阅读说明：本技术 含氮磷结构的生物基阻燃环氧树脂及其制备方法 (Bio-based flame-retardant epoxy resin containing nitrogen and phosphorus structures and preparation method thereof ) 是由 敖玉辉 迟至远 尚垒 庄海林 杜巍峰 郭宗伟 于 2019-10-14 设计创作，主要内容包括：本发明提供一种含氮磷结构的生物基阻燃环氧树脂及其制备方法,属于生物基环氧树脂领域。该环氧树脂结构式如式(Ⅰ)所示,本发明还提供一种含氮磷结构的生物基阻燃环氧树脂的制备方法,该方法以二乙醇胺、多聚甲醛和DOPO为反应原料单体,利用Kabachnik-Fields反应对DOPO进行化学改性,改性的DOPO化合物与生物基平台化合物—双酚酸酯化反应生成环氧树脂中间体,最后环氧树脂中间体与环氧氯丙烷反应生成阻燃环氧树脂。该方法制备得到的环氧树脂阻燃性能优异,且力学性能稳定。(The invention provides a bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure and a preparation method thereof, belonging to the field of bio-based epoxy resin. The structural formula of the epoxy resin is shown as a formula (I), the invention also provides a preparation method of the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure, the method takes diethanol amine, paraformaldehyde and DOPO as reaction raw material monomers, the chemical modification is carried out on the DOPO by utilizing Kabachnik-Fields reaction, the modified DOPO compound and the bio-based platform compound-diphenolic acid are subjected to esterification reaction to generate an epoxy resin intermediate, and finally the epoxy resin intermediate is reacted with epoxy chloropropane to generate the flame-retardant epoxy resin. The epoxy resin prepared by the method has excellent flame retardant property and stable mechanical property.)

1. The bio-based flame-retardant epoxy resin with the nitrogen-phosphorus containing structure is characterized in that the structural formula is shown as the formula (I):

2. the preparation method of the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 1, characterized by comprising the following steps:

the method comprises the following steps: adding diethanolamine, paraformaldehyde and DOPO into a reaction device, then adding a solvent, and stirring at 45-65 ℃ for 8-12 h to obtain a first intermediate;

step two: adding diphenolic acid into a reaction device, adding a solvent for dissolving, dissolving dicyclohexylcarbodiimide and 4-dimethylaminopyridine into the solvent to form a mixed solution, dropwise adding the mixed solution into the reaction device for stirring, then adding the first intermediate obtained in the first step, and reacting for 24-48 hours at 30-40 ℃ to obtain a second intermediate;

step three: adding the second intermediate obtained in the step two and epoxy chloropropane into a reaction device, then adding a catalyst, reacting for 5 hours at the temperature of 80-110 ℃, cooling to the temperature of 60-70 ℃ after the reaction is finished, dropwise adding a NaOH solution into the reaction system, reacting for 3-5 hours after the dropwise adding is finished, and performing post-treatment to obtain an epoxy resin monomer;

step four: and (3) heating the epoxy resin monomer obtained in the step three to 90-120 ℃, keeping the temperature for 20-40 min, adding a curing agent 4, 4-diaminodiphenylmethane, stirring and mixing uniformly, removing bubbles in vacuum, pouring into a preheated mold, and curing to obtain the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure.

3. The method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the molar ratio of the diethanolamine, the paraformaldehyde and the DOPO in the first step is 1: 1.5: 1.

4. the method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the molar ratio of the diphenolic acid, the dicyclohexylcarbodiimide, the 4-dimethylaminopyridine and the first intermediate is 2.5: 3: 0.2: 1.

5. the method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the molar ratio of the second intermediate, the epichlorohydrin and the catalyst in the third step is 1: 15: 0.01.

6. the method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2 or 5, wherein the catalyst is tetrabutylammonium bromide.

7. The preparation method of the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the three post-treatment steps are specifically as follows: naturally cooling the reaction system to room temperature, adding a solvent for dilution, filtering to remove solids, extracting the liquid with NaCl solution, then extracting with deionized water, retaining an organic phase, adding anhydrous magnesium sulfate into the organic phase, standing for 8-12 h, filtering to remove the anhydrous magnesium sulfate, and carrying out reduced pressure rotary evaporation on the solvent and excessive epichlorohydrin to obtain the epoxy resin monomer.

8. The preparation method of the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the vacuum defoaming time in the fourth step is 5-8 min.

9. The method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the curing is performed at 120 ℃ for 2h and then at 155 ℃ for 2 h.

10. The method for preparing the bio-based flame retardant epoxy resin containing the nitrogen and phosphorus structure according to claim 2, wherein the molar ratio of the epoxy resin monomer to the curing agent 4, 4-diaminodiphenylmethane in the fourth step is 1: 0.9.

Technical Field

The invention belongs to the field of bio-based epoxy resin, and particularly relates to bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure and a preparation method thereof.

Background

Petroleum-based plastics can provide various raw materials and products for various industries such as buildings, automobiles, mechanical manufacturing, electronic information and the like due to various excellent properties, and play an important role in modern social life, but in the face of the increasing problems of petroleum energy crisis and environmental pollution in the world, people begin to search for new materials which take biomass and renewable resources as raw materials and are manufactured to meet the requirements to replace petroleum-based materials. Most biological materials are non-toxic and harmless, have rich content, can relieve the pressure of energy exhaustion and pollution aggravation, reduce the dependence of the plastic industry on petroleum-based chemical product supply, and reduce the environmental pollution caused in the production process of high polymer materials. Currently, researches on bio-based polymer materials are mainly limited to some natural polymers or thermoplastic materials such as starch plastics, cellulose-based materials, PHBV, PLA, PBS, bio-based PE, etc., and relatively few bio-based thermosetting resins are studied.

Compared with other thermosetting resins, the epoxy resin has unique epoxy groups, hydroxyl groups, ether bonds and other groups, so that the epoxy resin has excellent performances of adhesion, corrosion resistance, electric insulation, high strength and the like. The epoxy resin can be used as an adhesive, a corrosion-resistant coating, an insulating material and a molding material, is used in the fields of electronics, electricity, optical machinery, chemistry and chemical engineering, aerospace, transportation and other industries, and is an indispensable basic material in all industrial fields at present. However, the Limiting Oxygen Index (LOI) of conventional epoxy resins is only around 20%, and the highly flammable nature greatly limits their application in these areas. In addition, the epoxy resin can generate a large amount of dense smoke, toxic gas and molten drops in the combustion process, and is easy to cause secondary ignition and secondary disasters. Therefore, it is a major subject of research on the application type to improve the flame retardant property of epoxy resins and to expand the application range.

The epoxy resin is subjected to flame retardant modification, and chemical elements with flame retardant property can be introduced into an epoxy resin curing system. There are generally two methods of introducing flame retardant elements into the curing system: reactive and non-reactive. Non-reactive, in which the substrate is treated by physical means and the flame retardant is added directly to the substrate to be flame-retarded, the reaction is simple and easy, but the mechanical properties of the material are reduced due to incompatibility of the flame retardant and the substrate: the reactive type is that flame retardant elements are introduced into an epoxy molecular framework and are covalently linked to a polymer molecular chain, so that the migration of a flame retardant can be avoided, and the flame retardant efficiency is improved. The traditional halogen-containing flame-retardant epoxy resin has high cost performance and wide applicability, but toxic and carcinogenic substances released in the combustion process cause great harm to the environment and human health, so the use of the halogen-containing flame retardant is limited by the Stockholm convention and the laws and regulations of Ro HS, REACH and the like of European Union. Because the epoxy resin contains a large amount of hydroxyl, the phosphorus flame retardant is suitable for the phosphorus flame retardant to play a condensed phase flame retardant role, the phosphorus flame retardant has high flame retardant efficiency, and corrosive and carcinogenic substances are not generated during combustion, so that the application of the phosphorus flame retardant in the epoxy resin is rapidly developed, particularly, the reactive flame retardant DOPO can be introduced into epoxy resin body macromolecules in various ways, the influence on the physical and mechanical properties of the epoxy resin is small, the DOPO containing a phosphaphenanthrene structure has high hydrolytic stability and thermal stability, and the obtained flame retardant epoxy resin has good comprehensive performance. In addition, the nitrogen-based flame retardant system has the characteristics of low toxicity, low corrosion, low smoke generation during combustion, stability to heat and light, environmental friendliness, high flame retardant efficiency, proper price and the like, and is rapidly developed since the early 90 s of the 20 th century. It is generally believed that nitrogen-based flame retardant systems primarily perform flame retardant functions in the gas phase, where they are heated to release a nonflammable gas, such as ammonia, which can act to dilute the combustibles and oxygen and carry away the heat generated during combustion. For a phosphorus-containing nitrogen-series flame-retardant system, phosphorus can also play a flame-retardant role in a gas phase and a condensed phase, and the flame-retardant efficiency is improved based on a phosphorus-nitrogen synergistic effect.

Diphenolic acid (DPA) is one of the most prominent bio-based platform compounds. It is synthesized by a condensation reaction between levulinic acid and phenol. Levulinic acid is a multifunctional compound from carbohydrates, and is considered an inexpensive platform chemical for large-scale production. As for phenol, its biological production from glucose has been described. Thus, DPA may be referred to as whole plant-derived compounds in the future. In addition, DPA has a chemical structure similar to that of bisphenol a and is very versatile in its properties, its pendant carboxylic acid groups making it very versatile for use in material synthesis. Bisphenol A is cheap, so that the market share is high. But on the one hand, the price of the levulinic acid is reduced along with the improvement of the environmental protection requirement and the rapid development of renewable resources, so that the price of the diphenolic acid is also reduced; on the other hand, bisphenol A is known to have a certain destructive effect on the secretion system in human body, which also makes people pay more attention to the development of diphenolic acid. Therefore, it is a very significant matter to increase the research on diphenolic acid and expand the application range of diphenolic acid.

Disclosure of Invention

The invention aims to solve the problems of poor flame retardance, poor mechanical property, toxic raw materials and non-regenerability of the traditional synthetic resin, and provides a bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure and a preparation method thereof.

In order to achieve the above object, the technical solution of the present invention is as follows:

the invention firstly provides a bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure, which has a structural formula shown in a formula (I):

the invention also provides a preparation method of the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure, which comprises the following steps:

the method comprises the following steps: adding diethanolamine, paraformaldehyde and DOPO into a reaction device, then adding a solvent, and stirring at 45-65 ℃ for 8-12 h to obtain a first intermediate;

step two: adding diphenolic acid into a reaction device, adding a solvent for dissolving, dissolving dicyclohexylcarbodiimide and 4-dimethylaminopyridine into the solvent to form a mixed solution, dropwise adding the mixed solution into the reaction device for stirring, then adding the first intermediate obtained in the first step, and reacting for 24-48 hours at 30-40 ℃ to obtain a second intermediate;

step three: adding the second intermediate obtained in the step two and epoxy chloropropane into a reaction device, then adding a catalyst, reacting for 5 hours at the temperature of 80-110 ℃, cooling to the temperature of 60-70 ℃ after the reaction is finished, dropwise adding a NaOH solution into the reaction system, reacting for 3-5 hours after the dropwise adding is finished, and performing post-treatment to obtain an epoxy resin monomer;

step four: and (3) heating the epoxy resin monomer obtained in the step three to 90-120 ℃, keeping the temperature for 20-40 min, adding a curing agent 4, 4-diaminodiphenylmethane, stirring and mixing uniformly, removing bubbles in vacuum, pouring into a preheated mold, and curing to obtain the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure.

Preferably, the molar ratio of diethanolamine, paraformaldehyde and DOPO in the first step is 1: 1.5: 1.

preferably, the molar ratio of the diphenolic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine and the first intermediate is 2.5: 3: 0.2: 1.

preferably, the molar ratio of the second intermediate, the epichlorohydrin and the catalyst in the third step is 1: 15: 0.01.

preferably, the catalyst is tetrabutylammonium bromide.

Preferably, the post-treatment step of the third step is specifically: naturally cooling the reaction system to room temperature, adding a solvent for dilution, filtering to remove solids, extracting the liquid with NaCl solution, then extracting with deionized water, retaining an organic phase, adding anhydrous magnesium sulfate into the organic phase, standing for 8-12 h, filtering to remove the anhydrous magnesium sulfate, and carrying out reduced pressure rotary evaporation on the solvent and excessive epichlorohydrin to obtain the epoxy resin monomer.

Preferably, the time for vacuum defoaming in the fourth step is 5-8 min.

Preferably, the curing is carried out first at 120 ℃ for 2h and then at 155 ℃ for 2 h.

Preferably, the molar ratio of the epoxy resin monomer to the curing agent 4, 4-diaminodiphenylmethane in the fourth step is 1: 0.9.

the invention has the advantages of

The invention provides a bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure, which has a structural formula shown in formula (I), wherein the structure contains a DOPO structure and nitrogen element, and a phosphorus-nitrogen synergistic flame-retardant effect is formed during combustion, so that the flame-retardant epoxy resin has excellent flame-retardant performance; in addition, the epoxy resin is halogen-free and non-toxic, avoids great harm to ecological environment and human health, is prepared from renewable resources, saves fossil resources, and is green and environment-friendly. The experimental results show that: the epoxy resin has the limit oxygen index of 42.3, the UL-94 test reaches the V-0 grade, the tensile strength and the bending strength are equivalent to the performance of commercial resin E51, and the modulus is higher than that of E51 resin.

The invention also provides a preparation method of the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure, which takes diethanol amine, paraformaldehyde and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as reaction raw material monomers, utilizes the classical Kabachnik-Fields reaction to chemically modify the DOPO, generates an epoxy resin intermediate by the esterification reaction of the modified DOPO compound and a bio-based platform compound, namely diphenolic acid (DPA), and finally generates the flame-retardant epoxy resin by the reaction of the epoxy resin intermediate and epichlorohydrin. The epoxy resin prepared by the method has excellent flame retardant property and stable mechanical property.

The bio-based flame-retardant epoxy resin containing the nitrogen and phosphorus structure provided by the invention can be prepared into products for application in automotive interior.

Drawings

FIG. 1 is a comparison graph of IR spectra of a flame-retardant epoxy resin prepared in example 1 of the present invention with DOPO as a raw material, a first-step product, and a second-step product;

FIG. 2 is a graph comparing the heat release rates of a flame retardant epoxy resin prepared in example 1 of the present invention and a bisphenol A resin;

FIG. 3 is a comparison graph of the mechanical properties of the flame-retardant epoxy resin prepared in example 1 of the present invention and bisphenol A resin.

Detailed Description

The invention firstly provides a bio-based flame-retardant epoxy resin containing a nitrogen-phosphorus structure, which has a structural formula shown in a formula (I):

according to the invention, the structure of the formula (I) contains a DOPO structure and nitrogen elements, and a phosphorus-nitrogen synergistic flame retardant effect is formed during combustion, so that the flame retardant epoxy resin has excellent flame retardant property.

The invention also provides a preparation method of the bio-based flame-retardant epoxy resin containing the nitrogen-phosphorus structure, which comprises the following steps:

the method comprises the following steps: adding diethanolamine, paraformaldehyde and DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) into a reaction device, then adding a solvent, preferably chloroform, stirring at 45-65 ℃ for 8-12 h, preferably cooling the obtained mixture to room temperature, filtering the solid, thoroughly washing the solid with ethanol, and heating the solid in a vacuum oven at 120-130 ℃ for 8-12 h to obtain a first intermediate; the mol ratio of the diethanol amine, the paraformaldehyde and the DOPO is preferably 1: 1.5: 1;

step two: adding diphenolic acid (DPA) into a reaction device, adding a solvent for dissolving, wherein the solvent is Tetrahydrofuran (THF) preferably, dissolving Dicyclohexylcarbodiimide (DCC) and 4-Dimethylaminopyridine (DMAP) in the solvent to form a mixed solution, the solvent is Tetrahydrofuran (THF) preferably, dripping the mixed solution into the reaction device, stirring for 0.5-2 h preferably, then adding the first intermediate obtained in the first step, dissolving the first intermediate into the solvent before adding, wherein the solvent is Tetrahydrofuran (THF) preferably, reacting for 24-48 h at 30-40 ℃, filtering to remove solids preferably, freezing the liquid in a refrigerator for 12-24 h, filtering again, and spin-drying the solvent under reduced pressure to obtain a second intermediate; the molar ratio of diphenolic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine to the first intermediate is preferably 2.5: 3: 0.2: 1.

step three: adding the second intermediate obtained in the second step and Epoxy Chloropropane (ECH) into a reaction device, then adding a catalyst, wherein the catalyst is preferably one or more of organic sulfonic acid, quaternary ammonium salt and alkali metal hydroxide, more preferably tetrabutylammonium bromide (TBAB), reacting for 5 hours at 80-110 ℃, cooling to 60-70 ℃ after the reaction is finished, dropwise adding NaOH solution into the reaction system, wherein the concentration of the NaOH solution is preferably 30-50%, reacting for 3-5 hours after the dropwise adding is finished, and performing post-treatment to obtain an epoxy resin monomer; the molar ratio of the second intermediate to the epichlorohydrin to the catalyst is preferably 1: 15: 0.1;

the post-treatment step is preferably specifically: naturally cooling the reaction system to room temperature, adding a solvent for dilution, filtering to remove solids, extracting the liquid with NaCl solution, then extracting with deionized water, retaining an organic phase, adding anhydrous magnesium sulfate into the organic phase, standing for 8-12 h, filtering to remove the anhydrous magnesium sulfate, and carrying out reduced pressure rotary evaporation on the solvent and excessive epoxy chloropropane to obtain an epoxy resin monomer;

step four: heating the epoxy resin monomer obtained in the third step to 90-120 ℃, keeping the temperature for 20-40 min, adding a molten curing agent 4, 4-diaminodiphenylmethane (DDM), uniformly stirring and mixing, and then carrying out vacuum defoaming, wherein the stirring time is preferably 3-8 min, the vacuum defoaming time is preferably 5-8 min, pouring the mixture into a preheated mold for curing, preferably curing at 120 ℃ for 2h, and then curing at 155 ℃ for 2h to obtain the bio-based flame-retardant epoxy resin with the nitrogen-phosphorus containing structure, wherein the molar ratio of the epoxy resin monomer to the curing agent 4, 4-diaminodiphenylmethane is preferably 1: 0.9.

the following examples are used to specifically illustrate the preparation method of the bio-based flame retardant epoxy resin containing nitrogen and phosphorus structures of the present invention. The present invention will be described in further detail with reference to examples, which are not intended to limit the scope of the present invention, and the raw materials used in the examples are commercially available.