A method for the in-situ polymerization of short fiber reinforced composites

Abstract

The application discloses a kind of in-situ polymerization short fiber reinforced composite material preparation methods, belong to composite material technical field.The application method includes the following steps: (1) short fiber is treated on surface and dried after being placed into mould, and the dosage of short fiber is 40%~60% of the specific volume of mould;(2) after drying caprolactam and adding metal sodium into reaction kettle, vacuum is stirred evenly to obtain monomer and catalyst mixture;(3) hexamethylene diisocyanate is added into monomer and catalyst mixture, and the vacuum stirring time is 3~5min, to obtain injection molding solution;(4) injection molding solution is injected into mould using vacuum assisted resin molding method with 0.8~2bar vacuum pressure, after polymerization, it is demoulded to obtain in-situ polymerization short fiber reinforced composite material.The preparation method of the application reduces short fiber movement and deformation in process, and improves the mechanical properties of composite material.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a method for preparing short fiber reinforced composite materials. Background Technology

[0002] Liquid composite molding (LCM) is a process in which liquid resin is injected into a mold containing pre-laid fiber reinforcement, impregnating the fiber reinforcement with the liquid resin, and then heated to create the composite product. This process is widely used in aerospace, shipbuilding, and automotive industries. However, during the injection process, the high concentration and injection pressure of the liquid resin can cause fiber displacement within the mold, particularly affecting short fibers and leading to uneven distribution and ultimately a decrease in mechanical properties. Therefore, reducing fiber displacement during the process is a crucial issue in the field of fiber-reinforced composites. One key solution is to use low-viscosity liquid resins and reduce injection pressure.

[0003] Caprolactam is a monomer of nylon 6. It has a viscosity similar to water (3-4 mPa·s) at 110°C, which allows for the molding process of fiber-reinforced composites with relatively low injection pressure. However, its polymerization reaction is fast under the action of catalysts and initiators. Therefore, it is necessary to design process parameters reasonably to avoid problems such as fiber displacement and incomplete injection of liquid resin. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem of poor mechanical properties caused by the displacement of high volume fraction of short fibers during the preparation of composite materials in the prior art. This invention provides an in-situ polymerized short fiber reinforced composite material preparation method, which reduces the movement and deformation of short fibers during the process, making them uniformly distributed in the composite material, and improving the mechanical properties of the composite material.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing in-situ polymerized short fiber reinforced composite materials, comprising the following steps:

[0006] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 40% to 60% of the mold volume;

[0007] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0008] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 to 5 minutes to obtain an injection molding solution;

[0009] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.8 to 2 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0010] Furthermore, in step (1), the short fiber is one or more of carbon fiber and glass fiber, and the length of the short fiber is 4 to 6 cm.

[0011] Furthermore, in step (1), the surface treatment involves removing the adhesive from the fiber surface with acetone, and the short fiber drying temperature is 80°C, with a drying time of 5–10 min.

[0012] Furthermore, in step (2), the caprolactam drying temperature is 40°C and the drying time is 24 hours.

[0013] Furthermore, in step (2), the mass fraction of caprolactam is 94-98 wt%, the mass fraction of metallic sodium is 1-3 wt%, the temperature of the reactor is 70-110°C, and the stirring time is 30-60 min.

[0014] Further, the mass fraction of hexamethylene diisocyanate in step (3) is 1-3 wt%, and the stirring time is 3-5 min.

[0015] Furthermore, in step (4), the polymerization reaction temperature is 100-200℃ and the polymerization reaction time is 3-10 min.

[0016] The in-situ polymerized short fiber reinforced composite material prepared by the above method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. By using a low-concentration injection molding solution and low-pressure injection, the poor wettability when the volume fraction of short fibers is above 50% is solved. The injection molding solution can be completely injected into the fiber layer. At the same time, it also reduces the problem of short fibers moving and deforming with the flow of the injection molding solution during the injection molding process.

[0019] 2. The high volume fraction of short fibers and their small movement and deformation, along with their uniform distribution in the composite material, improve the mechanical properties of the composite material.

[0020] 3. No high pressure is required during the injection molding solution transfer process, and the cooling and demolding process can be omitted after the polymerization reaction, reducing the process time. Therefore, the preparation method of this invention has a short preparation cycle, low energy consumption, and can be mass-produced. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the embodiments.

[0022] Example 1

[0023] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0024] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0025] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0026] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0027] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.9 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0028] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0029] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0030] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0031] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0032] Example 2

[0033] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0034] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 40% of the mold volume.

[0035] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0036] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0037] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.8 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0038] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 120℃.

[0039] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 97wt%, the mass fraction of sodium metal in the injection molding solution is 2wt%, the stirring temperature is 70℃, and the time is 30min.

[0040] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0041] In step (4), the polymerization reaction temperature is 120℃ and the polymerization reaction time is 5min.

[0042] Example 3

[0043] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0044] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0045] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0046] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 5 minutes to obtain an injection molding solution;

[0047] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 2 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0048] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 160℃.

[0049] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 60min.

[0050] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0051] In step (4), the polymerization reaction temperature is 160℃ and the polymerization reaction time is 10min.

[0052] Comparative Example 1

[0053] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0054] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0055] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0056] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 1 minute to obtain an injection molding solution;

[0057] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.9 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0058] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0059] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0060] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0061] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0062] Comparative Example 2

[0063] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0064] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0065] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0066] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 7 minutes to obtain an injection molding solution;

[0067] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.9 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0068] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0069] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0070] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0071] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0072] Comparative Example 3

[0073] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0074] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 35% of the mold volume.

[0075] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0076] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0077] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.9 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0078] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0079] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0080] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0081] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0082] Comparative Example 4

[0083] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0084] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 65% of the mold volume.

[0085] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0086] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0087] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.9 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0088] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0089] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0090] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0091] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0092] Comparative Example 5

[0093] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0094] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0095] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0096] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0097] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.6 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0098] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0099] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0100] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0101] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0102] Comparative Example 6

[0103] This embodiment provides a method for preparing in-situ polymerized short fiber reinforced composite materials, the method comprising the following steps:

[0104] (1) After surface treatment and drying, the short fibers are placed into the mold, and the amount of short fibers is 60% of the mold volume;

[0105] (2) After drying caprolactam, add it and metallic sodium into the reactor and stir under vacuum to obtain a mixture of monomer and catalyst.

[0106] (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3 minutes to obtain an injection molding solution;

[0107] (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 3 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

[0108] In step (1), the short fiber is carbon fiber with a length of 6cm. The surface treatment is to remove the adhesive on the fiber surface with acetone. The drying temperature of the short fiber is 80℃, the drying time is 5min, and the mold temperature is set to 140℃.

[0109] In step (2), the drying temperature of caprolactam is 40℃, the drying time is 24 hours, the mass fraction of caprolactam in the injection molding solution is 98wt%, the mass fraction of sodium metal in the injection molding solution is 1wt%, the stirring temperature is 70℃, and the time is 30min.

[0110] In step (3), the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1 wt%.

[0111] In step (4), the polymerization reaction temperature is 140℃ and the polymerization reaction time is 5min.

[0112] The present invention conducts mechanical property tests on the short fiber reinforced composite materials prepared in Examples 1-3 and Comparative Examples 1-6, specifically including: tensile property tests, flexural property tests, and impact property tests on the short fiber reinforced composite material samples obtained in the examples according to ASTM specifications. The results are shown in Table 1.

[0113] Table 1. Mechanical properties of short fiber reinforced composite materials in Examples 1-3 and Comparative Examples 1-6

[0114]

[0115] As shown in Table 1, the preparation method of the present invention used in Examples 1-3 can reduce the problem of short fibers moving and deforming during the injection molding process due to the flow of the injection molding solution, so that they are evenly distributed in the composite material, and at the same time improve the mechanical properties of the composite material.

[0116] Compared to Comparative Example 1, Example 1 had a shorter stirring time, resulting in a lower concentration of the injection molding liquid. This caused the liquid to flow too quickly during injection, leaving some corners of the mold unfilled. Consequently, the composite material sample had defects and did not require mechanical property testing. Compared to Comparative Example 2, Example 1 had a longer stirring time, resulting in a higher concentration of the injection molding liquid. During transport, the injection molding liquid became clogged in the transport tube due to the polymerization reaction, preventing the preparation process from continuing. Consequently, the sample had defects and did not require mechanical property testing.

[0117] Compared with Comparative Example 3, Example 1 has too little short fiber volume fraction, resulting in poor mechanical properties that cannot meet the mechanical performance requirements of actual large components. Compared with Comparative Example 4, Example 1 has too much short fiber volume fraction, and the short fibers are not completely wetted by the injection molding solution in the mold, resulting in defects in the composite material sample that do not require mechanical property testing.

[0118] Compared with Comparative Example 5, Example 1 had too low a vacuum pressure, resulting in a slow flow rate of the injection molding liquid, which caused the sample to not be fully formed. The sample had defects and therefore did not require mechanical property testing. Compared with Comparative Example 6, Example 1 had too high a vacuum pressure, causing short fibers to shift and accumulate at the injection liquid outlet, making the sample unusable. The sample had defects and therefore did not require mechanical property testing.

Claims

1. A method for preparing an in-situ polymerized short fiber reinforced composite material, characterized in that, Includes the following steps: (1) After surface treatment and drying, the short fibers are placed into the mold. The amount of short fibers is 40% to 60% of the mold volume. In step (1), the short fibers are one or more of carbon fiber and glass fiber, and the length of the short fibers is 4 to 6 cm. (2) After drying caprolactam, add it and metallic sodium into the reaction vessel and stir under vacuum to obtain a mixture of monomer and catalyst; (3) Add hexamethylene diisocyanate to the monomer and catalyst mixture obtained in step (2), and stir under vacuum for 3-5 minutes to obtain an injection molding solution; wherein, the mass fraction of caprolactam in the injection molding solution is 94-98 wt%, the mass fraction of sodium metal in the injection molding solution is 1-3 wt%, and the mass fraction of hexamethylene diisocyanate in the injection molding solution is 1-3 wt%. (4) The injection molding solution obtained in step (3) is injected into the mold at a vacuum pressure of 0.8~2 bar using a vacuum-assisted resin molding method. After polymerization reaction, the mold is demolded to obtain an in-situ polymerized short fiber reinforced composite material.

2. The method for preparing in-situ polymerized short fiber reinforced composite material according to claim 1, characterized in that, In step (1), the surface treatment involves removing the adhesive from the fiber surface with acetone, and the short fiber drying temperature is 80°C, with a drying time of 5 to 10 minutes.

3. The method for preparing in-situ polymerized short fiber reinforced composite material according to claim 1, characterized in that, In step (2), the drying temperature of caprolactam is 40°C and the drying time is 24 hours.

4. The method for preparing in-situ polymerized short fiber reinforced composite material according to claim 1, characterized in that, In step (2), the temperature of the reactor is 70~110℃ and the stirring time is 30~60min.

5. The method for preparing in-situ polymerized short fiber reinforced composite material according to claim 1, characterized in that, In step (4), the polymerization reaction temperature is 100~200℃ and the polymerization reaction time is 3~10min.

6. An in-situ polymerized short fiber reinforced composite material prepared by any one of claims 1-5.

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