1. A preparation method of a core-shell flame retardant modified epoxy resin coating is characterized by comprising the following steps:

(1) preparing an ammonium polyphosphate suspension: adding ammonium polyphosphate into deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding chitosan into an acetic acid solution, and stirring and mixing uniformly to obtain a chitosan solution;

(3) preparation of polyglutamate solution: adding polyglutamate into the ammonia solution, and stirring and mixing uniformly to obtain polyglutamate solution;

(4) preparing chitosan-coated ammonium polyphosphate: dripping chitosan solution into the ammonium polyphosphate suspension, stirring and mixing uniformly, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(5) preparing polyglutamate and chitosan co-coated ammonium polyphosphate: dispersing chitosan-coated ammonium polyphosphate in deionized water, adding polyglutamate solution into the deionized water under a stirring state, and then centrifuging and washing to obtain polyglutamate and chitosan co-coated ammonium polyphosphate;

(6) preparing a core-shell flame retardant modified epoxy resin coating: adding the epoxy resin, polyglutamate and chitosan co-coated ammonium polyphosphate, dispersant stearic acid monoglyceride, brightener organic micro wax powder and defoamer dimethyl silicone oil into deionized water, and stirring and mixing uniformly to obtain the core-shell flame retardant modified epoxy resin coating.

2. The preparation method of the core-shell flame retardant modified epoxy resin coating according to claim 1, wherein in the step (1), the mass ratio of the ammonium polyphosphate to the deionized water is 4-6: 100.

3. The preparation method of the core-shell flame retardant modified epoxy resin coating material according to claim 1, wherein in the step (2), the mass ratio of the chitosan to the acetic acid solution is 1-2:100, and the mass fraction of the acetic acid solution is 1-2 wt%.

4. The preparation method of the core-shell flame retardant modified epoxy resin coating material according to claim 1, wherein in the step (3), the mass ratio of the polyglutamate to the ammonia solution is 1-2:100, and the mass fraction of the ammonia solution is 1-2 wt%.

5. The preparation method of the core-shell flame retardant modified epoxy resin coating as claimed in claim 1, wherein in the step (4), the mass ratio of the chitosan solution to the ammonium polyphosphate suspension is 100: 150-200.

6. The preparation method of the core-shell flame retardant modified epoxy resin coating as claimed in claim 1, wherein in the step (5), the mass ratio of the chitosan coated ammonium polyphosphate, the deionized water and the polyglutamate solution is 4-6:100: 150-200.

7. The preparation method of the core-shell flame retardant modified epoxy resin coating according to claim 1, wherein in the step (6), the mass ratio of the ammonium polyphosphate, the dispersant of stearic acid monoglyceride, the brightener of organic wax powder and the defoamer of dimethyl silicone oil which are coated by epoxy resin, polyglutamate and chitosan is 100:2-5:1-2:1.5-2.5: 0.5-1.

8. The epoxy resin coating modified by the core-shell flame retardant obtained by the preparation method of any one of claims 1 to 7.

Background

Epoxy resin (EP) is a common thermosetting material, has good mechanical property and bonding property, and is widely applied to the fields of electronic and electric appliances, coatings, composite materials and the like. However, EP is extremely flammable in air, and a large amount of black smoke and toxic gas are generated during combustion, and in order to solve this problem, flame retardant technical studies on epoxy resins have been carried out, and currently, flame retardant studies on epoxy resins are mainly classified into three types: the flame-retardant epoxy resin comprises an additive flame retardant, a reactive flame retardant and a synergistic flame retardant.

The flame retardant is a functional auxiliary agent capable of endowing a flammable polymer with flame retardancy, and is divided into the following components: halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, silicon flame retardants, boron flame retardants, hydroxide flame retardants, and intumescent flame retardants. The flame retardant mechanism is mainly classified into three types, (1) the gas-phase flame retardant mechanism means that substances capable of generating free radicals in the heating process are added into combustible materials to prevent the combustion from continuing, and in addition, a large amount of non-combustible gas is decomposed by heating the flame retardant, so that the effect of preventing or delaying the combustion is achieved; (2) the condensed phase flame retardant mechanism is that a compact protective layer is formed on the surface of the polymer, so that oxygen can be isolated, and combustible gas is prevented from entering a combustion range, so that the thermal decomposition of the polymer is prevented or inhibited; (3) the interruption of the heat exchange flame-retardant is to release most of the heat generated during the combustion of the polymer so that the temperature of the system is lower than that at which thermal decomposition occurs, and finally to terminate the combustion.

Patent document CN106318116A discloses a fireproof flame-retardant environment-friendly paint, which is composed of the following components in parts by weight: 30-38 parts of epoxy resin, 25-29 parts of acrylic resin, 16-19 parts of ammonium polyphosphate, 19-25 parts of polyvinyl chloride resin, 3-9 parts of rosin, 6-12 parts of mica powder, 3-5 parts of modified nano diatomite powder, 2-7 parts of acrylonitrile, 11-13 parts of an organic silicon defoamer, 1-4 parts of a curing agent, 0.8-1.2 parts of a flatting agent and 31-38 parts of water, but the ammonium polyphosphate is an inorganic polymer and has poor compatibility with a base material, so that the flame retardant efficiency is low when the flame retardant epoxy resin is singly added.

Patent document CN111138715A is a method for ultraviolet curing epoxy acrylate microencapsulated ammonium polyphosphate, which comprises adding a catalyst and a polymerization inhibitor into an epoxy resin/acrylic acid solution at a certain ratio, and diluting with a diluent to obtain an epoxy acrylate prepolymer; adding a certain amount of ammonium polyphosphate into the prepolymer, adding a photoinitiator, uniformly stirring to form stable turbid liquid, and curing by ultraviolet light to obtain a required product.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a core-shell flame retardant modified epoxy resin coating and a preparation method thereof, and solves the technical problems that the shell thickness of the traditional ammonium polyphosphate core-shell flame retardant is difficult to control and the flame retardant effect is poor.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a core-shell flame retardant modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding ammonium polyphosphate into deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding chitosan into an acetic acid solution, and stirring and mixing uniformly to obtain a chitosan solution;

(3) preparation of polyglutamate solution: adding polyglutamate into the ammonia solution, and stirring and mixing uniformly to obtain polyglutamate solution;

(4) preparing chitosan-coated ammonium polyphosphate: dripping chitosan solution into the ammonium polyphosphate suspension, stirring and mixing uniformly, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(5) preparing polyglutamate and chitosan co-coated ammonium polyphosphate: dispersing chitosan-coated ammonium polyphosphate in deionized water, adding polyglutamate solution into the deionized water under a stirring state, and then centrifuging and washing to obtain polyglutamate and chitosan co-coated ammonium polyphosphate;

(6) preparing a core-shell flame retardant modified epoxy resin coating: adding the epoxy resin, polyglutamate and chitosan co-coated ammonium polyphosphate, dispersant stearic acid monoglyceride, brightener organic micro wax powder and defoamer dimethyl silicone oil into deionized water, and stirring and mixing uniformly to obtain the core-shell flame retardant modified epoxy resin coating.

Preferably, in the step (1), the mass ratio of the ammonium polyphosphate to the deionized water is 4-6: 100.

Preferably, in the step (2), the mass ratio of the chitosan to the acetic acid solution is 1-2:100, and the mass fraction of the acetic acid solution is 1-2 wt%.

Preferably, in the step (3), the mass ratio of the polyglutamate to the ammonia solution is 1-2:100, and the mass fraction of the ammonia solution is 1-2 wt%.

Preferably, in the step (4), the mass ratio of the chitosan solution to the ammonium polyphosphate suspension is 100: 150-.

Preferably, in the step (5), the mass ratio of the chitosan-coated ammonium polyphosphate, the deionized water and the polyglutamate solution is 4-6:100: 150-200.

Preferably, in the step (6), the mass ratio of the epoxy resin, the polyglutamate and the chitosan to coat the ammonium polyphosphate, the dispersant of stearic acid monoglyceride, the brightener of organic micro-wax powder and the defoamer of dimethyl silicone oil is 100:2-5:1-2:1.5-2.5: 0.5-1.

The invention also provides the epoxy resin coating modified by the core-shell flame retardant prepared by the preparation method.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention provides a core-shell flame retardant modified epoxy resin coating and a preparation method thereof, the invention constructs a core-shell biologically-derived flame retardant in water by a self-assembly method in the synthesis process, wherein, the ammonium polyphosphate is taken as a core, a shell is formed on the surface by utilizing different electrical characteristics of chitosan and polyglutamate, the positively charged chitosan is deposited on the surface of the negatively charged ammonium polyphosphate under the electrostatic interaction, then the negatively charged polyglutamate is deposited on the surface of the chitosan coated ammonium polyphosphate at a positive point under the electrostatic interaction to form the polyglutamate and chitosan co-coated ammonium polyphosphate, and can be prepared by forming a multi-layer coated ammonium polyphosphate by the same method, introducing them into an epoxy resin by melt blending, and blending and modifying the epoxy resin to obtain the core-shell flame retardant modified epoxy resin coating.

(2) The invention provides a core-shell flame retardant modified epoxy resin coating and a preparation method thereof, wherein a polyglutamate and chitosan co-coated ammonium polyphosphate core-shell flame retardant is synthesized by taking ammonium polyphosphate, chitosan and polyglutamate sugar as raw materials through molecular structure design, wherein chitosan and ammonium polyphosphate form a core shell on the surface of ammonium polyphosphate through different electrode characteristics, the obtained core-shell flame retardant has good flame retardant synergistic effect, phosphoric acid and polyphosphate derived from ammonium polyphosphate promote dehydration and carbonization of chitosan and polyglutamate in the thermal decomposition process, so that more carbon residues are remained, further decomposition of epoxy resin is inhibited along with the remaining of more carbon residues, thereby reducing the maximum thermal weight loss rate, and the thickness of a shell layer of the polyglutamate and chitosan co-coated ammonium polyphosphate flame retardant is controllable, can further control the formation of the carbon layer and obviously improve the flame retardant capability of the epoxy resin.

(3) The invention provides a core-shell flame retardant modified epoxy resin coating and a preparation method thereof, wherein epoxy resin is connected with an ammonium polyphosphate core-shell flame retardant which is coated by polyglutamate and chitosan through hydrogen bonds, the polyglutamate and the ammonium polyphosphate core-shell flame retardant which is coated by the chitosan form a physical crosslinking network in an epoxy resin matrix, a part of energy is absorbed under the action of external force, and the toughness of the epoxy resin is improved to a certain extent; compared with the traditional epoxy resin, the surface of the epoxy resin modified by the core-shell flame retardant is provided with more deformed elongated holes, and the holes can effectively absorb energy when the material is stretched, thereby being beneficial to enhancing the mechanical property of the epoxy resin to a certain extent.

Detailed Description

The present invention will be described in more detail with reference to specific preferred embodiments, but the present invention is not limited to the following embodiments.

It should be noted that, unless otherwise specified, the chemical reagents involved in the present invention are commercially available.

Example 1

A preparation method of a core-shell flame retardant modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding 10g of ammonium polyphosphate into 200g of deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding 1g of chitosan into 100g of 1 wt% acetic acid solution, and uniformly stirring and mixing to obtain a chitosan solution;

(3) preparation of polyglutamate solution: adding 3g of sodium polyglutamate into 300g of 1 wt% ammonia solution, and stirring and mixing uniformly to obtain a sodium polyglutamate solution;

(4) preparing chitosan-coated ammonium polyphosphate: dripping 100g of chitosan solution into 180g of ammonium polyphosphate suspension, uniformly stirring and mixing, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(5) preparing polyglutamate and chitosan co-coated ammonium polyphosphate: dispersing 8g of chitosan-coated ammonium polyphosphate in 200g of deionized water, adding 300g of a sodium polyglutamate solution into the mixture under a stirring state, and then centrifuging and washing the mixture to obtain the co-coated ammonium polyphosphate of the sodium polyglutamate and the chitosan;

(6) preparing a core-shell flame retardant modified epoxy resin coating: 100g of epoxy resin, 3g of sodium polyglutamate and chitosan co-coated ammonium polyphosphate, 1g of dispersant stearic acid monoglyceride, 1.5g of brightener organic micro-wax powder and 0.5g of defoamer simethicone are added into 200g of deionized water, stirred and mixed uniformly to obtain the core-shell flame retardant modified epoxy resin coating.

Example 2

A preparation method of a core-shell flame retardant modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding 8g of ammonium polyphosphate into 200g of deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding 1g of chitosan into 100g of 1 wt% acetic acid solution, and uniformly stirring and mixing to obtain a chitosan solution;

(3) preparation of polyglutamate solution: adding 3g of sodium polyglutamate into 300g of 1 wt% ammonia solution, and stirring and mixing uniformly to obtain a sodium polyglutamate solution;

(4) preparing chitosan-coated ammonium polyphosphate: dripping 100g of chitosan solution into 150g of ammonium polyphosphate suspension, uniformly stirring and mixing, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(5) preparing polyglutamate and chitosan co-coated ammonium polyphosphate: dispersing 10g of chitosan-coated ammonium polyphosphate in 200g of deionized water, adding 300g of a sodium polyglutamate solution into the mixture under a stirring state, and then centrifuging and washing the mixture to obtain the co-coated ammonium polyphosphate of the sodium polyglutamate and the chitosan;

(6) preparing a core-shell flame retardant modified epoxy resin coating: 100g of epoxy resin, 4g of sodium polyglutamate and chitosan co-coated ammonium polyphosphate, 1.5g of dispersant stearic acid monoglyceride, 1.8g of brightener organic micro-wax powder and 0.8g of defoamer simethicone are added into 200g of deionized water, stirred and mixed uniformly to obtain the core-shell flame retardant modified epoxy resin coating.

Example 3

A preparation method of a core-shell flame retardant modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding 12g of ammonium polyphosphate into 200g of deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding 1g of chitosan into 100g of 1 wt% acetic acid solution, and uniformly stirring and mixing to obtain a chitosan solution;

(3) preparation of polyglutamate solution: adding 3g of sodium polyglutamate into 300g of 1 wt% ammonia solution, and stirring and mixing uniformly to obtain a sodium polyglutamate solution;

(4) preparing chitosan-coated ammonium polyphosphate: dripping 100g of chitosan solution into 200g of ammonium polyphosphate suspension, uniformly stirring and mixing, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(5) preparing polyglutamate and chitosan co-coated ammonium polyphosphate: dispersing 10g of chitosan-coated ammonium polyphosphate in 200g of deionized water, adding 300g of a sodium polyglutamate solution into the mixture under a stirring state, and then centrifuging and washing the mixture to obtain the co-coated ammonium polyphosphate of the sodium polyglutamate and the chitosan;

(6) preparing two layers of polyglutamate and chitosan co-coated ammonium polyphosphate: uniformly dispersing 10g of sodium polyglutamate and chitosan co-coated ammonium polyphosphate in 200g of deionized water, then adding 100g of chitosan solution, stirring and uniformly mixing, then centrifuging and washing to obtain a composite coating material, dispersing 10g of the composite coating material in 200g of deionized water, adding 300g of sodium polyglutamate solution in a stirring state, and then centrifuging and washing to obtain two layers of sodium polyglutamate and chitosan co-coated ammonium polyphosphate;

(7) preparing a core-shell flame retardant modified epoxy resin coating: 100g of epoxy resin, 4g of ammonium polyphosphate co-coated by two layers of sodium polyglutamate and chitosan, 1.5g of dispersant stearic acid monoglyceride, 1.8g of brightening agent organic micro-wax powder and 0.8g of defoaming agent dimethyl silicone oil are added into 200g of deionized water, and the mixture is stirred and mixed uniformly to obtain the core-shell flame retardant modified epoxy resin coating.

Comparative example 1

A preparation method of ammonium polyphosphate modified epoxy resin paint comprises the following steps:

100g of epoxy resin, 4g of ammonium polyphosphate, 1.5g of dispersant stearic acid monoglyceride, 1.8g of brightening agent organic micro-wax powder and 0.8g of defoaming agent dimethyl silicone oil are added into 200g of deionized water, and the mixture is stirred and mixed uniformly to obtain the ammonium polyphosphate modified epoxy resin coating.

Comparative example 2

A preparation method of a modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding 10g of ammonium polyphosphate into 200g of deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparing a chitosan solution: adding 1g of chitosan into 100g of 1 wt% acetic acid solution, and uniformly stirring and mixing to obtain a chitosan solution;

(3) preparing chitosan-coated ammonium polyphosphate: dripping 100g of chitosan solution into 180g of ammonium polyphosphate suspension, uniformly stirring and mixing, and then centrifuging and washing to obtain chitosan-coated ammonium polyphosphate;

(4) preparing a modified epoxy resin coating: 100g of epoxy resin, 3g of chitosan-coated ammonium polyphosphate, 1g of dispersant stearic acid monoglyceride, 1.5g of brightening agent organic micro-wax powder and 0.5g of defoaming agent dimethyl silicone oil are added into 200g of deionized water, and the mixture is stirred and mixed uniformly to obtain the modified epoxy resin coating.

Comparative example 3

A preparation method of a modified epoxy resin coating comprises the following steps:

(1) preparing an ammonium polyphosphate suspension: adding 10g of ammonium polyphosphate into 200g of deionized water, and uniformly stirring and mixing to obtain an ammonium polyphosphate suspension;

(2) preparation of polyglutamate solution: adding 3g of sodium polyglutamate into 300g of 1 wt% ammonia solution, and stirring and mixing uniformly to obtain a sodium polyglutamate solution;

(3) preparing polyglutamic acid sodium coated ammonium polyphosphate: dripping 100g of a sodium polyglutamate solution into 180g of an ammonium polyphosphate suspension, uniformly stirring and mixing, and then centrifuging and washing to obtain sodium polyglutamate-coated ammonium polyphosphate;

(4) preparing a modified epoxy resin coating: 100g of epoxy resin, 3g of poly sodium glutamate coated ammonium polyphosphate, 1g of dispersant stearic acid monoglyceride, 1.5g of brightener organic micro wax powder and 0.5g of defoamer simethicone are added into 200g of deionized water, stirred and mixed uniformly to obtain the modified epoxy resin coating.

The modified epoxy resin coatings prepared in examples 1-3 and comparative examples 1-3 were subjected to a limiting oxygen index test and a bending resistance test, and the specific steps were as follows:

limiting oxygen index test: the modified epoxy resin coatings prepared in examples 1 to 3 and comparative examples 1 to 3 were mixed with an epoxy curing agent by stirring, poured into a polytetrafluoroethylene mold at room temperature, air-dried and cured, demolded, cut into square sample strips, tested on a K-R2406S oxygen index analyzer, placed vertically, and ignited to measure the oxygen concentration, and the data of the limiting oxygen index were as follows:

as can be seen from the table, the modified epoxy resin coating prepared in the embodiment has good flame retardant effect, ammonium polyphosphate is not modified in comparative example 1, chitosan-coated ammonium polyphosphate is modified in comparative example 2, and polyglutamic acid sodium-coated ammonium polyphosphate is modified in comparative example 3, so that the flame retardant effect of the modified epoxy resin coating prepared in comparative example 2 and comparative example 3 is improved to a certain extent compared with that of comparative example 1, but the modified epoxy resin coating is still inferior to the embodiment, which shows that the flame retardant effect of polyglutamate and chitosan-coated ammonium polyphosphate is independently coated in the embodiment.

And (3) testing the bending resistance: the modified epoxy resin coatings prepared in examples 1 to 3 and comparative examples 1 to 3 were mixed with an epoxy curing agent by stirring, poured into a polytetrafluoroethylene mold at room temperature, air-dried, cured, demolded, cut into square sample strips, and subjected to corresponding tests on a WY-2000A tensile bending tester, the test results are shown in the following table:

as can be seen from the table, the modified epoxy resin coating prepared in the example has good bending resistance, ammonium polyphosphate is not modified in comparative example 1, chitosan-coated ammonium polyphosphate is modified in comparative example 2, and polyglutamic acid sodium-coated ammonium polyphosphate is modified in comparative example 3, which is inferior to that of the example in bending resistance because the polyglutamate and chitosan co-coated ammonium polyphosphate core-shell flame retardant forms a physical cross-linked network in an epoxy resin matrix, can absorb a part of energy under the action of external force, and improves the toughness of the epoxy resin to a certain extent.

Finally, it is to be noted that: the above examples do not limit the invention in any way. It will be apparent to those skilled in the art that various modifications and improvements can be made to the present invention. Accordingly, any modification or improvement made without departing from the spirit of the present invention is within the scope of the claimed invention.