RU2538687C2 - Method of determining degree of impregnation of carbon fibre braids with pitches and device for its realisation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to field of producing carbon-carbon composite materials for various purposes, and is intended for comparative characteristic of impregnation of carbon fibre (CF) braids with melts of pitches, and can be used in improvement of technologies of producing carbon-carbon composite materials, possessing various properties, by modification or replacement of pitch binder and/or carbon fibre, for instance, in research laboratories, in particular, in carrying out laboratory work. To determine degree of impregnation of carbon fibre braids with pitches, carbon fibre braid is placed into glass tube in such a way that the end of braid protrudes from glass tube, and carbon fibres in braid are oriented along glass tube axis, with braid thickness being selected in such a way that it tightly fits glass tube, protruding end of carbon fibre braid is brought in contact with melted pitch and keep in such position, after which carbon fibre braid is extracted from tube and height of impregnation of carbon fibre braid with pitch is determined.

EFFECT: simplification and acceleration of determination are achieved.

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Description

The invention relates to the production of carbon-carbon composite materials for various purposes, is intended for the comparative assessment of the impregnation of carbon fiber bundles with pitch melts and can be used to develop technologies for the production of carbon-carbon composite materials having various properties by modifying or replacing the pitch binder and / or carbon fiber, for example, in scientific laboratories, in particular, during laboratory work.

Carbon fibers are characterized by a unique combination of physico-mechanical and chemical properties, combining high strength with chemical inertness, which allows them to be used to create composite materials not only for general purposes, but also for aviation and space purposes. The strength and reliability of such materials, as well as the simplification of the technological scheme for their preparation, depends on the nature of the interaction at the carbon fiber / matrix interface. Functionalization of carbon fiber, binder modification, etc. helps to increase the adhesion of carbon fiber to the matrix and increase the mechanical properties of the resulting material.

One of the factors determining the strength of a composite material consisting of a reinforcing component in the form of bundles of carbon fiber and a polymer matrix in the form of pitch is the ability of the binder to wet the carbon fiber, in other words, the affinity of carbon fiber and pitch. Wetting, in turn, determines the degree of impregnation of the fiber filler with a binder during molding and the uniformity of the material obtained.

A known method for determining the wetting of carbon fiber with pitch, which was carried out by the Wilhelmy plate method on a power tensiometer (Shornikova ON, et al. Wetting carbon fibers with melts of coal tar pitch // Chemical fibers. - 2012. - No. 4. - P. 64-68) . This method is adopted as a prototype. The essence of the Wilhelmy plate method is to immerse a plate with known geometric parameters in the test liquid: when the plate is immersed in a liquid, the buoyancy force F acts on it, which depends on the depth of immersion of the plate in the liquid. In this case, at the first stage of work, the wetting angles of carbon fibers were measured with model liquids, monofilament samples were placed in cylindrical hollow holders, and fixed with a wire so that the length of the free end of the fiber did not exceed 5 mm. The holder was mounted on the balance and the sample was brought into contact with the model fluid. The measurements were carried out for 10 fiber samples of the same type; within each measurement, 5 fiber dipping / extraction cycles were performed. In each cycle, a wetting curve was recorded — the dependence of the force acting on the sample on the immersion depth. Then, equilibrium wetting angles, polar and dispersion components of the free surface energy of the fibers were calculated. Then the characteristics of the pitch were determined. For this, a pitch sample was placed in a glass with a diameter of 70 mm and a height of 40 mm, so that the glass was half full. A glass with a pitch was placed in a thermostatic cell with a temperature of 160 ° C. Next, the surface tension of the pitch melts was measured by the Du Nui ring method. For each sample, 10 measurements were performed. Next, the contact angle of the Teflon plate was measured with the pitch melt, and the polar and dispersion components of the pitch melts were calculated. At least 5 measurements were performed for each sample. Between measurements, the pitch was thermostated for 10 minutes with the lid closed.

This technology for determining the wetting of carbon fiber by pitch is very complex, time-consuming and requires a lot of time for the measurement process and the process of decrypting data. Another disadvantage of the described method is the complexity of its hardware design.

In addition, measuring the wetting of the fibers with a polymer binder (pitch) directly is not always possible due to the small diameters of the monofilaments and the viscosity of the binder.

The objective of the invention is to simplify and accelerate the process of determining the degree of impregnation of carbon fibers with pitch, as well as the simplification of equipment for determining the degree of impregnation of carbon fibers with pitch.

The technical result is achieved by a method for determining the degree of impregnation of carbon fiber bundles with pitch, which is characterized in that the carbon fiber bundle is placed in a glass tube so that the end of the bundle protrudes from the glass tube and the carbon fibers in the bundle are oriented along the axis of the glass tube, while the thickness the tow is selected so that it is held tightly in the glass tube, the protruding end of the carbon fiber tow is brought into contact with the molten pitch and kept in such position m, then the carbon fiber bundle is removed from the tube and determine the height of the carbon fiber bundle impregnation pitch.

The technical result is also achieved by means of an apparatus for determining the degree of impregnation of carbon fiber bundles with pitch, with which the method described above can be carried out and which contains a furnace, a base with the possibility of placing it in a furnace, a bath installed on the base, and a holder for at least one vertically mounted glass tube located on the base above the bath with the possibility of vertical reciprocating movement.

The above features and advantages of the present invention will be clear from the following description of preferred examples of their implementation with reference to the accompanying drawings, in which the same elements are denoted by the same positions:

figure 1 presents a diagram of an installation for determining the degree of impregnation of bundles of carbon fiber pitch in accordance with the present invention;

figure 2 - diagram of the base with installed on it a tray and a holder in its original position in accordance with the present invention;

figure 3 is a diagram of the base with a bath and holder mounted on it in a position where the protruding end of the carbon fiber tow is lowered into the molten pitch, in accordance with the present invention.

The method for determining the degree of impregnation of carbon fiber bundles with pitch in accordance with the present invention is based on the phenomenon of capillary absorption of a liquid (solution, melt) in the region between the carbon fibers collected in the bundle. To implement the inventive method, at least one glass tube 1 is used in which a carbon fiber tow 2 is placed. The thickness of the tow 2 is selected so that it is held tightly in the glass tube 1. The carbon fibers in the tow 2 are oriented along the axis of the glass tube (almost parallel). The free end of the carbon fiber tow 2 protruding from the glass tube 1 is brought into contact with the impregnating liquid — molten pitch 4 and held in this position for a fixed period of time. Since the sizing is applied to the carbon fibers and also defects are present, no matter how dense the packaging of the carbon fibers in the tow 2, there are long and narrow spaces between them. If the carbon fiber is wetted by molten pitch 4, then due to the effect of capillary absorption, it will rise along the carbon fibers and fill the distance between them. If the packaging of the bundle of 2 carbon fibers is not tight, then the gravitational force will exceed the force of capillary absorption, and the melt of the pitch will not impregnate the bundle of carbon fibers. Then, the carbon fiber tow 2 is removed from the glass tube 1 and the path traveled by the molten pitch 4 in the central part of the tow 2 is determined. the height of the impregnation of the tow of 2 carbon fiber pitch 4.

The method described above can be carried out on an installation for determining the degree of impregnation of carbon fiber bundles with pitch, which contains a furnace 5 and a base 6, which is arranged to be placed in a furnace 5. As a furnace 5, a drying cabinet or a muffle furnace can be used, providing temperatures up to 350 ° C. On the base 6, a tray 7 for the pitch 4 is mounted. On the base 6, a holder 8 for at least one vertically mounted glass tube 1 is arranged with a possibility of vertical reciprocating movement over the tray 7.

Work on the installation for determining the degree of impregnation of carbon fiber tows with pitch is carried out as follows.

Carbon fibers are cut to the same length and folded together to form a tow 2. The resulting tow 2 is placed in the glass tube 1 so that the end of the tow 2 protrudes from the glass tube. 1, and the carbon fibers in the bundle 2 were oriented along the axis of the glass tube 1, while the thickness of the bundle 2 was chosen so that it held tightly in the glass tube 1.

Pitch pitch 4 is poured into the bath 7 and a holder 8 for at least one glass tube 1 is mounted above it. At least one glass tube 1 is vertically fixed to the holder 8 so that the protruding end of the carbon fiber tow 2 is at some distance from the pitch level.

The base 6 with a bath 7 filled with pitch 4 and a holder 8 with at least one glass tube 1 with a carbon fiber bundle 2 is placed in a furnace 5 heated to a temperature that is 80 ° C above the softening point of the pitch (~ 190 ° C) . After the molten pitch 4 is further incubated for 30 minutes. After that, the holder 8 is lowered to such a level that the protruding end of the carbon fiber bundle 2 comes into contact with the molten pitch 4, and the edge of the glass tube 1 is above the level of the pitch 4. The holder 8 is fixed and held in this position. Then the base 6 is removed from the furnace 5, and the holder 8 is raised to its original position. After cooling, the carbon fiber tow 2 is removed from the glass tube 1 and the impregnation height of the carbon fiber tow 2 is determined (for example, tactilely) by pitch 4.

The described method is proposed for a comparative assessment of the impregnation of carbon fiber bundles with pitch melts, the results of which can be used to develop technologies for the production of carbon-carbon composite materials, depending on their mechanical and operational properties, by modifying or replacing the pitch binder and / or carbon fiber.

Example.

The installation for determining the degree of impregnation of carbon fiber tows with pitch contains:

- the base 6 with located on it with the possibility of vertical reciprocating movement of the holder 8 for glass tubes 1;

- glass tubes 1 with an inner diameter of 8 mm (5 pieces);

- a bath 7 for melt pitch 4;

- furnace 5, providing a temperature of up to 350 ° C.

The determination of the degree of impregnation of carbon fiber tows with pitch in the specified installation was carried out as follows.

1. Preparation of carbon fiber samples.

Carbon fibers were cut into 100 mm lengths and folded together into bundles 2 so that the resulting linear density was 27,000 tex.

The obtained carbon fiber tows were placed in glass tubes 1 so that the end of the tow 2 protruded 10-13 mm from the edge of the glass tube 1. The ends of the harness 2 were trimmed with scissors.

2. Preparation of the installation to determine the degree of impregnation.

Pitch 4 was poured into the bath 7 and a holder 8 was installed over it, into which 5 glass tubes 1 with a carbon fiber tow 2 were fixed so that the distance from the pitch level to the end of the carbon fiber tow 2 was 15–20 mm. The initial position of the installation before analysis is shown in figure 2

3. Carrying out the determination of the degree of impregnation.

The base 6 with a bath 7 and a holder 8, in which glass tubes 1 with bundles of carbon fiber 2 are placed, were placed in a furnace 5 heated to a temperature that was 80 ° C above the softening point of the pitch (~ 190 ° C). After the pitch 4 was molten, the installation was additionally held for 30 minutes. After that, the holder 8 was lowered to such a level that the ends of the carbon fiber bundles 2 were immersed in the molten pitch 4, while the edges of the glass tubes 1 were 1-2 mm above the level of the pitch 4 (see figure 3). The position of the holder 8 was fixed and held for 2 hours. Then the base 6 was removed from the furnace 5 and the holder 8 was raised to its original position (see figure 2).

After cooling, the carbon fiber tows 2 were removed from the glass tubes 1 and the impregnation height of the carbon fiber tow 2 was determined (tactilely) with pitch 4.

This example confirms that the proposed method and installation can simplify and speed up the process of determining the degree of impregnation of carbon fiber bundles with pitch, as well as simplify the hardware and reduce the operation to decrypt the data.

The embodiment described above should in all aspects be considered merely illustrative and not limiting. Therefore, other embodiments of the present invention and implementation examples that do not go beyond the essential features described herein may be used.

Claims (1)

A method for determining the degree of impregnation of carbon fiber bundles with pitch, characterized in that the carbon fiber bundle is placed in a glass tube so that the end of the bundle protrudes from the glass tube and the carbon fibers in the bundle are oriented along the axis of the glass tube, the thickness of the bundle being selected in this way so that it fits tightly in the glass tube, the protruding end of the carbon fiber tow is brought into contact with the molten pitch and held in this position, then the carbon fiber tow is removed from the tube and determine the height of impregnation of the carbon fiber tow with pitch.

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