A high-strength solvent-resistant closed-loop recyclable plastic and its preparation method and recycling method

Abstract

The present invention provides a high-strength solvent-resistant closed-loop recyclable plastic and a preparation method and a recycling method thereof, and belongs to the technical field of recyclable plastics. The monomers used in the present invention are all difunctionalized, and the obtained plastic contains multiple imine bonds inside. Since the entire polymer body is a fully aromatic ring molecule, the obtained plastic has a high fracture strength and excellent water resistance. At the same time, the imine bond and the adjacent benzene ring will form a conjugated structure, which increases the π-π interaction between the segments, further increases the strength and modulus of the plastic, and at the same time gives the plastic excellent resistance to organic solvents. The imine bond can be disconnected under acidic conditions to regenerate the original amino and aldehyde molecules, and the obtained plastic can be depolymerized in a mixed system of an organic solvent and an acidic substance. Based on the difference in solubility between amino and aldehyde molecules in a specific solvent, the present invention can use a solution precipitation method to quickly and efficiently separate the monomer raw material by adding a poor solvent for a dialdehyde functionalized aromatic ring monomer.

Description

Technical Field

[0001] The present invention relates to the technical field of recyclable plastics, and in particular to a high-strength solvent-resistant closed-loop recyclable plastic and a preparation method and a recycling method thereof. Background Art

[0002] Plastics play a vital role in our daily lives. With the continuous improvement of living standards, global plastic production has increased annually in recent years. However, most plastics end up in landfills or incineration after use, with only a small portion being recycled, resulting in significant resource waste. Because traditional plastics are synthesized from petroleum-based molecules and are difficult to degrade in the wild, discarded plastics cause significant pollution to soil and water environments. Imparting plastics with excellent recyclability can effectively address post-use plastic disposal issues and make a significant contribution to the development of a circular economy.

[0003] To date, most commercial plastics can only be mechanically recycled through reprocessing at high temperatures. However, mechanical recycling inevitably causes polymer chain fragmentation, resulting in a significant decrease in the performance of the recycled plastic, effectively achieving downgraded recycling. In contrast, closed-loop recycling, where all recovered monomers are remanufactured into virgin material without compromising quality after depolymerization, has great potential to improve recycling efficiency and enhance the quality of recycled materials, and is currently a top priority in the plastics recycling field.

[0004] Currently, closed-loop recyclable plastics are mostly based on poly(thio)esters or polyamides produced through the ring-opening polymerization of cyclic monomers. These plastics require specially designed metal-organic catalysts for both polymerization and depolymerization, which are relatively expensive and complex to purify. Furthermore, because these plastics are produced through solution casting in organic solvents, they are intolerant to many organic solvents. Furthermore, their fracture strength or yield strength is often below 40 MPa, and their mechanical properties still need to be further improved. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a high-strength solvent-resistant closed-loop recyclable plastic and its preparation method and recycling method. The high-strength solvent-resistant closed-loop recyclable plastic provided by the present invention can realize the closed-loop recycling of plastic products, and the plastic products reproduced after closed-loop recycling still have good strength and solvent resistance.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a high-strength solvent-resistant closed-loop recyclable plastic, which is prepared from raw materials comprising the following molar percentages:

[0008] 45-65% diamino-functionalized aromatic ring monomer;

[0009] The content of dialdehyde functionalized aromatic ring monomer is 35-55%.

[0010] Preferably, the bisamino-functionalized aromatic ring monomer is one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-diaminobenzophenone and 4,4'-diaminodiphenyl sulfone.

[0011] Preferably, the bisaldehyde functionalized aromatic ring monomer is one or more of phthalaldehyde, 2,5-furandicarboxaldehyde, 2,6-pyridinedicarboxaldehyde, 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone, dehydrovanillin and 5-hydroxy-1,3-phthalaldehyde.

[0012] The present invention provides a method for preparing the above-mentioned high-strength solvent-resistant closed-loop recyclable plastic, comprising the following steps:

[0013] A diamino-functionalized aromatic ring monomer, a dialdehyde-functionalized aromatic ring monomer and a polar organic solvent are mixed, subjected to a Schiff base reaction, and a high-strength solvent-resistant closed-loop recyclable plastic is obtained after removing the polar organic solvent.

[0014] Preferably, the polar organic solvent is one or more of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone and N,N-dimethylacetamide.

[0015] Preferably, the temperature of the Schiff base reaction is 65-200° C., and the time is 12-30 hours.

[0016] The present invention provides a method for recycling the high-strength solvent-resistant closed-loop recyclable plastic prepared by the above preparation method, comprising the following steps:

[0017] Mixing the high-strength solvent-resistant closed-loop recyclable plastic with a first solvent to perform a depolymerization reaction to obtain a plastic dissolving solution;

[0018] The plastic dissolving liquid is mixed with a second solvent, and solid-liquid separation is performed after solid precipitation, whereby the obtained solid is a dialdehyde functionalized aromatic ring monomer, and the obtained liquid is a diamino functionalized aromatic ring monomer;

[0019] The first solvent is a mixture of an organic solvent and an acid;

[0020] The second solvent is a poor solvent for the bisaldehyde functionalized aromatic ring monomer.

[0021] Preferably, the organic solvent in the first solvent includes one or more of tetrahydrofuran, acetonitrile, dimethyl sulfoxide, N,N-dimethylacetamide, isopropanol and acetone;

[0022] The acid in the first solvent is one or more of concentrated hydrochloric acid, glacial acetic acid and phosphoric acid.

[0023] Preferably, the volume ratio of the organic solvent to the acid is 3 to 8:1.

[0024] Preferably, the poor solvent for the dialdehyde functionalized aromatic ring monomer is one or more of diethyl ether, ethyl acetate, ethanol, petroleum ether, n-hexane and 1,4-dioxane;

[0025] The volume ratio of the first solvent to the second solvent is 1:2.5-15.

[0026] The present invention provides a high-strength, solvent-resistant, closed-loop recyclable plastic, prepared from raw materials comprising the following molar percentages: 50-60% diamino-functionalized aromatic ring monomers; 40-50% dialdehyde-functionalized aromatic ring monomers. Aromatic amino molecules and aromatic aldehyde molecules react via a Schiff base to form imine bonds. Because both the amino and aldehyde molecules used in the present invention are difunctionalized, a polymer material containing multiple imine bonds can be prepared. Because the entire polymer is composed of fully aromatic ring molecules, the resulting plastic exhibits high fracture strength and excellent water resistance. Furthermore, the imine bonds form conjugated structures with adjacent benzene rings, enhancing the π-π interactions between the chain segments, further increasing the strength and modulus of the plastic while imparting excellent resistance to organic solvents.

[0027] The present invention provides a method for preparing the above-mentioned high-strength solvent-resistant closed-loop recyclable plastic. The present invention obtains the high-strength solvent-resistant closed-loop recyclable plastic through Schiff base reaction. This method is simple to operate, low in cost, and easy to realize industrial mass production.

[0028] The present invention provides a method for recycling the above-mentioned high-strength solvent-resistant closed-loop recyclable plastic. In the present invention, the imine bond can be broken under acidic conditions to regenerate the original amino and aldehyde molecules, so the high-strength solvent-resistant closed-loop recyclable plastic provided by the present invention can be depolymerized in a mixed system of an organic solvent and an acidic substance. Based on the difference in solubility between amino and aldehyde molecules in specific solvents, the present invention can use a solution precipitation method to quickly and efficiently separate the diamino-functionalized aromatic ring monomer and the dialdehyde-functionalized aromatic ring monomer by adding a poor solvent for the dialdehyde-functionalized aromatic ring monomer. The two monomers recovered by the present invention can be used to prepare the initial plastic again, and the re-prepared plastic products still have good strength and water resistance and organic solvent resistance, realizing efficient closed-loop recycling under mild conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a real picture of the plastic of Example 1 of the present invention;

[0030] Figure 2 is the stress-strain curve of the plastic of Example 2 of the present invention;

[0031] Figure 3 This is the closed-loop recycling process of plastics according to Example 3 of the present invention;

[0032] Figure 4 This is a water resistance and organic solvent resistance test of the plastic of Example 4 of the present invention;

[0033] Figure 5 This is the stress-strain curve of the plastic of Example 5 of the present invention after multiple closed-loop recycling. DETAILED DESCRIPTION

[0034] The present invention provides a high-strength solvent-resistant closed-loop recyclable plastic, which is prepared from raw materials comprising the following molar percentages:

[0035] 45-65% diamino-functionalized aromatic ring monomer;

[0036] The content of dialdehyde functionalized aromatic ring monomer is 35-55%.

[0037] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0038] The raw materials for preparing the high-strength, solvent-resistant, closed-loop recyclable plastic provided by the present invention include, by mole percentage, 45-65% of a bisamino-functionalized aromatic ring monomer, preferably 45-55%, and more preferably 50%. In the present invention, the bisamino-functionalized aromatic ring monomer is preferably one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-diaminobenzophenone, and 4,4'-diaminodiphenyl sulfone.

[0039] The raw materials for preparing the high-strength, solvent-resistant, closed-loop recyclable plastic provided by the present invention include, by mole percentage, 35-55% of a dialdehyde-functionalized aromatic ring monomer, preferably 45-55%, and more preferably 50%. In the present invention, the dialdehyde-functionalized aromatic ring monomer is preferably one or more of phthalaldehyde, 2,5-furandicarboxaldehyde, 2,6-pyridinedicarboxaldehyde, 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone, dehydrovanillin, and 5-hydroxy-1,3-phthalaldehyde.

[0040] The present invention provides a method for preparing the above-mentioned high-strength solvent-resistant closed-loop recyclable plastic, comprising the following steps:

[0041] A diamino-functionalized aromatic ring monomer, a dialdehyde-functionalized aromatic ring monomer and a polar organic solvent are mixed, subjected to a Schiff base reaction, and a high-strength solvent-resistant closed-loop recyclable plastic is obtained after removing the polar organic solvent.

[0042] In the present invention, the polar organic solvent is preferably one or more of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone and N,N-dimethylacetamide.

[0043] The present invention has no special requirements for the mixing method, and any mixing method well known to those skilled in the art can be used, such as stirring mixing.

[0044] In the present invention, the temperature of the Schiff base reaction is preferably 65 to 200°C, and the time is preferably 12 to 30 hours. In the present invention, when the polar organic solvent is tetrahydrofuran, the temperature of the Schiff base reaction is preferably 65°C; when the polar organic solvent is dimethyl sulfoxide, the temperature of the Schiff base reaction is preferably 180°C; when the polar organic solvent is N,N-dimethylformamide, the temperature of the Schiff base reaction is preferably 150°C; when the polar organic solvent is acetonitrile, the temperature of the Schiff base reaction is preferably 70°C; when the polar organic solvent is N-methylpyrrolidone, the temperature of the Schiff base reaction is preferably 200°C; when the polar organic solvent is N,N-dimethylacetamide, the temperature of the Schiff base reaction is preferably 170°C.

[0045] In the present invention, the heating rate for the Schiff base reaction is preferably 2° C. / min.

[0046] In the present invention, the polar organic solvent is preferably removed by heating the solvent to volatilize it. In the present invention, the temperature of heating the solvent to volatilize it is preferably 25 to 90°C, more preferably 35 to 80°C.

[0047] In the present invention, when the polar organic solvent is tetrahydrofuran, the temperature of the heated volatile solvent is preferably 25°C; when the polar organic solvent is dimethyl sulfoxide, the temperature of the heated volatile solvent is preferably 80°C; when the polar organic solvent is N,N-dimethylformamide, the temperature of the heated volatile solvent is preferably 70°C; when the polar organic solvent is acetonitrile, the temperature of the heated volatile solvent is preferably 40°C; when the polar organic solvent is N-methylpyrrolidone, the temperature of the heated volatile solvent is preferably 90°C; when the polar organic solvent is N,N-dimethylacetamide, the temperature of the heated volatile solvent is preferably 60°C.

[0048] The present invention has no special requirements on the time of heating to volatilize the solvent, and it only needs to remove the polar organic solvent completely.

[0049] The present invention provides a method for recycling the above-mentioned high-strength solvent-resistant closed-loop recyclable plastic, comprising the following steps:

[0050] Mixing the high-strength solvent-resistant closed-loop recyclable plastic with a first solvent to perform a depolymerization reaction to obtain a plastic dissolving solution;

[0051] The plastic dissolving liquid is mixed with a second solvent, and solid-liquid separation is performed after solid precipitation, whereby the obtained solid is a dialdehyde functionalized aromatic ring monomer, and the obtained liquid is a diamino functionalized aromatic ring monomer;

[0052] The first solvent is a mixture of an organic solvent and an acid;

[0053] The second solvent is a poor solvent for the bisaldehyde functionalized aromatic ring monomer.

[0054] The present invention mixes a high-strength, solvent-resistant, closed-loop recyclable plastic with a first solvent and performs a depolymerization reaction to obtain a plastic dissolving solution. In the present invention, the first solvent is a mixture of an organic solvent and an acid; in the present invention, the organic solvent preferably includes one or more of tetrahydrofuran, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, isopropyl alcohol, and acetone; and the acid is preferably one or more of concentrated hydrochloric acid, glacial acetic acid, and phosphoric acid.

[0055] In the present invention, the combination of the first solvent preferably includes one or more of the combinations of tetrahydrofuran and concentrated hydrochloric acid, acetonitrile and concentrated hydrochloric acid, dimethyl sulfoxide and glacial acetic acid, N,N-dimethylformamide and glacial acetic acid, isopropyl alcohol and phosphoric acid, and acetone and phosphoric acid.

[0056] In the present invention, the volume ratio of the organic solvent to the acid is preferably 3 to 8:1, more preferably 5 to 7:1.

[0057] The present invention has no special requirements for the mixing method, and any mixing method known to those skilled in the art can be used, such as stirring. In the present invention, the depolymerization reaction temperature is preferably room temperature, and the time is preferably 2 to 6 hours, more preferably 3 to 5 hours.

[0058] The present invention mixes the plastic dissolving liquid with a second solvent, precipitates a solid, and then performs solid-liquid separation. The resulting solid is a dialdehyde-functionalized aromatic ring monomer, and the resulting liquid is a diamino-functionalized aromatic ring monomer. In the present invention, the second solvent is a poor solvent for the dialdehyde-functionalized aromatic ring monomer, preferably one or more of diethyl ether, ethyl acetate, ethanol, petroleum ether, n-hexane, and 1,4-dioxane.

[0059] In the present invention, the volume ratio of the first solvent to the second solvent is preferably 1:2.5-15, more preferably 1:5-10.

[0060] The present invention has no particular requirements for the solid-liquid separation method; any solid-liquid separation method familiar to those skilled in the art may be used. After obtaining the solid, the present invention preferably dries the solid; after obtaining the liquid, the present invention preferably removes the solvent from the liquid and then dries it. The present invention has no particular requirements for the specific methods of solvent removal and drying; any methods familiar to those skilled in the art may be used.

[0061] After recovering the bisaldehyde-functionalized aromatic ring monomer and the bisamino-functionalized aromatic ring monomer, the present invention preferably uses the recovered monomers to re-prepare a high-strength, solvent-resistant, closed-loop recyclable plastic. In the present invention, the preparation method is the same as above and will not be repeated here.

[0062] The high-strength solvent-resistant closed-loop recyclable plastic provided by the present invention, as well as its preparation method and recycling method are described in detail below with reference to the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0063] Example 1

[0064] A high-strength, solvent-resistant, closed-loop recyclable plastic. Calculated by mole fraction, the amounts of each raw material are as follows:

[0065] p-phenylenediamine (bisamino functionalized aromatic ring molecule), 56%; dehydrovanillin (bisaldehyde functionalized aromatic ring molecule), 44%.

[0066] The preparation method is as follows:

[0067] Paraphenylenediamine and dehydrovanillin were separately dispersed in N-methylpyrrolidone to a 190 mg / mL solution. The mixture was then mixed at room temperature. Once both monomers were completely dissolved, the temperature was raised to 190°C and stirred for 24 hours. After the reaction, the hot solution was poured into a 5 × 5 × 3 cm glass mold. The mold was then placed on a 90°C hot plate to slowly evaporate the solvent. After 40 hours, the solvent evaporated completely, resulting in a plastic film.

[0068] The actual picture of the obtained plastic film is as follows Figure 1 As shown by Figure 1 It can be seen that the plastic film prepared by the present invention has good transparency.

[0069] The tensile strength of the obtained plastic film was tested using a universal material testing machine. The test showed that the tensile strength of the obtained plastic film was 60.5 MPa, which is a high tensile strength plastic.

[0070] The resulting plastic film was immersed in water and organic solvents (ethanol, tetrahydrofuran, and dimethyl sulfoxide) to test its water and solvent resistance. The tests showed that the resulting plastic film had good resistance to water and different organic solvents, and it did not dissolve or depolymerize even after immersion for 60 hours.

[0071] The recycling method of high-strength solvent-resistant closed-loop recyclable plastics adopts the following steps:

[0072] The plastic film prepared in Example 1 is placed in a mixed solvent of ethanol and glacial acetic acid in a volume ratio of 5:1. The plastic depolymerizes and dissolves. Subsequently, an excess of n-hexane is added to the solution, producing a large amount of precipitate. The precipitate is collected and dried to obtain high-purity dehydrovanillin. The solution is collected and dried to obtain high-purity p-phenylenediamine.

[0073] The recycled monomers can be used to prepare the initial high-strength, solvent-resistant, closed-loop recyclable plastic again, and the mechanical properties of the plastic remain almost unchanged during the five recycling processes, thus realizing multiple closed-loop recycling of the material.

[0074] Example 2

[0075] A high-strength, solvent-resistant, closed-loop recyclable plastic. Calculated by mole fraction, the amounts of each raw material are as follows:

[0076] 4,4'-bis(3-aminophenoxy)benzophenone (bisamino-functionalized aromatic ring molecule), 50%; 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone (bisaldehyde-functionalized aromatic ring molecule), 50%.

[0077] The preparation method is as follows:

[0078] 4,4'-bis(3-aminophenoxy)benzophenone and 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone were dispersed in N,N-dimethylacetamide to prepare 250 mg / mL solutions. The mixture was then mixed at room temperature. Once both monomers were completely dissolved, the temperature was raised to 165°C and the reaction was continued with stirring for 24 hours. After the reaction was complete, the hot solution was poured into a 5×5×3 cm glass mold. The mold was then placed on an 80°C hot plate to slowly evaporate the solvent. After 60 hours, the solvent evaporated completely, resulting in a plastic film.

[0079] The tensile strength of the obtained plastic film was tested using a universal material testing machine. The test showed that the tensile strength of the obtained plastic film was 58.2 MPa, which is a high tensile strength plastic. Its stress-strain curve is shown in Figure 2. Figure 2 shown.

[0080] The resulting plastic film was immersed in water and organic solvents (ethanol, tetrahydrofuran, and dimethyl sulfoxide) to test its water and solvent resistance. The tests showed that the resulting plastic film had good resistance to water and different organic solvents, and it did not dissolve or depolymerize even after immersion for 60 hours.

[0081] The recycling method of high-strength solvent-resistant closed-loop recyclable plastics adopts the following steps:

[0082] The plastic film prepared in Example 2 was placed in a mixed solvent of tetrahydrofuran and concentrated hydrochloric acid in a volume ratio of 5:1. The plastic depolymerized and dissolved. An excess of ethanol was then added to the solution to produce a large amount of precipitate. The precipitate was collected and dried to obtain high-purity 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone. The solution was collected and dried to obtain high-purity 4,4'-bis(3-aminophenoxy)benzophenone.

[0083] The recycled monomers can be used to prepare the initial high-strength, solvent-resistant, closed-loop recyclable plastic again, and the mechanical properties of the plastic remain almost unchanged during the five recycling processes, thus realizing multiple closed-loop recycling of the plastic.

[0084] Example 3

[0085] A high-strength, solvent-resistant, closed-loop recyclable plastic. Calculated by mole fraction, the amounts of each raw material are as follows:

[0086] 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine (bisamino-functionalized aromatic ring molecule), 53%; terephthalaldehyde (bisaldehyde-functionalized aromatic ring molecule), 47%.

[0087] The preparation method is as follows:

[0088] 3,3-Bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine and terephthalaldehyde were separately dispersed in dimethyl sulfoxide to prepare 230 mg / mL solutions. The mixture was then mixed at room temperature. Once both monomers were completely dissolved, the temperature was raised to 185°C and stirred for 24 hours. After the reaction, the hot solution was poured into a 5×5×3 cm glass mold. The mold was then placed on a 95°C hot plate to slowly evaporate the solvent. After 50 hours, the solvent evaporated completely, resulting in a plastic film.

[0089] The tensile strength of the obtained plastic film was tested using a universal material testing machine. The test showed that the tensile strength of the obtained plastic film was 72.3 MPa, which is a high tensile strength plastic.

[0090] The resulting plastic film was immersed in water and organic solvents (ethanol, tetrahydrofuran, and dimethyl sulfoxide) to test its water and solvent resistance. The tests showed that the resulting plastic film had good resistance to water and different organic solvents, and it did not dissolve or depolymerize even after immersion for 60 hours.

[0091] The recycling method of high-strength solvent-resistant closed-loop recyclable plastics adopts the following steps:

[0092] The plastic film prepared in Example 3 is placed in a mixed solvent of acetonitrile and concentrated hydrochloric acid in a volume ratio of 5:1. The plastic is depolymerized and dissolved. Then, an excess of ether is added to the solution to produce a large amount of precipitation. The precipitate is collected and dried to obtain high-purity 2,5-furandicarboxaldehyde; the solution is collected and dried to obtain high-purity 4,4'-diaminodiphenyl ether. The closed-loop recycling process of plastics is as follows: Figure 3 shown.

[0093] The recycled monomers can be used to prepare the initial high-strength, solvent-resistant, closed-loop recyclable plastic again, and the mechanical properties of the plastic remain almost unchanged during the five recycling processes, thus realizing multiple closed-loop recycling of the plastic.

[0094] Example 4

[0095] A high-strength, solvent-resistant, closed-loop recyclable plastic. Calculated by mole fraction, the amounts of each raw material are as follows:

[0096] 4,4'-diaminodiphenyl ether (bisamino functionalized aromatic ring molecule), 60%; 2,5-furandicarboxaldehyde (bisaldehyde functionalized aromatic ring molecule), 40%.

[0097] The preparation method is as follows:

[0098] 4,4'-Diaminodiphenyl ether and 2,5-furandicarboxaldehyde were separately dispersed in tetrahydrofuran to prepare 200 mg / mL solutions. The mixture was then mixed at room temperature. Once both monomers were completely dissolved, the mixture was heated to 60°C and stirred for 24 hours. After the reaction, the hot solution was poured into a 5×5×3 cm glass mold. The mold was then placed on a 30°C hot plate to slowly evaporate the solvent. After 20 hours, the solvent evaporated completely, resulting in a plastic film.

[0099] The tensile strength of the obtained plastic film was tested using a universal material testing machine. The test showed that the tensile strength of the obtained plastic film was 44.8 MPa, which is a high tensile strength plastic.

[0100] The obtained film plastic was immersed in water and organic solvents (ethanol, tetrahydrofuran, dimethyl sulfoxide) to test its water resistance and solvent resistance. The test showed that the obtained plastic film had good tolerance in water and different organic solvents, and would not dissolve or depolymerize after immersion for 60 hours. The test pictures of water resistance and solvent resistance are as follows: Figure 4 shown.

[0101] The recycling method of high-strength solvent-resistant closed-loop recyclable plastics adopts the following steps:

[0102] The plastic film prepared in Example 4 was placed in a mixed solvent of acetonitrile and concentrated hydrochloric acid in a volume ratio of 5:1. The plastic depolymerized and dissolved. Subsequently, an excess of diethyl ether was added to the solution, producing a large amount of precipitate. The precipitate was collected and dried to obtain high-purity 2,5-furandicarboxaldehyde. The solution was collected and dried to obtain high-purity 4,4'-diaminodiphenyl ether.

[0103] The recycled monomers can be used to prepare the initial high-strength, solvent-resistant, closed-loop recyclable plastic again, and the mechanical properties of the plastic remain almost unchanged during the five recycling processes, thus realizing multiple closed-loop recycling of the plastic.

[0104] Example 5

[0105] A high-strength, solvent-resistant, closed-loop recyclable plastic. Calculated by mole fraction, the amounts of each raw material are as follows:

[0106] 4,4'-Diaminodiphenyl sulfone (bisamino functionalized aromatic ring molecule), 50%; 5-hydroxy-1,3-phthalaldehyde (bisaldehyde functionalized aromatic ring molecule), 50%.

[0107] The preparation method is as follows:

[0108] 4,4'-Diaminodiphenyl sulfone and 5-hydroxy-1,3-phthalaldehyde were dispersed in acetonitrile to prepare 160 mg / mL solutions, respectively. The mixture was then mixed at room temperature. Once both monomers were completely dissolved, the temperature was raised to 80°C and stirred for 24 hours. After the reaction, the hot solution was poured into a 5×5×3 cm glass mold. The mold was then placed on a 40°C hot plate to slowly evaporate the solvent. After 45 hours, the solvent evaporated completely, resulting in a plastic film.

[0109] The tensile strength of the obtained plastic film was tested using a universal material testing machine. The test showed that the tensile strength of the obtained plastic film was 57.1 MPa, which is a high tensile strength plastic.

[0110] The film was immersed in water and organic solvents (ethanol, tetrahydrofuran, and dimethyl sulfoxide) to test its water and solvent resistance. The test showed that the resulting plastic film had good resistance to water and different organic solvents, and did not dissolve or depolymerize after immersion for 60 hours.

[0111] The recycling method of high-strength solvent-resistant closed-loop recyclable plastics adopts the following steps:

[0112] The plastic film prepared in Example 5 was placed in a mixed solvent of acetone and phosphoric acid in a volume ratio of 5:1. The plastic depolymerized and dissolved. An excess of petroleum ether was then added to the solution, producing a large amount of precipitate. The precipitate was collected and dried to obtain high-purity 5-hydroxy-1,3-phthalaldehyde. The solution was collected and dried to obtain high-purity 4,4'-diaminodiphenyl sulfone.

[0113] The recycled monomers can be used to prepare the original high-strength solvent-resistant closed-loop recycled plastic again, and the mechanical properties of the plastic remain almost unchanged during the five recycling processes, thus achieving multiple closed-loop recycling of the plastic. The stress-strain curve of the plastic after multiple closed-loop recycling is shown in Figure 2. Figure 5 shown.

[0114] The original tensile strength of the high-strength solvent-resistant closed-loop recyclable plastics obtained in Examples 1 to 4 and the tensile strength of the plastics after multiple closed-loop recycling are shown in Table 1.

[0115] Table 1 Tensile strength of high-strength solvent-resistant closed-loop recyclable plastics (unit: MPa)

[0116] Example 1 Example 2 Example 3 Example 4 Example 5 Original tensile strength 60.5 58.2 72.3 44.8 57.1 First closed-loop recycling tensile strength 60.2 58.7 71.9 44.7 57.2 Second closed-loop recycling tensile strength 60.6 59.1 73.0 44.1 57.9 The third closed-loop recycling tensile strength 60.0 57.6 72.2 45.0 58.0 The fourth closed-loop recycling tensile strength 61.1 57.9 72.7 44.9 57.3 The fifth closed-loop recycling tensile strength 60.2 59.0 72.3 44.6 57.7

[0117] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recycling high-strength solvent-resistant closed-loop recyclable plastics, comprising the following steps: The high-strength solvent-resistant closed-loop recyclable plastic is mixed with the first solvent to perform a depolymerization reaction to obtain a plastic dissolving liquid; The plastic dissolving liquid is mixed with a second solvent, and solid-liquid separation is performed after solid is precipitated, wherein the obtained solid is a dialdehyde functionalized aromatic ring monomer, and the obtained liquid is a diamino functionalized aromatic ring monomer; The high-strength solvent-resistant closed-loop recyclable plastic is prepared from raw materials including the following molar percentages: Diamino functionalized aromatic monomer 45-65%; 35-55% of dialdehyde functionalized aromatic ring monomer; The first solvent is a mixture of an organic solvent and an acid; the volume ratio of the organic solvent to the acid is 3 to 8:1; The second solvent is a poor solvent for the dialdehyde functionalized aromatic ring monomer; The volume ratio of the first solvent to the second solvent is 1:2.5-15.

2. The recycling method according to claim 1, characterized in that: The organic solvent in the first solvent includes one or more of tetrahydrofuran, acetonitrile, dimethyl sulfoxide, N,N-dimethylacetamide, isopropanol and acetone; The acid in the first solvent is one or more of concentrated hydrochloric acid, glacial acetic acid and phosphoric acid.

3. The recycling method according to claim 1, characterized in that: The poor solvent for the dialdehyde functionalized aromatic ring monomer is one or more of diethyl ether, ethyl acetate, ethanol, petroleum ether, n-hexane and 1,4-dioxane.

4. The recycling method according to claim 1, characterized in that: The bisamino functionalized aromatic ring monomer is one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-diaminobenzophenone and 4,4'-diaminodiphenyl sulfone.

5. The recycling method according to claim 1, characterized in that: The bisaldehyde functionalized aromatic ring monomer is one or more of phthalaldehyde, 2,5-furandicarboxaldehyde, 2,6-pyridinedicarboxaldehyde, 4,4'-bis((4-formyl)-benzamido-3-aminophenoxy)benzophenone, dehydrovanillin and 5-hydroxy-1,3-phthalaldehyde.

6. The recycling method according to claim 1, characterized in that: The method for preparing the high-strength solvent-resistant closed-loop recyclable plastic comprises the following steps: A diamino-functionalized aromatic ring monomer, a dialdehyde-functionalized aromatic ring monomer and a polar organic solvent are mixed, and a Schiff base reaction is carried out. After removing the polar organic solvent, a high-strength solvent-resistant closed-loop recyclable plastic is obtained.

7. The recycling method according to claim 6, characterized in that: The polar organic solvent is one or more of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone and N,N-dimethylacetamide.

8. The recycling method according to claim 6 or 7, characterized in that: The temperature of the Schiff base reaction is 65-200° C., and the time is 12-30 hours.

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