CN118638067A - A novel bio-based epoxy curing agent containing triazole structure and a preparation method of epoxy resin - Google Patents

Abstract

The invention discloses a novel bio-based epoxy curing agent containing a triazole structure and a preparation method of an epoxy resin, and belongs to the field of material science and technology. A novel bio-based epoxy curing agent HHM containing a triazole structure is prepared by using a bio-based compound 4-hydroxy-3-methoxybenzonitrile which can be simply synthesized based on vanillin as a raw material, and reacting with hydrazine hydrochloride and hydrazine hydrate to form a closed ring. The epoxy resin curing agent prepared by this method has a high degree of greenness. Due to the nitrogen heterocyclic structure of triazole, the cured epoxy resin has a higher carbonization ability and lower flammability than the common aromatic amine epoxy curing agent, which effectively improves the intrinsic flame retardant properties of the cured epoxy resin.

Description

A novel bio-based epoxy curing agent containing triazole structure and preparation method of epoxy resin

Technical Field

The invention belongs to the technical field of material science and relates to a novel bio-based epoxy curing agent containing a triazole structure based on vanillin and a preparation method of an epoxy resin.

Background Art

Epoxy resin is one of the most widely used thermosetting resins. Due to its low cost, convenient curing process, and excellent resistance to chemical solvents, electrical insulation and thermal stability, it is widely used in adhesives, coatings, electronics and aerospace. Among them, bisphenol A epoxy resin (DGEBA) is the largest and most comprehensive epoxy resin, accounting for about 90% of the total epoxy resin production. However, the current epoxy resin is highly dependent on non-renewable petroleum energy, which will bring about problems such as greenhouse gas emissions and environmental pollution, which is not in line with the concept of green and sustainable development.

As an indispensable component of epoxy resin system, epoxy curing agent largely determines the structure and comprehensive properties of the cross-linked network of cured epoxy resin. In recent years, sustainable development resources have gradually become known for their advantages in ecological environmental protection due to their excellent properties, and the use of sustainable bio-based raw materials to synthesize epoxy resin has also become a research hotspot. However, the research on bio-based epoxy resin mainly focuses on the synthesis of new bio-based epoxy precursors, while the epoxy curing agent used is still heavily dependent on petroleum-based products.

The currently reported bio-based epoxy curing agents mainly include plant oil curing agents (ZHANG H, YANG LT. Preparation and properties of soybean oil-based curing agents for epoxy resin [J]. Journal of Applied Polymer Science, 2017, 134 (17): 44754.), bio-acid/anhydride curing agents (Zhu Z M, Shang K. Synthesis of an effective bio-based flame-retardant curing agent and its application in epoxy resin: Curing behavior, thermal stability and flame retardancy [J]. Polymer Degradation and Stability, 2019, 167: 179-188.) and lignin curing agents (NIKAFSHAR S, FANG Z. Development of a novel curing accelerator-blowing agent for formulating epoxy rigid foam containing aminated-lignin [J]. Industrial & Engineering Chemistry Research, 2020, 59(34):15146-15154.). Due to the lack of rigid structure, flexible chain length, and no flame retardant elements, most epoxy resins using bio-based curing agents have problems with reduced heat resistance and flame retardancy. At the same time, some bio-based curing agents use a modification method in which petroleum-based curing agents are linked to bio-based compounds in a grafted form during the synthesis process, thereby having curing ability, which also reduces its greenness.

Summary of the invention

In order to solve the above existing problems, the present invention provides a novel bio-based epoxy curing agent containing a triazole structure and a preparation method of an epoxy resin.

The technical solution of the present invention:

A novel bio-based epoxy curing agent containing a triazole structure has the following structure:

A method for preparing a novel bio-based epoxy resin containing a triazole structure, the steps are as follows:

(1) 4-hydroxy-3-methoxybenzonitrile, hydrazine hydrochloride and hydrazine hydrate are mixed in a molar ratio of 1:0.9-1.2:2.7-3.6, diethylene glycol is added, and the mixture is heated under reflux, and reacted for 2-6 hours under a _N2 atmosphere; after the reaction, the mixture is immersed in deionized water, stirred, and filtered to collect the solid product; after washing with deionized water three times, the solid product is dried under reduced pressure to obtain a novel bio-based epoxy curing agent HHM containing a triazole structure;

(2) The novel bio-based epoxy curing agent HHM containing a triazole structure obtained in step (1) is uniformly mixed with an epoxy resin in any proportion, and an accelerator having a mass of 0.5-2% of the epoxy resin is added for vacuum degassing, and then poured into a mold and thermosetted to obtain a novel bio-based epoxy resin containing a triazole structure.

The accelerator is a tertiary amine or imidazole and its derivatives. At 140-170°C, a novel bio-based epoxy curing agent HHM containing a triazole structure and an accelerator are added to the epoxy resin. After uniform mixing and vacuum degassing, the resin is poured into a mold and kept at 80-100°C for 1-4 hours, then kept at 110-130°C for 1-4 hours, then kept at 140-160°C for 1-4 hours, then kept at 160-190°C for 1-4 hours, and finally cured at 190-210°C for 1-4 hours.

The tertiary amine is 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, 4-dimethylaminopyridine, triethylamine, triethanolamine, or o-hydroxybenzyldimethylamine;

The imidazole and its derivatives are imidazole, 2-methylimidazole, 1-benzyl-2-ethylimidazole, 1-aminoethyl-2-methylimidazole and 2-ethyl-4-methylimidazole.

Beneficial effects of the present invention: The present invention uses 4-hydroxy-3-methoxybenzonitrile which is simply synthesized based on bio-based raw material vanillin as raw material, obtains a novel bio-based epoxy curing agent HHM containing a triazole structure through a closed-ring reaction, and improves the greenness of the epoxy resin after curing. Due to the unique nitrogen heterocyclic structure of triazole, after curing with common bisphenol A type epoxy resin, it has higher carbonization ability and lower flammability than using common aromatic amine epoxy curing agents DDM or DDS, and the residual carbon rate of the cured product at 700°C ( _N2 atmosphere) is increased to 25.8%, the peak heat release rate (PHRR) in the trace combustion test is reduced to 336.7W/g, and the total heat release (THR) is reduced to 15.6kJ/g, which effectively improves the intrinsic flame retardant properties of the epoxy resin after curing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a TGA curve of epoxy resin prepared by curing. (Example 1, Comparative Example 1 and Comparative Example 2)

DETAILED DESCRIPTION

The specific implementation of the present invention is further described below in conjunction with FIG1 and the technical solution.

Example 1

(1) Synthesis of bio-based epoxy curing agent HHM containing triazole structure:

4-Hydroxy-3-methoxybenzonitrile (44.75 g, 0.3 mol), hydrazine hydrochloride (31.51 g, 0.3 mol), and hydrazine hydrate (5.06 g, 0.9 mol) were transferred into a three-necked flask equipped with a stirring magnet, a condensed water reflux device, and a nitrogen introduction device, and 150 mL of diethylene glycol was added and heated to reflux, and the mixture was reacted for 4 hours under a _N2 atmosphere; after the reaction, the mixture was sunk into 500 mL of deionized water, stirred until all solid products were precipitated, and the solid products were collected by suction filtration; after washing three times with deionized water, the mixture was dried under reduced pressure to obtain a novel bio-based epoxy curing agent HHM containing a triazole structure.

(2) HHM curing:

The bisphenol A epoxy resin DGEBA with an epoxy value of 0.51 mol/100 g and the bio-based epoxy curing agent HHM were mixed evenly in a molar ratio of epoxy: NH=1:1, and the accelerator 4-dimethylaminopyridine (DMAP) with a mass% of the epoxy resin was added, heated to melt at 150°C, and then vacuum degassed until no bubbles were generated. The mixture was poured into a mold, and the curing procedure was as follows: keeping warm at 100°C for 2 hours, keeping warm at 130°C for 2 hours, keeping warm at 160°C for 2 hours, keeping warm at 180°C for 2 hours, and keeping warm at 210°C for 2 hours. The cured bio-based epoxy resin obtained was named DGEBA/HHM, and its properties were as follows: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) was 371°C, the residual carbon rate at 700°C ( _Cy700 ) was 25.2%, the maximum decomposition rate temperature ( _Tmax ) was 428°C, the peak heat release rate (PHRR) of trace combustion was 336.7W/g, the peak temperature ( _Tpeak ) was 430°C, and the total heat release (THR) was 15.6kJ/g.

Example 2

The difference from Example 1 is that (2) is added with an accelerator 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) with a mass of 0.5% of epoxy resin, heated to 150°C for melting, and then vacuum degassed until no bubbles are generated, and poured into a mold. The curing procedure is: keep warm at 80°C for 2 hours, keep warm at 110°C for 2 hours, keep warm at 140°C for 2 hours, keep warm at 160°C for 2 hours, and keep warm at 190°C for 2 hours. The properties of the cured bio-based epoxy resin obtained are as follows: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) is 371°C, the residual carbon rate at 700°C ( _Cy700 ) is 25.2%, the maximum decomposition rate temperature ( _Tmax ) is 428°C, the peak heat release rate (PHRR) of trace combustion is 336.7W/g, the peak temperature ( _Tpeak ) is 430°C, and the total heat release (THR) is 15.6kJ/g.

Example 3

Different from Example 1, in (2), 1% of the mass of epoxy resin was added as accelerator 2-methylimidazole (2MZ), heated to 170°C for melting, and then vacuum degassed until no bubbles were generated, and poured into a mold. The curing procedure was: 90°C for 2 hours, 120°C for 2 hours, 140°C for 2 hours, 170°C for 2 hours, and 200°C for 2 hours. The properties of the cured bio-based epoxy resin obtained were: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) was 371°C, the residual carbon rate at 700°C ( _Cy700 ) was 26.1%, the maximum decomposition rate temperature ( _Tmax ) was 431°C, the peak heat release rate (PHRR) of trace combustion was 331.5W/g, the peak temperature ( _Tpeak ) was 433°C, and the total heat release (THR) was 15.4kJ/g.

Example 4

Different from Example 1, in (2), 1% of the mass of the epoxy resin is added as an accelerator imidazole (IMZ), heated to 150°C for melting, and then vacuum degassed until no bubbles are generated, and poured into a mold. The curing procedure is: 90°C for 2 hours, 120°C for 2 hours, 140°C for 2 hours, 170°C for 2 hours, and 200°C for 2 hours. The properties of the cured bio-based epoxy resin are as follows: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) is 371°C, the residual carbon rate ( _Cy700 ) at 700°C is 26.2%, the maximum decomposition rate temperature ( _Tmax ) is 432°C, the peak heat release rate (PHRR) of trace combustion is 329.1W/g, the peak temperature ( _Tpeak ) is 434°C, and the total heat release (THR) is 15.3kJ/g.

Comparative Example 1

Bisphenol A epoxy resin (DGEBA) with an epoxy value of 0.51 mol/100 g and petroleum-based epoxy curing agent 4,4'-diaminodiphenylmethane (DDM) were mixed evenly in a molar ratio of epoxy: NH=1:1, and accelerator 4-dimethylaminopyridine (DMAP) was added in an amount of 2% by mass of the epoxy resin, heated to melt at 120°C, and then vacuum degassed until no bubbles were generated, and poured into a mold. The curing procedure was: 100°C for 2 hours, 130°C for 2 hours, 160°C for 2 hours, 180°C for 2 hours, and 210°C for 2 hours. The cured bio-based epoxy resin obtained was named DGEBA/DDM, and its properties were as follows: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) was 371°C, the residual carbon rate at 700°C ( _Cy700 ) was 14.6%, the maximum decomposition rate temperature ( _Tmax ) was 403°C, the peak heat release rate (PHRR) of trace combustion was 577.9W/g, the peak temperature ( _Tpeak ) was 407°C, and the total heat release (THR) was 25.1kJ/g.

Comparative Example 2

Bisphenol A epoxy resin (DGEBA) with an epoxy value of 0.51 mol/100 g and petroleum-based epoxy curing agent 4,4'-diaminodiphenyl sulfone (DDS) were mixed evenly in a molar ratio of epoxy: NH=1:1, and accelerator 4-dimethylaminopyridine (DMAP) was added in an amount of 2% by mass of the epoxy resin, heated to melt at 200°C, and then vacuum degassed until no bubbles were generated, and poured into a mold. The curing procedure was: 100°C for 2 hours, 130°C for 2 hours, 160°C for 2 hours, 180°C for 2 hours, and 210°C for 2 hours. The obtained cured bio-based epoxy resin was named DGEBA/DDS, and its properties were as follows: under _N2 atmosphere, the 5% thermal weight loss temperature (Td5 _% ) was 381°C, the residual carbon rate at 700°C ( _Cy700 ) was 16.0%, the maximum decomposition rate temperature ( _Tmax ) was 408°C, the peak heat release rate (PHRR) of trace combustion was 455.9W/g, the peak temperature ( _Tpeak ) was 423°C, and the total heat release (THR) was 21.2kJ/g.

Table 1 Summary of thermal and combustion properties of bisphenol A resins cured with different curing agents under DMAP catalysis

Thermogravimetric test: Mettler TGA 1 thermogravimetric analyzer was used to increase the temperature from 30°C to 800°C at a heating rate of 10°C/min in a nitrogen atmosphere. The results are shown in FIG1 .

The micro combustion test was conducted using a FTT0001 micro calorimeter in a nitrogen atmosphere with a flow rate of 80 mL/min and a heating rate of 10°C/min from 100°C to 700°C. The test standard was based on ASTM D7309-13.

The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions and changes, or improvements and modifications made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims (5)

1. A novel bio-based epoxy curing agent containing a triazole structure, characterized in that the novel bio-based epoxy curing agent has the following structure: 2. A method for preparing a novel bio-based epoxy resin containing a triazole structure, characterized in that the steps are as follows: (1) 4-hydroxy-3-methoxybenzonitrile, hydrazine hydrochloride and hydrazine hydrate are mixed in a molar ratio of 1:0.9-1.2:2.7-3.6, diethylene glycol is added, and the mixture is heated under reflux, and reacted for 2-6 hours under a _N2 atmosphere; after the reaction, the mixture is immersed in deionized water, stirred, and filtered to collect the solid product; after washing with deionized water three times, the solid product is dried under reduced pressure to obtain a novel bio-based epoxy curing agent HHM containing a triazole structure; (2) The novel bio-based epoxy curing agent HHM containing a triazole structure obtained in step (1) is uniformly mixed with an epoxy resin in any proportion, and an accelerator having a mass of 0.5-2% of the epoxy resin is added for vacuum degassing, and then poured into a mold and thermosetted to obtain a novel bio-based epoxy resin containing a triazole structure. 3. The preparation method according to claim 2 is characterized in that the accelerator is a tertiary amine or imidazole and its derivatives, and at 140-170°C, a new bio-based epoxy curing agent HHM containing a triazole structure and an accelerator are added to the epoxy resin, mixed evenly and vacuum degassed, poured into a mold and kept warm at 80-100°C for 1-4 hours, then kept warm at 110-130°C for 1-4 hours, then kept warm at 140-160°C for 1-4 hours, then kept warm at 160-190°C for 1-4 hours, and finally cured at 190-210°C for 1-4 hours. 4. The preparation method according to claim 2, characterized in that the tertiary amine is 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, 4-dimethylaminopyridine, triethylamine, triethanolamine or o-hydroxybenzyldimethylamine. 5. The preparation method according to claim 2, characterized in that the imidazole and its derivatives are imidazole, 2-methylimidazole, 1-benzyl-2-ethylimidazole, 1-aminoethyl-2-methylimidazole or 2-ethyl-4-methylimidazole.