A method for preparing a modified polymer pellet of multi-scale micro-nano fibers in a directional manner

Abstract

The application discloses a method for preparing modified polymer granules with oriented multi-scale micro-nano fibers, and adopts a method of "liquid hydrophobic-coupling double-coated micro-nano fibers" to modify the multi-scale micro-nano fibers, which not only improves the compatibility of the micro-nano fibers and the plastic matrix, but also enhances the stability and dispersibility of the micro-nano fibers, so that the aggregation of the micro-nano fibers is obviously reduced; in combination with the screw mixing action of an extruder, the micro-nano fibers are more easily arranged in the flow direction, so that the mechanical properties and other physical properties of the modified polymer granules are improved. The preparation method is simple in process and low in preparation cost, and can effectively reduce the consumption of fossil resources; the modified polymer granules prepared by the application have excellent performance, high strength and size stability, and can be widely applied to the fields of automobile manufacturing, electronic products, building substrates and the like, and have the value of industrialization.

Description

Technical Field

[0001] This invention relates to a method for the directional preparation of multi-scale micro / nanofiber modified polymer granules, belonging to the field of composite material technology. Background Technology

[0002] The depletion of fossil resources is increasing daily, and traditional petroleum-based materials are non-renewable and lack biodegradability, leading to increasingly severe resource scarcity and environmental pollution problems. Biomass fiber, a natural polymer material, possesses advantages such as abundant resources, excellent biocompatibility, and high renewability, allowing it to degrade naturally without polluting the environment. Decomposing biomass fibers into micro- and nano-scale fibers yields micro- and nanofibers (MNFs) with characteristics such as low density, high crystallinity, high surface area, and high mechanical properties, along with tunable surface chemistry. These properties make MNFs excellent reinforcing materials for polymers. MNF-modified polymer composites not only enhance performance but also have significant environmental protection implications and can reduce material costs.

[0003] In recent years, research on using MNF to reinforce polymers has been ongoing, but the following problems still exist:

[0004] ① MNF is unevenly dispersed and prone to agglomeration in the polymer matrix. This reduces the contact area between MNF and the polymer, significantly increasing the difficulty of bonding. ② The interfacial bonding between the fiber and polymer phases is weak; because the surface groups of MNF exhibit significant hydrophilicity, while polymers are generally hydrophobic, insufficient interfacial bonding leads to a weak composite effect when fibers and polymers are combined. Currently, chemical modification or coupling agents are mainly used to address this. Commonly used solid coupling agents, such as maleic anhydride-grafted polyethylene particles, cannot be uniformly coated onto the fibers when added in small amounts, affecting the coupling effect. ③ The composite material exhibits poor strength, toughness, and dimensional stability.

[0005] There are generally two ways to prepare MNF-reinforced composite materials: (1) Solution casting method, which involves dissolving the polymer in an organic solvent or other way and then compounding it with MNF; the composite material obtained by this method has good uniformity, but it is not suitable for mass production, and the organic solvents used are expensive and pollute the environment. (2) Compound molding method, which involves blending and melting MNF with plastics and then processing them into shape through mechanical methods such as extrusion, injection molding, and compression molding. This method is suitable for mass production and is environmentally friendly. Solving the agglomeration problem in the compound molding process of MNF composite materials, improving the orientation of MNF, and enhancing the strength and dimensional stability of composite materials are of great significance for the application of MNF-modified polymer composite materials in a wider range of fields. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a method for the directional preparation of multi-scale micro / nanofiber modified polymer granules, which improves the orientation of micro / nanofibers during the melt mixing process in an extruder, and the prepared modified polymer granules have high strength and dimensional stability.

[0007] Technical solution: This invention provides a method for the directional preparation of multi-scale micro / nanofiber modified polymer granules, comprising the following steps:

[0008] (1) The softwood pulp board is crushed into micron fibers with a diameter of 50-150μm, and the micron fibers are fully swollen; a portion of the swollen micron fibers are placed in a high-speed mixer to de-fiber into micron fibers with a diameter of 10-100μm.

[0009] (2) The micron fibers after high-speed stirring in step (1) are placed in an ultrafine grinding mill and further de-fibriled into micro-nano fibers with a diameter of 100nm-10μm;

[0010] (3) Mix the microfibers with a diameter of 10-100μm obtained in step (1) and the micro-nanofibers with a diameter of 100nm-10μm obtained in step (2) in a certain proportion to obtain multi-scale micro-nanofibers.

[0011] (4) The multi-scale micro-nanofibers were immersed in a hydrophobic modifier and vacuum filtered; then a coupling agent dispersion was added and stirred evenly, and vacuum filtered and dried again to obtain the modified multi-scale micro-nanofibers.

[0012] (5) Mix the modified multi-scale micro-nano fibers, plastic powder and additives, and stir at high speed to mix them evenly to obtain a mixture;

[0013] (6) Melt granulation of the mixture.

[0014] The preparation method of this invention addresses the problems of uneven fiber dispersion and agglomeration in the production process of micro / nanofiber / polymer composite materials. It employs a "liquid hydrophobic-coating double-coating micro / nanofiber" method to modify the micro / nanofibers, which are then melt-blended with plastic in an extruder to improve the orientation effect of the micro / nanofibers. Specifically, the method includes:

[0015] 1. Liquid hydrophobication treatment

[0016] After treatment with a liquid hydrophobic modifier, the surface properties of micro / nanofibers change, becoming hydrophobic and reducing the interfacial tension with the plastic matrix. This can: ① Improve compatibility: Liquid hydrophobic modification can form a uniform protective film on the surface of MNFs. The hydrophobically treated micro / nanofibers (MNFs) have better compatibility with the hydrophobic plastic matrix, which helps the fibers to be evenly distributed and oriented within the plastic matrix. ② Reduce hygroscopicity: Hydrophobic treatment reduces the hygroscopicity of MNFs, avoiding expansion and curling during the mixing process, and helping the fibers maintain their orientation.

[0017] 2. Coupling agent treatment

[0018] The coupling agent dispersion can be uniformly mixed with MNF, allowing the coupling agent to be effectively distributed throughout the MNF and enhancing the compatibility between MNF and the plastic matrix. This helps to: ① Enhance interfacial bonding: The coupling agent forms chemical bonds between MNF and the plastic matrix, strengthening the interfacial bonding and making MNF more stable and easier to maintain orientation during mixing. ② Reduce fiber agglomeration: Coupling treatment makes MNF more uniformly dispersed in the plastic matrix, reducing agglomeration between MNF fibers and thus contributing to fiber orientation.

[0019] 3. Extruder mixing

[0020] During melt compounding in an extruder, the rotation and shearing action of the screw help MNFs orient themselves within the plastic matrix. MNFs treated with hydrophobic coupling exhibit stronger interfacial bonding with the plastic matrix, resulting in more uniform dispersion and reduced fiber randomness and agglomeration during compounding, thus improving the orientation effect.

[0021] The liquid hydrophobic agent soaking and coupling agent dispersion mixing used in this invention can ensure the effective distribution of hydrophobic agent and coupling agent in various parts of MNF, so that the MNF surface forms a hydrophobic-coupling double coating. When compounded with plastic, it can enable MNF to achieve better orientation during the flow process of melt blending and extrusion, forming an intercalation structure.

[0022] In this method, the fibers are mechanically defibriled into MNF, which has a good brooming effect and can easily achieve good physical interface bonding when combined with plastics, i.e., mechanical riveting bonding; the resulting fibers are multi-scale micro-nano fibers with a certain aspect ratio.

[0023] Furthermore, the swelling treatment described in step (1) includes a primary swelling treatment with NaOH solution and a secondary swelling treatment with hydrochloric acid.

[0024] Further, the specific steps of the swelling treatment are as follows: place the microfiber in a 3-5% NaOH solution, treat it in a 95°C water bath for 2 hours, then place it at room temperature for 12 hours, and wash it with distilled water or deionized water until neutral; then treat it with 1% hydrochloric acid in an 80°C water bath for 2-4 hours, and wash it with distilled water or deionized water until neutral.

[0025] Furthermore, the mass ratio of the microfibers and micro / nanofibers mentioned in step (3) is 7:3.

[0026] Furthermore, the hydrophobic modifier mentioned in step (4) includes γ-aminopropyltriethoxysilane or alkenyl succinic anhydride.

[0027] Furthermore, the coupling agent mentioned in step (4) includes maleic anhydride-grafted polyethylene powder or maleic anhydride-grafted polypropylene powder.

[0028] Furthermore, the mass ratio of the modified multi-scale micro / nanofibers, plastic powder, and additives in step (5) is 10-50%: 46-88%: 2-4%.

[0029] Furthermore, in step (6), the extruder temperature is set to 158-165℃ and the screw speed is set to 20-30rpm during melt granulation.

[0030] The present invention also provides modified polymer granules prepared according to the above method.

[0031] This invention also provides the application of the above-mentioned modified polymer granules in the preparation of automotive parts, electronic product parts, and building substrates.

[0032] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention uses a "liquid hydrophobic-coated double-coated micro / nanofiber" method to modify micro / nanofibers, which not only improves the compatibility between micro / nanofibers and the plastic matrix but also enhances the stability and dispersibility of the fibers, significantly reducing fiber aggregation. Combined with the screw mixing action of an extruder, the fibers can be more easily oriented along the flow direction, thereby improving the mechanical properties and other physical characteristics of the composite material. The preparation method of this invention is simple and low-cost, effectively reducing the consumption of fossil resources. The resulting composite material exhibits excellent performance, high strength, and dimensional stability, and can be widely used in automobile manufacturing, electronic products, building materials, and other fields, possessing industrial value. Attached Figure Description

[0033] Figure 1 Transmission electron microscopy images of broom-like micro / nanofibers (MNF), (a) magnified 1000 times, (b) magnified 5000 times;

[0034] Figure 2The image shows a cross-sectional scanning electron microscope (SEM) image of polyethylene from the control group.

[0035] Figure 3 The images are cross-sectional scanning electron microscope images of MNF-modified polyethylene, (a) magnified 250 times, (b) magnified 800 times.

[0036] Figure 4 The results of the flexural mechanical properties of MNF-modified polymer granules are shown in the figures: (a) flexural strength and (b) flexural modulus.

[0037] Figure 5 The linear thermal expansion coefficient of MNF-modified polymer granules is shown in the results. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0039] Example 1

[0040] (1) Take an appropriate weight of softwood pulp board and cut it into pieces approximately 0.5 × 0.5 cm in size. 2 Small pieces of softwood pulp were broken into micron-sized fibers using a conventional turbine mill. The fibers had a diameter distribution of 50-150 μm and a length of approximately 1-3 mm. These micron-sized fibers were then subjected to a swelling treatment: placed in a 5% sodium hydroxide solution and treated in a 95°C water bath for 2 hours. The fibers were then left at room temperature for 12 hours and washed with deionized water until neutral. Next, they were treated with a 1% hydrochloric acid solution in an 80°C water bath for 3 hours to further swell the fibers. After swelling, the fibers were washed with deionized water until neutral.

[0041] (2) Place the swollen microfibers from step (1) into a high-speed mixer and stir for 3-5 minutes at a speed of 10,000 rpm to break them down into fibers with a diameter of approximately 10-100 μm. Then place them into an ultrafine grinder and, by adjusting the scale, obtain micro / nanofibers with a diameter of 100 nm-10 μm.

[0042] The fiber effect was observed using transmission electron microscopy. The micro-nano fibers were stirred and ground. Figure 1 As can be seen, after mechanical defiberization, the micro- and nano-sized fibers (100nm-10μm) exhibited a good brooming effect, with individual fibers being defibered and nanofibers accompanying the micron fibers. During high-temperature melt mixing in an extruder, the broomed fibers can significantly increase the specific surface area for bonding with the polymer matrix, and the two can easily form a mechanical rivet bond, thereby improving mechanical properties.

[0043] (3) Take the micron fiber (10-100μm) and micro-nano fiber (100nm-10μm) from step (2) and mix them for later use. The mass ratio of micron fiber to micro-nano fiber is 7:3 to obtain multi-scale micro-nano fiber (MNF).

[0044] (4) The multi-scale MNF from step (3) above is modified in a liquid hydrophobic modifier (such as γ-aminopropyltriethoxysilane). Specifically, MNF and γ-aminopropyltriethoxysilane are mixed and stirred at a 1:1 mass ratio to prevent the agglomeration of the defibrilated micro / nano wood fibers. The hydrophobic MNF is then placed in a coupling agent dispersion. Specifically, maleic anhydride-grafted polyethylene powder (micro / nano scale) and a solvent (such as ethyl acetate) are mixed at a 1:20 ratio to form a dispersion. The MNF and coupling agent dispersion are then mixed at a 1:2 mass ratio using high-speed stirring to ensure effective distribution of the coupling agent in all parts of the micro / nano fibers. After uniform mixing, the mixture is vacuum filtered to obtain a hydrophobic-coupled modified MNF slurry. The MNF slurry is then dried to obtain modified MNF for later use.

[0045] The micro / nano-fibers of this application undergo liquid hydrophobic coupling, resulting in a double coating on the fiber surface. This liquid hydrophobic coupling treatment enhances the compatibility of the MNF with the hydrophobic plastic matrix, making the fibers easier to disperse uniformly and reducing MNF aggregation.

[0046] (5) The modified MNF, plastic powder (high-density polyethylene), and additives (polyethylene wax) are placed in a high-speed mixer at a certain ratio and dispersed evenly to obtain a mixture. The speed is 10,000 rpm. Three mixtures with different mass ratios are prepared: 1. Modified MNF content is 30%, plastic powder content is 67%, and additive content is 3%; 2. Modified MNF content is 20%, plastic powder content is 77%, and additive content is 3%; 3. Modified MNF content is 10%, plastic powder content is 90%, and no additives are required.

[0047] (6) The mixture was placed in an extruder to extrude a sample. The temperature of the extruder was set to 165℃ and the screw speed was set to 30rpm. Micro-nanofiber modified polyethylene samples were obtained.

[0048] The control group polyethylene ( Figure 2 Electron microscopy was performed on polyethylene modified with micro / nanofibers containing 20% ​​modified MNF. Figure 3 The results showed that the cross-sectional morphology of the control group polyethylene was relatively smooth and lacked a strong sense of layering, while the surface of the micro / nanofiber modified polyethylene was... Figure 3 (a) Fracture morphology reveals a layered, intercalated structure with layer-by-layer assembly and bonding, and micro / nanofibers are oriented along the flow direction of the polymer matrix. For example... Figure 3 (b) The fibers are uniformly dispersed in the polymer matrix and have obvious filamentous appearance, which helps to improve its mechanical properties.

[0049] (7) Granulate the mixture sample obtained by extrusion molding to obtain modified polymer granules.

[0050] (8) The granules were injection molded into flexural specimens at an injection molding machine at a temperature of 166℃. The flexural strength of the flexural specimens with different fiber contents was tested using a universal testing machine. Figure 4 The coefficient of thermal expansion of the samples was determined using a static thermomechanical analyzer (TMA) over a temperature range of -30 to 60 degrees Celsius. A polyethylene (HDPE) sample was used as a control group.

[0051] The results showed that the flexural strength of the flexural specimen containing mixture 1 was 42.9 MPa, and the flexural modulus was 2060.8 MPa, which were 100% and 162% higher than those of the control polyethylene sample, respectively. The linear coefficient of thermal expansion was 84 × 10⁻⁶. -6 The flexural strength of the sample containing compound 2 was approximately half that of the control group polyethylene sample, indicating a significant improvement in thermal stability. The flexural strength of the flexural specimen reached 35 MPa, and the flexural modulus reached 1600.9 MPa, representing increases of 64% and 103% respectively compared to the control group polyethylene sample. The linear thermal expansion coefficient was 94 × 10⁻⁶. -6 / K, which was 83 × 10⁻⁶ compared to the control group of polyethylene. -6 / K. The flexural strength of the flexural specimen containing compound 3 reached 28.2 MPa, and the flexural modulus reached 1180.8 MPa, representing a 32% and 50% increase in strength and strength, respectively, compared to the pure high-density polyethylene sample. The linear coefficient of thermal expansion was 122 × 10⁻⁶. -6 / K, which was 55 × 10⁻⁶ compared to the control group of polyethylene. -6 / K indicates that the flexural strength and modulus of the modified polymer granules both increase with increasing modified MNF content. The linear thermal expansion coefficient of the modified polymer granules decreases with increasing modified MNF content, representing a significant improvement in dimensional stability with increasing modified MNF content.

Claims

1. A method for directionally preparing multi-scale micro / nanofiber modified polymer granules, characterized in that, Includes the following steps: (1) The softwood pulp board is crushed into micron fibers with a diameter of 50-150μm, and the micron fibers are fully swollen; the swollen micron fibers are placed in a high-speed mixer to defiber into micron fibers with a diameter of 10-100μm. (2) The micron fibers after high-speed stirring in step (1) are placed in an ultrafine grinding mill and further de-fibriled into micro-nano fibers with a diameter of 100nm-10μm; (3) Mix the microfibers with a diameter of 10-100μm obtained in step (1) and the micro-nanofibers with a diameter of 100nm-10μm obtained in step (2) in a certain proportion to obtain multi-scale micro-nanofibers. (4) The multi-scale micro-nanofibers were immersed in a hydrophobic modifier and vacuum filtered; then a coupling agent dispersion was added and stirred evenly, and vacuum filtered and dried again to obtain the modified multi-scale micro-nanofibers. (5) Mix the modified multi-scale micro-nano fibers, plastic powder and additives, and stir at high speed to mix them evenly to obtain a mixture; (6) Melt granulation of the mixture.

2. The method according to claim 1, characterized in that, The swelling treatment described in step (1) includes a primary swelling treatment with NaOH solution and a secondary swelling treatment with hydrochloric acid.

3. The method according to claim 2, characterized in that, The specific steps of the swelling treatment are as follows: place the microfiber in a 3-5% NaOH solution, treat it in a 95°C water bath for 2 hours, then place it at room temperature for 12 hours, and wash it with distilled water or deionized water until neutral; then treat it with 1% hydrochloric acid in an 80°C water bath for 2-4 hours, and wash it with distilled water or deionized water until neutral.

4. The method according to claim 1, characterized in that, The mass ratio of the microfibers and micro / nanofibers mentioned in step (3) is 7:

3.

5. The method according to claim 1, characterized in that, The hydrophobic modifier mentioned in step (4) includes γ-aminopropyltriethoxysilane or alkenyl succinic anhydride.

6. The method according to claim 1, characterized in that, The coupling agent mentioned in step (4) includes maleic anhydride-grafted polyethylene powder or maleic anhydride-grafted polypropylene powder.

7. The method according to claim 1, characterized in that, The mass ratio of the modified multi-scale micro / nano fibers, plastic powder, and additives mentioned in step (5) is 10-50%: 46-88%: 2-4%.

8. The method according to claim 1, characterized in that, In step (6), the extruder temperature is set to 158-165℃ and the screw speed is set to 20-30rpm during melt granulation.

9. A modified polymer granule prepared according to any one of claims 1 to 8.

10. The application of the modified polymer granules according to claim 9 in the preparation of automotive parts, electronic product parts, and building substrates.

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