Method for measuring density of carbon fiber

Abstract

The invention discloses a method for measuring the density of carbon fibers, which comprises the following steps: S1, taking a carbon fiber sample which is not subjected to sizing treatment, and putting the carbon fiber sample into a vacuum drying oven for drying treatment; s2, placing the dried carbon fiber sample in a dryer for standing, and cutting the carbon fiber sample after standing to obtain a carbon fiber short bundle; s3, weighing the weight of the sample crucible, vertically placing the cut short carbon fiber bundles in the sample crucible, and weighing again to obtain the actual weight of the to-be-measured fiber sample; s4, putting the sample crucible filled with the short carbon fiber bundles into a hydrometer, and purging with helium to replace air in the sample crucible; and S5, setting test parameters, starting a test function of the hydrometer, and obtaining the volume of the carbon fiber sample to be tested, thereby obtaining the density of the carbon fiber. The method has the advantages of simple and convenient operation process, no need of dipping liquid, environmental protection, safety, no influence of carbon fiber disintegrating slag, and high test accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon fiber determination, and particularly relates to a method for determining the density of carbon fiber. BACKGROUND

[0002] The density of carbon fiber is one of important parameters for representing the physical performance of carbon fiber, and is also a key control index in the development and production process of carbon fiber, which depends on the composition, organization form and internal defects of the raw material. The density of carbon fiber affects the macro performance of the subsequent composite material to some extent, and therefore, accurately representing the density of carbon fiber can effectively guide the development and production, and is also of great significance to the application performance.

[0003] At present, the determination of the density of carbon fiber in China is mainly based on the national standard GB / T 30019-2013, which provides three determination methods of liquid displacement method, float-sink method and density gradient column method. Although the three methods are different in test principle and operation process, they all need to immerse the fiber sample to be tested in liquid, and the operation process is complicated, and a large number of instruments and materials are needed. There are also certain safety hazards in using the immersion liquid, and the immersion liquid needs to be frequently replaced due to the residue of fiber debris, which increases the test cost and is not conducive to environmental protection.

[0004] The existing related technologies and improvement researches are still focused on the three methods in the national standard. The Chinese patent with publication number CN 116429635 A discloses a carbon fiber density testing device and method, which mainly improves the testing device of the density gradient column method to improve the accuracy of density determination. The Chinese patent CN 209640141 U and the Chinese patent CN 215574444 U provide an asphalt-based carbon fiber density testing tool, which also makes corresponding design and improvement to the testing device of the liquid displacement method to reduce the operation difficulty. However, the above technologies are still based on the liquid displacement method or the density gradient column method in the national standard, and the fiber needs to be immersed in liquid during operation. The carbon fiber will have the problem of dropping debris and broken filaments as soon as it enters the liquid. The repeated use of the immersion liquid with residual fiber debris will affect the test accuracy, and the immersion liquid needs to be replaced after several tests. Therefore, there is also the problem of frequent replacement of the immersion liquid.

[0005] In view of the above situation, it is urgent to develop a carbon fiber density determination method which is simple and convenient in operation process, does not need to use immersion liquid, and is environmentally friendly and safe. SUMMARY

[0006] In view of the defects in the prior art, the present application aims to provide a method for determining the density of carbon fiber, which is simple and convenient in operation process, does not need to use immersion liquid, is environmentally friendly and safe, and is not affected by carbon fiber debris, and has high test accuracy.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for determining the density of carbon fibers, comprising the following steps:

[0009] S1. Take a carbon fiber sample that has not undergone sizing treatment and place it in a vacuum drying oven for drying treatment;

[0010] S2, Place the dried carbon fiber sample in a desiccator and let it stand, then cut the carbon fiber sample after standing to obtain short bundles of carbon fiber.

[0011] S3, weigh the sample crucible, and place the cut carbon fiber bundle vertically in the sample crucible, weigh it again to obtain the actual weight of the fiber sample to be tested;

[0012] S4. Place the sample crucible containing the short bundles of carbon fibers into the hydrometer and purge it with helium to replace the air inside the sample crucible.

[0013] S5, set the test parameters and start the hydrometer's test function to obtain the volume of the carbon fiber sample to be tested, thereby obtaining the carbon fiber density.

[0014] Preferably, in step S1, the amount of the unsized carbon fiber sample is 1-3g.

[0015] Preferably, in step S1, the drying temperature is 120-200°C and the drying time is 1-2 hours.

[0016] Preferably, in step S2, the settling time is 0.5 to 1.5 hours.

[0017] Preferably, in step S2, the length of the carbon fiber bundle is 1.8 to 2.2 cm.

[0018] Preferably, in step S3, the actual weight of the fiber sample to be tested is m = m2 - m1, where m is the actual weight of the fiber sample to be tested in g, m2 is the total weight of the sample crucible containing the short bundles of carbon fibers in g, and m1 is the weight of the sample crucible in g.

[0019] Preferably, in step S4, the number of helium purging cycles is ≥3.

[0020] Preferably, in step S5, the test parameters are set as follows: the pressure is 14-17 psi and the test temperature is 21-25°C.

[0021] Preferably, in step S5, the carbon fiber density ρ = m / v, where ρ is the carbon fiber density in g / cm³.3 m is the actual weight of the fiber sample to be tested, in grams, and v is the volume of the carbon fiber sample to be tested, in centimeters. 3 .

[0022] The beneficial effects of this invention are as follows:

[0023] 1. Based on the inherent properties of carbon fiber and combined with the hydrometer testing principle, this invention determines the optimal sample processing method and testing parameters to improve the accuracy and repeatability of test results.

[0024] 2. This invention does not require the use of impregnation liquid, reducing safety hazards. It requires fewer instruments and materials, lowering testing costs. The operation process is simple, and the drying process of the fiber to be tested can be carried out in batches, resulting in high testing efficiency.

[0025] 3. Since this invention does not require immersing the fibers in liquid, fiber debris will not affect the test results, resulting in higher test accuracy; in addition, it does not require the use and replacement of immersion liquid, making it more environmentally friendly. Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0027] The present invention provides a method for determining the density of carbon fibers, comprising the following steps:

[0028] S1. Take a carbon fiber sample that has not undergone sizing treatment and place it in a vacuum drying oven for drying treatment;

[0029] In the above steps, the amount of carbon fiber sample that has not undergone sizing treatment is 1-3g; during the drying treatment, the drying temperature is 120-200℃ and the drying time is 1-2h.

[0030] S2, Place the dried carbon fiber sample in a desiccator and let it stand, then cut the carbon fiber sample after standing to obtain short bundles of carbon fiber.

[0031] In the above steps, the settling time is 0.5 to 1.5 hours; the length of the carbon fiber short bundles obtained after cutting is 1.8 to 2.2 cm.

[0032] S3, Weigh the sample crucible, place the cut carbon fiber bundle vertically in the sample crucible, weigh it again to obtain the actual weight of the fiber sample to be tested.

[0033] First, weigh the sample crucible using an electronic balance and record the weight m1. Then, place the cut carbon fiber bundles vertically into the sample crucible. Next, weigh the sample crucible containing the carbon fiber bundles again using an electronic balance and record the total weight m2. Thus, the actual weight of the fiber sample to be tested is m = m2 - m1, where m is the actual weight of the fiber sample to be tested (in grams), m2 is the total weight of the sample crucible containing the carbon fiber bundles (in grams), and m1 is the weight of the sample crucible (in grams).

[0034] S4. Place the sample crucible containing the short bundle of carbon fiber into a hydrometer and purge it with helium gas to replace the air inside the sample crucible; wherein the number of helium purging times is ≥3.

[0035] S5, set the test parameters and start the hydrometer's test function to obtain the volume of the carbon fiber sample to be tested, thereby obtaining the carbon fiber density.

[0036] After activating the hydrometer's testing function, the test parameters are set as follows: pressure of 14–17 psi and test temperature of 21–25 °C, to obtain the volume v of the carbon fiber sample to be tested.

[0037] Based on the volume obtained above and the weight obtained in step S3, and according to the density calculation formula, the carbon fiber density ρ = m / v is obtained, where ρ is the carbon fiber density in g / cm³. 3 m is the actual weight of the fiber sample to be tested, in grams, and v is the volume of the carbon fiber sample to be tested, in centimeters. 3 .

[0038] The method for determining carbon fiber density according to the present invention will be further described below with specific examples.

[0039] Example 1

[0040] This embodiment measures the density of our company's self-developed and self-produced pitch-based low-density carbon fiber (carbonized at 900℃). The process is as follows:

[0041] 1) Take about 2g of three groups of 900℃ carbonized fiber samples that have not undergone sizing treatment as carbon fiber samples, place them in a vacuum drying oven, dry them at 150℃ for 1h, take them out and place them in a desiccator to stand for 0.5h;

[0042] 2) Take out a sample of carbon fiber to be tested and cut it into short bundles of fibers about 2cm long.

[0043] 3) Weigh the sample crucible, tare it, and then vertically place the cut fiber bundles into the sample crucible and weigh it again to obtain the actual weight of the carbon fiber sample to be tested.

[0044] 4) Place the sample crucible containing the short fiber bundles into a hydrometer and purge it with helium three times to replace the air inside the sample crucible;

[0045] 5) Set the pressure to 15 psi and the temperature to 23 ℃, then turn on the hydrometer test function to obtain the volume of the carbon fiber sample to be tested, and then calculate the density of the carbon fiber to be tested.

[0046] 6) After testing the three sets of parallel samples in sequence, the results are shown in Table 1. Calculate the average density of the carbon fiber samples to be tested.

[0047] Table 1. Data from the three sets of parallel samples in Example 1

[0048]

[0049] In this embodiment, the densities of the three parallel samples tested were 1.8376 g / cm³. 3 1.8393 g / cm 3 1.8382 g / cm 3 Thus, the average density of the fiber to be tested was found to be 1.8384 g / cm³. 3 The deviation coefficient was 0.05%. The fiber density, measured using the liquid displacement method according to national standards, was 1.8278 g / cm³. 3 The deviation coefficient is 0.42%.

[0050] Example 2

[0051] This embodiment measures the density of our company's self-developed and self-produced pitch-based carbon fiber (carbonized at 1500℃), and the process is as follows:

[0052] 1) Take about 2.5g of carbonized fiber at 1500℃ without sizing treatment from three groups as carbon fiber samples, place them in a vacuum drying oven, dry them at 150℃ for 1h, take them out and place them in a desiccator to stand for 1h;

[0053] 2) Take out a sample of carbon fiber to be tested and cut it into short bundles of fibers about 2cm long.

[0054] 3) Weigh the sample crucible, tare it, and then vertically place the cut fiber bundles into the sample crucible and weigh it again to obtain the actual weight of the carbon fiber sample to be tested.

[0055] 4) Place the sample crucible containing the fiber to be tested into the hydrometer and purge it with helium three times to replace the air in the sample crucible;

[0056] 5) Set the pressure to 15 psi and the temperature to 23 ℃, then turn on the hydrometer test function to obtain the volume of the carbon fiber sample to be tested, and then calculate the density of the carbon fiber to be tested.

[0057] 6) After testing the three sets of parallel samples in sequence, the results are shown in Table 2. Calculate the average value.

[0058] Table 2. Data from the three sets of parallel samples in Example 2.

[0059]

[0060] In this embodiment, the densities of the three parallel samples tested were 2.0825 g / cm³. 3 2.0862 g / cm 3 2.0829 g / cm 3 Thus, the average density of the fiber to be tested was found to be 2.0839 g / cm³. 3 The deviation coefficient was 0.10%. The fiber density, measured using the liquid displacement method according to national standards, was 2.0780 g / cm³. 3 The deviation coefficient is 0.86%.

[0061] Example 3

[0062] This embodiment measures the density of our company's self-developed and self-produced pitch-based graphite fiber (graphitized at 2800℃), and the process is as follows:

[0063] 1) Take about 3g of graphitized fibers at 2800℃ without sizing treatment from three groups as carbon fiber samples, place them in a vacuum drying oven, dry them at 200℃ for 2 hours, take them out and place them in a desiccator to stand for 1 hour;

[0064] 2) Take out a sample of carbon fiber to be tested and cut it into short bundles of fibers about 2cm long.

[0065] 3) Weigh the sample crucible, tare it, and then vertically place the cut fiber bundles into the sample crucible and weigh it again to obtain the actual weight of the carbon fiber sample to be tested.

[0066] 4) Place the sample crucible containing the short fiber bundles into a hydrometer and purge it with helium three times to replace the air inside the sample crucible;

[0067] 5) Set the pressure to 15 psi and the temperature to 23 ℃, then turn on the hydrometer test function to obtain the volume of the carbon fiber sample to be tested, and then calculate the density of the carbon fiber to be tested.

[0068] 6) After testing the three sets of parallel samples in sequence, the results are shown in Table 3. Calculate the average value.

[0069] Table 3. Data from the three sets of parallel samples in Example 3

[0070]

[0071] In this embodiment, the densities of the three parallel samples tested were 2.2177 g / cm³. 3 2.2180g / cm 3 2.2112 g / cm 3 Thus, the average density of the fiber to be tested was found to be 2.2156 g / cm³. 3 The deviation coefficient was 0.17%. The fiber density, measured using the liquid displacement method according to national standards, was 2.1998 g / cm³. 3 The deviation coefficient is 1.10%.

[0072] Example 4

[0073] This embodiment measures the density of our company's self-developed and self-produced T400 grade PAN-based carbon fiber, and the process is as follows:

[0074] 1) Take about 2g of PAN-based carbon fiber from three groups that have not undergone sizing treatment as carbon fiber samples, place them in a vacuum drying oven, dry them at 150℃ for 1.5h, take them out and place them in a desiccator to stand for 1h;

[0075] 2) Take out a sample of carbon fiber to be tested and cut it into short bundles of fibers about 2cm long.

[0076] 3) Weigh the sample crucible, tare it, and then vertically place the cut fiber bundles into the sample crucible and weigh it again to obtain the actual weight of the carbon fiber sample to be tested.

[0077] 4) Place the sample crucible containing the short fiber bundles into a hydrometer and purge it with helium three times to replace the air inside the sample crucible;

[0078] 5) Set the pressure to 15 psi and the temperature to 23 ℃, then turn on the hydrometer test function to obtain the volume of the carbon fiber sample to be tested, and then calculate the density of the carbon fiber to be tested.

[0079] 6) After testing the three parallel samples in sequence, the results are shown in Table 4. Calculate the average value.

[0080] Table 4. Data from the three sets of parallel samples in Example 4

[0081]

[0082] In this embodiment, the densities of the three parallel samples tested were 1.8050 g / cm³. 3 1.7989 g / cm³ 3 1.7992 g / cm³ 3 Thus, the average density of the fiber to be tested was found to be 1.8010 g / cm³. 3The deviation coefficient was 0.19%. The fiber density, measured using the liquid displacement method according to national standards, was 1.7944 g / cm³. 3 The deviation coefficient is 0.45%.

[0083] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the density of carbon fibers, characterized in that, Includes the following steps: S1. Take a carbon fiber sample that has not undergone sizing treatment and place it in a vacuum drying oven for drying treatment; S2, Place the dried carbon fiber sample in a desiccator and let it stand, then cut the carbon fiber sample after standing to obtain short bundles of carbon fiber. S3, weigh the sample crucible, and place the cut carbon fiber bundle vertically in the sample crucible, weigh it again to obtain the actual weight of the fiber sample to be tested; S4. Place the sample crucible containing the short bundles of carbon fibers into the hydrometer and purge it with helium to replace the air inside the sample crucible. S5, set the test parameters and start the hydrometer's test function to obtain the volume of the carbon fiber sample to be tested, thereby obtaining the carbon fiber density.

2. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S1, the amount of the unsized carbon fiber sample used is 1-3g.

3. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S1, the drying process is carried out at a temperature of 120-200°C for 1-2 hours.

4. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S2, the settling time is 0.5 to 1.5 hours.

5. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S2, the length of the carbon fiber short bundle is 1.8 to 2.2 cm.

6. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S3, the actual weight of the fiber sample to be tested is m = m2 - m1, where m is the actual weight of the fiber sample to be tested in g, m2 is the total weight of the sample crucible containing the short bundles of carbon fibers in g, and m1 is the weight of the sample crucible in g.

7. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S4, the number of helium purging cycles is ≥3.

8. The method for determining carbon fiber density as described in claim 1, characterized in that, In step S5, during the hydrometer test, the pressure applied is 14-17 psi and the test temperature is 21-25℃.

9. The method for determining carbon fiber density as described in claim 1, characterized in that, The carbon fiber density ρ = m / v, where ρ is the carbon fiber density in g / cm³. 3 m is the actual weight of the fiber sample to be tested, in grams, and v is the volume of the carbon fiber sample to be tested, in centimeters. 3 .

Images