-spun fiber that calculates is 47.85%.

Example 3

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

Adjust the speed of the metering pump, the polymer linear velocity of the polymerization spinneret holes is 30m/min, all the other process parameters and steps are the same as in Example 1, the calculated precursor tensile strength is 6.9cN/Dtex, and the calculated crystallinity of the as-spun fibers was 46.35%.

Example 4

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

The coagulation bath adopts the mixed solution of dimethyl sulfoxide and diethylene glycol (the mass ratio is adjusted to 3.5:6.5), and all the other process parameters and steps are the same as in Example 2. The calculated tensile strength of the precursor is 6.6cN/Dtex, and the calculated The crystallinity of the as-spun fiber is 43.72%.

Example 5

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

The coagulation bath adopts a mixed solution of dimethyl sulfoxide and diethylene glycol (the mass ratio is adjusted to 2:8), and the remaining process parameters and steps are the same as in Example 2. The calculated tensile strength of the precursor is 6.1cN/Dtex, and the calculated The crystallinity of the as-spun fiber is 44.34%.

Example 6

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

The quality of the coagulation bath is as in Example 4, and the temperature of the coagulation bath is adjusted to 40°C. The remaining process parameters are as in Example 2, the calculated tensile strength of the precursor is 5.6 cN/Dtex, and the calculated crystallinity of the primary fiber is 40.04%.

Example 7

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

The coagulation bath temperature and quality are as in Example 4, and the coagulation bath draft ratio is adjusted to -60%. All the other process parameters and steps are as in Example 2. The calculated tensile strength of the precursor is 5.5cN/Dtex, and the calculated crystallinity of the primary fiber is 39.01%.

Comparative example 1

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1.

The coagulation bath adopts the mixed solution of dimethyl sulfoxide and water (mass ratio is 3:7), and all the other process parameters and steps are the same as in Example 1. The calculated tensile strength of the precursor is 5.3cN/Dtex, and the calculated The crystallinity is 35.51%.

Comparative example 2

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1. The coagulation bath adopts the mixed solution of dimethyl sulfoxide and water (the mass ratio is adjusted to 3:7), and the remaining process parameters and steps are the same as in Example 2. The calculated tensile strength of the precursor is 6.2cN/Dtex, and the calculated as-spun fiber The crystallinity is 36.52%.

Comparative example 3

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization technique is as embodiment 1. The coagulation bath adopts a mixed solution of dimethyl sulfoxide and water (mass ratio is 3:7), and the remaining process parameters are as in Example 3. The calculated tensile strength of the precursor is 5.5cN/Dtex, and the calculated crystallinity of the primary fiber is 31.65%.

Comparative example 4

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization technique is as embodiment 1. The coagulation bath adopts a mixed solution of dimethyl sulfoxide and water (mass ratio is 3.5:6.5), and the remaining process parameters are as in Example 4. The calculated tensile strength of the precursor is 5.8cN/Dtex, and the calculated crystallinity of the primary fiber is 40.31%.

Comparative example 5

The polyacrylonitrile copolymer is obtained by solution polymerization. Using acrylonitrile and itaconic acid as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C, and finally obtain acrylonitrile-itaconic acid binary Copolymer, the ratio of comonomer is 99:1, and polymerization process is as embodiment 1. The coagulation bath adopts a mixed solution of dimethyl sulfoxide and water (mass ratio is 2:8), and the remaining process parameters are as in Example 5. The calculated tensile strength of the precursor is 5.1cN/Dtex, and the calculated crystallinity of the primary fiber is 41.48%.

Table 1 is the comparison table of the polyacrylonitrile precursor tensile strength and the crystallinity of the as-spun fiber that embodiment and comparative example make

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A solidification molding method for improving homogenization and crystallinity of polyacrylonitrile nascent fiber is characterized in that: the method comprises the following steps:

the polyacrylonitrile stock solution obtained by copolymerizing acrylonitrile and comonomer is sprayed into a coagulating bath and is drawn to obtain nascent fibers;

the coagulating bath comprises coagulating agent and solvent, wherein the coagulating agent is diethylene glycol, and the solvent is selected from dimethyl sulfoxide, dimethylformamide, dimethylacetamide, acetone, naSCN water solution or ZnCl ₂ The mass percentage of the coagulant in the aqueous solution and the coagulating bath is 20-80%;

the comonomer is selected from itaconic acid, sodium acrylate, sodium methacrylate, methyl acrylate, methyl methacrylate, methacrylic acid or acrylamide.

2. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: the temperature of the coagulating bath is 20-70 ℃.

3. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 2, wherein: the temperature of the coagulating bath is 30-60 ℃.

4. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: the comonomer is itaconic acid.

5. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: the solvent of the coagulating bath is dimethyl sulfoxide.

6. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: the linear velocity of the sprayed polyacrylonitrile stock solution after spinning is 5-50m/min.

7. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 6, wherein: the linear velocity of the sprayed polyacrylonitrile stock solution after spinning is 15-40m/min.

8. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: the draft ratio is-10% to-100%.

9. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 1, wherein: in the coagulating bath, the mass percentage of the coagulating agent is 30-70%.

10. The solidification molding method for improving homogenization and crystallinity of a primary polyacrylonitrile fiber according to claim 9, wherein: in the coagulating bath, the mass percentage of the coagulating agent is 30% -60%.

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