CN103614801A - Method for preparing high-crystallinity polyacrylonitrile nascent fiber - Google Patents

Abstract

The invention provides a method for preparing a high-crystallinity polyacrylonitrile nascent fiber and belongs to the technical field of carbon fiber precursors. The method comprises the following steps: ejecting an acrylonitrile polymer solution obtained by performing free radical polymerization on acrylonitrile and a comonomer through a spinneret orifice, performing coagulating phase separation in a coagulating bath, standing at normal temperature and drying at a constant temperature in a solution with the same composition as the coagulating bath; and taking a P value as a polarity index of the solution in the coagulating bath, regulating the composition of the coagulating bath, so that the polarity is in the range that an absolute value of (P-0.444) is more than 0.05 and less than 0.35, and the crystallinity of the prepared polyacrylonitrile nascent fiber is higher than 45 percent.

Description

A method for preparing high crystallinity polyacrylonitrile primary fiber

【Technical field】

The invention belongs to the technical field of polyacrylonitrile fiber precursors, and in particular relates to a method for preparing high-crystallinity polyacrylonitrile primary fibers.

【Background technique】

The crystalline structure of the polyacrylonitrile fiber precursor is a key factor in determining the properties of the final carbon fiber. This is because the reaction process and mechanism of the precursor in the subsequent pre-oxidation and carbonization processes are closely related to the crystalline structure, which ultimately affects the structure and performance of carbon fibers. Especially in the thermo-oxidative stabilization stage, the crystalline structure of the precursor determines the diffusion rate of oxygen inside the fiber, which affects the reaction process of the thermal-oxidative stabilization reaction. High crystallinity indicates that the more regular the fiber structure, the more favorable it is for thermal oxygen stabilization. The stabilization process is resistant to the formation of trapezoidal structures. At the same time, the exothermic curve of the thermo-oxidative stabilization reaction is also closely related to the composition of the crystalline structure. Too concentrated heat release, or too fast or too slow heat release has a great influence on the final performance of the fiber. Therefore, the crystal structure of the polyacrylonitrile fiber precursor or the degree of crystallinity plays a decisive role in the performance of the carbon fiber, and experience shows that the crystallinity of the polyacrylonitrile precursor is positively correlated with the crystallinity of the primary fiber , so if you want to increase the crystallinity of the precursor, you can start by increasing the crystallinity of the primary fiber. At present, most of the methods to control the crystallinity of spun fibers are realized by changing the coagulation bath temperature and coagulation bath concentration. A unified law has not been obtained, and there is no accurate theory as a support.

【Content of invention】

In order to overcome the defect in the prior art that there is no theoretical basis for accurate control of the crystallinity of primary fibers, the present invention regulates the solidification phase separation process of polyacrylonitrile spinning fine stream by adjusting the polar p value of the coagulation bath solution composition, and then adjusts the primary fiber crystallinity. The formation of the crystalline structure of the fiber finally achieves the improvement of the crystallinity of the polyacrylonitrile primary fiber.

To achieve the above object, the present invention adopts the following technical solutions:

The invention provides a method for preparing high crystallinity polyacrylonitrile as-spun fibers, comprising the steps of:

a) Free radical polymerization: at 50-60°C, in a dimethyl sulfoxide solvent containing azobisisobutyronitrile, carry out free radical polymerization of acrylonitrile and other comonomers to obtain an acrylonitrile polymer solution;

b) De-single-degassing, coagulation and molding: after de-single-degassing and degassing, the acrylonitrile polymer solution spinning thin stream is sprayed out through the spinneret, and coagulated and formed in the coagulation bath to obtain primary fibers; wherein the p value of the coagulation bath is 0.0094<P<0.794;

c) Drying: Put the obtained as-spun fiber into a solution containing the same composition as the coagulation bath, let it stand at room temperature for 24 hours, take out the fiber and put it in a vacuum oven for 12 hours at a constant temperature of 70°C to volatilize to obtain a as-spun fiber sample; the crystallinity of the obtained as-spun fiber sample ≥45%.

In the preparation method provided by the present invention, the P value of the coagulation bath is: 0.05<|P-0.444|<0.35.

In the preparation method provided by the invention, the crystallinity of the as-spun fiber sample is ≥45%.

In the preparation method provided by the present invention, acrylonitrile can undergo radical polymerization with comonomers, and the comonomers are itaconic acid, methyl acrylate, methyl methacrylate, methacrylic acid, acrylamide, etc. without strong polar groups. Any one or any combination of two or more of the molecules of the group can obtain a mass fraction of acrylonitrile in the acrylonitrile polymer solution higher than 95%.

In the preparation method provided by the invention, the coagulation bath is a pure reagent or a mixed solution, and the pure reagent is ethylene glycol, anhydrous acetic acid, ethanol, acetone, ethyl acetate; the mixed reagent is water, dimethyl sulfoxide, ethanol, Mixture of any two or more of acetone, acetic acid, and ethyl acetate.

In the present invention, P is used as a physical quantity representing the polarity of the coagulation bath solution, and the polarity of the mixed solution can be obtained through the empirical formula P=P ₁ ×V ₁ +P ₂ ×V ₂ , wherein P ₁ and V ₁ represent a Polarity and volume fraction of the reagent (the polar value P of the reagent among the present invention all uses the polarity of water as the relative polarity of the standard value 1), and P ₂ and V ₂ represent the polarity and volume of another reagent Fraction. The fine flow of spinning solution entering the coagulation bath will undergo a solidification phase separation process, and the dimethyl sulfoxide in the thin flow will be gradually removed under the action of the concentration difference, while the precipitant part in the coagulation bath solution will enter the thin flow, As the phase separation proceeds, nascent fibers are gradually formed. In the present invention, step 2) and step 3) are immersed in the coagulation bath twice. Since the solidification time of step 2) is inconsistent according to different experimental conditions, the re-immersion of step 3) makes it fully solidified to ensure that the error caused by different solidification times is sufficient. Small. The solution in step 2) has the same composition as the coagulation bath in step 3), and the P value of both is the same.

Carry out XRD scanning on the as-spun fiber, and use the crystallinity formula crystallinity=Ac/(Ac+Aa)×100% to obtain the crystallinity of the as-spun fiber.

The present invention adopts the P value as the parameter of the polarity of the coagulation bath solution in the preparation process of the primary fiber, uses the P value as a standard to regulate the components of the coagulation bath, controls the polarity of the coagulation bath solution within a certain range, and finally coagulates to obtain crystallinity in the range of More than 45% primary fiber.

Effect of the present invention: use the p value as a parameter to measure the polarity of the coagulation bath solution. The P value is regulated by changing the coagulation bath composition, so that the P value is in the range of 0.05<|P-0.444|<0.35, and the crystallinity of the polyacrylonitrile primary fiber obtained by coagulation is above 45%. Proved by examples, any pure reagent or mixed solution can use the above-mentioned standard deployment coagulation bath composition.

【Detailed ways】

Example 1

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1. Spinning can be carried out after 12 hours of single and degassing. The coagulation bath is ethylene glycol, the pump supply of the metering pump is 1.5ml/r, the spinning fine stream is sprayed out through the spinneret, and enters the coagulation bath to coagulate and form, the coagulation time is 8 seconds, and the coagulation bath draft is -10% , the temperature is room temperature. The obtained as-spun fibers were put into a jar containing the same solution as that of the coagulation bath. After standing at room temperature for 24 hours, the fibers were taken out and placed in a vacuum oven at 70°C for 12 hours of constant temperature volatilization. Cut the dried fiber into powder, and use the X`Pert PRO X-ray diffractometer produced by PANalytical in the Netherlands to test the powder. The scanning range is 5°-50°, and the scanning rate is 0.089°/s. For the XRD curve of acrylonitrile fiber, use the peak-splitting software in JADE software to fit the curve by peak-splitting, and use the calculation formula of crystallinity: crystallinity=Ac/(Ac+Aa)×100% to obtain the crystallization of the fiber In the formula, Ac represents the area of the crystalline peak around 2θ=17°, and Aa represents the area of the amorphous peak.

Example 2

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is anhydrous acetic acid, and all the other process parameters and steps are the same as in Example 1.

Example 3

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is ethanol, and all the other process parameters and steps are the same as in Example 1.

Example 4

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. Coagulation bath is acetone, and all the other processing parameters and steps are with embodiment 1.

Example 5

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is ethyl acetate, and all the other process parameters and steps are the same as in Example 1.

Example 6

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is a mixture of water and dimethyl sulfoxide, wherein the volume ratio of water and dimethyl sulfoxide is 1:1, and the rest of the process parameters and steps are the same as in Example 1.

Example 7

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is a mixture of water and dimethyl sulfoxide, wherein the volume ratio of water and dimethyl sulfoxide is 1:2, and the remaining process parameters and steps are the same as in Example 2.

Example 8

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is a mixture of water and dimethyl sulfoxide, wherein the volume ratio of water and dimethyl sulfoxide is 1:3, and the remaining process parameters and steps are the same as in Example 3.

Example 9

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 99:1, and the polymerization process is the same as in Example 1. The coagulation bath is a mixture of water and dimethyl sulfoxide, wherein the volume ratio of water and dimethyl sulfoxide is 1:4, and the rest of the process parameters and steps are the same as in Example 4.

Example 10

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of water and dimethyl sulfoxide, wherein the volume ratio of water and dimethyl sulfoxide is 1:2, and the remaining process parameters and steps are the same as in Example 7.

Example 11

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of water and ethanol, wherein the volume ratio of water and ethanol is 1:2, and the remaining process parameters and steps are the same as in Example 10.

Example 12

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of water and acetone, wherein the volume ratio of water and acetone is 1:2, and the remaining process parameters and steps are the same as in Example 10.

Example 13

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of water and acetic acid, wherein the volume ratio of water and acetic acid is 1:2, and the remaining process parameters and steps are the same as in Example 10.

Example 14

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of ethanol and acetic acid, wherein the volume ratio of ethanol and acetic acid is 1:2, and all the other process parameters and steps are the same as in Example 10.

Example 15

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 to obtain acrylonitrile-itaconic acid binary copolymers , the comonomer ratio is 98:2, the coagulation bath is a mixture of acetone and ethyl acetate, wherein the volume ratio of acetone and ethyl acetate is 1:2, and the remaining process parameters and steps are the same as in Example 10.

Example 16

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid -Methyl acrylate terpolymer, the comonomer ratio is 98:1:1, the coagulation bath is water and ethanol, wherein the volume ratio of water and ethanol is 1:2, and the remaining process parameters and steps are the same as in Example 11.

Example 17

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid -Methyl acrylate terpolymer, the comonomer ratio is 98:1:1, the coagulation bath is water, ethanol and acetic acid, wherein the volume ratio of water, ethanol, and acetic acid is 1:1:1, and the remaining process parameters and steps Same as Example 16.

Example 18

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid - Methyl acrylate terpolymer, the comonomer ratio is 98:1:1, the coagulation bath is water, ethanol and dimethyl sulfoxide, wherein the volume ratio of water, ethanol and dimethyl sulfoxide is 1:1 : 1, all the other processing parameters and steps are with embodiment 16.

Example 19

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid -Methyl acrylate terpolymer, the comonomer ratio is 98:1:1, the coagulation bath is water, ethanol and acetone, wherein the volume ratio of water, ethanol and acetone is 1:1:1, and the remaining process parameters and steps Same as Example 16.

Example 20

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid -Methyl acrylate terpolymer, comonomer ratio is 98:1:1, coagulation bath is water, ethanol and ethyl acetate, wherein the volume ratio of water, ethanol, ethyl acetate is 1:1:1, the rest Process parameters and steps are the same as in Example 16.

Example 21

Using acrylonitrile, itaconic acid and methyl acrylate as comonomers, using dimethyl sulfoxide as a solvent, and azobisisobutyronitrile as an initiator, carry out free radical polymerization at 60°C to obtain acrylonitrile-itaconic acid -Methyl acrylate terpolymer, comonomer ratio is 98:1:1, coagulation bath is dimethyl sulfoxide, acetone and ethyl acetate, wherein the volume ratio of dimethyl sulfoxide and acetone, ethyl acetate It is 1:1:1, and all the other processing parameters and steps are with embodiment 16.

The polarity P of the coagulation bath solution in the above examples and the crystallinity of the corresponding as-spun fibers are listed in Table 1.

Table 1 Crystallinity of primary fibers

Example Coagulation bath polarity P Primary fiber crystallinity 1 0.79 45.27% 2 0.654 48.85% 3 0.648 47.58% 4 0.355 52.64% 5 0.228 50.33% 6 0.722 47.33% 7 0.629 49.12% 8 0.583 48.86% 9 0.555 50.25% 10 0.629 50.78% 11 0.769 49.63% 12 0.57 48.94% 13 0.765 47.17% 14 0.65 50.23% 15 0.27 51.99% 16 0.769 53.09% 17 0.767 48.40% 18 0.699 48.74% 19 0.670 47.98% 20 0.627 45.89% twenty one 0.342 48.37%

Claims (8)

1. A method for preparing high crystallinity polyacrylonitrile as-spun fibers, comprising the steps of: a) Free radical polymerization: at 50-60°C, in a dimethyl sulfoxide solvent containing azobisisobutyronitrile, carry out free radical polymerization of acrylonitrile and other comonomers to obtain an acrylonitrile polymer solution; b) Demolarization and degassing, coagulation and molding: after desingling and degassing, the acrylonitrile polymer solution is spun out through the spinneret, and coagulated in the coagulation bath to form primary fibers; The p value of described coagulation bath is 0.0094<P<0.794; c) Drying: put the obtained nascent fiber into a solution containing the same composition as the coagulation bath, let it stand at room temperature for 24 hours, take out the fiber and put it in a vacuum oven for 12 hours at a constant temperature of 70°C to volatilize to obtain a nascent fiber sample; The crystallinity of the as-spun fiber sample is ≥45%. 2. The preparation method according to claim 1, characterized in that: the value of P is: 0.05<|P-0.444|<0.35. 3. The preparation method according to claim 2, characterized in that: the crystallinity of the as-spun fiber sample is ≥45%. 4. The preparation method according to claim 1, characterized in that: the comonomer is itaconic acid, methyl acrylate, methyl methacrylate, methacrylic acid, any one or two of acrylamide and Any combination of 2 or more. 5. The preparation method according to claim 4, characterized in that, the mass fraction of acrylonitrile in the acrylonitrile polymer solution is higher than 95%. 6. The preparation method according to claim 1, characterized in that: the coagulation bath is a pure reagent or a mixed solution. 7. preparation method according to claim 6 is characterized in that: the pure reagent of described coagulation bath is ethylene glycol, anhydrous acetic acid, ethanol, acetone, ethyl acetate. 8. The preparation method according to claim 7, characterized in that: the mixed reagent of the coagulation bath is any two or more mixed solutions of water, dimethyl sulfoxide, ethanol, acetone, acetic acid, and ethyl acetate.