1. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin is characterized by comprising the following steps:

(1) dissolving natural polyphenol powder in a solvent, carrying out ultrasonic treatment to enable the natural polyphenol powder to generate coupling reaction and be stacked and assembled, and forming a microspherical to flat assembly with a large number of phenolic hydroxyl groups on the surface through ultrasonic treatment;

(2) dialyzing the suspension obtained in the step (1) and freeze-drying to obtain natural polyphenol assembly powder;

(3) and (3) mixing the powder obtained in the step (2) with an epoxy resin prepolymer to obtain the strengthened and toughened epoxy resin material modified by the bio-based assembled polyphenol curing agent.

2. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: the natural polyphenol is at least one of tea polyphenol, tannin, caffeic acid, chlorogenic acid, gallic acid, flavonoid, lignan and resveratrol.

3. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: the solvent is at least one of deionized water, ethanol, n-butanol, ethyl acetate and petroleum ether.

4. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: the epoxy resin is one or a mixture of E54, E44, E42, R130, R139, R144, NPEL127, NPEL239S and NPEL 134.

5. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: in the step (1), the ultrasonic treatment conditions are as follows: treating at 50-600W and 20-60Hz for 30-60 min.

6. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: in step (2), dialysis was performed for 7 days.

7. The preparation method of the bio-based nano-assembly curing agent for toughening epoxy resin according to claim 1, characterized in that: the mixed reaction conditions in the step (3) are as follows: stirring for not less than 5 hr, stirring to disperse uniformly, heating to 80-120 deg.C, and heating for not less than 3 hr.

8. The bio-based nano assembled curing agent for toughening epoxy resin is characterized in that: the method according to claims 1 to 7.

Background

Epoxy resins are an important class of thermosetting resins with the widest range of applications and the greatest amount. The annual capacity of epoxy resin in China is more than 200 ten thousand tons, and accounts for about 45 percent of the global capacity. The introduction of materials of biological origin into such widely used resins can effectively reduce the consumption of petroleum resources, and has important significance. In addition, the epoxy resin industry in China still has the conditions of serious low-end capacity surplus, insufficient high-end capacity and low overall profit rate, and the development of high-performance and toughened epoxy resin materials and systems has practical significance for the development of related industries in China.

The curing system is an important component of the epoxy resin, the selection of the curing system has important effect on various properties of the epoxy resin material, and the bio-based curing system can effectively reduce the consumption of petroleum resources in the production and use processes of the epoxy resin and meet the overall target of carbon neutralization. However, the bio-based curing agent generally faces bottleneck problems of high cost, poor curing effect, unexpected mechanical properties of the product and the like, and the comprehensive properties of the bio-based curing agent are difficult to compare with those of the commercial petroleum-based curing agent. Therefore, the high-performance curing agent based on the bio-based material is developed, the toughening of the epoxy resin is realized, the added value of the epoxy resin is improved, and the high-performance curing agent has important significance on the healthy and sustainable development of the industry.

At present, it has been reported that natural products having active groups such as polyphenol and chitosan are introduced into an epoxy resin system as a curing agent (Huyaqi. tannic acid based epoxy and curing agent preparation and performance [ D ]. Jiangxi university of science and technology 2020.; CN106496524B, etc.). However, although these bio-based curing agents can achieve chemical crosslinking of epoxy resins, the strength is low due to few reaction sites and low crosslinking density, and a new method for building bio-based materials to reinforce and toughen epoxy resins is urgently needed. The natural polyphenol can be coupled and assembled under certain conditions to obtain different micro-nano structures, based on the morphological characteristics and surface group characteristics regulation and control, the high-efficiency enhancement of the epoxy resin material can be realized through high-density interface crosslinking and the micro-nano assembly structure, meanwhile, a hydrogen bond network constructed by the polyhydroxy structure can effectively dissipate energy, the toughening and the greening of the epoxy resin material can be cooperatively realized, and the application prospect is wide.

Disclosure of Invention

The invention aims to overcome the defects and provides a bio-based nano-assembly curing agent for toughening epoxy resin and a preparation method thereof.

The specific technical scheme is as follows:

the preparation method of the bio-based nano assembly curing agent for toughening epoxy resin comprises the following steps:

(1) dissolving natural polyphenol powder in a solvent, carrying out ultrasonic treatment to enable the natural polyphenol powder to generate coupling reaction and to be stacked and assembled, and forming a microspherical to flat assembly with a large number of phenolic hydroxyl groups on the surface through ultrasonic treatment;

(2) dialyzing the suspension obtained in the step (1) and freeze-drying to obtain natural polyphenol assembly powder;

(3) and (3) mixing the powder obtained in the step (2) with an epoxy resin prepolymer for reaction to obtain the strengthened and toughened epoxy resin material modified by the bio-based assembled polyphenol curing agent.

The natural polyphenol is at least one of tea polyphenol, tannin, caffeic acid, chlorogenic acid, gallic acid, flavonoid, lignan and resveratrol.

The solvent is at least one of deionized water, ethanol, n-butanol, ethyl acetate and petroleum ether.

The epoxy resin is one or a mixture of E54, E44, E42, R130, R139, R144, NPEL127, NPEL239S and NPEL 134.

In the step (1), the ultrasonic treatment conditions are as follows: treating at 50-600W and 20-60Hz for 30-60 min.

In step (2), dialysis was performed for 7 days.

The mixed reaction conditions in the step (3) are as follows: stirring for not less than 5 hr, stirring to disperse uniformly, heating to 80-120 deg.C, and heating for not less than 3 hr.

The invention also discloses a bio-based nano-assembly curing agent for toughening epoxy resin, which is obtained according to the preparation method.

The invention firstly proposes that the self-coupling and self-assembly of natural polyphenol under the ultrasonic condition are utilized, the self-coupling and self-assembly is used as a curing agent based on the obvious nano-reinforcing effect and rich surface phenolic hydroxyl, a nano-reinforcing network can be constructed and effective high-density interface cross-linking points are formed, meanwhile, the non-covalent hydrogen bond network has obvious energy dissipation effect, and the high-performance toughening of the epoxy resin is effectively realized while the curing molding is carried out.

Compared with the prior art, the invention has the following advantages:

(1) the invention adopts cheap and easily-obtained natural polyphenol materials, realizes the micro-nano assembly of polyphenol by an ultrasonic self-coupling technology, is used as a bio-based green curing agent of an epoxy resin material, has low cost and environmental friendliness, does not relate to a fussy processing technology, can reduce the consumption of petroleum source resources in the production and use processes of epoxy resin, and meets the development requirement of carbon neutralization.

(2) The polyphenol assembly obtained by the invention has obvious nanometer enhancement effect and abundant surface phenolic hydroxyl, can construct a nanometer enhancement network and form effective high-density interface cross-linking points when being used as a curing agent, has obvious energy dissipation effect by using a non-covalent hydrogen bond network, and effectively realizes high-performance toughening of epoxy resin while curing and forming.

(3) The invention firstly proposes that the micro-nano assembly of the natural polyphenol is used for the curing system of the epoxy resin, realizes the high-valued and high-performance utilization of natural products, obviously improves the comprehensive performance of the epoxy resin composite material, is expected to realize the substitution of a bio-based curing agent for a petroleum-based curing agent, and effectively promotes the industrial upgrading and sustainable development.

Drawings

Figure 1 polyphenol assembly mechanism of the present invention;

FIG. 2 is a schematic diagram of interfacial crosslinking and hydrogen bonding of the curing agent provided by the present invention;

FIG. 3 is a scanning electron micrograph of the assembled polyphenols of micrometer scale obtained in example 1;

FIG. 4 is a second scanning electron microscope image of the assembled polyphenols of micron scale obtained in example 1;

FIG. 5 is a scanning electron micrograph of the nano-assembly polyphenols obtained in example 3;

FIG. 6 is a second scanning electron micrograph of the nano-assembly polyphenols obtained in example 3.

Detailed Description

The present invention is described in detail below by way of examples, it should be noted that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention, and that the skilled person in the art may make modifications and adaptations of the present invention in a manner not essential to the above description.

The mechanism of the combination of the present invention is shown in FIG. 1. The curing agent provided by the invention realizes the toughening and greening of the epoxy resin material through high-density interface crosslinking, a micro-nano assembly reinforcing network and a non-covalent hydrogen bond energy dissipation network, and the principle is shown in figure 2.

Example 1

Dissolving 500g of commercial tannic acid powder in 2L of deionized water, performing ultrasonic treatment for 30 minutes under the conditions of 400W and 25Hz, performing coupling reaction on tannic acid molecules under the action of ultrasonic activation, stacking and assembling to form a micron-sized flat assembly with a large number of phenolic hydroxyl groups on the surface, as shown in FIG. 3. The resulting suspension was dialyzed against deionized water for 7 days to remove unreacted small molecules. Taking out the assembly suspension, and freeze-drying to obtain tannin assembly powder. And (3) mixing 20 parts of the obtained powder with 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, and heating to 120 ℃ for treatment for more than 5 hours to fully cure the epoxy resin material to obtain the strengthened and toughened epoxy resin material modified by the bio-based assembled polyphenol curing agent.

Example 2

Dissolving 500g of commercial tannic acid powder in 2L of deionized water, carrying out ultrasonic treatment for 15 minutes under the conditions of 200W and 25Hz, carrying out coupling reaction on tannic acid molecules under the action of ultrasonic activation, and stacking and assembling to form a nanoscale flat assembly with a large number of phenolic hydroxyl groups on the surface. The resulting suspension was dialyzed against deionized water for 7 days to remove unreacted small molecules. And taking out the assembly suspension, and freeze-drying to obtain the tannin assembly powder. And (3) mixing 20 parts of the obtained powder with 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, heating to 120 ℃ for treatment for more than 5 hours to fully cure the obtained epoxy resin material, and thus obtaining the strengthened and toughened epoxy resin material modified by the bio-based assembled polyphenol curing agent.

Example 3

Dissolving 500g of commercial tannic acid powder in 2L of deionized water, performing ultrasonic treatment for 15 minutes under 200W and 25Hz conditions, performing coupling reaction on tannic acid molecules under the ultrasonic activation, stacking and assembling to form a nanoscale flat assembly with a large number of phenolic hydroxyl groups on the surface, as shown in FIGS. 5 and 6. The resulting suspension was dialyzed against deionized water for 7 days to remove unreacted small molecules. Taking out the assembly suspension, and freeze-drying to obtain tannin assembly powder. And mixing 30 parts of the obtained powder with 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, and heating to 120 ℃ for more than 5 hours to fully cure the epoxy resin material to obtain the bio-based assembly polyphenol curing agent modified toughened epoxy resin material.

Example 4

Dissolving 500g tea polyphenols powder in 2L deionized water, performing ultrasonic treatment under 200W and 25Hz conditions for 15 min, dialyzing the obtained suspension in deionized water for 7 days, and removing unreacted small molecules. Taking out the assembly suspension, and freeze-drying to obtain tea polyphenol assembly powder. And mixing 25 parts of the obtained powder with 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, and heating to 120 ℃ for treatment for more than 5 hours to fully solidify the epoxy resin material to obtain the strengthened and toughened epoxy resin material modified by the bio-based assembled tea polyphenol curing agent.

Comparative example 1

Mixing 20 parts of untreated tannic acid and 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, and heating to 120 ℃ for treatment for more than 5 hours to fully cure the epoxy resin material.

Comparative example 2

Mixing 25 parts of untreated tea polyphenol with 100 parts of epoxy resin prepolymer (No. 1009F), fully stirring for more than 5 hours until the mixture is uniformly dispersed, and heating to 120 ℃ for treatment for more than 5 hours to fully cure the epoxy resin material.

Comparative example 3

20 parts of common petroleum-based curing agent (brand T31) and 100 parts of epoxy resin prepolymer (brand 1009F) are mixed, fully stirred for more than 5 hours until the mixture is uniformly dispersed, and the mixture is heated to 120 ℃ for treatment for more than 5 hours, so that the epoxy resin material is fully cured.

Comparative example 4

20 parts of common petroleum-based curing agent (grade 593) and 100 parts of epoxy resin prepolymer (grade 1009F) are mixed, fully stirred for more than 5 hours until the mixture is uniformly dispersed, and the mixture is heated to 120 ℃ for treatment for more than 5 hours, so that the epoxy resin material is fully cured.

The mechanical property test of the sample strips obtained in the above examples and comparative examples is carried out, and the results are shown in the following table:

TABLE 1 test results

As can be seen from the table above, compared with the polyphenol material which is not treated at all, the natural polyphenol nano-scale assembly prepared by the invention has obvious improvement, and simultaneously, the toughening comprehensive performance of the natural polyphenol nano-scale assembly is obviously higher than that of the common petroleum-based curing agent. In conclusion, the invention firstly provides a curing system for assembling natural polyphenol for epoxy resin, realizes high-valued and high-performance utilization of natural products, obviously improves the comprehensive performance of epoxy resin composite materials, is expected to realize the substitution of petroleum-based curing agents by bio-based curing agents, and effectively promotes industrial upgrading and sustainable development.