CN114874470B

CN114874470B - Modified carbon fiber/phenolic resin composite material and preparation method thereof

Info

Publication number: CN114874470B
Application number: CN202210322184.8A
Authority: CN
Inventors: 苏志强; 赵鑫; 张晓媛; 王敏; 全皓月
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2023-06-13
Anticipated expiration: 2042-03-30
Also published as: CN114874470A

Abstract

The invention relates to a modified carbon fiber/phenolic resin composite material, which is obtained by hot-pressing and compounding after phenolic resin is coated on the surface of surface modified carbon fiber, and is characterized in that the surface modified carbon fiber is obtained by sequentially carrying out high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition on carbon nanotubes. According to the invention, various methods are used for modifying the surface of the carbon fiber, the multi-scale surface morphology is designed, the contact area of the carbon fiber and the resin substrate is enhanced, the interfacial binding force between the binding surfaces is effectively improved, and the comprehensive performance of the carbon fiber/phenolic resin composite material is finally improved.

Description

Modified carbon fiber/phenolic resin composite material and preparation method thereof

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a modified carbon fiber/phenolic resin composite material and a preparation method thereof.

Background

The carbon fiber has a series of excellent performances such as high specific strength, high specific modulus, high temperature resistance, fatigue resistance, corrosion resistance, good heat transfer performance and the like, can be used as a structural material for bearing load and can also be used as a functional material, the carbon fiber composite material is very widely applied in daily life by virtue of the excellent specific strength and specific elasticity characteristics, the product relates to the fields of transportation, construction engineering and the like, and the carbon fiber/phenolic resin composite material is widely applied to the fields of aerospace, transportation and the like due to the advantages of low cost, high temperature resistance, high specific strength specific modulus, corrosion resistance and the like. However, the carbon fiber has inert surface chemical activity, lacks functional groups with chemical activity, and has poor adhesion with a composite matrix, so that the performance of the carbon fiber composite material is limited. The interfacial bonding force of the carbon fiber and the phenolic resin matrix member determines the key to the overall performance of the composite material, while the option of developing a completely new fiber material requires a significant amount of capital and time. Therefore, the research at home and abroad mainly carries out surface modification on the carbon fiber, the surface activity of the carbon fiber is improved by a surface modification technology, the interface performance between the carbon fiber and a phenolic resin matrix material is enhanced, and the bonding effect between the carbon fiber and the matrix is improved, so that the value of the fiber material in industrial application is improved. The surface modification mode of the carbon fiber mainly comprises surface self-assembly, chemical vapor deposition, physical coating and the like.

The prior art has many studies on methods of modifying carbon fiber/phenolic resins.

CN110938281a discloses a modified carbon fiber reinforced phenolic resin matrix composite material, which is prepared by coating an organic-inorganic hybrid zirconium silicate sol coating on carbon fiber cloth, so that uniform and compact coating on the carbon fiber cloth is realized, and the modified carbon fiber reinforced phenolic resin matrix composite material is well combined with phenolic resin. However, in industry, the preparation of the inorganic-inorganic hybrid zirconium silicate sol coating is not economical per se, the labor and the time are complex, strict control of process conditions is needed, otherwise, a uniformly covered coating cannot be obtained, and the existence of weak points of the composite material is easy to cause.

CN109897337a discloses a carbon fiber reinforced phenolic resin composite material and a preparation method thereof, wherein graphene dispersion liquid and a phenolic resin matrix are mixed and then are mixed with carbon fibers to obtain a casting material, and casting, curing and curing are carried out to obtain the carbon fiber reinforced phenolic resin composite material. But the resulting composite material lacks gloss on the surface; and the graphene dispersion liquid can lead to the introduction of more micromolecular solvents into the resin matrix, so that the mechanical property of the composite material is reduced.

CN105754056a discloses a carbon fiber modified phenolic resin, which is prepared by soaking carbon fiber in acetone, washing and drying; soaking with a liquid oxidant, washing, and drying to obtain oxidized carbon fibers; finally, soaking the oxidized carbon fiber with a coupling agent solution, and drying to obtain a modified carbon fiber; adding phenol, aldehyde and an acid catalyst into a reaction kettle, reacting for 1-5 hours at 90-120 ℃, adding the modified carbon fiber, continuously reacting for 1-6 hours at 90-150 ℃, and dehydrating to obtain the carbon fiber modified phenolic resin. However, the composite material obtained by the method is only modified by functional groups at a molecular level, and the performance improvement of the composite material is limited.

CN114032669a discloses a method for synchronously modifying the surface interface of carbon fiber by electrophoretic deposition-electropolymerization, which is obtained by taking carbon fiber as an anode and performing electrophoretic deposition and electropolymerization. The modification mode is single, and the effect is general.

CN113046864a discloses a lignin carbon fiber modified by phenolic resin and a preparation method thereof, which adopts lignin carbon fiber. However, the cost of lignin carbon fiber is far higher than that of carbon fiber from polyacrylonitrile. The patented process is not economical.

Disclosure of Invention

In order to overcome the interfacial binding force of the carbon fiber/phenolic resin composite material in the prior art and further enhance the comprehensive performance of the composite material, the invention provides a carbon fiber surface activity technology which improves the binding compactness between the carbon fiber surface activity technology and the reinforced material and improves the comprehensive performance of the composite material.

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

a modified carbon fiber/phenolic resin composite material is obtained by hot-pressing and compounding after phenolic resin is coated on the surface of surface modified carbon fiber, wherein the surface modified carbon fiber is obtained by sequentially carrying out high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition on carbon nanotubes.

Further, the Raman spectrum of the surface modified carbon fiber has 1400-1500 cm ^-1 D band at the position and 1900-2000 cm ^-1 G band at the position, and the intensity ratio R of G/D is more than 2.

Further, the infrared spectrum of the surface modified carbon fiber is 1735+/-50 cm ^-1 ，1261±50cm ^-1 And 1091.+ -.50 cm ^-1 There is a characteristic peak.

The modified carbon fiber/phenolic resin composite material is prepared by a preparation method comprising the following steps:

(1) Carrying out high-temperature treatment on the carbon fiber cloth;

(2) Putting the carbon fiber treated at the high temperature in the step (1) into an electrolytic reaction tank as an electrolytic anode material, wherein the electrolyte is a dilute inorganic acid solution;

(3) Washing, suction filtering and drying the carbon fiber subjected to the electrochemical treatment in the step (2) for standby;

(4) Soaking the carbon fiber obtained in the step (3) in a polyisocyanate solution, and drying;

(5) Placing the carbon fiber obtained in the step (4) as an anode material into an electrodeposition reaction tank for electrochemical deposition, wherein the electrolyte is a carbon nano tube dispersion liquid;

(6) Washing, suction filtering and drying the electrochemically deposited carbon fiber obtained in the step (5) to obtain a surface modified carbon fiber;

(7) Adding p-phenylphenol, ammonia water, phenol and formaldehyde into a reaction container, and reacting to obtain liquid phenolic resin;

(8) Uniformly coating the surface of the carbon fiber subjected to surface modification obtained in the step (6) with the liquid phenolic resin obtained in the step (7) to obtain the carbon fiber with the surface coated, putting the carbon fiber into a mold, and carrying out hot pressing to obtain the modified carbon fiber/phenolic resin composite material.

Preferably, the surface of the carbon fiber subjected to surface modification in the step (8) is uniformly coated with liquid phenolic resin, so as to obtain a plurality of layers of carbon fiber coated with phenolic resin, and then the carbon fiber is put into a mould for hot pressing.

Further, the raw material carbon fiber used in the step (1) is not particularly limited, and is a conventional carbon fiber material in the art, and in one embodiment of the present invention, the carbon fiber is a PAN-based T300 carbon fiber cloth.

Preferably, the high temperature in the step (1) is 400-500 ℃, and the high temperature treatment time is 2-3 hours.

Preferably, in the step (2), the electrolysis voltage is 4-5V, and the electrochemical treatment time is 15-20min; the electrolyte solution is 30-50% dilute sulfuric acid solution.

Washing, suction filtration and drying in the step (3) and the step (7) are well known in the art, for example, washing is performed by using at least one of ultrapure water, deionized water and distilled water, suction filtration is performed for 30-50 times, and suction filtration is performed under the vacuum degree of-0.1 to-0.5 Mpa; the drying is oven drying at 60-80deg.C for 3-6 hr.

Further, the polyisocyanate in the step (4) is at least one selected from the group consisting of diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and triphenylmethane triisocyanate. Preferably triphenylmethane triisocyanate. Preferably, the concentration of the polyisocyanate solution is 10-20wt%, and the carbon fiber is immersed in the polyisocyanate agent for 30-60min.

Preferably, in the step (5), the carbon nanotube dispersion liquid is prepared by adding carbon nanotubes into an alcohol aqueous solution, mechanically stirring and then performing ultrasonic dispersion. The carbon nanotubes are multi-walled carbon nanotubes with an outer diameter of 5-50nm, preferably 10-20nm, and the concentration of the carbon nanotube dispersion is 5-10wt%. The rotation speed of the mechanical stirring is 400-1000rpm, and the ultrasonic dispersion condition is that the ultrasonic frequency is set to be 70-100KHZ, and the ultrasonic duration is 1-3h.

Preferably, in the electrochemical deposition in the step (5), the electrolytic voltage is 5-6V, and the electrodeposition time period is 10-12min.

Preferably, in the step (7), the mass ratio of phenol to formaldehyde is 1.33-1.67:1, most preferably 1.5:1. Para-phenylphenol is 15-30%, preferably 20-25% of formaldehyde by mass; the mass of ammonia is 15-30% of the mass of formaldehyde, preferably 20-25% of the mass of formaldehyde, the reaction is carried out in the presence of a basic catalyst, such as barium hydroxide, sodium hydroxide, ammonia, the catalyst being used in an amount of 0.1-1% of the total mass of p-phenylphenol, ammonia, phenol and formaldehyde. Firstly adding p-phenylphenol, ammonia water, phenol and 40-60% formaldehyde, heating to 90-98 ℃, preserving heat for 1-2h, adding an alkaline catalyst, preserving heat, slowly dripping residual formaldehyde, adjusting pH to be neutral after the mixed solution becomes turbid, and carrying out vacuum dehydration until the mixed solution is clear and stops dehydration, thus obtaining the liquid phenolic resin.

Preferably, in step (8), the mass ratio of the surface modified carbon fiber to the phenolic resin=1-2:1-2, preferably 1-1.5:1. And (3) repeating the coating process of the step (8) to obtain a plurality of layers of carbon fibers coated with phenolic resin, wherein the number of the plurality of layers is determined according to actual needs, and the number of the layers can be 3-10, such as 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers and 10 layers. The hot pressing is to put the obtained multi-layer carbon fiber aligned stack into a mould, cover a layer of mould pressing paper on the upper and lower surfaces respectively, and then put the mould into a plate vulcanizing instrument. Setting hot-pressing temperature and hot-pressing time. After the hot pressing is finished, successfully preparing the carbon fiber/phenolic resin composite material with excellent performance. The hot pressing process is well known in the art, and in one embodiment of the invention, a temperature gradient is set in a plate vulcanizing machine, the plate vulcanizing machine is hot pressed for 1 to 1.5 hours at a temperature of between 90 and 110 ℃, then the plate vulcanizing machine is hot pressed for 0.5 to 1 hour at a temperature of between 130 and 150 ℃, and finally the plate vulcanizing machine is hot pressed for 0.5 to 1 hour at a temperature of between 160 and 170 ℃.

FIG. 1 is a schematic illustration of the preparation flow of the surface modified carbon fiber/phenolic resin composite of the present invention. As can be seen from the schematic diagram, the surface modification technology of the carbon fiber mainly comprises the treatment methods of high-temperature treatment, electrochemical oxidation, surface grafting modification, electrochemical deposition and the like.

FIG. 2 is a schematic diagram of interfacial reinforcement mechanism of a surface modified carbon fiber/phenolic resin composite. The main reasons for improving the interfacial properties of the composite material by the surface modified carbon fiber are as follows: firstly, the sizing agent is removed by high-temperature treatment, so that the surface of the carbon fiber can be directly contacted with phenolic resin, and the interaction force between molecules is favorable for the contact between the carbon fiber and the phenolic resin; secondly, oxygen-containing functional groups such as C=O, C-O-C and the like are generated on the surface of the carbon fiber after electrochemical treatment and can form hydrogen bonds with resin molecules, so that the molecular level contact of the carbon fiber and phenolic resin at an interface is improved; thirdly, the polyisocyanate is grafted and modified to enable the surface of the carbon fiber to be grafted with more active groups, so that more covalent chemical reaction sites are generated between the carbon fiber and the phenolic resin; fourth, the carbon nanotube effectively improves the specific surface area, roughness and wettability of the carbon fiber, so that a strong mechanical meshing effect is generated between the fiber and the resin, thereby being beneficial to enhancing the interfacial bonding strength and mechanical properties of the composite material.

FIG. 3 is a schematic view of the surface modification technique of the present inventionIn-process carbon fiber electrochemical oxidation treatment device and carbon fiber electrodeposition treatment device diagram. In the electrochemical oxidation device diagram of the carbon fiber, the carbon fiber treated at high temperature is taken as an anode, a platinum electrode is taken as a cathode, and H in a dilute sulfuric acid electrolyte solution is used in the electrochemical oxidation process ⁺ Moving from anode to cathode, H being generated at cathode ₂ Simultaneous production of O at the anode ₂ Generated O ₂ Oxidation reaction with the anode carbon fiber occurs, so that more oxygen-containing functional groups are generated on the surface of the carbon fiber. In the figure of the carbon fiber electrodeposition device, carbon fibers subjected to electrochemical oxidation treatment are taken as anodes, and platinum electrodes are taken as cathodes; in the electrochemical deposition process, the carbon nano tube with electronegativity in the carbon nano tube dispersion liquid moves to the carbon fiber end; finally, the carbon nano tube is deposited on the surface of the carbon fiber under the drive of current.

The invention has the excellent effects that: 1. the carbon fiber surface is modified by adopting a plurality of methods such as high-temperature treatment, electrochemical oxidation, polyisocyanate grafting modification and electrochemical deposition. The high-temperature treatment aims at removing sizing agent on the surface of the carbon fiber, and the high temperature is beneficial to increasing carbon-oxygen bonds on the surface of the carbon fiber; electrochemical oxidation aims at introducing more active functional groups, such as-OH, -COOH, -c=o, -C-O-C, etc., on the surface of the carbon fiber; the purpose of the polyisocyanate grafting modification is to enable the surface of the carbon fiber to be grafted with more active groups, so that more covalent chemical reaction sites are generated between the carbon fiber and the phenolic resin; the electrochemical deposition aims at increasing the surface roughness of the fiber, increasing the contact area between the fiber and the resin, strengthening the mechanical engagement effect of the interface between the fiber and the resin, and improving the performance of the carbon fiber composite material by the synergistic effect of the carbon nano tube and the carbon fiber. According to the invention, through various means, various methods of changing the molecular structure, the functional group structure and the nanomaterial distribution of the surface of the carbon fiber, the multi-scale surface morphology is designed, the contact area of the carbon fiber and the resin substrate is enhanced, the interfacial binding force between the binding surfaces is effectively improved, and finally the comprehensive performance of the carbon fiber/phenolic resin composite material is improved.

2. The preparation process of the RTM liquid phenolic resin is improved, so that the formula proportion of the phenolic resin which is combined with the modified carbon fiber interface optimally is prepared, the interface binding force of the composite material is effectively enhanced, and the tensile strength and the impact resistance of the composite material are improved.

Drawings

FIG. 1 is a schematic illustration of a process for preparing a surface modified carbon fiber/phenolic resin composite;

FIG. 2 is a schematic diagram of interfacial reinforcement mechanism of a surface modified carbon fiber/phenolic resin composite;

FIG. 3 is a diagram of a carbon fiber electrochemical oxidation treatment device and a carbon fiber electrodeposition treatment device in the process of surface modification technology;

FIG. 4 is a Scanning Electron Microscope (SEM) image of carbon fibers after different temperature treatments during high temperature treatments at different temperatures;

FIG. 5 is a graph of the morphology of the shear surface of the composite material obtained under different electrochemical oxidation, electrochemical deposition and different raw material ratios;

FIG. 6 is a graph of the surface topography of the carbon fiber at various stages in example 1;

FIG. 7 is a Raman spectrum and an infrared spectrum of a carbon fiber at different stages of surface modification;

FIG. 8 is a graph of C after surface treatment of carbon fiber _1s XPS spectrogram after peak-splitting fitting;

fig. 9 is a diagram of the surface-modified carbon fiber/phenolic resin composite material prepared.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. The following examples facilitate a better understanding of the present invention, but are not intended to limit the same. The experimental methods in the following examples are conventional methods unless otherwise specified.

Example 1

The carbon fiber surface modification technology is characterized by comprising the following operation steps:

(1) Sizing agent for removing surface of carbon fiber at high temperature: placing 10 x 10 cm-sized T300 carbon fiber cloth into a muffle furnace for high-temperature treatment, wherein the treatment temperature is set to 400 ℃ and the working time is 120min;

(2) Electrochemical oxidation: placing the carbon fiber treated at the high temperature in the step (1) into an electrolytic reaction tank as an electrolytic anode material, wherein the electrolyte is dilute sulfuric acid solution with the volume fraction of 40%, the cathode material is platinum electrode, the electrolytic voltage is 5V, and the electrochemical treatment time is 20min;

(3) Washing: washing and suction-filtering the carbon fiber subjected to the electrochemical treatment in the step (2) by using a washing liquid at room temperature, wherein the washing liquid is 2kg of ultrapure water, the suction-filtering times are 50 times, and the suction vacuum degree is-0.1 Mpa; the drying temperature was set at 60℃and the drying time was set at 180min.

(4) Grafting TTI: and (3) immersing the carbon fiber obtained in the step (3) in a 20% Triphenylmethane Triisocyanate (TTI) chlorobenzene solution for 60min, and then drying.

(5) Adding the carbon nano tube into 70% ethanol water solution, magnetically stirring, then ultrasonically dispersing in an ultrasonic cleaner, and magnetically stirring at 800rpm for 1h; setting the ultrasonic frequency to 70KHZ, and preparing 8% carbon nano tube dispersion liquid after ultrasonic treatment for 1h; placing the carbon fiber obtained in the step (4) as an anode material into an electrodeposition reaction tank for electrochemical deposition, wherein electrolyte is the carbon nanotube dispersion liquid, a platinum electrode is selected as a cathode material, the electrolysis voltage is 6V, and the electrodeposition time is 10min;

(6) And (3) washing and suction filtering the carbon fiber subjected to the electrochemical deposition in the step (5) by using a washing liquid at room temperature. The washing liquid is 2kg of ultrapure water, the times of suction filtration are 50 times, and the suction vacuum degree is-0.1 Mpa; drying in a blast drying oven after washing, wherein the drying temperature is set to 60 ℃, and the drying time is set to 180 minutes, so as to finally obtain the surface modified carbon fiber;

(7) Adding 400g of p-phenylphenol, 32g of ammonia water, 2000g of phenol and 564g of formaldehyde into a flask, slowly heating to 96-98 ℃, preserving heat for 2h, and adding 8g of Ba (OH) ₂ The method comprises the steps of carrying out a first treatment on the surface of the 769g formaldehyde (mass ratio of phenol to formaldehyde 1.5:1) was slowly added dropwise over 1h while maintaining the temperature at 96 ℃. Keeping the temperature after the dripping is finished, adding H after the mixed solution becomes turbid ₃ PO ₄ The pH was adjusted to neutral. At this time, vacuum dehydration is started until the mixture is dissolvedStopping dehydration after the liquid becomes clear, and heating to 90 ℃ to prepare the liquid phenolic resin;

(8) Uniformly coating the surface of the surface modified carbon fiber obtained in the step (6) with the RTM phenolic resin prepared in the step (7), wherein the surface modified carbon fiber: RTM phenolic resin mass ratio = 1.5:1, repeating the steps to prepare 5 layers of carbon fibers coated with phenolic resin. And (3) stacking 5 layers of carbon fibers in an aligned manner, placing the stacked 5 layers of carbon fibers in a mold, covering a layer of molding paper on the upper surface and the lower surface of each layer of molding paper, and placing the mold in a plate vulcanizing machine. Setting a temperature gradient in a plate vulcanizing instrument, hot-pressing for 1.5h at 90 ℃, then heating to 130 ℃ for 1h, and finally heating to 170 ℃ for 1h. And after the hot pressing is finished, preparing the modified carbon fiber/phenolic resin composite material.

FIG. 6 is a graph of the surface topography of the carbon fiber at various stages in example 1. FIG. 6 (a) is a surface topography of a carbon fibril treated at 300℃for 120min; FIG. 6 (b) is a graph showing the surface morphology of the carbon fiber after electrochemical oxidation treatment of the carbon fiber treated at a high temperature under the conditions of 5V and 20min; FIG. 6 (c) is a surface topography of the carbon fiber grafted TTI after electrochemical oxidation treatment; fig. 6 (d) is a graph of the surface morphology of the carbon fiber after electrochemical deposition treatment of the carbon fiber grafted with TTI under the condition of 6v,10 min.

In the preferred embodiment 1 of the invention, in the electrochemical oxidation and the electrochemical deposition, proper electrochemical working voltage and working time are selected, the higher the electrochemical oxidation working voltage is, the longer the working time is, the lower the tensile strength of the carbon fiber monofilaments is, and the main reasons are that the surface structure of the carbon fiber changes in the electrochemical oxidation process, the overlong treatment time or the overhigh working voltage can cause the surface of the carbon fiber to generate structural defects, the rough surface morphology is and the carbon fiber structure is damaged. The working voltage in electrochemical deposition is larger than that in electrochemical oxidation, and the deposition of the carbon nano tube on the surface of the carbon fiber in the electrochemical deposition process fills some grooves and micro defects on the surface of the carbon fiber, so that the tensile strength of monofilaments of the carbon fiber is improved.

Example 2

The other conditions were the same as in example 1 except that in step (1), the temperature at the time of high-temperature treatment was 300 ℃.

Example 3

The other conditions were the same as in example 1 except that in step (1), the temperature at the time of high-temperature treatment was 500 ℃.

Example 4

The other conditions were the same as in example 1 except that in step (1), the temperature at the time of high-temperature treatment was 600 ℃.

FIG. 4 is a Scanning Electron Microscope (SEM) image of carbon fiber subjected to high temperature treatment at different temperatures, and FIG. 4 (a) is a carbon fiber morphology image;

FIG. 4 (b) is a surface morphology graph of the carbon fiber of example 2 treated at 300℃for 120min, in which it can be observed that some resin sizing agent is attached to the surface of the raw carbon fiber, which greatly reduces the interfacial binding force between the carbon fiber and the resin, so that the overall performance of the composite material is reduced; FIG. 4 (c) is a surface topography of the carbon fiber of example 1 treated at 400℃for 120min; FIG. 4 (d) is a surface topography of the carbon fiber treated at 600℃for 120 min. It can be seen that at 300 ℃, the carbon fiber still has part of sizing agents adhered to the surface of the carbon fiber due to lower treatment temperature and shorter treatment time, and the presence of the sizing agents seriously influences the modification effect of the post-treatment process on the surface of the carbon fiber and the performance of the composite material; and the high temperature treatment at 600 ℃ can damage the carbon fiber structure and generate partial defects on the surface. Therefore, the high temperature treatment temperature of the invention is in the range of 400-500 ℃.

Example 5

Other conditions were the same as in example 1 except that in step (2), the electrolysis voltage was 3V and the electrochemical treatment period was 20 minutes.

Example 6

Other conditions were the same as in example 1 except that in step (2), the electrochemical treatment period was 10 minutes.

Example 7

The other conditions were the same as in example 1 except that in step (2), the electrolysis voltage was 7V and the electrochemical treatment period was 20 minutes.

Example 8

The other conditions were the same as in example 1 except that in step (5), the electrolysis voltage was 4V and the electrolysis time was 10min.

Example 9

The other conditions were the same as in example 1 except that in step (5), the electrolysis voltage was 8V and the electrolysis time was 10min.

Example 10

The other conditions were the same as in example 1 except that in step (5), the concentration of carbon nanotubes was 5%.

Example 11

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.33:1.

Example 12

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.67:1.

Example 13

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.8:1.

Example 14

The other conditions were the same as in example 1 except that in step (7), the amount of phenol was changed so that the mass ratio of phenol to formaldehyde was 1.2:1.

FIG. 5 is a graph of the surface morphology of the carbon fiber after electrochemical oxidation and electrochemical deposition treatment in the surface modification process and a graph of the shear surface morphology of the composite material. FIG. 5 (a) is a graph showing the surface morphology of the carbon fiber after electrochemical oxidation treatment of the carbon fiber treated at a high temperature in example 5 under the conditions of 3V and 20min, wherein the carbon fiber surface treated at a low pressure cannot load more oxygen-containing functional groups, and the modification effect is not obvious; FIG. 5 (b) is a graph showing the surface morphology of the carbon fiber after electrochemical oxidation treatment of the carbon fiber treated at a high temperature of 5V for 20min in example 1; FIG. 5 (c) is a graph showing the surface morphology of the carbon fiber after electrochemical oxidation treatment of the carbon fiber at 7V for 20min in example 7, wherein the surface of the carbon fiber after high-pressure treatment has obvious structural defects, and the carbon fiber structure is destroyed, the surface is rough and uneven, and the modification effect is poor; FIG. 5 (d) is a graph showing the surface morphology of the carbon fiber after electrochemical deposition treatment of the electrochemical oxidized carbon fiber in example 8 under the conditions of 4V and 10min, wherein the fiber surface is only loaded with less carbon nanotubes, and the effect of less carbon nanotube deposition on the surface modification of the carbon fiber is not obvious; FIG. 5 (e) is a graph showing the surface morphology of the carbon fiber after electrochemical deposition treatment of the carbon fiber in example 1 under the conditions of 6V and 10min, wherein more carbon nanotubes are deposited on the surface of the carbon fiber, the carbon nanotubes with the optimal proportion are deposited to greatly increase the surface roughness of the carbon fiber, increase the contact area between the fiber and the resin, and strengthen the mechanical engagement effect of the interface between the fiber and the resin; FIG. 5 (f) is a graph showing the surface morphology of the carbon fiber after electrochemical deposition treatment of the electrochemical oxidized carbon fiber in example 9 under the conditions of 8V and 10min, wherein carbon nanotubes are stacked on the surface of the carbon fiber, and the carbon nanotubes are completely covered on the surface of the carbon fiber, so that the contact area between the carbon fiber and the resin is reduced, and the composite effect is poor; FIG. 5 (g) is a graph of surface modified carbon fiber and phenol in example 13: formaldehyde=1.8: the shearing surface morphology graph of the phenolic resin composite material with the mass ratio is 1, and a certain crack is observed between the resin and the carbon fiber interface from the graph, because the resin system viscosity is lower due to the fact that the mass of phenol is relatively large, part of the resin is uncured in the later heat curing process, and the bonding force between the resin and the carbon fiber is poor, so that the crack is generated; fig. 5 (h) shows the surface modified carbon fiber and phenol in example 1: formaldehyde=1.5: the appearance diagram of the shearing surface of the phenolic resin composite material with the mass ratio shows that the carbon fiber is tightly attached to the phenolic resin, no pore exists between the carbon fiber and the phenolic resin, and the mass ratio of the carbon fiber to the phenolic resin helps to improve the mechanical meshing degree between the resin and the carbon fiber; fig. 5 (i) is a view of surface-modified carbon fiber and phenol in example 14: formaldehyde=1.2: the shearing surface morphology graph of the phenolic resin composite material with the mass ratio is provided with a plurality of holes in the resin region, and the holes seriously affect the mechanical property of the composite material because bubbles generated in the curing process can not be removed in time due to the large viscosity of the resin in the early stage.

It can be seen that the composite material obtained by proper electrochemical oxidation, electrochemical deposition working voltage and working time and proper phenolic proportion is optimal in morphology, so that the composite material also has more excellent properties.

Application example

The modified carbon fiber/phenolic resin material obtained in the above example was subjected to the following performance test, and the results are shown in table 1 below:

surface O/C content: calculated according to the data value obtained after the C1s peak-splitting fitting in the XPS result.

Tensile Strength of monofilament: the test is carried out on a CMT7504 type electronic universal tester according to GB/T31290-2014 standard carbon fiber multifilament tensile property test method.

Interfacial shear Strength: according to the microdroplet visbreaking method, an FA620 type composite interface evaluation device is adopted to characterize the influence of the carbon fiber before and after modification on the interface shear strength of the composite.

TABLE 1

The carbon fiber O/C content and monofilament tensile strength at various stages of example 1, and the interfacial shear strength of the composite of carbon fiber and phenolic resin at various stages were also tested and the results are shown in Table 2 below:

TABLE 2

Wherein CF-0 is untreated carbon fibrils; CF-1 is carbon fiber after CF-0 is processed at high temperature; CF-2 is carbon fiber after CF-1 is subjected to electrochemical oxidation treatment; CF-3 is carbon fiber of CF-2 after TTI grafting treatment; CF-4 is carbon fiber after CF-3 is processed by electrochemical deposition. The monofilament tensile strength is the strength of the carbon fiber itself. The surface of the original carbon fiber is provided with a sizing agent, the tensile strength is strong, CF-2 is subjected to acid oxidation treatment, the surface is oxidized, the structure is changed, and the tensile strength is lower than that of the original carbon fiber. After the subsequent steps, the monofilament tensile strength is restored to the original level.

FIG. 7 is a Raman spectrum and an infrared spectrum of the carbon fiber of example 1 at each stage in the surface modification process; CF-0 is untreated carbon fibrils; CF-1 is carbon fiber after CF-0 is processed at high temperature; CF-2 is carbon fiber after CF-1 is subjected to electrochemical oxidation treatment; CF-3 is carbon fiber of CF-2 after TTI grafting treatment; CF-4 is carbon fiber after CF-3 is processed by electrochemical deposition. Wherein the Raman spectrum comprises 1400-1500 cm ^-1 D band at the position and 1900-2000 cm ^-1 G band at. The relative intensity of the D band reflects the degree of turbulence of the carbon and the relative intensity of the G band reflects the integrity of the sp2 bond structure in the carbon structure. The graphitization degree of the carbon fiber is generally evaluated by the strength ratio R of the D band to the G band, and a larger R indicates a larger number of defects and a higher degree of disorder of the carbon fiber. By calculation, the R values of the carbon fibrils, the high-temperature treated carbon fibers, the electrochemical oxidized carbon fibers, the TTI grafted carbon fibers and the electrochemical deposited carbon fibers are respectively 1.975, 1.944, 1.992, 1.987 and 2.026. The surface disorder degree of the carbon fiber is reduced after the carbon fiber is treated at high temperature, and the ordering degree is increased, which indicates that the sizing agent on the surface of the carbon fiber can be effectively removed at high temperature. The carbon fiber grafted with the TTI makes up the defect generated by oxidation of the surface of the fiber after electrochemical oxidation treatment, and the R value is reduced from 1.992 to 1.987. The disorder degree of the carbon fiber surface of the deposited carbon nano tube is increased, the number of unsaturated carbon atoms is increased, and the graphitization degree is reduced, so that the improvement of the interface performance of the composite material is effectively promoted. As can be seen from the infrared spectrogram, the carbon fibers subjected to electrochemical oxidation treatment, grafting TTI and electrochemical deposition are 1735, 1261 and 1091cm compared with the original carbon fibers ^-1 Three characteristic peaks exist at the position, namely, the stretching vibration peaks corresponding to C=O, C-O and C-O-C functional groups respectively, which indicate that the surface of the carbon fiber subjected to electrochemical oxidation treatment contains more oxygen-containing functional groups, and the oxygen-containing functional groups effectively increase the surface activity of the carbon fiber. Carbon fiber grafted with TTI at 2320cm ^-1 The formed-NCO stretching vibration peak indicates that the carbon fiber surface is successfully grafted with TTI.

FIG. 8 shows the carbon fiber of example 1 at the surfaceC in the process of treatment _1s XPS spectra after peak-split fitting. Wherein 8 (a) is C of carbon fibrils _1s XPS spectrogram after peak-splitting fitting; FIG. 8 (b) is a graph showing the carbon fiber C after the electrochemical oxidation treatment _1s XPS spectrogram after peak-splitting fitting; FIG. 8 (C) is C after carbon fiber grafting TTI _1s XPS spectra after peak-split fitting. It can be seen that the C-C content of the surface of the electrochemically oxidized carbon fiber is reduced compared to the untreated fiber; the content of O-c=o and C-O groups increases significantly. The electrochemical oxidation treatment shows that the effect of introducing polar groups on the surface of the carbon fiber is obvious, and the chemical activity of the fiber surface is improved, so that the interface combination of the composite material is improved. Compared with the carbon fiber subjected to electrochemical treatment, the carbon fiber with the surface grafted with the TTI has the advantages that the O-C= O, C-O and C-N groups are increased, the number of oxygen-containing active groups on the surface of the fiber is increased after the carbon fiber is subjected to the TTI grafted coating treatment, and the chemical activity is enhanced.

Claims

1. The preparation method of the modified carbon fiber/phenolic resin composite material comprises the following steps:

(1) Carrying out high-temperature treatment on the carbon fiber cloth; the high temperature is 400-500 ℃, and the high temperature treatment time is 2-3 hours;

(2) Putting the carbon fiber treated at the high temperature in the step (1) into an electrolytic reaction tank as an electrolytic anode material, wherein the electrolyte is a dilute inorganic acid solution; the electrolysis voltage is 4-5V, and the electrochemical treatment time is 15-20min;

(4) Soaking the carbon fiber obtained in the step (3) in a polyisocyanate solution, and drying; the polyisocyanate is triphenylmethane triisocyanate;

(5) Placing the carbon fiber obtained in the step (4) as an anode material into an electrodeposition reaction tank for electrochemical deposition, wherein the electrolyte is a carbon nano tube dispersion liquid; the electrolysis voltage is 5-6V, and the electrodeposition time is 10-12min;

(7) Adding p-phenylphenol, ammonia water, phenol and formaldehyde into a reaction container, and reacting to obtain liquid phenolic resin; the mass ratio of phenol to formaldehyde is 1.33-1.67:1, the mass of the p-phenylphenol is 20-25% of that of formaldehyde;

2. The method according to claim 1, wherein the raman spectrum of the surface-modified carbon fiber has 1400 to 1500cm ^-1 D band at the position and 1900-2000 cm ^-1 G band at the position, and the intensity ratio R of G/D is more than 2.

3. The method of claim 1, wherein the surface-modified carbon fiber has an infrared spectrum of 1735+ -50 cm ^-1 ，1261±50cm ^-1 And 1091.+ -.50 cm ^-1 There is a characteristic peak.

4. The method of claim 1, wherein the step (8) is repeated to uniformly coat the surface of the surface-modified carbon fiber with a liquid phenolic resin, thereby obtaining a multi-layer phenolic resin-coated carbon fiber, and the multi-layer phenolic resin-coated carbon fiber is put into a mold for hot pressing.

5. The method according to claim 1, wherein in the step (4), the concentration of the polyisocyanate solution is 10 to 20wt%, and the carbon fiber is immersed in the polyisocyanate agent for 30 to 60 minutes.

6. The method according to claim 1, wherein the carbon nanotubes in the step (5) are multiwall carbon nanotubes having an outer diameter of 5 to 50nm and a concentration of the carbon nanotube dispersion of 5 to 10wt%.

7. The method according to claim 1, wherein the outer diameter of the carbon nanotubes in the step (5) is 10 to 20nm.

8. The process according to claim 4, wherein in the step (7), the mass ratio of phenol to formaldehyde is 1.5:1.

9. The method according to claim 1, wherein in the step (8), the mass ratio of the surface-modified carbon fiber to the phenolic resin is 1-2:1-2.

10. The method according to claim 1, wherein in the step (8), the mass ratio of the surface-modified carbon fiber to the phenolic resin is 1-1.5:1.