CN109596464B - Method for testing interface performance of carbon nanotube surface modified fiber - Google Patents
Method for testing interface performance of carbon nanotube surface modified fiber Download PDFInfo
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Abstract
The invention provides a method for testing the interface performance of carbon nanotube surface modified fibers, which comprises the steps of spreading carbon nanotube surface modified fibers, sequentially carrying out gas desorption treatment and monofilament treatment, straightening the obtained fiber monofilaments, horizontally sticking two ends to a mold, and vertically placing the mold stuck with the fiber monofilaments into a clamping groove for fixing; then, dripping the resin solution on the fiber monofilament, airing and then testing the contact angle; and (3) curing the resin droplets, then carrying out a microbead debonding test, and calculating according to the test result and the diameter of the fiber monofilament to obtain the fiber/resin interface shear strength. The invention designs a special fiber pretreatment and test sample preparation method aiming at the unique micron-nanometer composite structure characteristics of the carbon nano tube surface modified fiber, and the test method provided by the invention can simultaneously test two important indexes of fiber/resin interface performance evaluation, namely interface shear strength and contact angle, and has the advantages of high efficiency, simple method and accurate representation result.
Description
Technical Field
The invention relates to the technical field of material performance testing, in particular to a method for testing the interface performance of a carbon nano tube surface modified fiber.
Background
The continuous fiber reinforced resin matrix composite material has the advantages of high specific strength, high specific modulus, light weight and designability, and is widely applied to various fields of aviation, aerospace, wind power, automobiles, sports and the like. The fiber/resin interface in the resin-based composite material plays a role in transferring load, and the mechanical property of the composite material is directly influenced by the level of the interface property, so that the research on the interface property of the composite material is always a hotspot and a focus in the field.
As a new one-dimensional nano material, the carbon nano tube has extremely high mechanical property, the tensile strength of a single carbon tube can reach 100GPa, and the tensile modulus can reach 1 TPa. Researchers at the national academy of Mazhou province of technology deposit carbon nanotubes on the surface of carbon fibers by a low-temperature chemical vapor deposition method, so as to improve the specific surface area of the fibers and strengthen the mechanical engagement effect to improve the interface bonding performance of the fibers/resin. (see the literature: structural carbon fiber indirect Composites with advanced properties [ J ] Composites Science and Technology,2015,117:139-145.) As research progresses, the deposition of carbon nanotubes on the surface of fibers by various methods has become a common and effective method for enhancing the properties of the fiber/resin interface. However, researchers have not established a uniform and effective approach to the characterization of the interfacial properties of this novel cross-scale micro-nanocomposite structured fiber.
The bead debonding method and the contact angle method are the two most common methods for characterizing the fiber/resin interface properties. The bead debonding method is a composite material interface evaluation method proposed by honor corporation of japan in 1997 in the journal of composite materials, and characterizes the fiber/resin interface bonding performance by directly pulling off resin beads on a single fiber. Due to simple operation and visual effect, the interface evaluation method is widely used for evaluating the interface performance of the composite material. The contact angle method is a method for evaluating the wettability of a fiber resin, in which the wettability of the fiber by the resin is observed by an optical microscope and the angle of wettability of the fiber by the resin is obtained by image data processing.
At present, researchers separate characterization tests of parameters almost necessary for evaluating the two fiber/resin interfaces, and research efficiency is low. Meanwhile, aiming at the novel fiber with the carbon nano tube deposited on the surface, the unique micron-nano composite structure of the novel fiber causes the characteristics that small molecular gases such as water vapor are easy to adsorb and macromolecular resin is difficult to infiltrate. The unique structure brings various uncertain factors to the infiltration of the resin and the combination of the resin and the fiber, which brings a plurality of difficulties and inconveniences to the representation of the interface performance by a microbead debonding method and a contact angle method, and seriously influences the development of the research field.
Disclosure of Invention
In view of this, the present invention aims to provide a method for testing the interfacial properties of carbon nanotube surface-modified fibers. The test sample prepared by the test method provided by the invention has good resin infiltration and no internal gap, can simultaneously carry out contact angle test and microbead debonding test, improves the test efficiency, and has simple method and accurate representation result.
In order to achieve the above object, the present invention provides the following technical solutions:
a method for testing the interface performance of carbon nanotube surface modified fiber comprises the following steps:
(1) spreading the carbon nano tube surface modified fiber, and then sequentially performing gas desorption treatment and monofilament treatment to obtain a fiber monofilament; the carbon nano tube surface modified fiber comprises a fiber and a carbon nano tube deposited on the surface of the fiber;
(2) straightening the fiber monofilaments, horizontally pasting the two ends of the fiber monofilaments on a mold, and vertically placing the mold pasted with the fiber monofilaments into a clamping groove for fixing; the mould is a concave metal sheet; the middle section of the fiber monofilament is suspended in the concave notch of the die;
(3) dripping the resin solution on the fiber monofilament, and measuring the contact angle between the fiber and the resin liquid drop after airing;
(4) and carrying out heat treatment on the fiber monofilaments with the resin droplets to solidify the resin droplets into resin microbeads, then carrying out a microbead debonding test, and calculating according to the test result and the diameters of the fiber monofilaments to obtain the fiber/resin interface shear strength.
Preferably, the deposition method of the carbon nanotubes on the surface of the fiber comprises chemical deposition or physical deposition.
Preferably, when the deposition method of the carbon nanotubes on the fiber surface is chemical deposition, the method further comprises, before filament spreading:
and placing the carbon nano tube surface modified fiber in liquid for ultrasonic treatment.
Preferably, the liquid comprises one or more of water, ethanol and acetone; the ultrasonic treatment frequency is 20 kHz-60 kHz, the power is 100W-500W, and the time is 5 min-30 min.
Preferably, the gas desorption treatment in the step (1) is carried out under a vacuum condition, the temperature of the gas desorption treatment is 60-120 ℃, and the time is 0.5-3 h.
Preferably, the resin solution in the step (3) comprises a resin, a curing agent and a diluent; the diluent is acetone and/or dichloromethane; the viscosity of the resin solution is 1Pa · s to 10Pa · s.
Preferably, the airing time in the step (3) is 0.5-3 h, the ambient temperature of the airing is 10-30 ℃, and the ambient humidity of the airing is 40-60 RH.
Preferably, the temperature of the heat treatment in the step (4) is 80-200 ℃.
Preferably, the diameter of the resin bead is 30-100 μm.
Preferably, the diameter of the fiber monofilament in the step (4) is obtained by the following method:
taking 10-20 fiber monofilaments of the carbon nanotube surface modified fibers to be detected, shooting the fiber monofilaments by using SEM, and calculating the average diameter as the diameter of the fiber monofilaments;
or calculating according to the linear density and the fiber body density of the carbon nano tube surface modified fibers to be detected and the number of monofilaments of each bundle of fibers to obtain the diameter of the fiber monofilaments;
or, retaining a fiber monofilament sample after the microsphere debonding test, and taking the diameter of the resin bead debonding part as the diameter of the fiber monofilament by SEM shooting;
alternatively, the diameter of the fiber monofilament without surface modification of the carbon nanotubes is used directly.
The invention provides a method for testing the interface performance of carbon nanotube surface modified fibers, which comprises the steps of spreading carbon nanotube surface modified fibers, sequentially carrying out gas desorption treatment and monofilament treatment, straightening the obtained fiber monofilaments, horizontally sticking two ends to a mold, and vertically placing the mold stuck with the fiber monofilaments into a clamping groove for fixing; then, dripping the resin solution on the fiber monofilament, airing and then testing the contact angle; and (4) carrying out a microbead debonding test after the resin liquid drops are solidified, and calculating to obtain the fiber/resin interface shear strength according to the test result and the diameter of the fiber monofilament. The method provided by the invention has the following beneficial effects:
(1) the method carries out filament spreading and gas desorption treatment on the carbon nano tube surface modified fiber, so that the gas adsorbed on the surface of the fiber can be fully desorbed, closed air holes between the fiber and the resin after the resin is cured are prevented from being generated, and the influence of water vapor on the interface strength and the resin strength is avoided;
(2) according to the invention, the fiber monofilament is directly adhered to the die after being divided, so that the contact angle test can be carried out without any other treatment before the resin is cured, and the fiber monofilament can be directly used for the microsphere debonding test after being cured, so that the test characterization efficiency is greatly improved, and the damage in the fiber monofilament transfer process is avoided;
(3) furthermore, the invention aims at the carbon nano tube surface modified fiber obtained by using a chemical deposition method, ultrasonic treatment is carried out before filament spreading, the surface of the fiber and the carbon nano tube covered on the surface of the fiber can be physically activated, and the infiltration of resin to the fiber is facilitated;
(4) furthermore, acetone or dichloromethane is used as a diluent to prepare a resin solution, so that the resin is favorable for fully infiltrating the fibers, the sizes of resin microbeads on the cured fibers are uniformly distributed in a range of 30-100 mu m by controlling the viscosity of the resin, the stress concentration on a single fiber sample is reduced, the fiber breakage is reduced, and the microsphere debonding test is favorably carried out.
(5) Furthermore, the invention provides a diameter obtaining method for various monofilament fibers, which can select a proper fiber diameter obtaining method according to experimental conditions and is beneficial to more accurately calculating the interface shear strength.
The embodiment result shows that the test sample obtained by the test method provided by the invention has good resin infiltration and no internal gap, can simultaneously test the fiber/resin contact angle and the interface shear strength, has accurate test result, and is beneficial to further development of related researches.
Drawings
FIG. 1 is a schematic structural diagram of a mold and a card slot used in an embodiment of the invention;
FIG. 2 is a schematic view of a microsphere debonding test;
in FIGS. 1 to 2: 1-a mould, 2-an adhesive, 3-a fiber monofilament, 4-openings at two sides of a clamping groove, 5-a clamping groove, 6-a resin microbead, 7-a clamping knife of a test device, and 8-a test fixture connected with a load sensor;
FIG. 3 is an SEM image of fibers before and after deposition of carbon nanotubes;
FIG. 4 is an image of the contact angle between the fiber filament to be tested and the resin in example 1;
FIG. 5 is a surface profile of a fiber monofilament to be measured and a profile of a position where resin beads fall off in example 1;
fig. 6 is the interface shear strength of the carbon nanotube surface modified T700S carbon fiber calculated in the different diameter obtaining manner in example 1;
FIG. 7 is a surface profile of a fiber monofilament to be measured and a profile of a position where resin beads fall off in example 2;
fig. 8 is the interface shear strength of the carbon nanotube surface-modified T300 carbon fiber calculated in the different diameter obtaining manner in example 2.
Detailed Description
The invention provides a method for testing the interface performance of carbon nanotube surface modified fibers, which comprises the following steps:
(1) spreading the carbon nano tube surface modified fiber, and then sequentially performing gas desorption treatment and monofilament treatment to obtain a fiber monofilament;
(2) straightening the fiber monofilaments, horizontally pasting the two ends of the fiber monofilaments on a mold, and vertically placing the mold pasted with the fiber monofilaments into a clamping groove for fixing; the mould is a concave metal sheet; the middle section of the fiber monofilament is suspended in the concave notch of the die;
(3) dripping the resin solution on the fiber monofilament, and measuring the contact angle between the fiber and the resin liquid drop after airing;
(4) and carrying out heat treatment on the fiber monofilaments hung with the resin droplets to solidify the resin droplets into resin microbeads, then carrying out a microbead debonding test, and calculating according to the test result and the diameters of the fiber monofilaments to obtain the fiber/resin interface shear strength.
The invention carries out gas desorption treatment and monofilament treatment in sequence after spreading the carbon nano tube surface modified fiber to obtain the fiber monofilament. In the invention, the carbon nanotube surface modified fiber comprises a fiber and a carbon nanotube deposited on the surface of the fiber; the deposition method of the carbon nano tube on the surface of the fiber preferably comprises chemical deposition or physical deposition; the invention has no special requirements on the specific methods of chemical deposition and physical deposition, such as chemical vapor deposition, chemical grafting and the like, and physical deposition methods such as electrophoretic deposition, spray deposition, solution dipping deposition and the like. The invention has no special requirements on the types of the fibers, and common types of fibers can be used, such as carbon fibers, glass fibers, basalt fibers, aramid fibers, PBO fibers, ceramic fibers and the like.
In the present invention, when the deposition method of the carbon nanotubes on the fiber surface is chemical deposition, the method further comprises, before filament spreading: and placing the carbon nano tube surface modified fiber in liquid for ultrasonic treatment. In the present invention, the liquid preferably comprises one or more of water, ethanol and acetone; the ultrasonic frequency of the ultrasonic treatment is preferably 20-60 kHz, more preferably 30-50 kHz, and most preferably 40 kHz; the ultrasonic power is preferably 100-500W, more preferably 200-400W, and most preferably 300W; the ultrasonic treatment time is preferably 5-30 min, more preferably 10-20 min, and most preferably 15 min.
The invention preferably immerses the carbon nano tube surface modified fiber in liquid to carry out ultrasonic treatment by using an ultrasonic cleaning machine, the liquid amount in a container is required to be not more than half of the volume of the container during ultrasonic treatment, and a preservative film is required to seal the container to prevent the liquid from volatilizing when ethanol or acetone is used. The invention physically activates the fiber and the carbon nano tube deposited on the surface by ultrasonic treatment.
When the carbon nano tube is attached to the surface of the fiber through physical deposition, the carbon nano tube surface modified fiber cannot be subjected to ultrasonic treatment, so that the phenomenon that the deposited carbon nano tube falls off from the surface of the fiber through ultrasonic treatment to influence the subsequent characterization of the fiber interface performance is avoided.
After the ultrasonic treatment is finished, the invention dries the fiber and then carries out the silk spreading treatment.
In the invention, the silk spreading is preferably performed by hand or by using a silk spreading machine; the carbon nano tube surface modified fiber is a fiber bundle, the stacking thickness of the fiber can be reduced through filament spreading, the surface area of the filament bundle is increased, and the follow-up desorption of small molecule gas is facilitated. The carbon nanotube surface modified fiber is preferably spread to the width of 0.5-1.0 mm, more preferably 0.6-0.7 mm through spreading.
After the filament spreading treatment is finished, the invention carries out gas desorption treatment on the fiber bundle after filament spreading. In the invention, the gas desorption treatment is preferably carried out under a vacuum condition, and the temperature of the gas desorption treatment is preferably 60-120 ℃, more preferably 80-100 ℃, and most preferably 85-95 ℃; the time of the gas desorption treatment is preferably 0.5 to 3 hours, more preferably 1 to 2 hours, and most preferably 1.5 hours. In the present invention, the gas desorption treatment is preferably performed in a vacuum oven, and in a specific embodiment of the present invention, both ends of the fiber bundle after filament spreading are preferably fixed on a polytetrafluoroethylene film, and then the fiber bundle is placed in the vacuum oven to perform the gas desorption treatment.
After the filament spreading treatment is finished, the invention carries out monofilament treatment on the fiber bundle after the filament spreading to obtain the fiber monofilament. In the present invention, the monofilament treatment is preferably: the fiber bundles are sheared to a length of about 8-10 cm, spread on a white polytetrafluoroethylene film, ejected and dispersed by using pointed tweezers, and clamped to obtain single fibers.
After the fiber monofilaments are obtained, the fiber monofilaments are straightened, two ends of the fiber monofilaments are horizontally adhered to a die, and the die adhered with the fiber monofilaments is vertically placed into a clamping groove to be fixed. In the invention, the die is a concave metal sheet, preferably a concave stainless steel sheet, the thickness of the concave metal sheet is preferably 0.1-0.3 mm, the size of the die has no special requirement, and the die can be adjusted according to the length of a fiber monofilament and a test device (a microbead debonding interface performance evaluation device), as a specific embodiment of the invention, the structure and the size of the die are shown in figure 1; two ends of the fiber monofilament are adhered to the die, and the middle section of the fiber monofilament is suspended in the concave notch of the die; toothed openings are formed in two sides of the clamping groove, and as shown in fig. 1, a plurality of concave metal sheets can be vertically fixed; the clamping groove is preferably made of metal materials, and more preferably made of stainless steel.
The invention preferably uses adhesive to bond two ends of the fiber monofilament on the mould; the adhesive is preferably an adhesive which is high-temperature resistant and can be rapidly cured at room temperature, such as 502, acrylate AB adhesive, R230 and the like. According to the invention, the contact position of the fiber and the mold is preferably coated with an adhesive by using a needle point, then the fiber monofilament is bonded, after the fiber monofilament is bonded, the bonded sample is preferably dried at room temperature for 5-30 min to solidify the adhesive, and then the mold is placed in the clamping groove shown in figure 1.
The operation is preferably repeated, 10-20 samples are prepared for standby, the surface performance of 10-20 samples is tested during testing, and the average value is obtained to improve the testing accuracy.
After the mold is fixed in the clamping groove, the resin solution is dripped on the fiber monofilament, and the contact angle between the fiber and the resin liquid drop is measured after the fiber monofilament is aired. In the present invention, the resin solution preferably includes a resin, a curing agent, and a diluent; the resin is preferably epoxy resin, bismaleimide resin, phenolic resin, polyester resin, cyanate resin or thermosetting polyimide resin; the diluent is preferably acetone and/or dichloromethane; the content of the diluent in the resin solution is preferably 10-40 wt%, more preferably 20-30 wt%, and most preferably 25 wt%; the present invention has no special requirement on the type and the dosage of the curing agent, and in the specific embodiment of the present invention, the corresponding curing agent is preferably selected according to the type of the resin, and the dosage of the curing agent is determined according to the curing ratio.
In the present invention, the viscosity of the resin solution is preferably 1Pa · s to 10Pa · s, more preferably 3Pa · s to 8Pa · s, and further preferably 5Pa · s; the concentration of the resin solution is controlled within the range, so that the size of the cured resin beads can be uniformly distributed in the range of 30-100 mu m, the stress concentration on the fibers is reduced, and the microsphere debonding test is facilitated.
In the specific embodiment of the invention, the resin, the curing agent and the diluent are preferably stirred and mixed, the stirring time is preferably 5-15 min, more preferably 10min, then a 1mL syringe is used for absorbing the resin solution, and the resin solution is uniformly dripped on the fiber monofilament drop by drop, and the use and the movement of the syringe needle are required to be smooth and slow; the invention preferably drops a plurality of resin solution drops on a fiber monofilament to select the resin drops with more proper size for testing, and one sample can test a plurality of data, so that the test result is more accurate.
In the invention, the airing time is preferably 0.5-3 h, more preferably 1-2 h, and most preferably 1.5 h; the air-drying environment temperature is preferably 10-30 ℃, and more preferably 15-25 ℃; the humidity of the drying environment is preferably 40-60% RH, and more preferably 45-55% RH. The invention volatilizes the solvent in the resin by airing.
After the air-drying is finished, the clamping grooves and the fibers hung with the resin drops in the clamping grooves are integrally transferred to a contact angle measuring instrument, a contact image of the fibers/resin is shot by using the contact angle measuring instrument, a fiber/resin contact angle is obtained by processing the image, each fiber sample is preferably tested by the method to obtain 5 numerical values, and the average value is taken to improve the detection accuracy.
After the contact angle test is finished, the fiber monofilament hung with the resin liquid drops is subjected to heat treatment, so that the resin liquid drops are solidified into the resin microbeads. The clamping groove, the die and the fibers bonded on the die are preferably integrally placed in an oven for heat treatment, the heat treatment temperature is preferably 80-200 ℃, the heat treatment time is not particularly required, and the specific heat treatment time is preferably determined according to the curing process system of specific resin; the diameter of the resin bead is preferably 30-100 μm, and more preferably 40-80 μm.
And after the solidification is finished, closing the oven to naturally cool the sample to room temperature, then taking out the sample to perform a microbead debonding test, and calculating according to the test result and the diameter of the fiber monofilament to obtain the fiber/resin interface shear strength. The invention has no special requirements on the specific method of the microsphere debonding test, and the microsphere debonding interface performance evaluation device well known by the technical personnel in the field can be used for testing. In the specific embodiment of the present invention, during the test, a bayonet in the apparatus for evaluating the performance of the microsphere debonding interface is used to clamp the resin microspheres on the fiber monofilaments, and then a certain tensile load is applied to the left, as shown in fig. 2, until the resin beads are pulled away from the fibers, and the maximum tensile force of the process is obtained for calculating the interface shear strength. If fiber breakage and resin bead fragmentation occur in the test process, determining the test result as invalid; according to the invention, 10-20 numerical values are preferably tested by each group of samples, and the average value is taken to improve the detection accuracy; the present invention preferably retains a sample of the fiber filaments after the separation of the resin beads from the fibers, and the fiber filament diameters at the separated positions of the resin beads are observed using SEM.
In the invention, the calculation formula of the fiber/resin interfacial shear strength measured by the microbead debonding method is shown as formula I:
in the formula I, FmaxThe maximum force (N) when the resin slips is directly given by an instrument after the test; dfFiber filament diameter (mm); leThe embedded length (mm) of the fiber for the resin drop was measured directly by the measuring tool in the test software after magnifying the sample by an optical microscope.
For fiber filament diameter dfThe measurement and calculation of the carbon nanotube surface modified fiber is different from the traditional fiber in that the carbon nanotubes are deposited on the surface of the fiber, the diameter of the fiber is apparently increased by the carbon nanotubes with a certain length, but the carbon nanotube layer has a large number of obvious gaps, and the diameters of the fiber before and after the carbon nanotubes are deposited are shown in fig. 3. And the fiber surface states and diameters show different conditions after different deposition methods and different resin bead debonding tests, and the selection of the fiber diameter directly determines the accuracy of the calculated interface shear strength. In view of the above, the present invention provides the following four fiber filament diameter obtaining methods, and the advantages and disadvantages of each obtaining method are explained.
The method comprises the steps of taking 10-20 fiber monofilaments of the carbon nanotube surface modified fibers to be detected, shooting the fiber monofilaments by using an SEM (scanning electron microscope), and calculating the average diameter to be used as the diameter of the fiber monofilaments. The acquisition mode is simple and intuitive, but most of the carbon nanotubes deposited on the fiber are pulled off together with the resin after the microsphere debonding test, so the diameter of the fiber which actually damages the interface is smaller than the diameter measured by the method, and the difference is possibly large.
And secondly, calculating according to the linear density and the bulk density of the carbon nano tube surface modified fibers and the number of monofilaments of each bundle of fibers to obtain the diameter of the fiber monofilaments. The method can effectively avoid the phenomenon that the apparent diameter of the fiber is larger due to the gaps among the carbon nano tubes deposited on the surface, but the actual fiber number is lower due to the possibility of fiber breakage in the actual operation, so that the diameter of the fiber obtained by the method is slightly larger.
And thirdly, reserving a fiber monofilament sample after the microbead debonding test, and taking the diameter of the resin bead debonding part as the diameter of the fiber monofilament by SEM shooting. The diameter obtained by the method can represent the stress area condition of the fiber/resin interface when the fiber/resin interface is damaged most accurately, so that the calculated interface shear strength is also most accurate. However, the method needs more complex post-test work, and the workload is the largest.
And fourthly, directly using the diameter of the fiber monofilament without the surface modification of the carbon nano tube. The method is suitable for the condition that the deposition and combination of the carbon nano tube is not firm and the action of a fiber/resin interface is poor, the fiber surface is smooth after the microbeads fall off, no resin and carbon nano tube residue exist, and the fiber diameter is basically the same as that of the fiber of the carbon nano tube which is not deposited.
The invention designs a special fiber pretreatment and test sample preparation method aiming at the unique micron-nanometer composite structure characteristics of the carbon nano tube surface modified fiber, and the test method provided by the invention can simultaneously test two important indexes of fiber/resin interface performance evaluation, namely interface shear strength and contact angle. Meanwhile, the method optimizes the selection details of the fiber diameter in the interface shear strength calculation, and greatly improves the evaluation efficiency and accuracy of the fiber/resin interface performance.
The embodiments of the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
The fibers to be measured are: 12K Dongli T700S carbon fiber with carbon nanotubes deposited on the surface by chemical vapor deposition;
and (2) immersing the carbon fiber bundle to be detected into ethanol, and carrying out ultrasonic treatment by using an ultrasonic cleaning machine, wherein the ultrasonic frequency of the ultrasonic treatment is 40kHz, the ultrasonic power is 400W, and the ultrasonic treatment time is 15 min. After the ultrasonic treatment, the fiber tows are spread to the width of 0.6mm by using a spreading machine. Fixing two ends of the fiber bundle after filament spreading on a polytetrafluoroethylene film, and putting the fiber bundle into a vacuum oven for vacuum desorption treatment. The treatment temperature is 100 ℃ and the treatment time is 2 h.
The treated fiber bundle was cut to a length of about 8cm, spread on a white polytetrafluoroethylene film, spread apart and dispersed with tweezers, and picked up and placed on a stainless steel mold as shown in fig. 1 for individual fibers. And (3) coating a needle point R230 adhesive on the contact position of the fiber and the mold, and airing at the room temperature of 25 ℃ for 10min for curing. A total of 20 samples were made. Simultaneously measuring the density of the fiber bunch to be measured to be 0.907g/m and the density of the fiber body to be measured to be 1.805g/cm3And taking the fiber monofilament to carry out SEM shooting to obtain the visual diameter.
After the fibers were attached to the mold, the mold was fixed in the neck shown in fig. 1, 10g of AG80 resin and 5.4g of DDS curing agent were weighed in a beaker, and 3.08g of acetone (20 wt% of the mass of the resin and curing agent, and greater viscosity of AG80 resin) was added to the resin for dilution. After weighing, the resin, curing agent and acetone were mixed with a glass rod for 8 min. The resin solution is absorbed by a 1mL syringe with a pinhole diameter of 0.3mm, then the solution is uniformly dripped on the carbon fiber monofilament drop by drop, and the solution is dried in an air environment at 25 ℃/50% RH for 2h to volatilize the acetone in the resin.
After the air-drying is finished, the clamping groove and the carbon fiber hung with the resin drop are transferred to a contact angle measuring instrument, a contact image of the fiber/resin is shot as shown in fig. 4, and contact angle data are obtained through processing. The average contact angle of T700/AG80/DDS was found to be 81.1 ° with a standard deviation of 2.5 °. And as can be seen from fig. 4, the resin and the fibers are well infiltrated, no voids appear inside, which also ensures the accuracy of the test.
And after the contact angle test is finished, putting the carbon fiber which is put into the clamping groove and hung with the resin drops into an oven, preserving heat for 3h to solidify resin beads at 180 ℃, closing the oven after solidification to naturally cool the sample to room temperature, taking out the sample, and performing a bead debonding test to obtain 20 data in total.
SEM images of the surface of the fiber and the separation position of the resin beads are shown in fig. 5, wherein (1) in fig. 5 is an SEM image of the surface of the fiber, and (2) in fig. 5 is an SEM image of the separation position of the resin beads; the fiber diameter directly obtained by SEM was 8.66 μm, the fiber diameter obtained by the fiber bundle line density and the fiber bulk density was 7.30 μm, the fiber diameter at the point where the resin beads fell off by fracture SEM was 7.56 μm, and the original diameter of the fiber where the carbon nanotubes were not deposited was 7.09 μm. The interfacial shear strength calculated from the respective diameters is shown in fig. 6.
As can be seen from the results of fig. 6, when the carbon nanotubes on the surface of the fiber to be measured are the chemical vapor deposition which is a firm method or the epoxy resin having a strong binding force with the fiber is used, more resin remains on the surface of the fiber, the interfacial shear strength calculated by taking the fiber diameter at the position where the resin beads are dropped using the SEM (mode three) is most accurate, the interfacial shear strength calculated by taking the fiber diameter obtained by the line density and the bulk density (mode two) is not much different from the former, and the accuracy of the interfacial shear strength calculated by directly obtaining the apparent fiber diameter of the fiber with the carbon nanotubes deposited by the SEM (mode one) and the original diameter of the fiber with the carbon nanotubes not deposited (mode four) is poor.
According to the embodiment, the method provided by the invention can efficiently and accurately obtain the interface shear strength and the contact angle of the carbon fiber with the carbon nano tube deposited on the surface and the epoxy resin, and is beneficial to further development of related researches.
Example 2
The fiber to be tested is 12K T300 carbon fiber with carbon nano tubes deposited on the surface by an electrophoretic deposition method.
And (3) unfolding the carbon fiber bundle to be detected to 0.7mm in width by using a filament unfolding machine, fixing two ends of the fiber bundle after filament unfolding on a polytetrafluoroethylene film, and putting the fiber bundle into a vacuum oven for vacuum desorption treatment. The treatment temperature is 90 ℃ and the treatment time is 3 h.
The treated carbon fiber bundles were cut to a length of about 10cm, spread on a white polytetrafluoroethylene film, dispersed by wearing rubber gloves, and gripped with individual fibers and placed on a stainless steel mold as shown in fig. 1. And (3) applying the uniformly mixed double-component acrylate AB adhesive to the contact position of the fiber and the mold by using a needle point, and airing at the room temperature of 30 ℃ for 30min for curing to obtain 15 samples in total. Simultaneously measuring the density of a fiber bundle line to be 1.02g/m and the density of a fiber body to be 1.810g/cm3And taking the fiber for SEM shooting to obtain the visual diameter.
After the fibers were attached to the mold, the mold was fixed in a neck as shown in fig. 2, 10g of E51 resin and 8.4g of BC126 curing agent were weighed in a beaker, and 1.84g of acetone (10 wt% of the mass of the resin and the curing agent) was added to the resin for dilution. After weighing, the resin, curing agent and acetone were mixed with a glass rod for 15 min. The resin solution was aspirated by a 1mL syringe with a pinhole diameter of 0.4mm, then uniformly dropped onto the carbon fiber monofilament drop by drop, and allowed to air at 30 ℃/45% RH for 1.5h to volatilize acetone in the resin.
After the airing is finished, the carbon fiber monofilaments which are placed into the clamping grooves and hung with the resin drops are integrally placed into an oven to be cured at the temperature of 120 ℃ for 3 hours, the oven is closed after the curing is finished, the sample is naturally cooled to the room temperature, the sample is taken out to be subjected to a microbead debonding test, and 20 data are measured in total.
The SEM images of the fiber surface and the resin bead detachment are shown in fig. 7, wherein fig. 7(1) is the SEM image of the fiber surface, and fig. 7(2) is the SEM image of the resin bead detachment; the fiber diameter directly obtained by SEM was 8.08 μm, the fiber diameter obtained by the fiber bundle density, the fiber bulk density was 7.75 μm, the fiber diameter at the point where the resin beads were detached in the fracture SEM was 7.50 μm, the fiber surface at the fracture was smooth, almost no resin and carbon nanotubes remained, and the original diameter of the fiber where the carbon nanotubes were not deposited was 7.45 μm. The interfacial shear strength calculated from the respective diameters is shown in fig. 8.
As can be seen from the results of fig. 8, when the carbon nanotubes on the surface of the fiber to be measured are physically deposited (the carbon nanotubes are not firmly bonded to the surface of the fiber) and a resin having a weak bonding force with the fiber is used, the resin and the carbon nanotubes remain on the surface of the fiber hardly. At this time, the interfacial shear strength calculated by taking an image of the fiber diameter at the resin bead drop position using SEM (method three) is most accurate, the interfacial shear strength calculated by the fiber diameter of the non-deposited carbon nanotube (method four) is substantially the same as the former, and the interfacial shear strength calculated by the apparent diameter of the fiber of the deposited carbon nanotube directly obtained by SEM (method one) and the average diameter obtained by using the tow line density/fiber bulk density/fiber number (method two) is less accurate.
According to the embodiment, by adopting the method provided by the invention, different fiber diameter obtaining methods are selected according to different deposition methods and resin binding force, the interface shear strength of the carbon fiber with the carbon nano tube deposited on the surface and the epoxy resin can be obtained more efficiently and accurately, and the further development of research is facilitated.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A method for testing the interface performance of carbon nanotube surface modified fibers is characterized by comprising the following steps:
(1) spreading the carbon nano tube surface modified fiber, and then sequentially performing gas desorption treatment and monofilament treatment to obtain a fiber monofilament; the carbon nano tube surface modified fiber comprises a fiber and a carbon nano tube deposited on the surface of the fiber;
(2) straightening the fiber monofilaments, horizontally pasting the two ends of the fiber monofilaments on a mold, and vertically placing the mold pasted with the fiber monofilaments into a clamping groove for fixing; the mould is a concave metal sheet; the middle section of the fiber monofilament is suspended in the concave notch of the die;
(3) dripping the resin solution on the fiber monofilament, and measuring the contact angle between the fiber and the resin liquid drop after airing;
(4) carrying out heat treatment on the fiber monofilaments with the resin droplets to solidify the resin droplets into resin microbeads, then carrying out a microbead debonding test, and calculating according to the test result and the diameters of the fiber monofilaments to obtain the fiber/resin interface shear strength;
the gas desorption treatment in the step (1) is carried out under the vacuum condition, the temperature of the gas desorption treatment is 85-95 ℃, and the time is 0.5-2 h; the deposition method of the carbon nano tube on the surface of the fiber comprises chemical deposition or physical deposition; when the deposition method of the carbon nano tube on the surface of the fiber is chemical deposition, the method before filament spreading further comprises: placing the carbon nano tube surface modified fiber in liquid for ultrasonic treatment;
the airing time in the step (3) is 0.5-3 h, the airing environment temperature is 10-30 ℃, and the airing environment humidity is 40-60 RH; the temperature of the heat treatment in the step (4) is 80-200 ℃; the resin solution in the step (3) comprises resin, a curing agent and a diluent; the diluent is acetone and/or dichloromethane; the viscosity of the resin solution is 1 Pa.s-10 Pa.s;
the diameter of the fiber monofilament in the step (4) is obtained by the following method:
taking 10-20 fiber monofilaments of the carbon nanotube surface modified fibers to be detected, shooting the fiber monofilaments by using SEM, and calculating the average diameter as the diameter of the fiber monofilaments;
or calculating according to the linear density and the fiber body density of the carbon nano tube surface modified fibers to be detected and the number of monofilaments of each bundle of fibers to obtain the diameter of the fiber monofilaments;
or, retaining a fiber monofilament sample after the microsphere debonding test, and taking the diameter of the resin bead debonding part as the diameter of the fiber monofilament by SEM shooting;
or, directly using the diameter of the fiber monofilament without surface modification of the carbon nanotube;
the diameter of the resin bead is 30-100 mu m;
the calculation formula of the fiber/resin interface shear strength measured by the microsphere debonding is shown as formula I:
in the formula I, FmaxThe maximum force (N) when the resin slips is directly given by an instrument after the test; dfFiber filament diameter (mm); leThe embedded length (mm) of the fiber for the resin drop was measured directly by the measuring tool in the test software after magnifying the sample by an optical microscope.
2. The test method of claim 1, wherein the liquid comprises one or more of water, ethanol, and acetone; the ultrasonic treatment frequency is 20 kHz-60 kHz, the power is 100W-500W, and the time is 5 min-30 min.
3. The test method according to claim 1, wherein the resin beads have a diameter of 30 to 100 μm.
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