Preparation method of regenerated carbon fiber granulation

Abstract

The invention discloses a regenerated carbon fiber granulation preparation method which comprises the following steps: S1, cutting disordered filaments into non-uniform short fibers, or crushing a waste carbon fiber plate into blocks; s2, pyrolyzing the obtained short fiber or fiber block waste to obtain regenerated short carbon fiber; s3, the regenerated short carbon fibers are added into a suspension granulation bin, a binder solution is sprayed, and the regenerated short carbon fibers collide with one another in the suspension granulation bin and are bonded into a ball shape; s4, adding the regenerated short carbon fiber clusters into a disc type granulator, kneading the clusters, screening, and discharging; s5, hot air is introduced for drying, and granulated regenerated carbon fibers are obtained. According to the preparation method of the regenerated carbon fiber granules, the stacking density, the water content and the blanking performance of the regenerated carbon fiber granules are remarkably improved by optimizing parameters such as the pyrolysis temperature, the type and the concentration of the binder and the like.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber reinforced plastic processing and modification, and in particular to a preparation method for granulating regenerated carbon fiber. Background Art

[0002] At present, most of the waste carbon fiber composite materials are composed of continuous fibers and thermosetting resins, which cannot be processed again, and they cannot be naturally degraded, so the excess waste is usually landfilled or incinerated as industrial waste. The sources of CFRP waste are aerospace, sports goods, and scrapped prepregs. Carbon beams and gas cylinders used in a large number of industrial applications are not the main sources due to their low production defect rate. At present, the amount of CFRP recycled and reused in the world is less than 1%, and the rest is landfilled, incinerated or shelved.

[0003] There are many recycling technologies, such as thermal decomposition and chemical decomposition. Regardless of the recycling method, the regenerated carbon fiber usually presents a messy, fluffy, non-continuous fiber state. At present, there are three main methods for processing regenerated carbon fiber. The most common one is to cut the regenerated carbon fiber to form short-cut carbon fiber with relatively stable macroscopic performance; the second is the non-woven felt method, that is, to prepare carbon fiber non-woven fabrics or three-dimensional carbon fiber non-woven materials by a certain method; the third is the orientation method, that is, to orient the recycled short-cut carbon fiber through electric field, magnetic field, pneumatic, fluid mechanics and other methods to prepare a well-oriented carbon fiber oriented felt. The first type of short-cut carbon fiber is suitable for the preparation of CFRP by injection molding, mass molding and other processes; carbon fiber non-woven felt and oriented felt can be prepared by wet molding, resin transfer molding and other processes through resin impregnation felt and molding curing molding to obtain CFRP. Although the orientation method can maximize the mechanical properties of recycled carbon fiber, the orientation process is cumbersome and immature, and is not suitable for large-scale application.

[0004] At present, recycled carbon fiber is still most widely used in the convenient, simple and low-cost thermoplastic composite injection molding technology. However, how to granulate recycled carbon fiber is still a difficult problem that needs to be solved urgently.

[0005] This patent provides a technical solution and application form for the granulation of recycled carbon fiber, aiming to broaden the application channels of recycled carbon fiber and open up ways and methods for the reuse of recycled carbon fiber. Summary of the invention

[0006] The purpose of the invention is to provide a method for preparing recycled carbon fiber granules, which solves the problem that the existing carbon fiber is fluffy and fuzzy when used in modified plastics.

[0007] The present invention provides a method for preparing granulated regenerated carbon fiber, comprising the following steps:

[0008] Step S1, cutting the messy fibers into uneven short fibers, or breaking the waste carbon fiber sheets into blocks;

[0009] Step S2, pyrolyzing the obtained short fibers or fiber block waste products to obtain regenerated short carbon fibers;

[0010] Step S3, adding the regenerated short carbon fibers into a suspension granulation bin, spraying a binder solution, and allowing the regenerated short carbon fibers to collide with each other and bond into a mass in the suspension granulation bin;

[0011] Step S4, adding the regenerated short carbon fiber balls into a disc granulator, kneading and screening the balls and then discharging them;

[0012] Step S5, drying with hot air to obtain granulated regenerated carbon fiber.

[0013] In certain embodiments, the length of the short fibers in step S1 is 3-5 mm, and the size of the broken pieces is 3-5 mm.

[0014] In certain embodiments, the pyrolysis process in step S2 includes two parts: anaerobic cracking and aerobic carbon removal;

[0015] The oxygen-free cracking process is an inert gas atmosphere at a temperature of 600-800°C;

[0016] The aerobic decarbonization process is carried out in an oxygen atmosphere at a temperature of 400-600°C.

[0017] In certain embodiments, the binder solution in step S3 is a molasses or lignin sulfonate aqueous solution with a concentration of 2-10 wt %.

[0018] In certain embodiments, step S3 is specifically as follows: compressed air is introduced into the bottom of the suspended granulation bin, a binder solution is sprayed on the top, the regenerated short carbon fibers are blown in from the bottom feed port, and are suspended upward by the compressed air, and collide and bond with each other into clumps at the top under the action of the sprayed binder solution, and gradually sink as the mass increases, and part of them escape from the top with the gas and re-enter the bottom fiber feed port.

[0019] In certain embodiments, the mass of the binder solution sprayed is 5%-20% of the mass of the fibers in the bin.

[0020] In certain embodiments, the disc granulator in step S4 is a general-purpose device, which compacts the agglomerated short carbon fibers through a scraper, and then discharges the granulated regenerated carbon fibers through screening.

[0021] In certain embodiments, in step S5, the drying temperature is 110-150° C., the drying time is 1-3 hours, and the moisture content is controlled to be less than 0.2 wt %.

[0022] Beneficial effects: The preparation method of the regenerated carbon fiber granules of the present invention significantly improves the bulk density, water content and feeding performance of the regenerated carbon fiber particles by optimizing parameters such as pyrolysis temperature, binder type and concentration. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below through embodiments.

[0024] Example 1

[0025] Cutting / crushing: Process the messy fibers or waste carbon fiber sheets into 3-5mm short fibers or blocks.

[0026] Pyrolysis: The anaerobic pyrolysis temperature was set at 700°C, and the aerobic decarbonization temperature was set at 500°C.

[0027] Suspension granulation: Add the regenerated short carbon fibers into the suspension granulation bin, spray the binder solution, and the regenerated short carbon fibers collide with each other and bond into a mass in the suspension granulation bin; a 5% lignin sulfonate aqueous solution is used as the binder.

[0028] Specifically: compressed air is introduced into the bottom of the suspended granulation bin, and adhesive is sprayed on the top. Regenerated short carbon fibers are blown in from the bottom feed port and suspended upward by the compressed air. At the top, they collide and bond with each other under the action of the sprayed adhesive to form clumps. As the mass increases, they gradually sink. Part of them escapes from the top with the gas and re-enters the bottom fiber feed port.

[0029] Disc granulation and screening: Standard disc granulator is used for kneading and screening.

[0030] Drying: Use hot air to dry until the moisture content of the product is less than 0.2wt%.

[0031] Example 2

[0032] Based on Example 1, some parameters were adjusted to observe the effect:

[0033] Pyrolysis: The anaerobic pyrolysis temperature was set at 600°C, and the aerobic decarbonization temperature was set at 400°C.

[0034] Suspension granulation: Use 10% honey solution as a binder.

[0035] The other steps remain the same.

[0036] Comparative design

[0037] Comparative Example 1

[0038] In order to compare the influence of the bonding process, the following operations were used:

[0039] An aqueous solution of lignin sulfonate was used at a concentration of 15%.

[0040] The other steps are the same as those in Example 1.

[0041] Comparative Example 2

[0042] To compare the effects of binder type and concentration, the following procedure was used:

[0043] An aqueous solution of lignin sulfonate was used at a concentration of 0.5%.

[0044] The other steps are the same as those in Example 1.

[0045] Through the design of the above embodiments and comparative examples, the influence of each step and parameter in the technical solution on the performance of the final product can be systematically evaluated, providing an experimental basis for optimizing the technical solution.

[0046] serial number Bulk density g / L Water content% Feeding performance Example 1 380 0.15 good Example 2 460 0.12 excellent Comparative Example 1 832 1.56 Large clumps, unable to unload Comparative Example 2 210 0.18 Very bad

[0047] Results Analysis

[0048] By analyzing the experimental results of Example 1, Example 2, and Comparative Examples 1 and 2, the following conclusions can be drawn:

[0049] 1. Effect of pyrolysis temperature (comparison between Example 1 and Example 2):

[0050] Bulk density: The bulk density of Example 1 is 380 g / L, while the bulk density of Example 2 is 460 g / L, an increase of about 80 g / L. This may be due to the lower pyrolysis temperature of Example 2, which results in a denser structure of the recycled carbon fiber, resulting in a heavier mass and a higher bulk density under the same volume. Therefore, a lower pyrolysis temperature may be conducive to obtaining particles with a higher bulk density.

[0051] Moisture content: The moisture content of both is low and the difference is not big, which means that the pyrolysis temperature has little effect on the moisture content of the final product within this range.

[0052] Feeding performance: The feeding performance of Example 2 is excellent, which is better than the good performance of Example 1. This may be because the particle structure of Example 2 is easier to flow, reducing friction and adhesion between particles.

[0053] 2. Effect of binder type and concentration (comparison between Example 1, Comparative Example 1 and Comparative Example 2):

[0054] Packing density: The packing density of Example 1 is 380 g / L, the packing density of Comparative Example 1 is 832 g / L (abnormally high, possibly due to the high concentration of binder resulting in too tight adhesion between particles to form large agglomerates), and the packing density of Comparative Example 2 is 210 g / L (lower, possibly due to the low concentration of binder resulting in insufficient adhesion between particles, resulting in loose particles).

[0055] Moisture content: The moisture content of the three is low and the difference is not big, which means that the type and concentration of binder have little effect on the moisture content of the final product within this range.

[0056] Feeding performance: Example 1 has good feeding performance, while Comparative Example 1 cannot be fed due to large agglomerates, and Comparative Example 2 has extremely poor feeding performance, indicating that the type and concentration of the binder have a significant impact on the feeding performance. Too high a binder concentration will cause the particles to be too tightly bonded, forming large agglomerates, which will affect feeding; while too low a binder concentration will cause insufficient bonding between particles, resulting in loose particles, which will also affect feeding.

[0057] In summary, by optimizing parameters such as pyrolysis temperature, binder type and concentration, the bulk density, water content and feeding performance of recycled carbon fiber particles can be significantly improved. The pyrolysis temperature of Example 2 is relatively low, but a higher bulk density and excellent feeding performance are obtained. This may be a special result caused by factors such as experimental conditions or the original state of the fiber, which requires further in-depth study. At the same time, the selection and concentration control of the binder are crucial to the preparation of particles and need to be fine-tuned according to specific needs. This technical solution provides a new way for the reuse of recycled carbon fiber and has broad application prospects.

[0058] The above description is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the creative concept of the present invention, and these should also be regarded as within the scope of protection of the invention.

Claims

1. A method for preparing granulated regenerated carbon fiber, characterized in that: The following steps are involved: Step S1, cutting the messy fibers into uneven short fibers, or breaking the waste carbon fiber sheets into blocks; Step S2, pyrolyzing the obtained short fibers or fiber block waste products to obtain regenerated short carbon fibers; Step S3, adding the regenerated short carbon fibers into a suspension granulation bin, spraying a binder solution, and allowing the regenerated short carbon fibers to collide with each other and bond into a mass in the suspension granulation bin; Step S4, adding the regenerated short carbon fiber balls into a disc granulator, kneading and screening the balls and then discharging them; Step S5, drying with hot air to obtain granulated regenerated carbon fiber.

2. The method for preparing granulated regenerated carbon fiber according to claim 1, characterized in that: In step S1, the length of the short fibers is 3-5 mm, and the size of the broken pieces is 3-5 mm.

3. The method for preparing regenerated carbon fiber granules according to claim 1, characterized in that: The pyrolysis process in step S2 includes two parts: anaerobic cracking and aerobic carbon removal; The oxygen-free cracking process is an inert gas atmosphere at a temperature of 600-800°C; The aerobic decarbonization process is carried out in an oxygen atmosphere at a temperature of 400-600°C.

4. The method for preparing regenerated carbon fiber granules according to claim 1, characterized in that: The binder solution in step S3 is a molasses or lignin sulfonate aqueous solution with a concentration of 2-10 wt%.

5. The method for preparing regenerated carbon fiber granules according to claim 1, characterized in that: Step S3 is specifically as follows: compressed air is introduced into the bottom of the suspended granulation bin, and a binder solution is sprayed on the top. The regenerated short carbon fibers are blown in from the bottom feed port and suspended upward by the compressed air. At the top, they collide and bond with each other to form a clumping shape due to the sprayed binder solution. As the mass increases, they gradually sink. After part of them escape from the top with the gas, they re-enter the bottom fiber feed port.

6. The method for preparing granulated regenerated carbon fiber according to claim 5, characterized in that: The spraying mass of the binder solution is 5%-20% of the mass of the fibers in the bin.

7. The method for preparing regenerated carbon fiber granules according to claim 1, characterized in that: The disc granulator in step S4 is a general-purpose device, which compacts the agglomerated short carbon fibers through a scraper, and then discharges the granulated regenerated carbon fibers through screening.

8. The method for preparing regenerated carbon fiber granules according to claim 1, characterized in that: In step S5, the drying temperature is 110-150° C., the drying time is 1-3 hours, and the moisture content is controlled to be less than 0.2 wt %.