A bio-based polyurethane-based epoxy resin, its preparation method and cured product

Abstract

A bio-based polyurethane-based epoxy resin, its preparation method and cured product relate to the technical field of bio-based epoxy resin materials, and solve the problems of non-renewable raw materials of existing epoxy resins, poor impact toughness, weather resistance and fatigue resistance. 4-coumaric acid, isophorone diisocyanate and a catalyst are added to a solvent, and after stirring and completely dissolving, the temperature is raised for sufficient reaction, and then the solvent is removed to obtain p-CAI; p-CAI and epichlorohydrin are mixed, stirred and heated to the reaction temperature, and after completely dissolving, tetrabutylammonium bromide is added for sufficient reaction; after cooling to a specific temperature and keeping it constant, an aqueous NaOH solution is added dropwise within a specific time, and after sufficient reaction, it is extracted, washed and evaporated with dichloromethane to obtain p-CAIE. The cured product includes an epoxy resin monomer, a curing agent and an accelerator; the epoxy resin monomer is a mixture of bisphenol A type epoxy resin and bio-based polyurethane-based epoxy resin.

Description

Technical Field

[0001] The present invention relates to the technical field of bio-based epoxy resin materials, and particularly relates to a bio-based polyurethane-based epoxy resin, its preparation method and cured product. Background Art

[0002] Epoxy resin refers to a thermosetting polymer oligomer containing two or more epoxy groups in one molecule, with an aliphatic or aromatic skeleton, and formed by curing with other active groups at normal temperature or heating through epoxy groups. Due to its good adhesion, small curing shrinkage rate, heat resistance, chemical resistance, corrosion resistance, excellent mechanical properties, good processability and excellent electrical insulation properties, epoxy resin plays an important role in application fields such as coatings, composites, adhesives, electronics and electricity, packaging materials, engineering plastics, chemical building materials, etc. However, due to the high crosslinking density after curing of epoxy resin and the large rigidity of the crosslinked network skeleton, it is difficult for the molecular chains to move relative to each other, so there are disadvantages such as brittleness, poor impact toughness, weather resistance and fatigue resistance, which limit its wide application.

[0003] Due to the combination of hard segment part and soft chain end part in the polyurethane structure, it not only has extremely outstanding toughness and strength, good temperature resistance, creep resistance, wear resistance and impact resistance, but also has excellent low temperature resistance, chemical resistance and anti-aging properties, and is widely used in fields such as transportation, national defense construction, machinery, electronics and electricity, furniture food processing, textile printing, petrochemical industry, water conservancy construction, sports medical equipment, etc. However, the raw materials used in polyurethane elastomer materials have obvious disadvantages. For example, polyether polyols, polyester polyols and polyisocyanates are all sensitive to water vapor, and the formed polyurethane elastomer has poor hydrolysis resistance, water resistance and wet heat aging resistance.

[0004] And at present, most epoxy resins, especially bisphenol A epoxy resin, are derived from non-renewable petroleum resources. With the decreasing of their reserves, it will inevitably cause the continuous increase of the cost of polymer materials. In the general environment of energy conservation and environmental protection, it is necessary to find sustainable, high-quality, cheap and non-toxic substitutes for petroleum resources to produce epoxy resin to reduce the dependence on petroleum resources. Studying bio-based renewable monomers is a feasible countermeasure, which conforms to the green sustainable development strategy of the polymer industry. Bio-based epoxy resin uses biomass renewable resources as the main raw material, which is an important development direction of current polymer materials and has important practical value and broad development space. Lignin is the second largest natural renewable resource after cellulose and is considered a promising biomass source to replace petroleum-based compounds on a large scale. Due to the huge and complex molecular structure of lignin, the resin directly obtained from it has poor processing performance and unstable performance and is difficult to apply. Summary of the Invention

[0005] In order to solve the problems of non-renewability of existing epoxy resin raw materials, poor impact toughness, weather resistance and fatigue resistance, the present invention proposes a bio-based polyurethane-based epoxy resin, its preparation method and cured product.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention first provides a bio-based polyurethane-based epoxy resin, the structural formula of which is as follows:

[0008]

[0009] The present invention also provides a preparation method of the above-mentioned bio-based polyurethane-based epoxy resin, which includes the following steps:

[0010] S1. Add 4-coumaric acid and isophorone diisocyanate to a reaction solvent, then add a catalyst, stir at a first temperature until completely dissolved, and then raise the temperature to a second temperature for sufficient reaction. Remove the solvent using a rotary evaporator to obtain a polyurethane prepolymer p-CAI;

[0011] S2. Mix p-CAI and epichlorohydrin, stir and heat to the reaction temperature, add tetrabutylammonium bromide after complete dissolution and react fully;

[0012] S3. Cool the reaction system to a specific temperature and keep it constant, dropwise add an aqueous NaOH solution within a specific time, after sufficient reaction, dissolve and extract with dichloromethane, wash with brine and evaporate to obtain a bio-based polyurethane-based epoxy resin p-CAIE.

[0013] Preferably, the molar ratio of isophorone diisocyanate to 4-coumaric acid in step S1 is 1:2 to 4.

[0014] Preferably, the reaction solvent in step S1 is 1,4-dioxane, and the catalyst is dibutyltin dilaurate.

[0015] Preferably, the first temperature in step S1 is 30°C to 60°C, the second temperature is 60°C to 90°C, and the reaction time is 3h to 5h.

[0016] Preferably, the molar ratio of p-CAI to epichlorohydrin in step S2 is 1:10 to 25, and the addition amount of tetrabutylammonium bromide is 2wt% to 6wt% of p-CAI.

[0017] Preferably, the stirring rate in step S2 is 200r / min to 400r / min, the reaction temperature is 80°C to 110°C, and the reaction time is 3h to 5h.

[0018] Preferably, the mass percentage of the aqueous NaOH solution in step S3 is 40wt%.

[0019] Preferably, the specific temperature in step S3 is 30°C to 50°C, the specific time is 1 h to 2 h, and the reaction time is 3 h to 5 h.

[0020] The present invention also provides an epoxy resin cured product, comprising raw materials in the following parts by weight:

[0021] 100 parts of epoxy resin monomer, 75 to 85 parts of curing agent, and 0.75 to 0.85 parts of accelerator;

[0022] The epoxy resin monomer is a mixture of bisphenol A epoxy resin and the bio-based polyurethane-based epoxy resin described in claim 1, wherein the mass fraction of the bio-based polyurethane-based epoxy resin is not higher than 20 parts.

[0023] Compared with the prior art, the specific beneficial effects of the present invention are as follows:

[0024] 1. The present invention solves the problems of high toxicity, non-renewability, and non-sustainability of the raw material sources of existing commercial epoxy resins. The main raw materials are derived from renewable resources, are inexpensive, environmentally friendly, and energy-saving. The entire reaction process is simple and low-toxic, does not require too harsh reaction conditions, and can obtain a high yield while being easy to prepare;

[0025] 2. The present invention solves the problems of poor water resistance, hydrolysis resistance, heat and humidity aging resistance, and weather resistance of existing polyurethane elastomers and poor flexibility, weather resistance, and fatigue resistance of epoxy resins; the flexible chain segments of the polyurethane-based epoxy resin interpenetrate in the epoxy resin with a high crosslinking density, increasing the tensile strength and impact toughness of the resin, and having a good toughening effect and impact resistance. Moreover, due to the presence of benzene rings in the polyurethane-based epoxy resin, hard segment microdomains are easily formed, resulting in a microphase separation structure of the resin and a loose interphase network structure. When subjected to external forces, it can disperse the stress to achieve a toughening effect; this epoxy resin still has operational performance within the range of 100°C to 150°C, is suitable for the preparation of cast epoxy resin cured products and vacuum infusion composite materials, and has excellent mechanical properties, good toughness, and fatigue resistance.

[0026] 2. The epoxy resin cured product provided by the present invention uses the bio-based polyurethane-based epoxy resin and bisphenol A epoxy resin to carry out graft copolymerization reaction, and the formed interpenetrating network structure and interpenetration of flexible chain segments improve the impact toughness of the epoxy resin cured product. The aromatic structure also helps to improve the thermal stability and mechanical properties of the material; it can be widely used in the field of composite materials industry, especially in the fields of road traffic and wind power industry, and has excellent high thermal stability, toughness, room temperature anti-fatigue, and low temperature anti-cracking properties. Description of the Drawings

[0027] Figure 1IR spectra of each product in the preparation process of Example 1;

[0028] Figure 2 1H NMR spectrum of Product 1 in Example 1;

[0029] Figure 3 1H NMR spectrum of Product 2 in Example 1. Detailed implementation manners

[0030] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0031] Example 1.

[0032] 0.05 mol of colorless liquid isophorone diisocyanate, 0.1 mol of 4-coumaric acid, 70 ml of 1,4-dioxane and 1 drop of catalyst dibutyltin dilaurate were added to a three-necked round-bottom flask, one neck of which was equipped with a stirrer, and the other neck was used for solvent reflux and azeotropic distillation device. After complete dissolution at 50 °C, the temperature was raised to 80 °C and the reaction was continued for 3 h. 1,4-dioxane was continuously refluxed into the reactor. After the reaction was completed, the solvent was removed using a rotary evaporator to obtain Product 1, named p-CAI;

[0033] A mixture of Product 1 (0.05 mol) and epichlorohydrin (1.0 mol) was added to a three-necked flask, stirred and heated to 80 °C. After Product 1 was completely dissolved, tetrabutylammonium bromide (1.38 g) was added, and the mixture was reacted at 80 °C for 5 h;

[0034] The mixture was cooled to 40 °C, and then a 40 wt% aqueous NaOH solution (4 g of NaOH and 6 g of water) was added dropwise within 1 h. The resulting mixture was kept at 40 °C for another 4 h; after the reaction was completed and cooled to room temperature, the mixture was dissolved in dichloromethane and extracted, and then washed with brine 5 times to remove residual salts. Most of the unreacted epichlorohydrin was removed by rotary evaporation at 80 °C, and vacuum dried at 70 °C to obtain an orange-red liquid product 2, named p-CAIE.

[0035] Figure 1 IR spectra of P-CA, p-CAI and p-CAIE described in this embodiment. It can be seen that p-CAI shows characteristic peaks at 2270 cm -1 、1244 cm -1 and 1686 cm -1 corresponding to the stretching vibrations of N=C=O, C-O and C=O respectively; p-CAIE shows a peak at 910 cm-1 Characteristic peaks appeared, which were attributed to the stretching vibration of epoxy groups.

[0036] Figure 2 This is the nuclear magnetic resonance hydrogen spectrum of product 1p-CAI described in this embodiment. The chemical shifts and integral areas of all signal peaks correspond to the expected chemical structure. Figure 3 This is the nuclear magnetic resonance hydrogen spectrum of product 2p-CAIE described in this embodiment. The chemical shifts and integral areas of all signal peaks correspond to the expected chemical structure.

[0037] The above spectra can confirm that product 1p-CAI was successfully synthesized according to the following route:

[0038]

[0039] Product 2P-CAIE was successfully synthesized according to the following route:

[0040]

[0041] The epoxy equivalent of p-CAIE was tested, and the measured epoxy equivalent W EEW = 360.14 g / mol.

[0042] Example 2.

[0043] 0.05 mol of colorless liquid isophorone diisocyanate, 0.15 mol of 4-coumaric acid, 70 ml of 1,4-dioxane, and 1 drop of catalyst dibutyltin dilaurate were added to a three-neck round-bottom flask. One neck was equipped with a stirrer, and the other neck was for the solvent reflux and azeotropic distillation device. After complete dissolution at 30 °C, the temperature was raised to 60 °C and the reaction continued for 5 h. 1,4-dioxane was continuously refluxed into the reactor. After the reaction was completed, the solvent was removed using a rotary evaporator to obtain product 1p-CAI;

[0044] A mixture of product 1 (0.05 mol) and epichlorohydrin (0.5 mol) was added to a three-neck flask, stirred and heated to 80 °C. After product 1 was completely dissolved, tetrabutylammonium bromide (1.38 g) was added, and the mixture was reacted at 100 °C for 4 h;

[0045] The mixture was cooled to 50 °C, and then a 40 wt% NaOH aqueous solution (4 g of NaOH, 6 g of water) was added dropwise within 2 h. The resulting mixture was kept at 50 °C for another 3 h; after the reaction was completed and cooled to room temperature, the mixture was dissolved in dichloromethane and extracted, and then washed with brine 5 times to remove residual salts. Most of the unreacted epichlorohydrin was removed by rotary evaporation at 80 °C to obtain the orange-red liquid product 2p-CAIE.

[0046] Example 3.

[0047] 0.05 mol of colorless liquid isophorone diisocyanate, 0.2 mol of 4-coumaric acid, 70 ml of 1,4-dioxane and 1 drop of catalyst dibutyltin dilaurate were added to a three-necked round-bottom flask. One neck was equipped with a stirrer, and the other neck was used for solvent reflux and azeotropic distillation device. After complete dissolution at 30 °C, the temperature was raised to 90 °C and the reaction continued for 2 h. 1,4-dioxane was continuously refluxed into the reactor. After the reaction was completed, the solvent was removed using a rotary evaporator to obtain product 1 p-CAI;

[0048] A mixture of product 1 (0.05 mol) and epichlorohydrin (1.25 mol) was added to a three-necked flask, stirred and heated to 80 °C. After product 1 was completely dissolved, tetrabutylammonium bromide (1.38 g) was added, and the mixture was reacted at 110 °C for 3 h;

[0049] The mixture was cooled to 30 °C, and then a 40 wt% aqueous NaOH solution (4 g of NaOH and 6 g of water) was added dropwise within 2 h. The resulting mixture was kept at 30 °C for another 5 h; after the reaction was completed and cooled to room temperature, the mixture was dissolved in dichloromethane and extracted, and then washed with brine 5 times to remove residual salts. Most of the unreacted epichlorohydrin was removed by rotary evaporation at 80 °C to obtain the orange-red liquid product 2 p-CAIE.

[0050] Example 4.

[0051] This example prepared a toughened polyurethane-based epoxy resin cured product:

[0052] It included the following raw materials in parts by weight: 95 parts of bisphenol A epoxy resin, 5 parts of the polyurethane-based epoxy resin prepared in Example 1, 80 parts of curing agent, 0.80 parts of accelerator. After uniform mixing at 80 °C and defoaming, it was cured under the conditions of 120 °C, 140 °C, and 160 °C for 2 h each to obtain a thermosetting toughened polyurethane-based epoxy resin cured product.

[0053] Example 5.

[0054] This example prepared a toughened polyurethane-based epoxy resin cured product:

[0055] It included the following raw materials in parts by weight: 90 parts of bisphenol A epoxy resin, 10 parts of the polyurethane-based epoxy resin prepared in Example 1, 80 parts of curing agent, 0.80 parts of accelerator. After uniform mixing at 80 °C and defoaming, it was cured under the conditions of 120 °C, 140 °C, and 160 °C for 2 h each to obtain a thermosetting toughened polyurethane-based epoxy resin cured product.

[0056] Example 6.

[0057] In this embodiment, a toughened polyurethane-based epoxy resin cured product was prepared:

[0058] It includes raw materials in the following parts by weight: 85 parts of bisphenol A epoxy resin, 15 parts of the polyurethane-based epoxy resin prepared in Example 1, 80 parts of a curing agent, and 0.80 parts of an accelerator. After uniformly mixing at 80 °C and defoaming, it was cured under the conditions of 120 °C, 140 °C, and 160 °C for 2 hours each to obtain a thermosetting toughened polyurethane-based epoxy resin cured product.

[0059] Comparative Example 1.

[0060] 100 parts of bisphenol A epoxy resin, 80 parts of a curing agent, and 0.80 parts of an accelerator were uniformly mixed at 70 °C - 90 °C and then defoamed, and cured under the conditions of 120 °C, 140 °C, and 160 °C for 2 hours each to obtain a bisphenol A epoxy resin cured product.

[0061] Effect Example.

[0062] Tensile mechanical property tests were respectively carried out on the cured products prepared in Example 4 and Comparative Example 1. The tensile moving speed was controlled at 5 mm / min, and the tensile strength and elongation at break were tested. The following data were obtained:

[0063] Tensile strength (MPa) Elongation at break (%) Example 4 62.3 6.3 Example 5 61.2 6.5 Example 6 62.0 5.8 Comparative Example 1 45.2 2.6

[0064] It can be seen from the above data that compared with the traditional bisphenol A epoxy resin cured product of Comparative Example 1, the tensile mechanical properties of the polyurethane-based epoxy resin cured products of Examples 4 - 6 have been significantly improved, indicating that the polyurethane-based epoxy resin can reduce the rigidity of its chain segments. The flexible chain segments of the polyurethane-based epoxy resin interpenetrate in the epoxy resin with a high crosslinking density, increasing the tensile strength of the resin and the impact toughness, and having good toughening effect and impact resistance. Moreover, due to the presence of benzene rings in the polyurethane-based epoxy resin, the hard segments are prone to form hard phase microdomains, resulting in a microphase separation structure in the resin and forming a loose interphase network structure. When subjected to external forces, it can disperse the stress to achieve a toughening effect.

Claims

1. A bio-based polyurethane-based epoxy resin, characterized in that The structural formula is as follows:

2. A method for preparing a bio-based polyurethane-based epoxy resin according to claim 1, characterized in that: The steps include: S1. Add 4-coumaric acid and isophorone diisocyanate to the reaction solvent, then add dibutyltin dilaurate as a catalyst, stir at 30°C to 60°C until completely dissolved, raise the temperature to 60°C to 90°C and fully react for 3h to 5h, and remove the solvent using a rotary evaporator to obtain a polyurethane prepolymer p-CAI; The p-CAI structural formula is S2. Mix p-CAI and epichlorohydrin, stir and heat to 80°C to 110°C. After complete dissolution, add tetrabutylammonium bromide and allow to react for 3h to 5h. S3, cooling the reaction system to 30° C. to 50° C. and maintaining the constant temperature, adding a NaOH aqueous solution dropwise within 1 to 2 hours, and fully reacting for 3 to 5 hours, followed by extraction with dichloromethane, washing with brine, and evaporation to obtain a bio-based polyurethane-based epoxy resin p-CAIE; The p-CAIE structural formula is 3. The method for preparing a bio-based polyurethane-based epoxy resin according to claim 2, wherein: The molar ratio of isophorone diisocyanate to 4-coumaric acid in step S1 is 1:2-4.

4. The method for preparing a bio-based polyurethane-based epoxy resin according to claim 2, wherein: The reaction solvent in step S1 is 1,4-dioxane.

5. The method for preparing a bio-based polyurethane-based epoxy resin according to claim 2, wherein: In step S2, the molar ratio of p-CAI to epichlorohydrin is 1:10-25, and the amount of tetrabutylammonium bromide added is 2 wt%-6 wt% of p-CAI.

6. The method for preparing a bio-based polyurethane-based epoxy resin according to claim 2, wherein: The stirring rate in step S2 is 200 r / min to 400 r / min.

7. The method for preparing a bio-based polyurethane-based epoxy resin according to claim 2, wherein: The mass percentage of the NaOH aqueous solution in step S3 is 40 wt %.

8. A cured epoxy resin, characterized in that: The composition comprises the following raw materials in parts by weight: 100 parts of epoxy resin monomer, 75 to 85 parts of curing agent, 0.75 to 0.85 parts of accelerator; The epoxy resin monomer is a mixture of bisphenol A epoxy resin and the bio-based polyurethane-based epoxy resin described in claim 1, wherein the mass fraction of the bio-based polyurethane-based epoxy resin is not more than 20 parts.

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