Intrinsic heat-conducting flame-retardant recycled epoxy resin and preparation method thereof

Abstract

The invention belongs to the technical field of flame-retardant macromolecules, and particularly relates to intrinsic heat-conducting flame-retardant recycled epoxy resin and a preparation method thereof. The preparation method comprises the following steps: (1) carrying out a reaction on diethanol amine and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) to obtain an intermediate A; and (2) carrying out condensation polymerization on the intermediate A and phenylphosphonic acid to prepare the phosphate-terminated polyester flame retardant (PEF). And (3) carrying out epoxidation on 4, 4 '-biphenol to prepare the liquid crystal epoxy precursor LEP. And (4) mixing PEF, LEP and 3, 3 '-dithiodipropionic acid, and heating and curing to prepare the epoxy resin. The prepared epoxy resin has intrinsic heat conduction, flame retardance and efficient recoverability, and is a high polymer material with great potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flame-retardant polymers, and more particularly to an intrinsically thermally conductive and flame-retardant recycled epoxy resin and a preparation method thereof. BACKGROUND

[0002] Epoxy resin, as a kind of widely used thermosetting resin, has been widely used in aerospace, adhesives, electronic packaging, coatings and composite materials, and has become an indispensable part of modern industry. However, epoxy resin is a flammable material, which can produce a large amount of heat and toxic gas during combustion, limiting its application in high safety fields. In addition, the non-recyclability of traditional thermosetting epoxy resin leads to a large amount of waste accumulation, which is contrary to the concept of green manufacturing. Although great progress has been made in the recycling of epoxy resin, the performance of the material inevitably deteriorates to varying degrees with the increase in the number of recycling, which seriously restricts its sustainable application in high-performance fields. Therefore, it is an urgent problem to prepare a flame-retardant epoxy resin with high recycling efficiency.

[0003] Conventional epoxy resin is amorphous structure, with poor thermal conductivity, usually less than 0.2 W / (m·K), which cannot meet the demand of high thermal conductivity for high-density electronic devices and thermal management materials. In recent years, with the improvement of the integration of electronic devices and the promotion of green environmental protection policy, the development of epoxy resin materials with high thermal conductivity has become a research hotspot. Although some studies have tried to improve the thermal conductivity by filling thermally conductive fillers (such as alumina, boron nitride, etc.) or introduce phosphorus-containing and nitrogen-containing structures to improve the flame-retardant performance, these strategies often have the following problems: the addition of external thermally conductive fillers may reduce the mechanical properties and transparency of the material, and the interfacial thermal resistance limits the thermal conductivity efficiency; the external addition of flame retardants may cause migration and precipitation, affecting the long-term stability of the material.

[0004] Therefore, it is urgent to develop an epoxy resin system with intrinsic thermal conductivity, flame retardancy and high recycling efficiency to realize the synergistic optimization of thermal management, safety and sustainability. At present, the related technology is still relatively limited. SUMMARY

[0005] Therefore, the present application provides an intrinsically thermally conductive and flame-retardant recycled epoxy resin and a preparation method thereof. The epoxy resin prepared by the present application has excellent intrinsic thermal conductivity, flame retardancy and high recycling efficiency, and has great application potential.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] A preparation method of an intrinsically thermally conductive and flame-retardant recycled epoxy resin, characterized in that it comprises the following steps:

[0008] (1) Synthesis of intermediate A containing phosphaphenanthrene and tertiary amine groups;

[0009] (2) Synthesis of terminal phosphonic polyester flame retardant (PEF) using intermediate A;

[0010] (3) Synthesis of liquid crystal epoxy precursor (LEP) using 4,4'-diphenol;

[0011] (4) Mixing the terminal phosphonic polyester flame retardant, the liquid crystal epoxy precursor and 3,3'-dithiodipropionic acid in a certain proportion, pouring into a mold, heating and curing to obtain an epoxy resin.

[0012] Preferably, the intermediate A in step (1) is prepared by reacting diethanolamine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide.

[0013] Preferably, the reaction conditions of step (1) are as follows: diethanolamine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), polyformaldehyde (POM) and chloroform are added to a reaction vessel under nitrogen, and the reaction is carried out for a period of time. After the reaction is completed, the mixture is slowly cooled to room temperature, the product is filtered, washed and vacuum dried to obtain a transparent gel product, which is the intermediate A.

[0014] Preferably, the molar ratio of diethanolamine to 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide is 1:1, the mass percentage of polyformaldehyde is 10%-20%, the reaction is carried out at 40-65°C for 10-24h, and the vacuum drying is carried out at 130-150°C for 6-12h.

[0015] The above process can be represented by the following chemical reaction formula:

[0016] .

[0017] Preferably, the terminal phosphonic polyester flame retardant in step (2) is prepared by condensation reaction of intermediate A and phenylphosphonic acid, and has the characteristic structure as shown in formula 1:

[0018]

[0019] Formula 1.

[0020] Preferably, the condensation reaction conditions are as follows: intermediate A and phenylphosphonic acid are added to a flask with stirring and a vacuum distillation device, the oil bath is heated to 160-200°C for 2-6h, and the water produced in the reaction is removed by the vacuum distillation device; the molar ratio of intermediate A to phenylphosphonic acid is (0.35-0.8):1.

[0021] The above process is represented by a chemical reaction formula as follows:

[0022] .

[0023] Preferably, the liquid crystal epoxy precursor in step (3) is prepared by epoxidation of 4,4'-diphenol;

[0024] The reaction conditions are as follows: under the condition of nitrogen, 4,4'-diphenol is added into a reaction container, then a certain mass ratio of epichlorohydrin and tetrabutylammonium bromide are added in sequence, the temperature is raised to 60-80℃, and the reaction is carried out for 2-4 h, then a strong alkali aqueous solution with a concentration of 30-50wt% is added drop by drop, and the reaction is continued for 1-3 h, then the solid is filtered, washed with water and ethanol in sequence, and vacuum dried at 70-90℃ for 12-24 h to obtain the liquid crystal epoxy precursor.

[0025] The mass ratio of 4,4'-diphenol to epichlorohydrin is 1:(3-4), and the addition amount of tetrabutylammonium bromide is 0.5%-2% of the total mass of 4,4'-diphenol and epichlorohydrin.

[0026] The above process is represented by a chemical reaction formula as follows:

[0027] .

[0028] Preferably, in step (4), the ratio of the number of moles of epoxy groups in the liquid crystal epoxy precursor to the number of moles of carboxyl groups of the end phosphoric acid group polyester flame retardant and 3,3'-dithiodipropionic acid is 1:(0.8-1.2).

[0029] Preferably, in step (4), the heating and curing is carried out by hot pressing, and the hot pressing conditions are as follows: hot pressing at 150℃ and 10 MPa for 6 h.

[0030] Another object of the present application is to provide the intrinsic heat-conductive flame-retardant recycled epoxy resin prepared by the above-mentioned preparation method of the intrinsic heat-conductive flame-retardant recycled epoxy resin.

[0031] According to the above technical solution, compared with the prior art, the present application has the following beneficial effects:

[0032] (1) The synthesis method of the end phosphoric acid group polyester flame retardant (PEF) in the present application is simple, does not need the participation of a solvent, does not need a complex post-treatment process, and only generates water as a byproduct.

[0033] (2) The prepared epoxy resin material has excellent intrinsic heat conductivity and flame retardancy.

[0034] (3) The prepared epoxy resin has triple dynamic covalent bonds, has excellent physical remolding property, and can be repeatedly processed for more than 5 times. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only aim to explain the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on the provided drawings.

[0036] Figure 1 NMR of flame retardant intermediate A in Example 1;

[0037] Figure 2 NMR of end phosphinyl polyester flame retardant (PEF1) in Example 1;

[0038] Figure 3 Stress relaxation curves of Example 1 and Comparative Examples 1, 2, 3;

[0039] Figure 4 Digital photo of physically remolded Example 1. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0041] Example 1:

[0042] 1. First, synthesize the flame retardant intermediate A containing the phosphaphenanthrene group. Under nitrogen conditions, diethanolamine (19.2 g, 0.2 mol), DOPO (43.2 g, 0.2 mol), paraformaldehyde (9 g), and chloroform (200 mL) are added to a reaction vessel, and reacted at 55°C for 12 h. After the reaction is completed, the mixture is slowly cooled to room temperature. The product is filtered, the filter residue is repeatedly washed with ethanol, and then vacuum dried at 130°C for 6 h to obtain a transparent gel product, which is the intermediate A.

[0043] 2. Under nitrogen conditions, intermediate A (33.3 g, 0.1 mol) and phenylphosphinic acid (31.6 g, 0.2 mol) are added to a flask equipped with stirring and a vacuum distillation device, and reacted at 180°C in an oil bath for 4 h to obtain an end phosphinyl polyester flame retardant (PEF1).

[0044] 3. Under nitrogen, 30 g of 4,4'-diphenol was added into a reaction vessel, followed by 90 g of epichlorohydrin and 1 g of tetrabutylammonium bromide, and the temperature was raised to 80°C for 3 h, then 50 g of 40wt% sodium hydroxide aqueous solution was added dropwise, and the reaction was continued for 1 h. After the reaction was completed, the solid was filtered, washed with water and ethanol, and dried at 80°C under vacuum for 4 h to obtain LEP.

[0045] 4. 10 g of LEP, 4.9 g of 3,3'-dithiodipropionic acid and 6.2 g of PEF1 were mixed and dissolved at 150°C, quickly poured into a mold, and cured at 10 MPa and 150°C for 6 h.

[0046] The material passed the UL 94 vertical burning test V-0 level; the limiting oxygen index (LOI) was 33.5%; the thermal conductivity was 1.12 W / (m·K); the tensile strength was 22.5 MPa; the stress relaxation time at 190°C was 58 s, the tensile strength after five physical recycling was 20.3 MPa, and the thermal conductivity after five physical recycling was 1.08 W / (m·K).

[0047] Example 2:

[0048] 10 g of LEP prepared in Example 1, 8.2 g of PEF1 and 4.2 g of 3,3'-dithiodipropionic acid were mixed and dissolved at 150°C, quickly poured into a mold, and cured at 10 MPa and 150°C for 6 h.

[0049] The material passed the UL 94 vertical burning test V-0 level; the limiting oxygen index (LOI) was 34.3%; the thermal conductivity was 1.15 W / (m·K); the tensile strength was 21.3 MPa; the stress relaxation time at 190°C was 61 s, the tensile strength after five physical recycling was 19.6 MPa, and the thermal conductivity after five physical recycling was 1.09 W / (m·K).

[0050] Example 3:

[0051] 1. Under nitrogen, 40 g of intermediate A prepared in the example (0.12 mol) and phenylphosphonic acid (31.6 g, 0.2 mol) were added to a flask equipped with stirring and vacuum distillation device, and the reaction was carried out at 180°C in an oil bath for 4 h to obtain a terminal phosphonic acid group-containing polyester flame retardant (PEF2).

[0052] 2. 10 g of LEP prepared in Example 1, 4.9 g of 3,3'-dithiodipropionic acid, and 6.2 g of PEF2 were mixed and dissolved at 150°C, quickly poured into a mold, and cured at 150°C for 6 h under 10 MPa.

[0053] The material passed the UL 94 vertical burning test V-0 class; the limiting oxygen index (LOI) was 33.0%; the thermal conductivity was 1.16 W / (m-K); the tensile strength was 21.5 MPa; the stress relaxation time at 190°C was 56 s, the tensile strength after five physical recycling was 19.4 MPa, and the thermal conductivity after five physical recycling was 1.1 W / (m-K).

[0054] Comparative Example 1:

[0055] 1. 5 g of E51 (bisphenol A type epoxy resin, epoxy value: 0.51 mol / 100 g) and 1.9 g of adipic acid were mixed and dissolved at 150°C.

[0056] 2. The mixture was poured into a metal mold and cured at 150°C for 6 h to obtain a thermosetting epoxy resin.

[0057] The material passed the UL 94 vertical burning test V-0 class; the limiting oxygen index (LOI) was 33.0%; the thermal conductivity was 1.16 W / (m-K); the tensile strength was 21.5 MPa; the stress relaxation time at 190°C was 56 s, the tensile strength after five physical recycling was 19.4 MPa, and the thermal conductivity after five physical recycling was 1.1 W / (m-K).

[0058] Comparative Example 2:

[0059] 1. 5 g of E51 and 2.7 g of 3,3'-dithiodipropionic acid were mixed and dissolved at 150°C.

[0060] 2. The mixture was poured into a metal mold and cured at 150°C for 6 h to obtain a thermosetting epoxy resin.

[0061] The material passed the UL 94 vertical burning test V-0 class; the limiting oxygen index (LOI) was 33.0%; the thermal conductivity was 1.16 W / (m-K); the tensile strength was 21.5 MPa; the stress relaxation time at 190°C was 56 s, the tensile strength after five physical recycling was 19.4 MPa, and the thermal conductivity after five physical recycling was 1.1 W / (m-K).

[0062] Comparative Example 3:

[0063] 1. 5 g of LEP prepared in Example 1 and 3.5 g of 3,3'-dithiodipropionic acid were mixed and dissolved at 150°C.

[0064] 2. Pour the above mixture into a metal mold, and cure at 150℃ for 6h to obtain a thermosetting epoxy resin.

[0065] The material was tested to have no UL 94 vertical burning rating; a limiting oxygen index (LOI) of 22.3%; a thermal conductivity of 0.98 W / (m·K); a tensile strength of 24.2 MPa; a stress relaxation time at 190℃ of 233 s; a tensile strength after five physical recycling of 11.1 MPa; and a thermal conductivity after five physical recycling of 0.66 W / (m·K).

[0066] In Comparative Example 1, Comparative Example 2, and Comparative Example 3, which do not contain PEF, the UL-94 tests are all no rating, and in Example 1, Example 2, and Example 3, which contain PEF1, the UL-94 tests all pass V-0 rating, indicating that PEF can effectively improve the flame retardant performance. Figure 3 For the stress relaxation curve, in Comparative Example 1, there is no stress relaxation behavior because there is no dynamic covalent bond, so physical recycling cannot be performed. In Comparative Example 2 and Comparative Example 3, after adding the curing agent containing disulfide bonds, stress relaxation behavior occurs, but only one dynamic covalent bond is contained, and the mechanical property retention rate after physical recycling is poor. In Example 1, Example 2, and Example 3, the tertiary amine structure in PEF can catalyze the transesterification reaction in situ, and the terminal phosphonic acid group in PEF can form a β-hydroxyphosphate structure after reaction with epoxy, so Example 1, Example 2, and Example 3 contain triple dynamic covalent bonds of β-hydroxy ester, β-hydroxy phosphate, and disulfide, and have excellent mechanical property retention rate after physical recycling. Comparative Example 1 and Comparative Example 2 do not contain LEP, and have low thermal conductivity. Comparative Example 3 uses liquid crystal epoxy resin LEP, and the thermal conductivity is significantly improved. In Example 1, Example 2, and Example 3, after adding PEF, the thermal conductivity is further improved. In summary, the epoxy resin prepared in Example 1, Example 2, and Example 3 has intrinsic thermal conductivity, flame retardant, and high-efficiency recycling performance.

[0067] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0068] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for the preparation of intrinsically heat-conductive flame-retardant recycled epoxy resin, characterized by, The method comprises the following steps: (1) synthesizing intermediate A containing phosphaphenanthrene and tertiary amine groups; (2) synthesizing a terminal phosphoric acid group polyester flame retardant by using the intermediate A; (3) synthesizing a liquid crystal epoxy precursor by using 4,4'-diphenol; (4) uniformly mixing the terminal phosphoric acid group polyester flame retardant, the liquid crystal epoxy precursor and 3,3'-dithiodipropionic acid in a certain proportion, pouring into a mold, and heating and curing to obtain an epoxy resin.

2. A process for the preparation of an intrinsically heat-conducting flame- retardant recycled epoxy resin according to claim 1, characterized in that, The intermediate A in step (1) is prepared by reacting diethanolamine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide.

3. A process for the preparation of an intrinsically heat-conducting flame- retardant recycled epoxy resin according to claim 2, characterized in that, The reaction conditions of step (1) are as follows: under the condition of nitrogen, diethanolamine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, paraformaldehyde and chloroform are added into a reaction container, and the mixture is slowly cooled to room temperature after reaction for a period of time, and then the product is filtered, washed and vacuum dried to obtain a transparent gel product, which is the intermediate A.

4. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 3, characterized in that, The molar ratio of diethanolamine to 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide is 1:1, the mass percentage of paraformaldehyde is 10%-20%, the reaction for a period of time is 10-24 h at 40-65℃, and the vacuum drying is at 130-150℃ for 6-12 h.

5. The process for the preparation of intrinsically heat conductive flame retardant recycled epoxy resin as claimed in claim 1, wherein, The terminal phosphoric acid group polyester flame retardant in step (2) is prepared by condensation reaction of intermediate A and phenyl phosphonic acid, and has a characteristic structure as shown in formula 1: Formula 1.

6. A process for the preparation of an intrinsically heat-conducting flame- retardant recycled epoxy resin according to claim 5, characterized in that, The condensation reaction conditions are as follows: intermediate A and phenyl phosphonic acid are added into a flask with stirring and a reduced pressure distillation device, the oil bath is heated to 160-200℃ for 2-6 h, and the water produced in the reaction is removed by the reduced pressure distillation device; the molar ratio of intermediate A to phenyl phosphonic acid is (0.35-0.8):

1.

7. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, The liquid crystal epoxy precursor in step (3) is prepared by epoxidation of 4,4'-diphenol; The reaction conditions are as follows: under the condition of nitrogen, 4,4'-diphenol is added into a reaction container, and then a certain mass ratio of epichlorohydrin and tetrabutylammonium bromide are added in sequence, the temperature is raised to 60-80℃ for 2-4 h, a strong alkali aqueous solution with a concentration of 30-50wt% is added drop by drop, and the reaction is continued for 1-3 h, then the solid is filtered, washed with water and ethanol in sequence, and vacuum dried at 70-90℃ for 12-24 h to obtain the liquid crystal epoxy precursor; The mass ratio of 4,4'-diphenol to epichlorohydrin is 1:(3-4), and the addition amount of tetrabutylammonium bromide is 0.5%-2% of the total mass of 4,4'-diphenol and epichlorohydrin.

8. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, In step (4), the molar ratio of the number of epoxy groups in the liquid crystal epoxy precursor to the number of carboxyl groups of the terminal phosphoric acid group polyester flame retardant and 3,3'-dithiodipropionic acid is 1:(0.8-1.2).

9. The method of preparing an intrinsically heat-conductive and flame-retardant recycled epoxy resin according to claim 1, characterized by, In step (4), the heating and curing is performed by hot pressing, and the hot pressing conditions are as follows: hot pressing at 150℃ and 10 MPa for 6 h.

10. An intrinsically heat-conductive, flame-retardant recycled epoxy resin, characterized in that, The intrinsic heat-conducting flame-retardant recycled epoxy resin is prepared by the method of any one of claims 1-9.

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