Crosslinked castor oil resin with remoldability as well as preparation method and application thereof

Abstract

The invention discloses a cross-linked castor oil resin with remoldability and a preparation method and application thereof, and belongs to the technical field of high polymer materials, the preparation method comprises the following steps: firstly, preparing acetoacetate oximido castor oil, then dissolving acetoacetate oximido castor oil in an organic solvent, adding an isocyanate cross-linking agent and a catalyst, uniformly mixing, and drying to obtain the cross-linked castor oil resin with remoldability. Acetoacetate oximido carbamate formed in a cross-linked structure is a novel dynamic covalent bond and has remoldability, the resin can be remolded for multiple times in a hot press molding mode, and good mechanical properties are kept. The method is of great significance in promoting sustainable development of high polymer materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a crosslinked castor oil resin with remolding property, and a preparation method and application thereof. Background Art

[0002] Traditional thermosetting resins have excellent mechanical properties and dimensional stability due to their inherent covalent crosslinking network. However, the irreversible covalent bonds also result in that thermosetting resins cannot be dissolved and melted, so it is difficult to reshape them. New materials with remolding properties not only have excellent mechanical properties and dimensional stability of thermosetting resins, but also have functions such as self-healing and shape memory, and have great potential in application fields such as intelligent manufacturing, sensors, and electronic skin.

[0003] The raw materials used to prepare resins mainly come from non-renewable petroleum-based resources. How to develop sustainable new polymer materials with renewable biomass resources as raw materials is gradually attracting the attention of researchers.

[0004] Castor oil is an industrial vegetable oil with rich resources and low price. It is inedible and does not compete with the food industry for resources, which conforms to the development principle of biomass materials. The chemical structure of castor oil contains active groups such as ester groups, hydroxyl groups and carbon-carbon double bonds, which provides a basis for its chemical modification, structure design and high-value utilization. At present, it has been used to prepare polymer products such as sealants, pharmaceuticals, cosmetics and coatings.

[0005] Chinese Patent CN 111925504A discloses a castor oil-based polyurethane acrylate resin and a preparation method and application thereof. The preparation method includes the following steps: (1) Reacting active diluent, isocyanate and castor oil as raw materials until the mass fraction of isocyanate groups in the feedstock reaches half of the theoretical value before the start of the reaction to obtain an isocyanate semi-blocked intermediate; (2) Reacting the isocyanate semi-blocked intermediate obtained in step (1) with acrylic hydroxy ester, adding an antioxidant until the content of isocyanate groups is less than 0.5%, and adding anhydrous ethanol for capping to obtain a castor oil-based polyurethane acrylate resin.

[0006] Chinese Patent CN 107353393A discloses a castor oil-modified polyurethane resin and a preparation method thereof. The castor oil-modified polyurethane resin is composed of the following components in the following proportions: 10-20 parts by weight of polyol A, 20-40 parts by weight of polyol B, 8-10 parts by weight of castor oil, 20-45 parts by weight of isocyanate, 5-8 parts by weight of hydrophilic chain extender, 1-3 parts by weight of diol chain extender, 3-5 parts by weight of diamine chain extender, 6-7 parts by weight of salt-forming agent, 100-200 parts by weight of solvent A, and 8-16 parts by weight of solvent B.

[0007] Although the above-mentioned prior art discloses some resins prepared from castor oil as raw materials, these resins do not have the property of being reprocessable, and the waste rate after use is relatively high, which will cause environmental pollution. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a crosslinked castor oil resin with reprocessability, its preparation method and application. It is obtained by crosslinking acetoacetate oxime-based castor oil under the action of an isocyanate crosslinking agent. The acetoacetate oxime-based carbamate formed in the crosslinked structure is a new type of dynamic covalent bond, which has reprocessability. This resin can be reshaped multiple times by hot pressing and maintain good mechanical properties, which is of great significance for promoting the sustainable development of polymer materials.

[0009] To achieve the above object, the technical solutions adopted by the present invention are as follows: A preparation method of a crosslinked castor oil resin with reprocessability, the preparation method comprising the following steps: (1) Prepare acetoacetate oxime-based castor oil; (2) Dissolve acetoacetate oxime-based castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix evenly, and then dry to obtain a crosslinked castor oil resin with reprocessability.

[0010] The preparation method specifically comprises the following steps: (1) Mix acetoacetate-based castor oil with glacial acetic acid, dropwise add an aqueous solution of sodium nitrite at -5 - 0 °C, stir and react for 12 - 24 h after addition, and obtain acetoacetate oxime-based castor oil through post-treatment; (2) Dissolve acetoacetate oxime-based castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix evenly, and then dry to obtain a crosslinked castor oil resin with reprocessability.

[0011] In step (1), the preparation method of the acetoacetate-based castor oil is: mix castor oil and tert-butyl acetoacetate evenly, stir and react at 90 - 140 °C for 1 - 3 h, and obtain acetoacetate-based castor oil through post-treatment.

[0012] Further, the molar ratio of castor oil to tert-butyl acetoacetate is 1:3 - 6.

[0013] The method of post-treatment is: pour the reaction solution into petroleum ether for precipitation and washing multiple times, and dry the precipitate to a constant weight.

[0014] In step (1), the molar ratio of acetoacetate-based castor oil, glacial acetic acid, and sodium nitrite is 1:6 - 9:3 - 6.

[0015] In step (1), the post-treatment method is as follows: extract with ethyl acetate, wash the organic phase with an aqueous sodium bicarbonate solution until neutral, and then concentrate and dry.

[0016] In step (2), the isocyanate crosslinking agent is selected from one of 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, sebacoyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate.

[0017] In step (2), the catalyst is selected from one of diisopropylamine, dimethylisopropylamine, dibutyltin dilaurate, 4-dimethylaminopyridine, 1,8-diazabicyclo[5,4,0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene.

[0018] In step (2), the organic solvent is selected from one of tetrahydrofuran, dichloromethane, chloroform, 1,4-dioxane, toluene, xylene.

[0019] In step (2), the drying conditions are: keep warm at 40 - 80 °C for 48 - 72 h.

[0020] In step (2), the molar ratio of the acetoacetic acid ester oxime group castor oil to the isocyanate crosslinking agent is 4:3 - 6; the mass ratio of the acetoacetic acid ester oxime group castor oil to the catalyst is 1000:1 - 10.

[0021] The present invention also provides a crosslinked castor oil resin with remolding property prepared according to the described preparation method, which can be remolded and used multiple times.

[0022] The present invention also provides the application of the crosslinked castor oil resin with remolding property in the preparation of new materials with remolding performance, which can be used to prepare polymer products such as sealants, pharmaceuticals, cosmetics, and coatings.

[0023] The preparation method of the crosslinked castor oil resin with remolding property provided by the present invention first prepares acetoacetic acid ester oxime group castor oil from acetoacetic acid ester group castor oil as the raw material, and then carries out a crosslinking reaction under the action of an isocyanate crosslinking agent. An acetoacetic acid ester oxime group carbamate will be formed in the structure after the crosslinking reaction, which is a new type of dynamic covalent bond and has remolding property. This resin can be remolded multiple times by hot pressing and maintain good mechanical properties, and can be recycled.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention prepares acetoacetic acid ester oxime group castor oil by continuously modifying the hydroxyl group in the castor oil structure, which is different from the method of modifying the keto group or aldehyde group into an oxime group. This preparation method is simple and the post-treatment is convenient.

[0025] 2) In the present invention, the acetoacetate oxime-based carbamate formed by the reaction of acetoacetate oxime group with isocyanate has been confirmed to be a novel dynamic covalent bond with reworkability.

[0026] 3) By introducing acetoacetate oxime-based carbamate into the crosslinked network, the present invention endows the crosslinked castor oil resin with good reworkability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the preparation route diagram of acetoacetate oxime group castor oil; Figure 2 is the 1H NMR spectra of acetoacetate oxime group castor oil (A) and acetoacetate group castor oil (B), and the solvent used for NMR measurement is DMSO- d 6; Figure 3 is the stress-strain curves of the crosslinked castor oil resins in Examples 1 to 3; Figure 4 is the stress relaxation curves and activation energy of AOxCOU-1.0 in Example 1 at different test temperatures; Figure 5 is the stress-strain curves of AOxCOU-1.0 before and after reshaping in Example 1; Figure 6 is the 1H NMR spectra of the small molecule AB of acetoacetate oxime-based carbamate in the experimental example, and the solvent used for NMR measurement is DMSO- d 6; Figure 7 is the small molecule model reaction and 1H NMR spectra, and the solvent used for NMR measurement is DMSO- d 6. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described in detail below with reference to the examples. Example 1

[0029] A preparation method of a crosslinked castor oil resin with reworkability, comprising the following steps: (1) Preparation of acetoacetate group castor oil: Weigh castor oil (9.33 g, 10 mmol) and tert-butyl acetoacetate (6.32 g, 40 mmol) and mix them evenly in a round-bottomed flask equipped with a stirrer. Stir at 130 °C for 3 h. After the reaction is completed, pour the solution into a large amount of petroleum ether for precipitation and wash it several times. Dry the precipitate to a constant weight to obtain acetoacetate group castor oil; (2) Preparation of acetoacetic ester oxime castor oil: Weigh acetoacetic ester castor oil (11.85 g, 10 mmol) and glacial acetic acid (4.8 g, 80 mmol), mix them evenly and cool down to -5 °C. Then, dropwise add 10 mL of an aqueous solution of sodium nitrite with a mass concentration of 27.6% (2.76 g, 40 mmol) and react for 12 h. Next, add ethyl acetate to the solution for extraction multiple times, retain the organic phase, wash it with an aqueous solution of sodium bicarbonate until neutral, and finally rotary evaporate and dry to constant weight to obtain acetoacetic ester oxime castor oil; (3) Preparation of crosslinked castor oil resin with remoldability: Weigh acetoacetic ester oxime castor oil (5.1 g, 4 mmol) and dissolve it in 80 mL of 1,4-dioxane. Then, add sebacoyl diisocyanate (1.18 g, 6 mmol) and dibutyltin dilaurate (0.006 g) in sequence. After mixing evenly, pour the solution into a polytetrafluoroethylene mold and place it in a forced-air drying oven at 60 °C for 72 h to obtain an acetoacetic ester oxime carbamate crosslinked castor oil film, denoted as AOxCOU-1.0.

[0030] The nuclear magnetic resonance hydrogen spectrum of the acetoacetic ester castor oil prepared in this example is as shown in Figure B in Figure 2 The nuclear magnetic resonance hydrogen spectrum of the acetoacetic ester oxime castor oil is as shown in Figure A in Figure 2 Compared with the nuclear magnetic resonance hydrogen spectrum of the acetoacetic ester castor oil, the signal peaks at 2.16 ppm and 3.5 ppm disappear, while new signal peaks appear at 2.33 ppm and 13.2 ppm, indicating that the acetoacetic ester group has been modified to the acetoacetic ester oxime group, proving the successful preparation of acetoacetic ester oxime castor oil. Example 2

[0031] Other conditions are the same as in Example 1, except that the addition amount of sebacoyl diisocyanate is changed to 0.94 g (4.8 mmol). The obtained acetoacetic ester oxime carbamate crosslinked castor oil film is denoted as AOxCOU-0.8. Example 3

[0032] Other conditions are the same as in Example 1, except that the addition amount of sebacoyl diisocyanate is changed to 0.71 g (3.6 mmol). The obtained acetoacetic ester oxime carbamate crosslinked castor oil film is denoted as AOxCOU-0.6. Example 4

[0033] Others are the same as Example 1, except that step (3) is as follows: Weigh acetoacetic ester oxime-based castor oil (5.1 g, 4 mmol) and dissolve it in 80 mL of toluene. Then, add isophorone diisocyanate (0.89 g, 4 mmol) and 4-dimethylaminopyridine (0.005 g) thereto. After mixing evenly, pour the solution into a polytetrafluoroethylene mold and leave it standing in a forced-air drying oven at 80 °C for 72 h to obtain an acetoacetic ester oxime-based carbamate crosslinked castor oil film. Through tensile testing, its breaking strength is 9.2 MPa and the elongation at break is 87%. Example 5

[0034] Others are the same as Example 1, except that step (3) is as follows: Weigh acetoacetic ester oxime-based castor oil (5.1 g, 4 mmol) and dissolve it in 80 mL of tetrahydrofuran. Then, add 4,4'-dicyclohexylmethane diisocyanate (1.3 g, 5 mmol) and diisopropylamine (0.009 g) thereto. After mixing evenly, pour the solution into a polytetrafluoroethylene mold and leave it standing in a forced-air drying oven at 40 °C for 72 h to obtain an acetoacetic ester oxime-based carbamate crosslinked castor oil film. Through tensile testing, its breaking strength is 8.5 MPa and the elongation at break is 103%. Comparative Example 1

[0035] Weigh castor oil (3.7 g, 4 mmol) and dissolve it in 80 mL of tetrahydrofuran. Then, add 1,6-hexamethylene diisocyanate (1.01 g, 6 mmol) and dibutyltin dilaurate (0.004 g) thereto. After mixing evenly, pour the solution into a polytetrafluoroethylene mold and leave it standing in a forced-air drying oven at 40 °C for 72 h to obtain a crosslinked castor oil film without acetoacetic ester oxime-based carbamate. Through tensile testing, its breaking strength is 5.7 MPa and the elongation at break is 168%. After the film is broken, use a flat vulcanizing machine for hot pressing forming operation. The instrument parameters are set as 10 MPa, 100 °C, and 1 h. After the hot pressing operation is completed and the temperature drops, it is still a broken film, proving that the crosslinked castor oil film without acetoacetic ester oxime-based carbamate cannot be reshaped. Test Example 1

[0036] Tensile tests were carried out on the three films obtained in Examples 1 - 3, and the stress-strain curves are as Figure 3 shown. As the addition amount of diisocyanate increases, the breaking strength of the film increases from 3.55 MPa (AOxCOU-0.6) to 7.06 MPa (AOxCOU-1.0), and at the same time, the elongation at break decreases from 214% to 132%. This is mainly because the more the amount of isocyanate added, the greater the crosslinking network density.

[0037] The stress relaxation curves of AOxCOU-1.0 at different temperatures are as follows Figure 4 shown. It can be seen from the figure that although there is a crosslinking network inside AOxCOU-1.0, within the test temperature range, the stress can relax to 0, indicating that the topological structure of the crosslinking network can be reshaped. Test Example 2

[0038] After crushing the AOxCOU-1.0 film, hot pressing forming operation is carried out using a flat vulcanizing machine, and the instrument parameters are set to 10 MPa, 100 °C, and 1 h. After the hot pressing operation is completed, the temperature is lowered and the film is taken out.

[0039] The stress-strain curves after multiple hot pressing reshaping are as follows Figure 5 shown. After AOxCOU-1.0 undergoes three hot pressing reshaping, the fracture strength (6.65 MPa) and elongation at break (113%) only slightly decrease compared with those before reshaping (7.06 MPa, 133%), proving that it still has good mechanical properties after reshaping. Experimental Example

[0040] To explore the mechanism by which the crosslinked castor oil resin has plasticity, the following experiments were carried out in this invention: Weigh ethyl acetoacetate oxime small molecule A (3.18 g, 20 mmol) and n-butyl isocyanate B (1.98 g, 20 mmol) and mix them evenly in 50 mL of petroleum ether, then add 0.001 g of dibutyltin dilaurate and stir at room temperature for 24 h. After the reaction is completed, silica gel chromatography column is used for separation and impurity removal, and the eluent is ethyl acetate and petroleum ether with a volume ratio of 2:1 to obtain acetyl acetoacetate oxime-based carbamate small molecule AB. Its nuclear magnetic resonance hydrogen spectrum is as follows Figure 6 shown. It can be seen from Figure 6 that AB is successfully prepared. 1 H NMR (500 MHz, DMSO- d 6) δ 7.98 (t, J = 5.9 Hz, 1H), 4.41 – 4.29 (m,2H), 3.11 (q, J = 6.7 Hz, 2H), 2.48 (d, J = 1.1 Hz, 3H), 1.47 (p, J = 7.2 Hz,2H), 1.36 – 1.20 (m, 5H), 0.95 – 0.83 (m, 3H). Weigh small molecule AB (2.5 mg, 0.01 mmol) and phenethyl isocyanate C (1.4 mg, 0.01 mmol) in 0.6 mL of anhydrous DMSO- dMix uniformly, and obtain its nuclear magnetic resonance hydrogen spectrum at 110 °C at different intervals as Figure 7 shown. From Figure 7 it can be found that the signal peak intensity of C-NH-C of AB molecules at 7.97 ppm decreases with the prolongation of the reaction time, while the signal peak intensity of C-NH-C of AC molecules at 8.08 ppm gradually increases. This confirms that the acetoacetate oxime-based carbamate can undergo a reversible cleavage-formation reaction under certain temperature conditions, that is, the acetoacetate oxime-based carbamate is a kind of dynamic covalent bond.

[0041] As can be seen from the above, the cross-linked castor oil resin provided by the present invention has the property of being reshaped because after the acetoacetate oxime-based castor oil undergoes a cross-linking reaction under the action of an isocyanate cross-linking agent, an acetoacetate oxime-based carbamate will be formed in the structure, which is a new type of dynamic covalent bond and has the property of being reshaped. The resin can be reshaped multiple times by hot pressing, and still maintain good mechanical properties after multiple reshaping.

[0042] The above detailed description of a cross-linked castor oil resin with the property of being reshaped and its preparation method and application with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a cross-linked castor oil resin with remodeling properties, characterized in that: The preparation method comprises the following steps: (1) Preparation of acetoacetate oxime castor oil; (2) Dissolve acetoacetate oxime castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix well, and dry to obtain a remodelable crosslinked castor oil resin.

2. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Mix acetoacetate castor oil with glacial acetic acid, add sodium nitrite aqueous solution dropwise at -5-0°C, stir and react for 12-24 hours after the addition is complete, and obtain acetoacetate oxime castor oil through post-treatment; (2) Dissolve acetoacetate oxime castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix well, and dry to obtain a remodelable crosslinked castor oil resin.

3. The preparation method according to claim 2, characterized in that: In step (1), the molar ratio of acetoacetate castor oil, glacial acetic acid and sodium nitrite is 1:6-9:3-6.

4. The preparation method according to claim 2, characterized in that: In step (2), the isocyanate cross-linking agent is selected from one of 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, decanediisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

5. The preparation method according to claim 2, characterized in that: In step (2), the catalyst is selected from one of diisopropylamine, dimethylisopropylamine, dibutyltin dilaurate, 4-dimethylaminopyridine, 1,8-diazabicyclo[5,4,0]undec-7-ene, and 1,5-diazabicyclo[4.3.0]non-5-ene.

6. The preparation method according to claim 2, characterized in that: In step (2), the organic solvent is selected from one of tetrahydrofuran, dichloromethane, chloroform, 1,4-dioxane, toluene and xylene.

7. The preparation method according to claim 2, characterized in that: In step (2), the drying conditions are: keeping warm at 40-80°C for 48-72 hours.

8. The preparation method according to any one of claims 2 to 7, characterized in that: In step (2), the molar ratio of the acetoacetate oxime castor oil to the isocyanate cross-linking agent is 4:3-6; the mass ratio of the acetoacetate oxime castor oil to the catalyst is 1000:1-10.

9. The cross-linked castor oil resin with remodelability obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the cross-linked castor oil resin with remodeling properties as claimed in claim 9 in preparing new materials with remodeling properties.

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