Aged prepreg reutilization judgment method and aged prepreg reutilization method

Abstract

The invention discloses an aged prepreg recycling judgment method and an aged prepreg recycling method. The aged prepreg recycling judgment method comprises the following steps: classifying aged prepregs according to categories; obtaining the curing enthalpy of the unaged prepreg; obtaining the curing residual enthalpy of the aged prepreg; calculating the aging degree of the aged prepreg; characteristic parameters at different heating rates are obtained and used for calculating a solidification kinetic equation of the characteristic parameters; the storage modulus abrupt change point of the resin in the unaged prepreg at the preset curing process temperature is tested, the curing degree corresponding to the point is calculated through a curing kinetic equation, and the curing degree is a gel point; and screening out the aged prepreg with the aging degree smaller than that of the gel point, and classifying the aged prepreg according to categories. The aged prepreg recycling method comprises the following steps: obtaining a viscosity-temperature curve during resin curing, and obtaining an optimal forming temperature through the viscosity-temperature curve; and laying the aged prepregs of the same type according to the designed layers, and heating to the optimal forming temperature for forming.

Description

Technical Field

[0001] The invention relates to the technical field of composite material recycling, in particular to a method for judging the reuse of aged prepreg and a method for reusing aged prepreg. Background Art

[0002] The epoxy matrix in unidirectional carbon fiber reinforced epoxy prepreg is composed of epoxy resin, curing agent and other components. Epoxy molecules are easily cross-linked and cured under the induction of factors such as light, moisture, heat and ultraviolet rays, forming an insoluble and infusible permanent three-dimensional cross-linked network, which leads to the deterioration of the overall quality of the prepreg and affects its final use. This leads to the problem of the service life of carbon fiber epoxy prepreg.

[0003] The industry generally believes that the curing of epoxy resin prepreg will have a great impact on the quality of the final product. Therefore, the aged prepreg is usually discarded or buried without evaluating whether the aged prepreg can be reused, resulting in huge economic losses and adverse impacts on the environment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for judging the reuse of aged prepreg and a method for reusing aged prepreg, so as to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0005] The solution of the present invention to solve its technical problem is:

[0006] The method for judging the reuse of aged prepreg comprises the following steps:

[0007] Classify aged prepregs by category;

[0008] Testing the unaged prepreg using a preset curing process to obtain the curing enthalpy of the unaged prepreg;

[0009] The aged prepreg is tested using a preset curing process to obtain the curing residual enthalpy of the aged prepreg; the aging degree of the aged prepreg is calculated by dividing the value obtained by subtracting the curing residual enthalpy from the curing enthalpy by the curing enthalpy;

[0010] Test the heat flow temperature curve of unaged prepreg at different heating rates, and obtain the characteristic parameters at different heating rates to calculate its curing kinetic equation;

[0011] Test the storage modulus mutation point of the resin in the unaged prepreg at the preset curing process temperature, and calculate the curing degree corresponding to the point by the curing kinetic equation, which is the gel point;

[0012] The aging degree and gel point of the aged prepregs were compared, and the aged prepregs with aging degree less than the gel point were screened out and classified by category.

[0013] As a further improvement of the above technical solution, the aged prepreg is classified and collected according to different grades of carbon fiber and different grades of epoxy resin.

[0014] As a further improvement of the above technical solution, before testing the unaged prepreg, the following steps are also included: the aged prepreg is stored at low temperature according to categories.

[0015] As a further improvement of the above technical solution, after screening out the reusable aged prepregs, the aged prepregs need to be stored at low temperatures according to their categories.

[0016] As a further improvement of the above technical solution, the storage temperature of the aged prepreg is lower than -18°C.

[0017] As a further improvement of the above technical solution, before the step of obtaining the curing residual enthalpy of the aged prepreg, the aged prepreg is first cut into small pieces, and then the small pieces of the aged prepreg are tested.

[0018] As a further improvement of the above technical solution, a differential scanning calorimeter is used to test the curing enthalpy and the curing residual enthalpy.

[0019] As a further improvement of the above technical solution, a rotational rheometer is used to test the storage modulus mutation point.

[0020] The method for recycling aged prepreg is applicable to the aged prepreg screened out by any of the above-mentioned methods for judging the recycling of aged prepreg, and the method for recycling aged prepreg comprises the following steps:

[0021] Extract uncured resin from unaged prepreg, cure the uncured resin to obtain resin with the same aging degree as that of aged prepreg, obtain viscosity-temperature curve of resin viscosity changing with temperature when the resin is cured, and obtain the temperature at which the viscosity of the resin with the aging degree is the lowest through the viscosity-temperature curve, which is the optimal molding temperature;

[0022] The aged prepregs of the same category are laid out according to the designed layers, heated to the optimum molding temperature and molded to reuse the aged prepregs.

[0023] As a further improvement of the above technical solution, the heating rate when curing the uncured resin is 5° C. / min.

[0024] The beneficial effects of the present invention are: whether the aged prepreg can be reused can be evaluated, and different molding temperatures are used corresponding to different aged prepregs, thereby ensuring high-quality molding of the prepreg.

[0025] The invention is used in the technical field of composite material recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly describes the drawings required for use in the description of the embodiments. Obviously, the drawings described are only part of the embodiments of the present invention, not all of the embodiments, and those skilled in the art can also obtain other design solutions and drawings based on these drawings without creative work.

[0027] Figure 1 is a flow chart of a method for determining the reuse of aged prepreg according to an embodiment of the present invention;

[0028] Figure 2 The figure is a flow chart of a method for recycling aged prepreg according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships mentioned in the text do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0030] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for recycling aged carbon fiber / epoxy resin prepreg to directly prepare composite materials, and utilizes the aged carbon fiber / epoxy resin prepreg to produce carbon fiber composite laminates and various types of profiles, thereby realizing the recycling of the aged carbon fiber / epoxy resin prepreg to overcome the shortcomings and problems of existing recycling and landfill technologies.

[0031] Reference Figure 1 , a method for judging the reuse of aged prepreg comprises the following steps:

[0032] S100, classify and collect the aged carbon fiber / epoxy resin prepregs according to different grades of carbon fiber and different grades of epoxy resin, and store the aged carbon fiber / epoxy resin prepregs at a low temperature (not higher than -18°C) according to the categories to prevent the aged carbon fiber / epoxy resin prepregs from further aging;

[0033] S200, obtaining an unaged carbon fiber / epoxy resin prepreg, and testing it using a DSC (differential scanning calorimeter) under a preset curing process of the prepreg (in this embodiment, the preset curing process is the most commonly used recommended curing process in the art, and in other embodiments, the parameters of the curing process may also be adjusted according to actual needs) to obtain the curing enthalpy of the prepreg;

[0034] S300, randomly cutting small pieces from various aged carbon fiber / epoxy resin prepregs stored at low temperatures, testing the curing residual enthalpy of the prepregs by using a DSC (differential scanning calorimeter) under the recommended curing process of the prepregs, and dividing the value obtained by subtracting the curing residual enthalpy from the curing enthalpy by the curing enthalpy to obtain the degree of curing, i.e., the degree of aging, of the aged carbon fiber / epoxy resin prepregs;

[0035] S400, obtaining unaged carbon fiber / epoxy resin prepreg, using DSC (differential scanning calorimeter) to test the heat flow temperature curve of the prepreg at different heating rates, and obtaining characteristic parameters at different heating rates to calculate its curing kinetic equation. By calculating the curing kinetic equation, the curing degree of the prepreg at any time in the curing process can be known;

[0036] S500, it is necessary to obtain unaged carbon fiber / epoxy resin prepreg, use a rotational rheometer to test the storage modulus mutation point of the resin in the prepreg at the recommended curing process temperature, and calculate the curing degree corresponding to the point by the curing kinetic equation, which is the gel point of the prepreg;

[0037] S600. If the aging degree of the carbon fiber / epoxy resin prepreg is greater than the gel point and cannot be reused by any method, various types of carbon fiber / epoxy resin prepregs whose aging degree does not exceed the gel point shall be screened out and classified according to the aging degree to ensure that the same type of prepregs have the same brand of carbon fiber, epoxy resin and the same aging degree, and the same type of prepregs shall be uniformly stored at low temperature (not higher than -18°C).

[0038] Reference Figure 2 , a method for recycling aged prepreg, comprising the following steps:

[0039] S700, scrape the uncured resin from the unaged carbon fiber / epoxy resin prepreg, set the temperature of the rotational rheometer according to the curing process calculated by the curing dynamics, and obtain the resin with the same aging degree as the aged prepreg. Test the change of resin viscosity with temperature by the rotational rheometer. In order to reduce the curing caused by heat accumulation and thus affect the viscosity, the heating rate is 5℃ / min. The temperature at which the viscosity of the resin with the aging degree is the lowest can be obtained through the viscosity-temperature curve, and this temperature is the optimal molding temperature;

[0040] S800, after laying out the same category of aged carbon fiber / epoxy resin prepreg according to the designed layer, heat it to the optimal molding temperature for molding. The prepreg at this molding temperature has the best interlayer friction and intralayer deformation capabilities, and is suitable for general molding methods such as thermal insulation molding and compression molding.

[0041] The present invention can give full play to the use value of aged prepregs, and the prepared composite laminates or profiles have excellent mechanical properties. Its advantages are: first, the present invention preserves the aged prepreg at low temperature for the first time to prevent it from further aging; second, the gel point of different types of carbon fiber / epoxy resin prepregs is determined, and by testing the curing degree of the aged prepregs, the carbon fiber / epoxy resin prepregs that cannot be used anymore can be quickly screened; finally, a complete curing kinetic equation is established for each aged carbon fiber / epoxy resin prepreg, and resins with any curing degree can be simulated through the curing process, and the viscosity-temperature curves of resins with different curing degrees can be measured, thereby obtaining the optimal molding temperature specific to each aged prepreg to ensure its high-quality molding.

[0042] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for determining the reuse of aged prepreg, characterized in that: The following steps are involved: Classify aged prepregs by category; Testing the unaged prepreg using a preset curing process to obtain the curing enthalpy of the unaged prepreg; The aged prepreg is tested using a preset curing process to obtain the curing residual enthalpy of the aged prepreg; The aging degree of the aged prepreg is calculated by dividing the value obtained by subtracting the residual enthalpy of curing from the curing enthalpy by the curing enthalpy; Test the heat flow temperature curve of unaged prepreg at different heating rates, and obtain the characteristic parameters at different heating rates to calculate its curing kinetic equation; Test the storage modulus mutation point of the resin in the unaged prepreg at the preset curing process temperature, and calculate the curing degree corresponding to the point through the curing kinetic equation. The curing degree is the gel point. The aging degree and gel point of the aged prepregs were compared, and the aged prepregs with aging degree less than the gel point were screened out and classified by category.

2. The method for determining the reuse of aged prepreg according to claim 1, characterized in that: Aged prepregs are classified and collected according to different brands of carbon fiber and different brands of epoxy resin.

3. The method for determining the reuse of aged prepreg according to claim 1, characterized in that: Before testing the unaged prepreg, the following steps are also included: Store aged prepregs at low temperatures according to categories.

4. The method for determining the reuse of aged prepreg according to claim 3, characterized in that: After selecting the reusable aged prepregs, they need to be stored at low temperatures according to their categories.

5. The method for determining the reuse of aged prepreg according to claim 4, characterized in that: The storage temperature of aged prepreg is below -18℃.

6. The method for determining the reuse of aged prepreg according to claim 1, characterized in that: Before the step of obtaining the curing residual enthalpy of the aged prepreg, the aged prepreg is first cut into small pieces, and then the small pieces of the aged prepreg are tested.

7. The method for determining the reuse of aged prepreg according to claim 1, characterized in that: The curing enthalpy and curing residual enthalpy were measured using a differential scanning calorimeter.

8. The method for determining the reuse of aged prepreg according to claim 1, characterized in that: The storage modulus mutation point was tested using a rotational rheometer.

9. A method for recycling aged prepregs, applicable to aged prepregs selected by the aged prepreg recycling judgment method according to any one of claims 1 to 8, characterized in that: The following steps are involved: Extract uncured resin from unaged prepreg, cure the uncured resin to obtain resin with the same aging degree as that of aged prepreg, obtain viscosity-temperature curve of resin viscosity changing with temperature when the resin is cured, and obtain the temperature at which the viscosity of the resin with the aging degree is the lowest through the viscosity-temperature curve, which is the optimal molding temperature; The aged prepregs of the same category are laid out according to the designed layers, heated to the optimum molding temperature and molded to reuse the aged prepregs.

10. The method for recycling aged prepreg according to claim 9, characterized in that: The heating rate when curing the uncured resin was 5°C / min.

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