CN111533931B

CN111533931B - CF/PEEK composite material with full transverse crystal structure and preparation method thereof

Info

Publication number: CN111533931B
Application number: CN202010419567.8A
Authority: CN
Inventors: 朱姝; 周剑锋; 任毅; 苏佳煜; 张铠; 马禹
Original assignee: Donghua University
Current assignee: Shanghai Donghua compound material technology Co.,Ltd.
Priority date: 2020-05-18
Filing date: 2020-05-18
Publication date: 2021-03-26
Anticipated expiration: 2040-05-18
Also published as: CN111533931A

Abstract

The invention relates to a CF/PEEK composite material with a full transverse crystal structure and a preparation method thereof, wherein the method comprises the following steps: (1) carrying out pyrolysis on the original sizing agent on the CF surface; (2) in a saturated water vapor environment, simultaneously carrying out microwave radiation and ultraviolet radiation on CF, and recording a product as ACF; (3) immersing the ACF into the polyetherimide/dichloromethane/carbon nanotube suspension, taking out and drying to obtain sizing modified carbon fiber MCF; (4) hot-pressing the MCF and PEEK material lamination; (5) in the cooling process, the resin obtains perturbation shear flow by instantly applying pressure and unloading, and the nucleation and growth of a full transverse crystal structure are induced; obtaining the CF/PEEK composite material with a full transverse crystal structure; the bending strength of the finally prepared composite material is 750-900MPa, the bending modulus is 63-75GPa, and the interlaminar shear strength is 90-100 MPa. The method has the characteristics of high efficiency, environmental protection and large-scale production realization, and the prepared composite material can replace metal and be used in the fields of aerospace, machinery, automobiles, rail traffic and the like.

Description

CF/PEEK composite material with full transverse crystal structure and preparation method thereof

Technical Field

The invention belongs to the technical field of carbon fiber reinforced polyether ether ketone (CF/PEEK) composite materials, and relates to a CF/PEEK composite material with a full transverse crystal structure and a preparation method thereof.

Background

In recent years, thermoplastic composite materials have attracted much attention because of their advantages such as good recyclability, secondary processability, high impact toughness, high specific strength, and high specific modulus. Among various thermoplastic composite materials, CF/PEEK has excellent performances such as high rigidity, high thermal stability, chemical corrosion resistance, wear resistance, biocompatibility and the like, is expected to be used as a structural material to replace metal or thermosetting composite materials with mature processes, and is widely applied to the fields of aerospace, machinery, automobiles, rail transit and the like.

However, the practical application of CF/PEEK thermoplastic composites is not optimistic. The main problems are that the interlaminar shear strength (ILSS) is low, so that the bending strength is also low, and the material is easy to delaminate or generate other damage and damage. The main reasons for this performance defect are that the interface interaction between the carbon fiber and the PEEK matrix is weak, the wettability is poor, and pores are easily generated during the molding process of the composite material. The fundamental reason is that CF is in a stable six-membered ring structure, the surface of the CF is composed of a nonpolar and highly ordered graphite basal plane, so that the surface of the fiber contains less active functional groups, and the melt viscosity of PEEK is high, so that the wettability between carbon fiber and PEEK resin is poor, and the interface bonding strength is weak. As a tie of load transmission between the fiber and the resin matrix, the bonding strength of the interface layer greatly influences the mechanical property of the whole composite material, when the composite material with low interface strength is damaged, cracks are expanded along the interface, the reinforcing effect of the fiber cannot be well exerted, and the strength of the composite material is far lower than the theoretical value.

The CF is subjected to surface modification treatment, so that the problems can be solved, and the properties such as the interlaminar shear strength of the composite material are improved. There are two types of known techniques, namely "activation (sometimes also referred to as oxidation)" and "sizing". Can be used singly or in combination and superposition. The principle of activation modification is to introduce active functional groups on the surface of the fiber, increase the number of chemical bonds or hydrogen bonds between the fiber and the polymer matrix, and improve the interface bonding strength of the composite material through strong chemical action. The principle of sizing modification is that a polymer (which can be different from a matrix) thin layer is attached to the surface of a fiber through a solution or emulsion coating, and a bridge is erected between the fiber and the matrix which originally have weak interaction by utilizing the characteristic that the polymer thin layer can generate strong interaction with the fiber and the matrix, so that the relevance of the fiber and the matrix is enhanced.

The prior activation techniques include plasma treatment, anodic electrolysis or electrodeposition treatment, strong acid treatment, ozone treatment, microwave ultrasonic co-treatment, and the like. The activation process may reduce the strength of the CF filaments by finding a balance between the number of reactive groups and the strength of the CF filaments, allowing the CF surface to generate as many hydroxyl and carboxyl groups as possible, creating as many grooves as possible to increase the contact area with the substrate, but at the same time losing as little strength as possible.

The existing sizing technology comprises a reaction type sizing agent, a coating type sizing agent and the like.

The prior art has effects in some aspects, but has various defects or shortcomings, so that the industrial production is difficult to realize when the PEEK substrate is used for a substrate which needs to be molded and processed at a high temperature of 400 ℃.

For example, when CF is treated by plasma, the effect difference between the outer layer and the inner layer of the filament bundle is obvious, and when the active groups of the outer layer are more and the strength of the monofilament is greatly damaged, the activity of the CF of the inner layer is not improved. Therefore, the stability is poor, the dispersion is large, and the method is not suitable for industrial production.

The anodic electrolysis or electrodeposition treatment process is effective in treating tows, but is difficult to treat the fabric, and the strength of the monofilaments is greatly reduced.

In the strong acid treatment, a large amount of waste acid and waste liquid is generated, so that the environmental pollution is large; the method is mostly operated intermittently, the required treatment time is long, and the method is difficult to match with a CF production line; and the corrosion resistance of equipment is high, and the operation risk coefficient is high, so the method is hardly considered in industrial production.

Ozone treatment can produce a large amount of ozone harmful to human body, the treatment of ozone-containing exhaust gas can greatly increase the cost, and the mode which is not environment-friendly is being abandoned gradually.

The strength of the CF monofilaments is greatly damaged by microwave ultrasonic co-treatment, and the damage degree is difficult to control.

The reactive sizing agents (surface grafts, coupling agents, etc.) have a low reaction rate and need to be used in conjunction with the several activation techniques previously described.

Coating-type sizing agents (relying on van der waals forces) can improve the wettability of the matrix to the fibers, but have limited effect on enhancing interfacial interactions.

The CF/PEEK composite material prepared by the known technology is generally lower than 85MPa in interlaminar shear strength, and the few technologies exceed 90MPa, but the industrial production is difficult to realize by using strong acid or plasma treatment in the preparation process. The oxygen/carbon (O/C) content ratio after the CF surface activation is improved by about 40%.

On the other hand, although the flexural modulus of the composite material in the CF direction is high, the flexural modulus perpendicular to the CF direction depends on the PEEK resin matrix, and since the modulus of the resin is much lower than that of the CF, the flexural modulus perpendicular to the CF direction of the composite material is usually not high, and the bidirectional mechanical properties can only be improved by 0/90 ° isogamy design or fabric form based on bidirectional arrangement (such as satin and the like). The flexural modulus of CF/PEEK composites prepared by known techniques is typically below 65 GPa.

Disclosure of Invention

The invention aims to provide a method for preparing a CF/PEEK composite material in an acid-free environment, and the prepared composite material has the advantages of full transverse crystal structure (the transverse crystal growth area accounts for more than 92% of the total area of a transverse crystal and a spherulite), high flexural modulus and the like.

One of the objectives of the present invention is to provide a CF/PEEK composite material with a full transverse crystalline structure and a high flexural modulus.

The invention also aims to provide a preparation method of the CF/PEEK composite material with a full transverse crystal structure and high flexural modulus, which is a preparation method under completely acid-free environmental conditions, is environment-friendly and can realize large-scale production; the adopted PEI sizing agent aiming at the PEEK substrate has good solubility and heat resistance; since both PEI and PEEK contain a large number of benzene rings, strong pi-pi bond interaction exists between the PEI and the PEEK; the carbonyl on the PEI and the carboxyl and the hydroxyl on the CF can form a hydrogen bond, and the interaction is strong; the carboxylated CNT with moderate content and good dispersion is added into the sizing agent, so that the interface interaction can be further enhanced through the pinning effect of the carboxylated CNT and PEEK matrix; the PEEK resin matrix is pressed and unloaded instantly in the cooling process, and the CF plays a role in flow guiding, so that the PEEK can obtain micro-disturbance shear flow along the CF direction, and molecular chains are oriented along the CF; meanwhile, due to the existence of a large amount of adjacent nucleation, the platelets formed by the PEEK on the surface of the CF through CNT-induced nucleation are limited by the space of adjacent nucleation sites during growth, are mutually extruded and finally grow into a full-transverse-crystal structure.

The preparation method of the CF/PEEK composite material with the full transverse crystal structure comprises the following steps:

(1) carrying out pyrolysis on the original sizing agent on the CF surface;

(2) simultaneously subjecting CF to microwave radiation and ultraviolet radiation in a saturated water vapor environment, and marking the product as activated-CF (ACF); the step carries out acid-free activation modification treatment on the CF, so that the method is environment-friendly and has the possibility of industrial mass production;

(3) immersing the ACF into Polyetherimide (PEI)/Dichloromethane (DCM)/Carbon Nano Tube (CNT) suspension, taking out and drying to obtain sizing Modified Carbon Fiber (MCF);

(4) hot-pressing the MCF and PEEK material lamination; the PEEK matrix is changed from solid to melt and is subjected to shear flow and soakage in the MCF tows under pressure;

(5) in the cooling process, the resin is subjected to micro-disturbance shear flow by instantaneous pressure application and unloading to induce nucleation and growth of a full transverse crystal structure (namely, the growth area of a transverse crystal accounts for more than 92 percent of the total area of the transverse crystal and the spherulite);

cooling to room temperature, and demolding to obtain the CF/PEEK composite material with the full transverse crystal structure.

As a preferred technical scheme:

with the above-described preparation method, the CF is in the form of satin fabric, and when the CF is in other forms, such as chopped fiber, long fiber, fiber mat, continuous fiber tow, or plain, twill, and non-crimp fabric, the composite material can also be compounded with PEEK by using the method of the present invention, but the performance of the prepared composite material is relatively poor.

In the preparation method, the pyrolysis refers to sintering at the temperature of 300-420 ℃ for 5-180 min. The original sizing agent is removed by pyrolysis. These sizing agents adhere to the surface of commercial-grade carbon fibers, typically epoxy resins, and must be sized before shipment to achieve fiber winding, or else, they can cause fuzz and even fiber breakage. However, these sizing agents are not removed to facilitate the compounding of CF and PEEK, because they decompose at the high temperature (400 ℃) of PEEK molding, form pores in the composite material, and reduce the mechanical properties such as material strength. Deviations from the recommended parameter intervals would be detrimental to an efficient control of the pyrolysis process. For example, if the pyrolysis temperature is too low or the pyrolysis time is too short, the original sizing agent cannot be completely removed, and the residual part still decomposes at the high temperature of the molding processing of the CF/PEEK composite material, so that various mechanical properties of the composite material are influenced; if the pyrolysis temperature is too high or the pyrolysis time is too long, part of the surface structure of the CF is damaged by oxidation reaction, the CF surface has ravines, the strength of the monofilament is reduced by more than a certain extent (e.g. 10%), and the mechanical performance indexes of the composite material are also greatly reduced. In the pyrolysis process, if a vacuum environment or an inert gas atmosphere such as nitrogen, helium and the like can be established, the effect is better, the oxidation reaction of the CF can be inhibited, and the strength retention rate of the CF monofilament is higher.

The preparation method is characterized in that the relative humidity of saturated water vapor is more than 95 percent; the microwave radiation time is 3-30min, and the microwave frequency is 300MHz-10 GHz; the wavelength of the irradiated ultraviolet light is 290-340nm, and the ultraviolet irradiance is 20-50W/m². This step has three functions: 1) the microwave irradiation can promote the graphitization of the carbon fiber surface and make up/offset the loss of the strength of the monofilament; 2) ultraviolet irradiation is carried out, the original sizing agent residue which is not high in temperature resistance in the groove on the surface of the carbon fiber is further cleaned, and the ultraviolet can break the double bonds of the residual organic matters on the surface of the CF through oxidation reaction; 3) the ultraviolet light and the water vapor jointly act to excite the hydroxyl, carboxyl and other groups on the surface of the CF.

It is particularly emphasized that the simultaneous addition of microwave action with the action of ultraviolet and saturated water vapor is necessary because microwave irradiation can heat CF uniformly during oxidation to promote hydroxylation and carboxylation. Comparing samples with microwaves and samples without microwaves, the O/C ratio in the samples with microwaves was higher, suggesting that the content of oxygen-containing groups was higher. Moreover, the microwave irradiation can promote the graphitization of the carbon fiber surface and make up/offset the loss of the strength of the monofilament.

If the humidity is too low, the microwave radiation time is too short, the microwave frequency is too low, the ultraviolet wavelength is too long or the irradiance is too low, the excited number of hydroxyl and carboxyl is less, the activation degree of CF is lower, the number of hydrogen bonds capable of being formed with a sizing agent is also less, and the interaction between the ACF and the sizing agent is smaller; if the microwave radiation time is too long, the microwave frequency is too high, the ultraviolet wavelength is too short or the irradiance is too high, the six-membered ring structure on the CF surface can be damaged too much, the strength of the CF monofilament is reduced too much, and thus various mechanical properties of the composite material are reduced.

The same activation modification method (generating hydroxyl groups and carboxyl groups on the surface and affecting the internal structure of the carbon nanotube-based carbon fiber as little as possible) can be applied to carbon materials such as Carbon Nanotubes (CNTs), Graphene Oxide (GO), Carbon Black (CB), and Carbon Nanofibers (CNF).

In the PEI/DCM/CNT suspension, PEI is completely dissolved and the content is 0.5-1.5 wt.%, CNT is contained in 0.01-0.1 wt.%, stable suspension is prepared by ultrasonic dispersion for 5-60min, CNT is carboxyl modified single-wall or multi-wall CNT, and the weight-average molecular weight of PEI is more than 50000; the immersion time is 10-180 min; drying to a water content of less than 0.5 wt.%.

PEI is an amorphous polymer and has good solubility, and a large number of hydrogen bonds can be formed between carbonyl groups on PEI and hydroxyl groups and carboxyl groups on the ACF, so that PEI solution can be effectively coated on the surface of the ACF; since the carboxyl group on the CNT and the carbonyl group on the PEI may also undergo hydrogen bonding, the CNT may be stably dispersed in the PEI solution; the PEI and the PEEK are similar in chemical structure, and pi-pi bond interaction occurs due to a large number of benzene rings, so that the PEI and the PEEK are good in wettability and compatibility; the PEI has good thermal stability, and does not degrade at the high temperature (400 ℃) of the molding processing of the CF/PEEK composite material; in addition, PEI does not need to be converted into a material component with good heat resistance through heat treatment like PAA, so that obvious shrinkage and strong internal stress cannot be generated in the forming process; the existence of CNT can increase the surface roughness of MCF on one hand, the CNT can be pricked in a PEEK matrix like a plurality of nails, the total sum of friction force is increased through a large contact area, and on the other hand, the strength of a PEI/CNT interface layer is enhanced by the CNT; CNT is used as a nucleation site to induce PEEK crystallization nucleation, and if the sites are arranged closely enough, adjacent sites form a transverse crystal structure due to the limited space for PEEK crystallization growth, so that the CF/PEEK composite material has high flexural modulus.

If the concentration of the PEI solution is too low or the immersion time is too short, a sufficient amount of the sizing agent cannot be applied to the ACF surface; if the concentration of the PEI solution is too high, the sizing agent wrapped on the surface of the ACF is too much, and the PEI is an amorphous polymer and can generate large creep at high temperature, so that the mechanical property of the composite material at high temperature is reduced; if the immersion time is too long, the production efficiency is affected and the cost is increased. If the molecular weight of the PEI is too low, the strength of the PEI layer serving as the transition layer is too low, the interface layer is easy to damage when the composite material is stressed, and the overall mechanical property is reduced. If the content of the CNT is too low, the number of the CNT which can generate the pinning effect between the CNT and the PEEK substrate is too small, the pinning effect is not obvious, the interaction force between the MCF and the PEEK is not large enough, and the number of the CNT-induced PEEK nucleation sites is not enough to limit the growth of PEEK platelets between adjacent sites so as to form transverse crystals; if the content of the CNT is too high or the ultrasonic dispersion time is too short, the CNT is insufficiently dispersed and agglomerated, so that the wetting of PEEK on MCF is influenced, and the effects of the CNT on PEEK induced nucleation and crystal growth space limitation are also influenced; if the ultrasound time is too long, not only is energy wasted, efficiency is reduced, but the structural integrity of the CNTs may also be compromised. If the water content after drying is too large, pores are formed in the forming process of the composite material due to water vapor volatilization, and the mechanical property of the composite material is influenced.

In the preparation method, the PEEK material is in the form of a film, a non-woven fabric felt, powder or fiber; the weight average molecular weight of the PEEK material is 30000-150000; the technological parameters of lamination hot pressing are as follows: the temperature is 370 ℃ and 420 ℃, the pressure is 0.5-5MPa, and the loading time is 3-30 min. In the process, because the interaction between the PEEK and the MCF is enhanced, the infiltration performance of the PEEK melt to the MCF is greatly improved, the possibility of forming pores in the composite material is reduced, the interface bonding strength of the PEEK and the MCF is increased when the composite material is damaged by external force, and the material failure mode is changed from fiber extraction to matrix fracture.

If the molecular weight of the PEEK material is too low, molecular chain entanglement in the matrix is less, the strength of the matrix is too low, and the overall strength of the composite material is limited; if the molecular weight is too high or the hot-pressing temperature is too low, the melt viscosity is too high, and the porosity of the composite material is increased; if the hot pressing temperature is too high or the heat preservation loading time is too long, PEEK is easy to degrade, discolor, age and the like at high temperature, and the strength of the resin is reduced; if the pressure is small or the loading time is too short, the shearing action on the melt is small, the CF infiltration is incomplete, and the porosity of the composite material is increased; if the pressure is too large, more resin flows out from the gaps of the die, and the composite material has the defects of poor adhesive and the like.

The preparation method comprises the following specific steps of (5): cooling the laminated material system to 350 ℃ at the speed of more than 50 ℃/min, applying the instantaneous pressure of 2-8MPa and keeping the pressure for 1s, unloading the pressure (i.e. removing the pressure), cooling to 300 ℃ at the speed of more than 50 ℃/min, applying the instantaneous pressure of 1-2.5MPa and keeping the pressure for 0.5-15min, and unloading the pressure (i.e. removing the pressure). The two cooling and pressurizing processes are used for inducing the growth of the PEEK full transverse crystal structure. The PEEK molecular chain is subjected to shear flow along CF in a melt state by first cooling and instant pressurization, so that the molecular chain of the PEEK is preferentially oriented along the CF at the initial stage of crystallization, and the subsequent chain folding crystal growth is preferentially carried out in a direction perpendicular to the CF direction, so that the nucleation of a transverse crystal structure becomes easier and quicker in the nucleation competition of the transverse crystal structure and a spherulite crystal structure; the second lowering to lower temperature and continuous loading are to inhibit the growth of spherulites and make the PEEK resin crystal grow into a full-transverse crystal structure (i.e. the transverse crystal growth area accounts for more than 92% of the total area of the transverse crystal and the spherulites).

If the cooling rate is too slow or the temperature of the first stage cooling is too low, partial crystallization or nucleation partially not along the CF orientation may be formed in the cooling process, which may result in partial spherulite growth and failure to form a full-transverse crystal structure; if the temperature of the first stage cooling is too high, it is meaningless to apply pressure immediately after the first stage cooling, because when the temperature is higher than the melting point of PEEK, molecular chains caused by shear flow are rapidly dissociated along CF orientation at such high temperature and become random melt molecular chains again; if the first stage pressurization is too small, the molecular chain orientation degree is not enough, and the transverse crystals cannot take a significant advantage in the competition of the transverse crystals and the spherulites; if the first stage is pressurized too much, it may cause melt fracture and form defects in the composite; if the temperature reduction rate of the second section is too slow, spherulite growth can be caused in a free state; if the temperature of the second section is too low, the molecular chain movement capability is too poor, the crystal growth is slow, and the efficiency is too low; if the temperature of the second section is too high, the molecular chain movement capacity is too strong, the chain folding is difficult, and the crystallization efficiency is low; if the loading pressure of the second section is too small or the duration is too short, the effect of inhibiting the growth of spherulites is not large, and the formation of a full-transverse crystal structure is interfered; the second section has too large loading pressure, the chain is difficult to fold under the pressure, and the crystal growth is difficult; if the second period is too long, energy consumption is wasted, efficiency is reduced, and cost is increased.

The CF/PEEK composite material with the full transverse crystal structure prepared by the preparation method has the bending strength of 750-900MPa, the bending modulus of 63-75GPa and the interlaminar shear strength of 90-100 MPa.

Due to the adoption of the technical scheme, the invention has the following beneficial effects:

the principle of the CF/PEEK composite material with the full transverse crystal structure prepared by the invention is that the original sizing agent on the CF surface is decomposed at high temperature. These sizing agents adhere to the surface of commercial grade carbon fibers to ensure that the fibers can be wound, however, these sizing agents decompose at the high temperatures (400 ℃) of PEEK molding, forming voids in the composite material, reducing mechanical properties such as material strength. Secondly, in a saturated water vapor environment, the CF is subjected to microwave radiation and ultraviolet radiation simultaneously. On one hand, the microwave irradiation can promote the graphitization of the carbon fiber surface and make up or offset the loss of the strength of the monofilament; in the second aspect, double bonds of residual organic matters on the surface of the CF can be broken through oxidation reaction by ultraviolet rays, so that the original sizing agent residue which is not high in temperature resistance in the groove on the surface of the carbon fiber can be further cleaned through ultraviolet irradiation; in the third aspect, the ultraviolet light and the water vapor jointly act to excite the hydroxyl, carboxyl and other groups on the CF surface. Therefore, active groups such as hydroxyl and carboxyl are grafted on the surface of CF through acid-free activation modification treatment, so that the method is environment-friendly and has the possibility of industrial mass production. Next, the ACF was dip-sized with a PEI/DCM/CNT suspension. PEI is good in solubility, and a large number of hydrogen bonds can be formed between carbonyl groups on PEI and hydroxyl groups and carboxyl groups on the ACF, so that PEI solution can be effectively coated on the surface of the ACF; since the carboxyl group on the CNT and the carbonyl group on the PEI may also undergo hydrogen bonding, the CNT may be stably dispersed in the PEI solution; the PEI and the PEEK are similar in chemical structure, and pi-pi bond interaction occurs due to a large number of benzene rings, so that the PEI and the PEEK are good in wettability and compatibility; the PEI has good thermal stability, and does not degrade at the high temperature (400 ℃) of the molding processing of the CF/PEEK composite material; in addition, PEI does not need to be converted into a material component with good heat resistance through heat treatment like PAA, so that obvious shrinkage and strong internal stress cannot be generated in the forming process; the existence of CNT can increase the surface roughness of MCF on one hand, the CNT can be pricked in a PEEK matrix like a plurality of nails, the total sum of friction force is increased through a large contact area, and on the other hand, the strength of a PEI/CNT interface layer is enhanced by the CNT; CNT is used as a nucleation site to induce PEEK crystallization nucleation, and if the sites are arranged closely enough, adjacent sites form a transverse crystal structure due to the limited space for PEEK crystallization growth, so that the CF/PEEK composite material has high flexural modulus. Then, the CF/PEEK composite material was prepared by lamination hot pressing. The PEEK matrix changes from a solid to a melt under heat and, under pressure, flows in shear, infiltrating the interior of the MCF tow. In the process, because the interaction between the PEEK and the MCF is enhanced, the infiltration performance of the PEEK melt to the MCF is greatly improved, the possibility of forming pores in the composite material is reduced, the interface bonding strength of the PEEK and the MCF is increased when the composite material is damaged by external force, and the material failure mode is changed from fiber extraction to matrix fracture. Finally, the resin is subjected to perturbation shear flow by instantaneous pressure application and unloading in the cooling process. The two cooling and pressurizing processes are used for inducing the growth of the PEEK full transverse crystal structure. The PEEK molecular chain is subjected to shear flow along CF in a melt state by first cooling and instant pressurization, so that the molecular chain of the PEEK is preferentially oriented along the CF at the initial stage of crystallization, and the subsequent chain folding crystal growth is preferentially carried out in a direction perpendicular to the CF direction, so that the nucleation of a transverse crystal structure becomes easier and quicker in the nucleation competition of the transverse crystal structure and a spherulite crystal structure; the second lowering to lower temperature and continuous loading are to inhibit the growth of spherulite crystal and make the PEEK resin crystal grow into full-transverse crystal structure.

One of the advantages of the method of the invention is that the CF surface activation process is acid-free treatment, is environment-friendly and has industrialization possibility, and the activation effect is equivalent to the activation effect by using strong acid.

The CF/PEEK composite material with the full transverse crystal structure, which is prepared by the preparation method, has the bending strength of 750-900MPa, the bending modulus of 63-75GPa and the interlaminar shear strength of 90-100MPa, wherein the bending modulus is higher than that of other known technologies which are environment-friendly and have industrialization conditions.

Drawings

FIG. 1 is an XPS plot of untreated CF and oxygen element/carbon element (O/C) content, wherein a higher O/C content ratio indicates a higher activation efficiency;

FIG. 2 is an XPS plot of UV irradiation treated CF in a saturated water vapor environment with oxygen element/carbon element (O/C) content;

FIG. 3 is an XPS plot of CF treated with simultaneous microwave and UV irradiation in a saturated water vapor environment and oxygen element/carbon element (O/C) content;

FIG. 4 is a schematic diagram of nucleation and growth of a full-transverse grain structure.

Detailed Description

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

Example 1

(1) sintering the T300 grade 3K5 satin fabric of CF for 180min at 300 ℃ to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 95.3 percent, and marking the product as ACF; the microwave radiation time is 30min, and the microwave frequency is 300 MHz; the wavelength of the irradiated ultraviolet light is 290nm, and the ultraviolet irradiance is 20W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 180min, wherein the weight average molecular weight of the polyetherimide is 50080, the carbon nanotube is a single-walled carbon nanotube modified by carboxyl, and drying the carbon nanotube after taking out until the water content is 0.48 wt% to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 0.5 wt.%, and the carbon nanotube content is 0.01 wt.%, and the stable suspension is prepared by 5min ultrasonic dispersion;

(4) laminating MCF and PEEK film with the weight-average molecular weight of 30000 for hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 370 ℃, the pressure is 5MPa, and the loading time is 3 min;

(5) cooling the material system after the lamination hot pressing to 300 ℃ at the speed of 51 ℃/min, applying the instantaneous pressure of 2MPa and keeping the pressure for 1s, unloading the pressure, cooling to 250 ℃ at the speed of 51 ℃/min, applying the instantaneous pressure of 1MPa and keeping the pressure for 0.5min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 750MPa, the bending modulus of 63GPa and the interlaminar shear strength of 90 MPa.

Comparative example 1

The preparation method of the CF/PEEK composite material is basically the same as the example 1, the steps (1) and (2) are omitted relative to the example 1, meanwhile, the material immersed in the polyetherimide/dichloromethane/carbon nanotube suspension in the step (3) is changed into T300 grade 3K5 satin fabric of CF from ACF, and other processes and parameters are the same as the example 1.

The bending strength of the finally prepared CF/PEEK composite material is 614MPa, the bending modulus is 61GPa, and the interlaminar shear strength is 67 MPa.

Comparing example 1 with comparative example 1, it can be seen that the bending strength and interlaminar shear strength of the CF/PEEK composite material prepared in example 1 are much higher than those of comparative example 1, the XPS curve and the oxygen element/carbon element (O/C) content of the untreated CF in comparative example 1 are shown in fig. 1, the XPS curve and the oxygen element/carbon element (O/C) content of the CF treated by simultaneous microwave and ultraviolet irradiation in a saturated water vapor environment in example 1 are shown in fig. 3, and it can be seen by comparison that the O/C ratio of the untreated CF is 0.0700, in which the content of O element is not high, indicating that CF is inert, while the O/C ratio of the uv + water vapor + microwave treated CF is 0.1782, in which the content of O element is significantly increased, and the O/C ratio is increased by 155% (up to 255% of the original%) as compared with the untreated CF, it is important to use microwave treatment in combination with UV + water vapor, which is why the bending strength and interlaminar shear strength of CF/PEEK composites prepared from untreated CF are low.

Comparative example 2

The preparation method of the CF/PEEK composite material is basically the same as the example 1, and is adjusted relative to the step (2) of the example 1, specifically, in a saturated water vapor environment, only ultraviolet radiation is carried out on CF, microwave radiation is not carried out, and other processes and parameters are the same as the example 1.

The bending strength of the finally prepared CF/PEEK composite material is 621MPa, the bending modulus is 62GPa, and the interlaminar shear strength is 70 MPa.

Comparing example 1 with comparative example 2, it can be seen that the bending strength and interlaminar shear strength of the CF/PEEK composite material prepared in example 1 are much higher than those of comparative example 2, the XPS curve and the oxygen element/carbon element (O/C) content of the CF subjected to ultraviolet irradiation treatment in a saturated water vapor environment in comparative example 2 are shown in FIG. 2, the XPS curve and the oxygen element/carbon element (O/C) content of the CF subjected to simultaneous microwave and ultraviolet irradiation treatment in a saturated water vapor environment in example 1 are shown in FIG. 3, and it can be seen by comparison that the O/C ratio of the CF subjected to ultraviolet + water vapor treatment is 0.0765, in which the content of O element is not significantly increased, indicating that the effect is not very good by using only ultraviolet + water vapor, while the O/C ratio of the CF subjected to ultraviolet + water vapor + microwave treatment is 0.1782, in which the content of O element is significantly increased, it is important to use microwave treatment in addition to UV + water vapor, which is why the bending strength and interlaminar shear strength of CF/PEEK composite materials prepared from CF treated with UV + water vapor are low.

Comparative example 3

The preparation method of the CF/PEEK composite material is basically the same as that of the example 1, the step (5) is omitted relative to the example 1, and other processes and parameters are the same as those of the example 1.

The bending strength of the finally prepared CF/PEEK composite material is 711MPa, the bending modulus is 55GPa, and the interlaminar shear strength is 89 MPa.

Comparing example 1 with comparative example 3, it can be seen that the flexural strength and flexural modulus of the CF/PEEK composite material prepared in example 1 are much higher than those of comparative example 3. Comparative example 3 does not induce the formation of PEEK transverse crystal structure by shear flow, and the crystal morphology is mainly spherulite, whereas example 1 applies pressure to two stages in the cooling process to orient the molecular chain along CF to form a fully oriented transverse crystal structure, and the transverse crystal area ratio reaches 92%. The comparison shows that if the shear perturbation of the matrix melt is realized without the step pressurization in the cooling process, a full transverse crystal structure cannot be formed in the composite material, and the bending strength and the modulus of the composite material cannot be obviously improved, which is why the bending strength and the bending modulus of the CF/PEEK composite material prepared by the two-stage pressurization step in the cooling process are not low.

Example 2

(1) sintering the T300 grade 3K5 satin fabric of CF at 350 ℃ for 138min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 95.8%, and marking the product as ACF; the microwave radiation time is 27min, and the microwave frequency is 820 MHz; the irradiation ultraviolet wavelength is 299nm, and the ultraviolet irradiance is 50W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 165min, wherein the weight average molecular weight of the polyetherimide is 52000, and the carbon nanotube is a carboxyl-modified single-walled carbon nanotube, taking out and drying until the water content is 0.45 wt.%, so as to obtain a sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 0.7 wt.%, and the carbon nanotube content is 0.03 wt.%, and the stable suspension is prepared by 10min ultrasonic dispersion;

(4) laminating MCF and PEEK film with the weight-average molecular weight of 60000 for hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 378 ℃, the pressure is 4.7MPa, and the loading time is 7 min;

(5) cooling the material system after the lamination hot pressing to 308 ℃ at the speed of 52 ℃/min, applying the instantaneous pressure of 3MPa and keeping the pressure for 1s, unloading the pressure, cooling to 258 ℃ at the speed of 52 ℃/min, applying the instantaneous pressure of 1.2MPa and keeping the pressure for 1min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 809MPa, the bending modulus of 65GPa and the interlaminar shear strength of 92 MPa.

Example 3

(1) sintering the T300 grade 3K5 satin fabric of CF at 420 ℃ for 5min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 95.9 percent, and marking the product as ACF; the microwave radiation time is 24min, and the microwave frequency is 1 GHz; the wavelength of the irradiated ultraviolet light is 305nm, and the ultraviolet irradiance is 35W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 134min, wherein the weight average molecular weight of the polyetherimide is 55000, and the carbon nanotube is a single-walled carbon nanotube modified by carboxyl, taking out and drying until the water content is 0.42 wt%, so as to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 0.95 wt.%, and the carbon nanotube content is 0.05 wt.%, and the stable suspension is prepared by ultrasonic dispersion for 20 min;

(4) laminating MCF and PEEK non-woven fabric felt with the weight-average molecular weight of 75000 for hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 381 ℃, the pressure is 3.4MPa, and the loading time is 11 min;

(5) cooling the laminated material system to 311 ℃ at the speed of 53 ℃/min, applying the instantaneous pressure of 4MPa and keeping the pressure for 1s, unloading the pressure, cooling to 261 ℃ at the speed of 53 ℃/min, applying the instantaneous pressure of 1.5MPa and keeping the pressure for 2min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 841MPa, the bending modulus of 68GPa and the interlaminar shear strength of 95 MPa.

Example 4

(1) sintering the T300 grade 3K5 satin fabric of CF for 168min at 335 ℃ to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 96.3 percent, and marking the product as ACF; the microwave radiation time is 20min, and the microwave frequency is 1.5 GHz; the irradiation wavelength of ultraviolet light is 313nm, and the ultraviolet irradiance is 24W/m²；

(3) Dipping the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 119min, wherein the weight average molecular weight of the polyetherimide is 59500, the carbon nanotube is a single-walled carbon nanotube modified by carboxyl, and drying the carbon nanotube after taking out until the water content is 0.41 wt.% to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 1.02 wt.%, and the carbon nanotube content is 0.04 wt.%, and the stable suspension is prepared by 30min ultrasonic dispersion;

(4) laminating MCF and PEEK non-woven fabric felt with the weight-average molecular weight of 82000 by hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 389 ℃, the pressure is 2.9MPa, and the loading time is 15 min;

(5) cooling the laminated material system to 319 ℃ at the speed of 54 ℃/min, applying the instantaneous pressure of 5MPa and keeping for 1s, unloading the pressure, cooling to 269 ℃ at the speed of 54 ℃/min, applying the instantaneous pressure of 1.8MPa and keeping for 5min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 873MPa, the bending modulus of 69GPa and the interlaminar shear strength of 97 MPa.

Example 5

(1) sintering the T300 grade 3K5 satin fabric of CF at 360 ℃ for 104min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 96.8%, and marking the product as ACF; the microwave radiation time is 16min, and the microwave frequency is 2.3 GHz; the wavelength of the irradiated ultraviolet light is 320nm, and the ultraviolet irradiance is 31W/m²；

(3) Immersing ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 81min, wherein the weight-average molecular weight of the polyetherimide is 63150, and the carbon nanotube is a carboxyl-modified multi-walled carbon nanotube, taking out and drying until the water content is 0.38 wt.%, so as to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 1.05 wt.%, and the carbon nanotube content is 0.06 wt.%, and the stable suspension is prepared by ultrasonic dispersion for 40 min;

(4) laminating MCF and PEEK powder with the weight-average molecular weight of 90000 for hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 395 ℃, the pressure is 2.3MPa, and the loading time is 19 min;

(5) cooling the material system after the lamination hot pressing to 325 ℃ at the speed of 55 ℃/min, applying the instantaneous pressure of 6MPa and keeping the pressure for 1s, unloading the pressure, cooling to 275 ℃ at the speed of 55 ℃/min, applying the instantaneous pressure of 2MPa and keeping the pressure for 8min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 881MPa, the bending modulus of 70GPa and the interlaminar shear strength of 100 MPa.

Example 6

(1) sintering the T300 grade 3K5 satin fabric of CF at 383 ℃ for 92min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 97.1 percent, and marking the product as ACF; the microwave radiation time is 12min, and the microwave frequency is 3.9 GHz; the irradiation ultraviolet wavelength is 330nm, and the ultraviolet irradiance is 45W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 78min, wherein the weight average molecular weight of the polyetherimide is 61680, and the carbon nanotube is a carboxyl-modified multi-walled carbon nanotube, taking out the carbon nanotube and drying the carbon nanotube until the water content is 0.35 wt%, so as to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 1.2 wt.%, and the carbon nanotube content is 0.08 wt.%, and the stable suspension is prepared by 50min ultrasonic dispersion;

(4) laminating MCF and PEEK powder with the weight-average molecular weight of 113000 by hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 405 ℃, the pressure is 1.2MPa, and the loading time is 23 min;

(5) cooling the material system after the lamination hot pressing to 335 ℃ at the speed of 58 ℃/min, applying the instantaneous pressure of 7MPa and keeping the pressure for 1s, unloading the pressure, cooling to 285 ℃ at the speed of 58 ℃/min, applying the instantaneous pressure of 2.1MPa and keeping the pressure for 10min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 900MPa, the bending modulus of 72GPa and the interlaminar shear strength of 96 MPa.

Example 7

(1) sintering the T300 grade 3K5 satin fabric of CF at 412 ℃ for 20min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 97.5 percent, and marking the product as ACF; the microwave radiation time is 8min, and the microwave frequency is 6.8 GHz; the wavelength of the irradiated ultraviolet light is 336nm, and the ultraviolet irradiance is 41W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 50min, wherein the weight average molecular weight of the polyetherimide is 61920, and the carbon nanotube is a carboxyl-modified multi-walled carbon nanotube, taking out and drying until the water content is 0.32 wt%, so as to obtain sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 1.4 wt.%, and the carbon nanotube content is 0.09 wt.%, and the stable suspension is prepared by ultrasonic dispersion for 60 min;

(4) laminating MCF and PEEK fiber with the weight-average molecular weight of 136000 by hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 411 ℃, the pressure is 1MPa, and the loading time is 27 min;

(5) cooling the material system after the lamination hot pressing to 341 ℃ at the speed of 59 ℃/min, applying the instantaneous pressure of 5MPa and keeping the pressure for 1s, unloading the pressure, cooling to 291 ℃ at the speed of 59 ℃/min, applying the instantaneous pressure of 2.2MPa and keeping the pressure for 12min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 868MPa, the bending modulus of 75GPa and the interlaminar shear strength of 93 MPa.

Example 8

(1) sintering the T300 grade 3K5 satin fabric of CF at 404 ℃ for 50min to decompose the original sizing agent on the surface at high temperature;

(2) simultaneously performing microwave radiation and ultraviolet radiation on CF in a saturated water vapor environment with the relative humidity of 98.2 percent, and marking the product as ACF; the microwave radiation time is 3min, and the microwave frequency is 10 GHz; the wavelength of the irradiated ultraviolet light is 340nm, and the ultraviolet irradiance is 39W/m²；

(3) Immersing the ACF into a polyetherimide/dichloromethane/carbon nanotube suspension for 10min, wherein the weight average molecular weight of the polyetherimide is 72000, and the carbon nanotube is a carboxyl-modified multi-walled carbon nanotube, taking out the carbon nanotube and drying the carbon nanotube until the water content is 0.28 wt%, thereby obtaining sizing modified carbon fiber MCF;

in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 1.5 wt.%, and the carbon nanotube content is 0.1 wt.%, and the stable suspension is prepared by 35min ultrasonic dispersion;

(4) laminating MCF and PEEK fiber with the weight-average molecular weight of 150000 for hot pressing; the technological parameters of lamination hot pressing are as follows: the temperature is 420 ℃, the pressure is 0.5MPa, and the loading time is 30 min;

(5) cooling the laminated material system to 350 ℃ at the speed of 61 ℃/min, applying the instantaneous pressure of 8MPa and keeping the pressure for 1s, unloading the pressure, cooling to 300 ℃ at the speed of 61 ℃/min, applying the instantaneous pressure of 2.5MPa and keeping the pressure for 15min, and unloading the pressure;

The finally prepared CF/PEEK composite material with the full transverse crystal structure has the bending strength of 768MPa, the bending modulus of 66GPa and the interlaminar shear strength of 91 MPa.

Claims

1. The preparation method of the CF/PEEK composite material with the full transverse crystal structure is characterized by comprising the following steps of:

(1) carrying out pyrolysis on the original sizing agent on the CF surface;

(2) in a saturated water vapor environment, simultaneously carrying out microwave radiation and ultraviolet radiation on CF, and recording a product as ACF; the relative humidity of saturated water vapor is more than 95 percent; the microwave radiation time is 3-30min, and the microwave frequency is 300MHz-10 GHz; the wavelength of the irradiated ultraviolet light is 290-340nm, and the ultraviolet irradiance is 20-50W/m²；

(3) Immersing the ACF into the polyetherimide/dichloromethane/carbon nanotube suspension, taking out and drying to obtain sizing modified carbon fiber MCF; in the polyetherimide/dichloromethane/carbon nanotube suspension, the polyetherimide content is 0.5-1.5 wt%, the carbon nanotube content is 0.01-0.1 wt%, stable suspension is prepared through 5-60min ultrasonic dispersion, the carbon nanotube is a carboxyl modified single-wall or multi-wall carbon nanotube, and the weight-average molecular weight of the polyetherimide is more than 50000; the immersion time is 10-180 min; drying to a water content of less than 0.5 wt.%;

(4) hot-pressing the MCF and PEEK material lamination;

(5) in the cooling process, the resin obtains perturbation shear flow by instantly applying pressure and unloading, and the nucleation and growth of a full transverse crystal structure are induced; the method specifically comprises the following steps: cooling the material system after the lamination hot pressing to 350 ℃ at the speed of more than 50 ℃/min, applying the instantaneous pressure of 2-8MPa and keeping the pressure for 1s, unloading the pressure, cooling to 300 ℃ at the speed of more than 50 ℃/min, applying the instantaneous pressure of 1-2.5MPa and keeping the pressure for 0.5-15min, and unloading the pressure;

thus obtaining the CF/PEEK composite material with the full transverse crystal structure.

2. The method for preparing a CF/PEEK composite material having a full-transverse-grain structure according to claim 1, wherein CF is in the form of satin fabric.

3. The method for preparing CF/PEEK composite material with full transverse crystal structure as claimed in claim 1, wherein the pyrolysis is sintering at 300-420 ℃ for 5-180 min.

4. The method for preparing CF/PEEK composite material with full transverse crystal structure as claimed in claim 1, wherein the PEEK material is in the form of film, non-woven fabric felt, powder or fiber; the weight average molecular weight of the PEEK material is 30000-150000; the technological parameters of lamination hot pressing are as follows: the temperature is 370 ℃ and 420 ℃, the pressure is 0.5-5MPa, and the loading time is 3-30 min.

5. The CF/PEEK composite material with the full transverse crystal structure prepared by the preparation method of the CF/PEEK composite material with the full transverse crystal structure as claimed in any one of claims 1 to 4, wherein: the bending strength is 750-900MPa, the bending modulus is 63-75GPa, and the interlaminar shear strength is 90-100 MPa.