阅读说明：本技术 一种酚醛树脂/改性聚乙烯醇复合纤维粘合剂的制备方法 (Preparation method of phenolic resin/modified polyvinyl alcohol composite fiber adhesive ) 是由 王彪 黄熙怡 陈彦坤 瞿同庆 于 2021-05-31 设计创作，主要内容包括：本发明涉及一种酚醛树脂/改性聚乙烯醇复合纤维粘合剂的制备方法,将酚醛树脂和改性聚乙烯醇加入到溶剂中配置粘度为100Pa·s～2000Pa·s的纺丝原液,采用干法纺丝工艺制得复合纤维粘合剂；所述改性聚乙烯醇为聚乙烯醇、聚乙烯醇缩甲醛和聚乙烯醇缩丁醛中的一种以上；所述复合纤维粘合剂中,所述酚醛树脂在所述改性聚乙烯醇中以岛状的形式均匀分散,且分散相的尺寸＜2μm；本发明的一种酚醛树脂/改性聚乙烯醇复合纤维粘合剂的制备方法,过程简单,可应用于碳/碳复合材料用预制体和燃料电池用碳纸,制品制备过程环保,性能优异,并可通过所制得的复合纤维粘合剂的组成、纤度、短切长度以及用量来调控所述预制体及碳纸的电导率、强度。(The invention relates to a preparation method of phenolic resin/modified polyvinyl alcohol composite fiber adhesive, which comprises the steps of adding phenolic resin and modified polyvinyl alcohol into a solvent to prepare a spinning stock solution with the viscosity of 100 Pa.s-2000 Pa.s, and preparing the composite fiber adhesive by adopting a dry spinning process; the modified polyvinyl alcohol is more than one of polyvinyl alcohol, polyvinyl formal and polyvinyl butyral; in the composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the size of a dispersed phase is less than 2 mu m; the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive has simple process, can be applied to a prefabricated body for a carbon/carbon composite material and carbon paper for a fuel cell, has environment-friendly product preparation process and excellent performance, and can regulate and control the conductivity and the strength of the prefabricated body and the carbon paper through the composition, the fineness, the short-cut length and the dosage of the prepared composite fiber adhesive.)

1. A preparation method of phenolic resin/modified polyvinyl alcohol composite fiber adhesive is characterized by comprising the following steps: adding phenolic resin and modified polyvinyl alcohol into a solvent to prepare a spinning solution with the viscosity of 100-2000 Pa.s, and preparing the phenolic resin/modified polyvinyl alcohol composite fiber adhesive by adopting a dry spinning process;

the modified polyvinyl alcohol is more than one of polyvinyl alcohol, polyvinyl formal and polyvinyl butyral;

in the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the size of a dispersed phase is less than 2 mu m.

2. The method for preparing the phenolic resin/modified polyvinyl alcohol composite fiber adhesive according to claim 1, wherein the phenolic resin is a thermoplastic phenolic resin and/or a thermosetting phenolic resin.

3. The method for preparing the phenolic resin/modified polyvinyl alcohol composite fiber adhesive according to claim 1, wherein the solvent is alcohol, water, dimethyl sulfoxide, or a mixture of ethanol and ethyl acetate;

the alcohol is more than one of methanol, ethanol, propylene glycol and n-butanol.

4. The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is characterized in that the mass ratio of the modified polyvinyl alcohol to the solvent in the spinning solution is 3: 10-5: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 9-5: 1-5.

5. The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is characterized in that the mass ratio of the thermoplastic phenolic resin to the thermosetting phenolic resin is 9-1: 1-9.

6. The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is characterized by comprising the following specific steps of:

(1) adding phenolic resin and modified polyvinyl alcohol into a solvent, and stirring at 25-98 ℃ until the phenolic resin and the modified polyvinyl alcohol are completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for more than 6 hours, and then performing vacuum defoaming to obtain a spinning stock solution;

(3) and (3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain the phenolic resin/modified polyvinyl alcohol composite fiber adhesive.

7. The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive according to claim 1, wherein the temperature of a charging bucket for dry spinning is 25-95 ℃, the drawing ratio of a spinning nozzle during dry spinning is 0.4-1.8, and the spinning speed is 100-180 m/min; the dry spinning channel is heated by single-section hot air at 25-190 deg.c or upper and lower sections at 25-50 deg.c and 60-190 deg.c.

8. The method for preparing the phenolic resin/modified polyvinyl alcohol composite fiber adhesive according to claim 1, wherein the residual carbon ratio of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 6-50%.

Technical Field

The invention belongs to the technical field of carbon/carbon composite materials, relates to a preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive, and particularly relates to a method for preparing a phenolic resin/modified polyvinyl alcohol composite fiber adhesive for a preform through dry spinning.

Background

The carbon/carbon composite material is widely applied to the field of aerospace due to the excellent properties of low density, good thermal conductivity, high electrical conductivity, corrosion resistance, thermal shock resistance and the like, is gradually expanded to the fields of new energy, civil use, medical treatment and the like, and becomes an irreplaceable material in modern science and technology.

Carbon/carbon composite preforms are typically prepared from carbon fibers and a binder. The adhesive is used as an important component in the carbon fiber preform and mainly used for bonding mutually overlapped carbon fibers to form a plane superposition structure, so that the structure of the carbon/carbon composite material is more compact, the mechanical property of the carbon/carbon composite material is improved, more conductive loops can be communicated, and the conductivity is improved. Therefore, the carbon residue of the binder, the bonding strength between the binder and the fibers, and the uniformity of the distribution of the binder and the fibers are important factors affecting the performance of the preform or the carbon/carbon composite. In order to meet the performance requirements of preforms for carbon/carbon composites, the binder generally needs to have good adhesion, high carbon residue, and the like.

The carbon residue rate of the common adhesive is low, and carbon fibers cannot be well bonded after carbonization, so that the phenolic resin with high carbon residue rate needs to be introduced into the prefabricated body by a liquid phase impregnation method, so that the mechanical property, the electric conductivity and the like of the carbon/carbon composite material are improved. However, phenolic resins also generally suffer from poor adhesion, non-uniform distribution, and low residual levels in the preform. The binder may be a solid, such as a powder or a fiber, or a liquid. However, the powder adhesive usually has the problem of uneven distribution, resulting in poor material performance; liquid adhesives generally have problems of uncontrollable adhesion and high contamination. Although the dispersibility of carbon fibers can be remarkably improved by adding a small amount of nano-cellulose, the problems that the resin is unevenly distributed in the carbon paper and the adhesion is difficult to control and the like due to the self-fluidity and the gravity action of the resin cannot be solved by immersing the adhesive resin into the carbon paper by adopting a vacuum negative pressure suction process, and finally the integral uniformity of the carbon paper is poor. US4818448 uses uncured granular phenolic resin as a binder, carbon fibers are dispersed in water together with the binder, a preform is prepared by a simple pressure filtration technique, and a carbon/carbon composite material is prepared by carbonization, but the final property distribution of the material is not uniform because a large amount of granular phenolic resin is not easy to be uniformly dispersed. Chinese patent CN101047253A provides a carbon fiber paper bonded by acrylic fibers, which is prepared by introducing the acrylic fibers into a carbon fiber lamination through a conventional wet papermaking process, and then curing and carbonizing.

Therefore, the invention provides a binder of a controllable and attachable preform for a carbon/carbon composite material with a high carbon residue rate, which can relieve environmental and energy crisis and also has strategic significance in promoting the development of carbon/carbon composite materials and carbon paper for fuel cells.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive, and particularly provides a method for preparing a phenolic resin/modified polyvinyl alcohol composite fiber adhesive for a preform through dry spinning.

In order to achieve the purpose, the invention adopts the following scheme:

a preparation method of phenolic resin/modified polyvinyl alcohol composite fiber adhesive is provided, phenolic resin and modified polyvinyl alcohol are added into solvent to prepare spinning dope with the viscosity of 100 Pa.s-2000 Pa.s, and the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is prepared by adopting dry spinning technology;

the modified polyvinyl alcohol is more than one of polyvinyl alcohol (PVA), polyvinyl formal (PVF) and polyvinyl butyral (PVB), which are known adhesives with good adhesion effect on carbon fibers.

In the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, the size of a dispersed phase is less than 2 mu m, and continuous dry spinning cannot be carried out if the size of the dispersed phase is too large.

As a preferred technical scheme:

the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following steps of mixing the phenolic resin with the thermoplastic phenolic resin and/or the thermosetting phenolic resin, and then drying the mixture. The phenolic resin is a commercial product, and is a low molecular weight thermoplastic phenolic resin with the molecular weight of 500-3000 and a thermosetting phenolic resin, wherein the thermosetting phenolic resin is an alcohol-soluble phenolic resin or a water-soluble phenolic resin.

According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the solvent is alcohol, water, dimethyl sulfoxide or a mixture of ethanol and ethyl acetate; since the mechanism of dry spinning is involved in solidifying the dope stream to form fibers by phase separation through solvent evaporation, the solvent selected for the present invention must be volatile.

The alcohol is more than one of methanol, ethanol, propylene glycol and n-butanol.

According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, in a spinning solution, the mass ratio of the modified polyvinyl alcohol to a solvent is 3: 10-5: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 9-5: 1-5.

According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the mass ratio of the thermoplastic phenolic resin to the thermosetting phenolic resin is 9-1: 1-9.

The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin and modified polyvinyl alcohol into a solvent, and stirring at 25-98 ℃ until the phenolic resin and the modified polyvinyl alcohol are completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution; if the temperature is less than 25 ℃, the dissolution efficiency is low, the phase separation phenomenon is easy to generate, the spinning stability and the product performance are influenced, if the temperature is more than 98 ℃, the solvent evaporation speed is high, the viscosity of the blending solution is difficult to control, and the polymer is easy to oxidize and discolor.

(2) Standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for more than 6 hours, and then performing vacuum defoaming to obtain viscous spinning solution; less than 6 hours, the air bubble removal is incomplete, and the spinning stability and the strength of the product are influenced.

(3) And (3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain the phenolic resin/modified polyvinyl alcohol composite fiber adhesive.

According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the temperature of a charging bucket for dry spinning is 25-95 ℃, and the drawing ratio of a spinning nozzle during dry spinning is 0.4-1.8. The spinning speed is 100-180 m/min, a single-section hot air heating mode is adopted in a shaft of dry spinning, the temperature is 25-190 ℃, or an upper section and a lower section are adopted for heating, the temperature of the upper section is 25-50 ℃, and the temperature of the lower section is 60-190 ℃. The temperature of a charging bucket for dry spinning is less than 25 ℃, the viscosity is too high, and smooth spinning cannot be realized; above 95 ℃, the solvent evaporates too fast, the viscosity cannot be controlled, and the spinning stability is influenced. The temperature of the hot air is less than 25 ℃, the solvent is not completely evaporated in the channel, the filaments are adhered and cannot be smoothly spun, the temperature of the hot air is more than 190 ℃, the filaments are broken in the channel and are heated in two sections, so that the spinning speed and the spinning stability can be improved. The stretch ratio of the spinning nozzle is less than 0.8, the spinning solution has the phenomenon of plate overflow, the broken filaments are serious, the stretch ratio of the spinning nozzle is more than 1.8, the filaments are easy to break, and the spinning is discontinuous. The spinning speed is less than 100m/min, the efficiency is low, and the fibers are easy to adhere; when the yarn diameter is larger than 180m/min, the yarn is easily broken and winding is difficult.

According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 6-50%.

When the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is used for preparing a prefabricated body for a carbon/carbon composite material and carbon paper for a fuel cell, the electrical conductivity and the strength of the prefabricated body and the carbon paper can be regulated and controlled through the composition, the fineness, the short-cut length and the using amount of the prepared composite fiber adhesive.

The mechanism of the invention is as follows:

the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive provided by the invention is characterized in that the fiber is solidified through volatilization of the solvent, so that the phenolic resin/modified polyvinyl alcohol composite fiber with a compact structure can be obtained, and the preparation method is simple in process, is obviously different from the prior art, and is embodied in that:

1. since the phenolic resin is a linear or branched oligomer before curing and it is difficult to spin it alone, it is common in the prior art to add a small amount of modified polyvinyl alcohol as a spinning aid, which has low fiber strength and cannot be used as a binder. The content of the modified polyvinyl alcohol is more than or equal to that of the phenolic resin, namely the structural main body of the fiber is the modified polyvinyl alcohol, so that the fiber can be used as an adhesive and has better mechanical property;

2. the phenolic resin is linear or branched oligomer before curing, has low viscosity, does not account for the main body in the spinning solution, so the viscosity of the spinning solution is not greatly influenced by the viscosity of the spinning solution, the viscosity of the spinning solution is mainly controlled by the concentration of the modified polyvinyl alcohol, and when the mass ratio of the modified polyvinyl alcohol to the solvent is 3: 10-5: 10 in the process of preparing the spinning solution, the viscosity of the spinning solution is in the range of 100 Pa.s-2000 Pa.s, so the requirement of dry spinning on the viscosity of the spinning solution is met;

3. furthermore, as the phenolic resin and the modified polyvinyl alcohol can be simultaneously dissolved in the solvent selected by the invention, particularly, when the mass of the modified polyvinyl alcohol, namely the phenolic resin, is more than or equal to 1, the phenolic resin and the modified polyvinyl alcohol have good compatibility in the solvent, and smooth spinning can be realized. In the dry spinning process, due to solvent evaporation, phenolic resin and modified polyvinyl alcohol are respectively solidified, the modified polyvinyl alcohol is a continuous phase, the phenolic resin is dispersed in the modified polyvinyl alcohol in an island form, and the size of a dispersed phase (phenolic resin) in the fiber is observed to be less than 2 mu m through SEM; when the mass of the modified polyvinyl alcohol-phenolic resin is less than 1, the modified polyvinyl alcohol becomes a disperse phase and the phenolic resin is a continuous phase in the solvent evaporation and solidification process, and the dry spinning process cannot be continuous due to the oversize of the disperse phase.

4. The invention also mixes the thermoplastic phenolic resin and the thermosetting phenolic resin for use, the thermosetting phenolic resin is used as a curing agent of the thermoplastic phenolic resin, the fibers do not need to be soaked in a hydrochloric acid formaldehyde solution to enable the thermoplastic phenolic resin to be crosslinked, and meanwhile, the aldehyde compounds decomposed from the modified polyvinyl alcohol can be used as the curing agent to carry out in-situ curing on the phenolic resin through heating treatment, so that the time for subsequent curing of the thermoplastic phenolic resin is shortened. In addition, since the thermosetting phenol resin forms a body-type polycondensate after curing, it has poor or no fluidity; the modified polyvinyl alcohol is usually a thermoplastic polymer, and in the process of heating the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the modified polyvinyl alcohol is heated and melted to flow and shrink, and simultaneously, the phenolic resin is driven to flow to the lap joint between the carbon fibers together to form an effective bonding structure, so that the bonding strength between the carbon fibers is enhanced, and the overall performance of the prefabricated body is improved.

5. The invention is used as a fibrous adhesive and is mainly applied to the preparation of carbon fiber preforms for carbon/carbon composite materials and carbon paper for fuel cells. The electrical conductivity and strength of the prefabricated body and the carbon paper can be regulated and controlled through the composition, titer, chopped length and dosage of the prepared composite fiber adhesive, so that the performance requirements of carbon fiber prefabricated bodies and carbon paper for different purposes are met, for example, the carbon paper for fuel cells needs to have the performances of good air permeability, high strength and high electrical conductivity, and therefore the used fiber adhesive has medium phenolic resin content, large titer and the like; the carbon/carbon composite material for the structural material needs to have higher density and mechanical property, so that the content of the fibrous adhesive in the preform is higher, the fineness is small, and the like. Since most of modified polyvinyl alcohols such as PVA, PVF, PVB and the like have been confirmed to have excellent adhesive properties, the binder can adhere well to carbon fibers; since the binder of the present invention contains a phenol resin having a high carbon residue ratio, the binder also has a high carbon residue ratio. Carbon fiber preforms and carbon papers are generally prepared by a conventional wet papermaking technique, and carbon fibers can be bonded into preforms (also called carbon fiber base paper) by mixing papermaking and hot pressing using the fibrous binder of the present invention and chopped carbon fibers; in the invention, the phenolic resin and the modified polyvinyl alcohol are compounded into fibers as the adhesive, thereby solving the problems of uneven distribution and difficult control of adhesion amount caused by fluidity and gravity in the phenolic impregnation process and the problem of low carbon residue rate of fiber adhesives such as pure PVA, PVF, PVB and the like. And the preparation process has less emission and is environment-friendly.

The adhesive used as the adhesive for the preform has the advantages of uniform distribution, controllable attachment amount, high carbon residue rate, good caking property and the like, has more advantages in the preparation of the carbon/carbon composite preform, and has great application prospect.

Advantageous effects

(1) According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the prepared composite fiber adhesive is high in carbon residue rate, good in cohesiveness and good in mechanical property.

(2) The preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is simple in process and can be applied to carbon paper for a prefabricated fuel cell for a C/C composite material.

(3) According to the preparation method of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the electrical conductivity and strength of the prefabricated body and the carbon paper can be regulated and controlled through the composition, fineness, short-cut length and dosage of the prepared composite fiber adhesive.

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.

The test method of the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following steps: and (3) testing by using a TA thermogravimetric analyzer (Q5000IR), wherein the sample sampling amount is 1-3 mg, the purging atmosphere is nitrogen, the nitrogen flow rate is more than 20ml/min, the temperature range is 40-700 ℃, and the temperature rising rate is 10 ℃/min.

Example 1

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (thermoplastic phenolic resin with the molecular weight range of 1000-2500 and the mark of PF-5400) and modified polyvinyl alcohol (polyvinyl butyral (PVB)) into ethanol, and stirring at 25 ℃ until the phenolic resin and the modified polyvinyl alcohol are completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution; in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the ethanol is 3: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 9: 1;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 6 hours, and then performing vacuum defoaming to obtain a spinning solution with the viscosity of 700Pa & s; the concentration of the spinning dope is 25 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein, the temperature of the charging bucket for dry spinning is 25 ℃, the temperature of the shaft for dry spinning is 90 ℃ by adopting single-section hot air for heating, the drawing ratio of a spinning nozzle during dry spinning is 0.8, and the spinning speed is 110 m/min;

in the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 2 mu m; the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 50%.

Example 2

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (thermosetting phenolic resin with the molecular weight range of 1500-3000 and the mark of PF2605) and modified polyvinyl alcohol (polyvinyl formal (PVF)) into methanol, and stirring at 25 ℃ until the phenolic resin and the modified polyvinyl alcohol are completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blended solution; in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the methanol is 4: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 5: 5;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 7 hours, and then performing vacuum defoaming to obtain a spinning solution with the viscosity of 1050Pa & s; the concentration of the spinning dope was 44.4 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein, the temperature of the charging bucket of the dry spinning is 25 ℃, the upper section and the lower section are adopted in the shaft of the dry spinning for heating, the temperature of the upper section is 35 ℃, the temperature of the lower section is 90 ℃, the drawing ratio of a spinning nozzle during the dry spinning is 1.1, and the spinning speed is 130 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 2 mu m; the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 50%.

Example 3

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (water-soluble phenolic resin with the molecular weight range of 500-1500 and the mark of PF3002) and polyvinyl alcohol (PVA) into water, and stirring at 98 ℃ until the phenolic resin and the PVA are completely dissolved to obtain a phenolic resin/polyvinyl alcohol blended solution; in the phenolic resin/polyvinyl alcohol blending solution, the mass ratio of polyvinyl alcohol to water is 5: 10; the mass ratio of the polyvinyl alcohol to the phenolic resin is 6: 4;

(2) standing the phenolic resin/polyvinyl alcohol blended solution at room temperature for 6 hours, and then performing vacuum defoaming to obtain a spinning stock solution with the viscosity of 1680Pa & s; the concentration of the spinning dope was 45.5 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein the temperature of the charging bucket for dry spinning is 95 ℃, the upper section and the lower section are adopted for heating in the shaft for dry spinning, the temperature of the upper section is 45 ℃, the temperature of the lower section is 150 ℃, the drawing ratio of a spinning nozzle during dry spinning is 1.2, and the spinning speed is 140 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 1 mu m; the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 32 percent.

Example 4

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (a mixture of thermoplastic phenolic resin (molecular weight range of 1000-2500, brand of PF-5400) and thermosetting phenolic resin (molecular weight range of 1500-3000, brand of PF2605) in a mass ratio of 9: 1) and modified polyvinyl alcohol (polyvinyl butyral (PVB)) into dimethyl sulfoxide, and stirring at 70 ℃ until the mixture is completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution; in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the dimethyl sulfoxide is 3: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 7: 3;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 8 hours, and then performing vacuum defoaming to obtain a spinning stock solution with the viscosity of 1950Pa & s; the concentration of the spinning dope is 30 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein the temperature of the charging bucket for dry spinning is 95 ℃, the temperature of the charging bucket for dry spinning is 180 ℃ by adopting single-section hot air heating in a channel for dry spinning, the drawing ratio of a spinning nozzle during dry spinning is 1.0, and the spinning speed is 150 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 1 mu m; the residual carbon rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 25 percent.

Example 5

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (a mixture of thermoplastic phenolic resin (molecular weight range of 1000-2500, brand of PF-5400) and thermosetting phenolic resin (molecular weight range of 1500-3000, brand of PF2605) in a mass ratio of 7: 3) and modified polyvinyl alcohol (polyvinyl butyral (PVB)) into a mixed solvent of ethanol and ethyl acetate in a mass ratio of 1:1, and stirring at 50 ℃ until the mixture is completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blended solution; wherein in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the mixed solvent is 5: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 5: 5;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 6 hours, and then performing vacuum defoaming to obtain a spinning solution with the viscosity of 1100Pa & s; the concentration of the spinning dope is 50 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein, the temperature of the charging bucket of the dry spinning is 75 ℃, the upper section and the lower section of the shaft of the dry spinning are heated, the temperature of the upper section is 45 ℃, the temperature of the lower section is 100 ℃, the drawing ratio of a spinning nozzle during the dry spinning is 1, and the spinning speed is 120 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 2 mu m; the residual carbon rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 37%.

Example 6

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (a mixture of thermoplastic phenolic resin (molecular weight range of 1000-2500, brand of PF-5400) and thermosetting phenolic resin (molecular weight range of 1500-3000, brand of PF2605) in a mass ratio of 7: 3) and modified polyvinyl alcohol (polyvinyl butyral (PVB)) into methanol, and stirring at 40 ℃ until the mixture is completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution; wherein in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the methanol is 5: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 7: 3;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 7 hours, and then performing vacuum defoaming to obtain a spinning solution with the viscosity of 800Pa & s; the concentration of the spinning dope was 41.7 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein, the temperature of the charging bucket of the dry spinning is 60 ℃, the upper section and the lower section of the shaft of the dry spinning are heated, the temperature of the upper section is 40 ℃, the temperature of the lower section is 90 ℃, the drawing ratio of a spinning nozzle during the dry spinning is 1.4, and the spinning speed is 140 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 1 mu m; the residual carbon rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 35%.

Example 7

A preparation method of a phenolic resin/modified polyvinyl alcohol composite fiber adhesive comprises the following specific steps:

(1) adding phenolic resin (a mixture of thermoplastic phenolic resin (molecular weight distribution of 1000-2500, and the brand is PF-5400) and thermosetting phenolic resin (molecular weight distribution of 1500-3000, and the brand is PF2605) in a mass ratio of 5: 5) and modified polyvinyl alcohol (polyvinyl butyral (PVB)) into n-butyl alcohol, and stirring at 50 ℃ until the mixture is completely dissolved to obtain a phenolic resin/modified polyvinyl alcohol blending solution; in the phenolic resin/modified polyvinyl alcohol blending solution, the mass ratio of the modified polyvinyl alcohol to the n-butyl alcohol is 5: 10; the mass ratio of the modified polyvinyl alcohol to the phenolic resin is 5: 5;

(2) standing the phenolic resin/modified polyvinyl alcohol blended solution at room temperature for 6h, and then performing vacuum defoaming to obtain a spinning stock solution with the viscosity of 1350Pa & s; the concentration of the spinning dope is 50 wt%;

(3) carrying out dry spinning on the spinning stock solution to obtain nascent fiber, and stretching the nascent fiber to obtain phenolic resin/modified polyvinyl alcohol composite fiber adhesive; wherein the temperature of the charging bucket for dry spinning is 75 ℃, the temperature of the charging bucket for dry spinning is 138 ℃, the stretch ratio of a spinning nozzle during dry spinning is 1.8, and the spinning speed is 180 m/min.

In the prepared phenolic resin/modified polyvinyl alcohol composite fiber adhesive, the phenolic resin is uniformly dispersed in the modified polyvinyl alcohol in an island form, and the maximum size of a dispersed phase is less than 2 mu m; the residual carbon rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is 45%.

Example 8

The phenolic resin/modified polyvinyl alcohol composite fiber binder prepared in example 7 was applied to a gas diffusion layer for a fuel cell, i.e., carbon paper;

the specific process is as follows: adding 3-10 mm long chopped carbon fibers and 3-10 mm composite fiber binder into 0.2% PEO solution for shearing and dispersing to obtain high-dispersion fiber suspension, papermaking the suspension by using a rectangular papermaking machine (PL6-A3, Xianyang Tester laboratory instruments Co., Ltd.) to obtain base paper, and drying the base paper in a flat-plate paper sample dryer at 50 ℃. Wherein the dosage of the chopped carbon fiber is 0.5 wt% of the dosage of water, and the addition amount of the composite fiber adhesive before carbonization accounts for 20 wt% of the base paper. Drying the prepared base paper, and then carrying out hot pressing solidification at 180 ℃ and 10MPa to obtain a prefabricated body; the preform was then carbonized and graphitized in 2200 ℃ inert gas to obtain carbon paper.

The tensile strength of the obtained carbon paper is 50N/cm, and the in-plane resistivity of the carbon paper is 5.6m omega/cm². The carbon paper is used for building a single cell, the ventilation pressure of fuel and oxidant is 150KPa, the test temperature is 60 ℃, the humidity is 95 percent, and the power density of the cell is more than 1W/cm when the voltage is 0.6V²。

Comparative example 1

A carbon paper, which is a gas diffusion layer for a fuel cell, was prepared in substantially the same manner as in example 8, except that a phenol resin/modified polyvinyl alcohol composite fiber binder was replaced with PVA fibers to prepare a carbon paper.

The tensile strength of the prepared carbon paper is 10-20N/cm, and the in-plane resistivity of the carbon paper is 11m omega/cm²。

As can be seen by comparing example 8 with comparative example 1, the tensile strength in example 8 is significantly better than that in comparative example 1 because: the residual carbon rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is far higher than that of PVA fibers, when a prefabricated body is carbonized and graphitized, the adhesive fibers shrink thermally and remove a large amount of non-carbon elements, and finally the carbon fibers can be bonded together only by the residual carbon of the adhesive, so that the composite fiber adhesive with high residual carbon rate can provide enough residual carbon to bond the carbon fibers tightly, and the stress can be continuously transmitted among the carbon fibers, so that the composite fiber adhesive has excellent tensile strength.

As can be seen by comparing example 8 with comparative example 1, the in-plane resistivity is significantly lower in example 8 than in comparative example 1 because: the carbon residue rate of the phenolic resin/modified polyvinyl alcohol composite fiber adhesive is far higher than that of PVA fiber, when a prefabricated body is carbonized and graphitized, the prefabricated body is uniformly distributed among thermosetting phenolic resin in the adhesive fiber, thermosetting phenolic resin and modified polyvinyl alcohol, and thermoplastic phenolic resin and thermosetting phenolic resin to generate cross-linking reaction, so that a cross-linked network structure is formed, the carbon residue rate and the graphitization degree of carbon residue are greatly improved, and meanwhile, the adhesive fiber generates thermal shrinkage and chemical shrinkage (shrinkage generated by cross-linking reaction) in the carbonization and graphitization processes, so that the point-to-point (cross point) effective bonding between short carbon fibers is realized through the carbon residue. Because the chopped carbon fibers have the characteristics of high strength and high conductivity, the conductivity and the strength of the carbon paper compounded by the carbon fibers and the resin residual carbon mainly depend on the amount of the residual carbon among the connected carbon fibers, the graphitization degree of the residual carbon and the bonding effectiveness, so that the phenolic resin/modified polyvinyl alcohol composite fiber adhesive improves the resin residual carbon rate, the graphitization degree of the residual carbon and the effective bonding among fibers on one hand, and further improves the conductivity (reduces the in-plane resistivity) and the strength of the carbon paper; on the other hand, due to the fact that point-to-point effective bonding between the chopped carbon fibers is achieved, when the conductivity and the strength of the carbon paper are improved, the porosity, the gas permeability and the like of the carbon paper are not obviously reduced, and therefore the assembled single cells under the same conditions have higher power density. However, the PVA with a low carbon residue ratio cannot provide enough carbon residue to tightly bond the carbon fibers or even form a bonding structure between the carbon fibers, so that the carbon paper has fewer conductive loops, and thus has higher resistivity and low strength.