Method for preparing ultra-high molecular weight polyethylene nanofiber

Abstract

The application provides a preparation method of ultra-high molecular weight polyethylene nanofiber. The method first performs liquid paraffin pre-swelling on UHMWPE powder (UHMWPE: liquid paraffin = 2:8), then melt-blends the swollen UHMWPE gel, a nucleating agent and CAB by using a double screw extruder, realizes the drawing and refinement of UHMWPE through the stretching and extrusion effect of UHMWPE online crystal regulation and CAB blending in the extrusion process, then extracts the CAB phase and liquid paraffin by using acetone, and obtains the UHMWPE nanofiber, thereby realizing the macro preparation of the UHMWPE nanofiber with a diameter of less than 300 nm. The method realizes the macro preparation of the UHMWPE nanofiber by combining the sea-island spinning and the crystal structure regulation, realizes the flexible regulation of the UHMWPE nanofiber by changing the component ratio and experimental parameters, meets the controllable preparation of the UHMWPE nanofiber with various sizes, and solves the problems of difficult preparation and single product of the UHMWPE nanofiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-high molecular weight nanofiber, and particularly relates to a preparation method of ultra-high molecular weight polyethylene nanofiber. BACKGROUND

[0002] Ultra-high molecular weight polyethylene (UHMWPE) has the problems of poor melt flowability and difficult molding processing, and the preparation of UHMWPE nanofiber has always been an industry problem difficult to solve, especially the nanofiber with a size of less than 300 nm. The optimal preparation method at present is to use the electrospinning method, but the size is usually more than 500 nm, and the preparation efficiency is low and the cost is high.

[0003] In the prior art, a patent with the publication number CN102041557B discloses a production method of high-strength and high-modulus polyethylene fiber. The method is to perform swelling and dissolving, filtering, spinning, freezing and solidifying, pre-stretching, extracting, drying, super-drawing and winding. The swelling and dissolving step is performed in a kneader, and the transparent and uniform spinning solution obtained through the swelling and dissolving step is quantitatively fed into a single-screw extruder for extrusion while stirring, so as to obtain the high-strength and high-modulus polyethylene fiber. However, the polyethylene fiber prepared by the method is still in the micron level, which greatly limits the application range, and the preparation of ultra-high molecular weight polyethylene nanofiber is still a bottleneck problem.

[0004] Therefore, it is necessary to design an improved preparation method of ultra-high molecular weight polyethylene nanofiber to solve the above problems. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a preparation method of ultra-high molecular weight polyethylene nanofiber. The preparation method realizes the batch preparation of UHMWPE nanofiber by combining the island spinning and the crystal structure regulation, realizes the further refinement of UHMWPE fiber by combining the extrusion, stretching and grain refinement of two components, and realizes the macro preparation of the fiber with a diameter of less than 300 nm.

[0006] To achieve the above purpose, the present application provides a preparation method of ultra-high molecular weight polyethylene nanofiber, which comprises the following steps:

[0007] S1, pre-swelling the ultra-high molecular weight polyethylene powder with a relative average molecular mass of 4.5 million and liquid paraffin according to the mass ratio of ultra-high molecular weight polyethylene powder: liquid paraffin = 2:8 to obtain an ultra-high molecular weight polyethylene gel;

[0008] S2, feeding the UHMWPE gel, nucleating agent and cellulose acetate butyrate into a twin-screw extruder for melt blending and extrusion to obtain modified gel UHMWPE fiber; the nucleating agent is dibenzylidene sorbitol, di(p-methylbenzylidene) sorbitol or titanium oxalate;

[0009] S3, soaking the modified gel UHMWPE fiber obtained in step S2 in an acetone solution to extract CAB phase and liquid paraffin by acetone to obtain UHMWPE nanofiber with a diameter of less than 300 nm.

[0010] Further, in step S2, the mass ratio of the UHMWPE, nucleating agent and cellulose acetate butyrate is 20:(0.5-2):(78-79.5). Preferably, the mass ratio of the UHMWPE, nucleating agent and cellulose acetate butyrate is 20:1:79.

[0011] The mass concentration of the nucleating agent is 0.5-2.0 wt%, preferably, the mass concentration of the nucleating agent is 1.0 wt%.

[0012] Further, in step S2, the temperature for melt blending is 200-240℃.

[0013] The beneficial effects of the present application are:

[0014] 1. The present application provides a preparation method of UHMWPE nanofiber. First, UHMWPE powder is pre-swollen with liquid paraffin (UHMWPE: liquid paraffin = 2:8), then the swollen UHMWPE gel, nucleating agent and CAB are melt blended by a twin-screw extruder. Through the online crystal regulation of UHMWPE and the stretching and extrusion effect of CAB on UHMWPE during the extrusion process, the drawing and refinement of UHMWPE during the melt blending process are realized. Then, the CAB phase and liquid paraffin are extracted by acetone to obtain UHMWPE nanofiber, realizing the macro preparation of UHMWPE nanofiber with a diameter of less than 300 nm.

[0015] 2. The present application uses nucleating agent dibenzyl sorbitol, di (p- methylbenzyl) sorbitol or titanium oxalate to induce new large number of crystal nucleus by nucleating agent induced local stress instability, to refine the grain size, increase the number of crystal, promote UHMWPE more easily stretched, fiber size more easily refined. The nucleating agent is preferably titanium oxalate, because when UHMWPE is melted and crystallized, the surface of titanium oxalate acts as an electron donor to form a hydrogen bond with the methylene of UHMWPE, and the molecular chain of UHMWPE crystal sheet is more easily grown on the surface of titanium oxalate, forming a transcrystalline region between the interfaces, which is more obvious for refining the grain size and increasing the number of crystals. The grain refinement enhances the intermolecular force, so that UHMWPE is not easily broken after being stretched by a large proportion, and the fiber size is smaller. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The flowchart of the preparation method of the ultra-high molecular weight polyethylene nanofiber of the present application.

[0017] Figure 2 The electron microscope image of the ultra-high molecular weight polyethylene nanofiber prepared in Example 1.

[0018] Figure 3 The XRD comparison chart of the ultra-high molecular weight polyethylene fibers prepared in Example 1 and Comparative Example 1.

[0019] Figure 4 The optical microscope comparison chart of the ultra-high molecular weight polyethylene fibers prepared in Example 1 and Comparative Example 1 after hot pressing into a plate.

[0020] Figure 5 The electron microscope image of the ultra-high molecular weight polyethylene nanofiber prepared in Example 2.

[0021] Figure 6 The electron microscope image of the ultra-high molecular weight polyethylene nanofiber prepared in Example 3.

[0022] Figure 7 The electron microscope image of the ultra-high molecular weight polyethylene nanofiber prepared in Comparative Example 2. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is described in detail below with reference to the drawings and specific examples.

[0024] In addition, it should be further noted that the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0025] Referring to Figure 1 As shown in the drawings, the present application provides a preparation method of ultra-high molecular weight polyethylene nanofiber, comprising the following steps:

[0026] S1, the relative average molecular weight of 4.5 million of ultra-high molecular weight polyethylene powder and liquid paraffin is pre-swollen according to the mass ratio of ultra-high molecular weight polyethylene powder: liquid paraffin = 2:8, and the ultra-high molecular weight polyylene gel is obtained;

[0027] S2, the UHMWPE gel containing 20g solid content, 1g titanium oxalate and 79g cellulose acetate butyrate are fed into a double screw extruder for melt blending and extrusion, and a modified gel ultra-high molecular weight polyethylene fiber is obtained; the temperature of melt blending is 220℃, the screw pressure is 2.0-2.2MPa, and the spinneret size is 200μm.

[0028] S3, the modified gel ultra-high molecular weight polyethylene fiber obtained in step S2 is soaked in an acetone solution, and the CAB phase and liquid paraffin are extracted by acetone, and the UHMWPE nanofiber with a diameter less than 300nm is obtained.

[0029] In step S2, the mass ratio of the ultra-high molecular weight polyethylene, the nucleating agent and the cellulose acetate butyrate is 20:(0.5-2):(78-79.5). Preferably, it is 20:1:79.

[0030] The mass concentration of the nucleating agent is 0.5-2.0wt%. Preferably, it is 1.0wt%.

[0031] The preparation method of the ultra-high molecular weight polyethylene nanofiber provided by the present application will be described below in conjunction with specific examples.

[0032] Example 1

[0033] The present application provides a preparation method of ultra-high molecular weight polyethylene nanofiber, comprising the following steps:

[0034] S1, the relative average molecular weight of 4.5 million of ultra-high molecular weight polyethylene powder and liquid paraffin is pre-swollen according to the mass ratio of ultra-high molecular weight polyethylene powder: liquid paraffin = 2:8, and the ultra-high molecular weight polyylene gel is obtained;

[0035] S2, the UHMWPE gel containing 20g solid content, 1g titanium oxalate and 79g cellulose acetate butyrate are fed into a double screw extruder for melt blending and extrusion, and a modified gel ultra-high molecular weight polyethylene fiber is obtained; the temperature of melt blending is 220℃, the screw pressure is 2.0-2.2MPa, and the spinneret size is 200μm.

[0036] S3, the modified gel UHMWPE fiber obtained in step S2 is soaked in an acetone solution, and CAB phase and liquid paraffin are extracted by acetone to obtain UHMWPE nanofiber with a diameter of 100-300 nm.

[0037] Referring to Figure 2 Figure 1 is an electron microscope image of the UHMWPE nanofiber prepared in Example 1, and it can be seen from the figure that the average fiber diameter is 266 nm, and the macro preparation of UHMWPE nanofiber below 300 nm is achieved.

[0038] Comparative Example 1

[0039] Comparative Example 1 provides a method for preparing nanofiber, which is different from Example 1 in that no nucleating agent titanium oxalate is added in step S2, and the rest is substantially the same as Example 1, which will not be repeated here.

[0040] Figure 3 Figure 2 is an XRD comparison chart of the UHMWPE fibers prepared in Example 1 and Comparative Example 1, and it can be seen that the intensity of the α crystal diffraction peak at 17.3° position of the diffraction spectrum obtained in Example 1 is obviously increased, which indicates that the addition of nucleating agent titanium oxalate greatly promotes the formation of α crystal, and the grain size calculated according to the Scherrer formula is smaller and the number is increased. That is, the addition of titanium oxalate in Example 1 makes the UHMWPE crystal sheet more susceptible to the action of interfacial hydrogen bond, forms a transcrystalline region, greatly refines the grain size and greatly increases the grain number, and forms more α crystal. In Comparative Example 1, the crystal structure shows the XRD spectrum of conventional UHMWPE, and the enhanced α crystal diffraction peak cannot be obtained, resulting in insufficient drawing ratio in the final UHMWPE melting process, and the fiber size cannot reach below 300 nm.

[0041] Figure 4 Figure 3 is an optical microscope comparison chart of the UHMWPE fibers prepared in Example 1 and Comparative Example 1 after hot pressing into a plate. It can be seen that compared with the picture without adding nucleating agent, the number of crystal grains in the microscope picture containing nucleating agent is greatly increased, and the crystal size is greatly reduced, while the crystal size of the picture without adding nucleating agent is larger and the number of crystal is less. Again, titanium oxalate can refine the grain size, increase the number of crystals, and promote the easy drawing of UHMWPE and the easy refinement of fiber size.

[0042] Example 2-3 and Comparative Example 2

[0043] Example 2-3 and Comparative Example 2 provide a method for preparing UHMWPE nanofiber, which is different from Example 1 in that the nucleating agent used in step S2 is changed, as shown in Table 1 below, and the rest is substantially the same as Example 1. Hereinafter, it will not be repeated.

[0044] Table 1

[0045]

[0046]

[0047] Figure 1 is a TEM image of UHMWPE nanofiber prepared in Example 1. Figure 5 Figure 2 is a TEM image of UHMWPE nanofiber prepared in Example 2. As can be seen from the figure, the size of the prepared UHMWPE nanofiber is 200-300 nm. This is mainly due to the hydrogen bond formed between dibenzylidene sorbitol and the surface of UHMWPE, which enhances the shish-kebab region formed by UHMWPE on the surface of dibenzylidene sorbitol, effectively increases the draw ratio of UHMWPE phase during the melt drawing process, and the fiber size reaches below 300 nm.

[0048] Figure 3 is a TEM image of UHMWPE nanofiber prepared in Example 3. As can be seen from the figure, the size of the prepared UHMWPE fiber is 180-280 nm. This is mainly due to the hydrogen bond formed between di(p-methylbenzylidene) sorbitol and the surface of UHMWPE, which enhances the shish-kebab region formed by UHMWPE on the surface of di(p-methylbenzylidene) sorbitol, effectively increases the draw ratio of UHMWPE phase during the melt drawing process, and the fiber size reaches below 300 nm. Figure 6 Figure 4 is a TEM image of UHMWPE nanofiber prepared in Comparative Example 2. As can be seen from the figure, the size of the UHMWPE fiber prepared with talc as a nucleating agent is larger, all greater than 300 nm.

[0049] Figure 7 Table 2 shows the test results of the UHMWPE nanofiber prepared in Examples 1-3 and Comparative Examples 1-2.

[0050] Table 2

[0051] Table 2

[0052]

[0053] Comparing Examples 1-3 with Comparative Example 1, when no nucleating agent is added, the obtained fiber diameter is larger due to the larger size and fewer number of UHMWPE crystals. Compared with the comparative example, the UHMWPE fiber prepared in the example has a smaller diameter, all less than 300 nm, and has better fiber strength.

[0054] Comparing Examples 1-3 with Comparative Example 2, when the added nucleating agent is talc. Although the size of the obtained UHMWPE fiber decreases (1000-1500 nm). However, due to the limited regulation of talc on the crystal structure of UHMWPE, the effect of forming UHMWPE nanofiber is not good.

[0055] ​Examples 4-8 and Comparative Examples 3-4

[0056] The difference between Examples 4-8 and Comparative Examples 3-4 and Example 1 is mainly that the type of nucleating agent in step S2 is changed, and the proportion of the ultra-high molecular weight polyethylene gel content, the nucleating agent, and the cellulose acetate butyrate is changed, as shown in Table 3 below, and the others are substantially the same as in Example 1, which will not be repeated here.

[0057] Table 3

[0058]

[0059] The UHMWPE nanofibers prepared in Examples 4-8 and Comparative Examples 3-4 were tested, and the results are shown in Table 4.

[0060] Table 4

[0061]

[0062]

[0063] According to the above table, for different nucleating agents, the optimal addition amount is 1wt%, and the fiber strength and modulus are optimal. When the addition amount of the nucleating agent is too small, the nucleating agent is limited in regulating the crystal structure of UHMWPE, mainly manifested as a substantial reduction in nucleation sites, a limited number of new crystal nuclei, and a large crystal size. In Comparative Example 3, the addition amount of titanium oxalate, a nucleating agent, is only 0.2wt%, and the fiber diameter reaches 600-1600nm.

[0064] When the addition amount of the nucleating agent is too large, the nucleating agent is prone to agglomeration and bonding, which greatly reduces the regulation effect on the UHMWPE crystal, including a limited decrease in grain size and a small increase in grain number. In Comparative Example 4, the addition amount of titanium oxalate, a nucleating agent, is 3.0wt%, and the fiber diameter reaches 500-1500nm.

[0065] In summary, the present application provides a preparation method of ultra-high molecular weight polyethylene nanofiber. First, the UHMWPE powder is pre-swollen with liquid paraffin (UHMWPE: liquid paraffin = 2:8), then the swollen UHMWPE gel, nucleating agent and CAB are melt blended by using a twin-screw extruder, the UHMWPE is stretched and refined through the online crystal regulation of UHMWPE and the stretching and extrusion effect of CAB blending during the extrusion process, then the CAB phase and liquid paraffin are extracted by using acetone, and the UHMWPE nanofiber is obtained, realizing the macro preparation of UHMWPE nanofiber with a diameter of less than 300nm.

[0066] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing ultra-high molecular weight polyethylene nanofibers, characterized in that, Includes the following steps: S1, ultra-high molecular weight polyethylene powder with a relative average molecular weight of 4.5 million and liquid paraffin were pre-swelled at a mass ratio of ultra-high molecular weight polyethylene powder: liquid paraffin = 2:8 to obtain ultra-high molecular weight polyethylene gel. S2, ultra-high molecular weight polyethylene gel, nucleating agent, and cellulose acetate butyrate are fed into a twin-screw extruder for melt blending and extrusion to obtain modified gel ultra-high molecular weight polyethylene fiber; the nucleating agent is dibenzyl sorbitol, di(p-methylbenzyl)sorbitol, or titanium oxalate; the mass ratio of ultra-high molecular weight polyethylene, nucleating agent, and cellulose acetate butyrate is 20:(0.5-2):(78-79.5); S3, the modified gel ultra-high molecular weight polyethylene fiber obtained in step S2 is immersed in acetone solution, and the CAB phase and liquid paraffin are extracted by acetone to obtain UHMWPE nanofibers with a diameter of less than 300 nm.

2. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 1, characterized in that: The nucleating agent is dibenzylidene sorbitol, and the mass concentration of dibenzylidene sorbitol is 0.5-2.0 wt%.

3. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 2, characterized in that: The mass ratio of ultra-high molecular weight polyethylene, dibenzyl sorbitol, and cellulose acetate butyrate is 20:(0.5-2):(78-79.5).

4. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 1, characterized in that: The nucleating agent is di(p-methylbenzyl)sorbitol, and the mass concentration of di(p-methylbenzyl)sorbitol is 0.5-2.0 wt%.

5. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 4, characterized in that: The mass ratio of ultra-high molecular weight polyethylene, di(p-methylbenzyl)sorbitol, and cellulose acetate butyrate is 20:(0.5-2):(78-79).

6. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 1, characterized in that: The nucleating agent is titanium oxalate, and the mass concentration of titanium oxalate is 0.5-2.0 wt%.

7. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 6, characterized in that: The mass ratio of ultra-high molecular weight polyethylene, titanium oxalate, and cellulose acetate butyrate is 20:(0.5-2):(78-79.5).

8. The method for preparing ultra-high molecular weight polyethylene nanofibers according to claim 1, characterized in that: In step S2, the melt blending temperature is 200-240℃.

Images