Method for chemically recovering lactam polyamide through one-pot method and application of lactam polyamide

Abstract

The invention relates to a method for chemically recovering lactam polyamide by a one-pot method and application thereof. The method comprises the following steps: feeding lactam polyamide, binary acid, diamine or dihydric alcohol; then carrying out a depolymerization reaction in an inert atmosphere at the reaction temperature of 100-250 DEG C for 0.5-12 h; and finally, carrying out polymerization reaction under a vacuum condition at the reaction temperature of 150-280 DEG C for 0.5-12 hours. According to the method, lactam polyamide is directly and chemically recovered to regenerated polyamide or regenerated polyesteramide based on a one-pot method, so that the step of chemically recovering lactam polyamide to a monomer or a prepolymer in the prior art is omitted, and the monomer purification cost is reduced; meanwhile, a part of cyclic lactam can be formed and separated in the reaction process, the cyclic lactam can be reused for synthesizing lactam polyamide, a regenerated product polyamide or polyesteramide is finally generated, the mechanical property of the regenerated product is equivalent to that of lactam polyamide, and particularly, the regenerated polyesteramide has the biodegradability in soil due to the introduction of ester bonds.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic recycling, and particularly relates to a one-pot chemical recycling method for lactam polyamide and application thereof. Background Art

[0002] As plastic production continues to increase, these materials are widely used in various products and fields to meet growing demand. Currently, global plastic production has reached 400 million tons. However, most plastics are discarded after a single use, wasting precious carbon resources and posing a serious and irreversible threat to the environment. Global production of polyamide plastics alone has reached 8 million tons. Polyamide products possess excellent mechanical strength, thermal stability, wear resistance, and corrosion resistance. However, these excellent properties confer long-term stability, but also limit their potential for biodegradation under natural conditions. The indiscriminate landfilling or incineration of large amounts of discarded polyamide will harm the ecological environment and is inconsistent with the concepts of "sustainable economy" and "green chemistry."

[0003] Driven by the development strategy of the "circular plastic economy", people have developed methods for recycling waste polyamide, which can be divided into energy recovery, mechanical recovery, and chemical recovery. Energy recovery is to destroy the chemical bonds between molecules of polyamide plastic waste through incineration, recover the energy released, and use it for power generation and heat generation. Although this recycling method has a low technical threshold and simple operation, it has the lowest utilization rate and produces toxic and harmful gases, which increase the cost of post-processing. Mechanical recycling is to directly use waste polyamide for molding and reprocessing after sorting, cleaning, crushing, melting, and granulation. However, during the processing, polyamide will undergo side reactions such as degradation or oxidation, resulting in a decrease in molecular weight and deterioration of material properties. It can only be converted into "equal value or low value" products. It is a "downgraded recycling" method, and the number of mechanical recycling is limited.

[0004] Chemical recycling is the recycling method with the greatest potential to solve the problem of plastic waste accumulation and achieve its reuse. It depolymerizes waste polyamide into oligomers or monomers, and then repeatedly polymerizes them into recycled products for use. Chemical recycling can achieve closed-loop recycling of waste polyamide and is a cyclic and sustainable recycling model. According to the chemical depolymerization pathway, it is divided into hydrolysis, aminolysis, alcoholysis, hydrogenolysis and ionic liquid depolymerization. At present, the chemical recycling of waste polyamide is a "polymer-monomer (prepolymer)-polymer" recycling model, but these recycling conditions are harsh (such as strong acid, strong alkali, high pressure, etc.), the monomer purification is cumbersome, and the cycle from waste polyamide to recycled products is long. These factors lead to high chemical recycling costs, and recycled products have no competitive advantage over original products. Summary of the Invention

[0005] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a one-pot chemical recovery method for lactam polyamides and its application that meet one or more of the above-mentioned needs.

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

[0007] The one-pot chemical recovery method of lactam polyamide comprises: feeding lactam polyamide, dibasic acid, diamine or diol; then carrying out a depolymerization reaction under an inert atmosphere at a reaction temperature of 100 to 250° C. and a reaction time of 0.5 to 12 hours; and finally carrying out a polymerization reaction under vacuum conditions at a reaction temperature of 150 to 280° C. and a reaction time of 0.5 to 12 hours.

[0008] As a preferred embodiment, the molar ratio of the lactam polyamide, dicarboxylic acid, diamine or diol is 1:(0.1-3):(0.1-3).

[0009] As a preferred embodiment, the reaction formula of the lactam polyamide, dibasic acid and diamine is:

[0010]

[0011] wherein R1 is an alkane having 3 to 13 carbon atoms;

[0012] R2 is an aliphatic hydrocarbon having 3 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000;

[0013] R3 is an aliphatic hydrocarbon or aromatic hydrocarbon having 2 to 36 carbon atoms.

[0014] As a preferred embodiment, the reaction of the lactam polyamide, dibasic acid and diol is carried out under the condition of a catalyst, and the reaction formula is:

[0015]

[0016] wherein R1 is an alkane having 3 to 13 carbon atoms;

[0017] R2 is an aliphatic hydrocarbon having 3 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000;

[0018] R4 is an aliphatic hydrocarbon having 2 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000.

[0019] As a preferred embodiment, the catalyst is antimony trioxide, antimony acetate, antimony glycolate, zinc acetate, stannous chloride, stannous octoate or p-toluenesulfonic acid;

[0020] The amount of the catalyst used is 0.01 to 5 wt% of the total mass of the dibasic acid and the diol.

[0021] As a preferred embodiment, the lactam polyamide is one or more of polypropiolactam, polybutyrolactam, polyvalerolactam, polycaprolactam, polyheptylamide, polyoctylamide, polynonylamide, polydecanoylamide, polyundecanolactam, polylaurylamide, and polytridecanamide.

[0022] As a preferred embodiment, the dibasic acid includes malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, methylmalonic acid, 2-butyl suberic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyladipic acid, maleic acid, fumaric acid, itaconic acid, isopropylmalonic acid, 2,3-dibromosuccinic acid, para- One or more of phthalic acid, isophthalic acid, orthophthalic acid, 5-methylisophthalic acid, phenylsuccinic acid, benzylmonic acid, furandicarboxylic acid, pyridinedicarboxylic acid, cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, dimer acid, hydrogenated dimer acid, hydrogenated dimer oleic acid, dimer linoleic acid, dimer linolenic acid, dimer myristic acid, polyethylene glycol terminated with carboxyl groups at both ends, polypropylene glycol terminated with carboxyl groups at both ends, and polytetrahydrofuran terminated with carboxyl groups at both ends.

[0023] As a preferred embodiment, the diamine is one or more of ethylenediamine, propylenediamine, butylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octanediamine, nonanediamine, dodecanediamine, 1,2-pentamethylenediamine, 1,2-propylenediamine, 1,4-pentamethylenediamine, 1,3-pentanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluenediamine, naphthalene-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, and dimeramine.

[0024] As a preferred embodiment, the diol includes one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, octanediol, undecanediol, dodecanediol, tetradecanediol, phthalic acid methanol, isophthalic acid methanol, o-phthalic acid methanol, furan dimethanol, furan dimethanol, pyridine dimethanol, cyclohexanedimethanol, catechol, resorcinol, hydroquinone, 1,3-adamantanediol, phenyl glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran.

[0025] The present invention also provides a one-pot chemical recovery method for lactam polyamide as described in any of the above schemes to synthesize regenerated polyamide or regenerated polyester amide.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention discloses a method for directly chemically recycling lactam polyamide into regenerated polyamide or regenerated polyesteramide in a one-pot process based on a melt polycondensation process. This method adopts a "polymer-polymer" recovery mode, which saves the traditional chemical recovery step to monomer or prepolymer and reduces the cost of monomer purification. At the same time, a portion of cyclic lactam is separated during the reaction process and can be reused to synthesize lactam polyamide. The dibasic acid acts as a depolymerizing agent, and the carboxylic acid of the dibasic acid dissociates to release protons H + , combined with the carbonyl oxygen of the amide, it enhances the positive charge of the carbonyl carbon, promotes the nucleophilic attack reaction of the carboxyl, hydroxyl and amine groups with the carbonyl carbon, and depolymerizes into a low molecular weight prepolymer; in addition, the by-product water generated by the esterification reaction of the diol and the dibasic acid or the amidation reaction of the diamine and the dibasic acid can participate in the hydrolysis reaction of the lactam polyamide to generate a terminal carboxyl oligomer, and then the terminal carboxyl oligomer reacts with the amino / hydroxyl group; the introduction of inert gas and the formation of a vacuum negative pressure environment are to remove the by-product water and a small amount of cyclic lactam, promote the forward progress of the polymerization reaction, and finally generate a regenerated polyamide or polyester amide.

[0028] The mechanical properties of the recycled product of the present invention are comparable to those of lactam polyamides, and in particular, the recycled polyester amide has the ability to biodegrade in soil due to the introduction of ester bonds; experimental results show that the molecular weights of the recycled polyamide and recycled polyester amide can reach 30 kDa and 27 kDa, respectively, the decomposition temperatures can reach 385°C and 388°C, respectively, the tensile strengths can reach 26 MPa and 33 MPa, respectively, and the tensile strengths can reach 676% and 886%, respectively, and they have excellent thermal stability and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Graphs showing the tensile strength of the recycled products obtained in Example 1, Comparative Example 1, Example 9, and Comparative Example 2 of the present invention;

[0030] Figure 2 The TGA graphs of the regenerated products obtained in Examples 1 and 9 of the present invention are as follows;

[0031] Figure 3 This is a graph showing the molecular weight change of the regenerated polyester amide obtained in Example 9 of the present invention after composting. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further explained below through specific embodiments.

[0033] The one-pot chemical recovery method of lactam polyamide of the present invention utilizes depolymerization reaction and polymerization reaction of lactam polyamide, dicarboxylic acid and diamine / diol to obtain a regenerated product; wherein the depolymerization reaction of lactam polyamide is carried out in an inert atmosphere and the polymerization reaction is carried out under vacuum conditions, and the reaction formula is as follows:

[0034]

[0035] wherein R1 is an alkane having 3 to 13 carbon atoms;

[0036] R2 is an aliphatic hydrocarbon having 3 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000;

[0037] R3 is an aliphatic hydrocarbon or aromatic hydrocarbon having 2 to 36 carbon atoms;

[0038] R4 is an aliphatic hydrocarbon having 2 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000.

[0039] Specifically, the above-mentioned lactam polyamide is preferably recycled waste lactam polyamide, which is used to recycle and reuse the waste lactam polyamide.

[0040] The lactam polyamide preferably includes one or more of polypropiolactam, polybutyrolactam, polyvalerolactam, polycaprolactam, polyheptamide, polyoctamide, polynonanamide, polydecanoic acid, polyundecanolactam, polydodecanoic acid, and polytridecanamide, and more preferably one or more of polybutyrolactam, polyvalerolactam, polycaprolactam, polyheptamide, and polyoctamide. The present invention limits the type of lactam polyamide to the above range so that recycled products can be produced.

[0041] The above-mentioned dicarboxylic acids preferably include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, methylmalonic acid, 2-butyl suberic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyladipic acid, maleic acid, fumaric acid, itaconic acid, isopropylmalonic acid, 2,3-dibromosuccinic acid, terephthalic acid, isophthalic acid, phthalic acid, 5-methylisophthalic acid, One or more of phenylsuccinic acid, benzylmonic acid, furandicarboxylic acid, pyridinedicarboxylic acid, cyclohexanedicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, dimer acid, hydrogenated dimer acid, hydrogenated dimer oleic acid, dimer linoleic acid, dimer linolenic acid, dimer myristic acid, polyethylene glycol terminated with carboxyl groups at both ends, polypropylene glycol terminated with carboxyl groups at both ends, and polytetrahydrofuran terminated with carboxyl groups at both ends, and more preferably one or more of tetradecanedioic acid, hexadecanedioic acid, terephthalic acid, furandicarboxylic acid, hydrogenated dimer acid, and hydrogenated dimer oleic acid. The present invention limits the types of dibasic acids to those within the above ranges in order to produce recycled products.

[0042] The above-mentioned diamines preferably include one or more of ethylenediamine, propylenediamine, butylenediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, octanediamine, dodecanediamine, 1,2-pentanediamine, 1,2-propylenediamine, 1,4-pentanediamine, 1,3-pentanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluenediamine, naphthalene-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, and dimeramines, and more preferably one or more of hexanediamine, octanediamine, octanediamine, dodecanediamine, dodecanediamine, 1,2-pentanediamine, 1,2-propylenediamine, 1,4-pentanediamine, 1,3-pentanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluenediamine, naphthalene-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, and dimeramines. The present invention limits the types of diamines to those within the above ranges so that the recycled product can be prepared.

[0043] The above-mentioned diols preferably include one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, terephthalic acid glycol, undecanediol, dodecanediol, tetradecanediol, terephthalic acid methanol, m-terephthalic acid methanol, o-terephthalic acid methanol, furan dimethanol, furan dimethanol, pyridine dimethanol, cyclohexanedimethanol, catechol, resorcinol, hydroquinone, 1,3-adamantanediol, phenyl glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran, and more preferably one or more of butanediol, dodecanediol, tetradecanediol, terephthalic acid methanol, cyclohexanedimethanol, and polyethylene glycol. The present invention limits the type of diol to the above range so that the recycled product can be prepared.

[0044] The catalyst preferably includes one or more of antimony trioxide, antimony acetate, antimony glycolate, zinc acetate, stannous chloride, stannous octoate, and p-toluenesulfonic acid, and more preferably one or more of antimony trioxide, stannous chloride, and p-toluenesulfonic acid. The present invention limits the type of catalyst to within the above range to allow the production of a regenerated product. The amount of catalyst added is preferably 0.01 to 5 wt% of the total mass of the dibasic acid and diol, and more preferably 0.1 to 2 wt%. Limiting the catalyst content within the above range ensures smooth and rapid reaction.

[0045] The molar ratio of the lactam polyamide, dibasic acid, and diamine / diol is preferably 1:(0.1-3):(0.1-3), more preferably 1:1:1. In the present invention, limiting the molar ratio of the lactam polyamide, dibasic acid, and diamine / diol to the above range can ensure that the regenerated product has good performance.

[0046] The depolymerization reaction is carried out in an inert atmosphere, preferably argon. The present invention does not specify the flow rate of the argon gas; a flow rate commonly used by those skilled in the art can be used. The depolymerization reaction temperature is preferably 100-250°C, more preferably 150-220°C; and the depolymerization reaction time is preferably 0.5-12 hours, more preferably 5-8 hours. Limiting the depolymerization reaction temperature and time to these ranges ensures that the dibasic acid fully decomposes the waste lactam polyamide into low-molecular-weight prepolymers.

[0047] In addition, the depolymerization reaction is preferably carried out under stirring conditions, and the stirring speed is preferably >100 rpm, more preferably 150 to 500 rpm. In the present invention, stirring can promote the reaction.

[0048] The above-mentioned polymerization reaction is carried out under vacuum conditions, and the vacuum degree of the vacuum conditions is preferably <150Pa, more preferably <30Pa. The introduction of argon gas and the formation of a vacuum negative pressure environment in the present invention can separate the by-products water and cyclic lactam produced in the reaction from the polymerization system, thereby promoting the forward progress of the polymerization reaction. Among them, the polymerization reaction temperature under vacuum conditions is preferably 150-280°C, more preferably 200-260°C; the polymerization reaction time under vacuum conditions is preferably 0.5-12h, more preferably 0.5-8h. The present invention limits the polymerization reaction temperature and time to the above ranges to ensure that the reaction is fully carried out, thereby obtaining a regenerated product with a higher molecular weight and better performance.

[0049] In addition, the polymerization reaction is preferably carried out under stirring conditions; the stirring speed is preferably >100 rpm, more preferably 150-500 rpm. The present invention can promote the progress of the repolymerization reaction by stirring.

[0050] The recycled product chemically recovered from waste lactam polyamides synthesized based on the one-pot chemical recovery method of lactam polyamides has good mechanical properties, and the polyesteramide has biodegradability.

[0051] Example 1:

[0052] The one-pot method of this embodiment is used to prepare recycled polyamide from polycaprolactam (waste polycaprolactam), tetradecanedioic acid and hexamethylenediamine. The specific steps are as follows:

[0053] 10 g of polycaprolactam (i.e., recycled waste polycaprolactam PA6), 22.8 g of tetradecanedioic acid, and 10.3 g of hexamethylenediamine were put into a 250 mL three-necked flask. First, argon was passed through, and the mixture was gradually heated to 220° C. under stirring at 200 rpm for reaction for 5 h; then, under vacuum conditions (pressure less than 100 Pa), the polymerization reaction was carried out at 250° C. under stirring at 200 rpm for 5 h to obtain regenerated polyamide.

[0054] The recycled polyamide obtained in this example has a viscosity-average molecular weight of 30 kDa, a tensile strength of 26 MPa, a tensile strength of 676%, and a cyclic caprolactam recovery rate of 8%. A lower recovery rate indicates that the polycaprolactam is decomposed into a smaller proportion of caprolactam monomer, with most of the waste polycaprolactam directly reacting to form recycled polymer.

[0055] Comparative Example 1:

[0056] The two-step method of this comparative example is used to prepare recycled polyamide from polycaprolactam (waste polycaprolactam), tetradecanedioic acid and hexamethylenediamine. The difference from Example 1 is that the two-step method is used. The raw materials, amounts and process conditions are the same. The specific steps are as follows:

[0057] 10 g of polycaprolactam (waste polycaprolactam) and 22.8 g of tetradecanedioic acid were first put into a 250 mL three-necked flask, and argon was first introduced. The mixture was gradually heated to 220° C. with stirring at 200 rpm for 5 h to depolymerize the polycaprolactam. Then, 10.3 g of hexamethylenediamine was added, and the mixture was stirred at 200 rpm under vacuum conditions (pressure less than 100 Pa) and polymerized at 250° C. for 5 h to obtain regenerated polyamide.

[0058] The viscosity-average molecular weight of the recycled polyamide obtained in this comparative example is 15 kDa, the tensile strength is 10.5 MPa, the tensile strength is 92%, and the recovery rate of cyclic caprolactam is 60%.

[0059] Example 2:

[0060] The difference between this embodiment and embodiment 1 is that polycaprolactam (recycled polycaprolactam) is replaced by polyvalerolactam (recycled waste polyvalerolactam), polyvalerolactam 10g, tetradecanedioic acid 26g, hexamethylenediamine 11.7g, and the mass ratio of polyvalerolactam, tetradecanedioic acid, and hexamethylenediamine is 1:2.6:1.17;

[0061] Other steps are the same as in Example 1.

[0062] The viscosity-average molecular weight of the recycled polyamide obtained in this embodiment is 25 kDa, the tensile strength is 26 MPa, and the tensile strength is 676%.

[0063] Example 3:

[0064] The only difference between this embodiment and embodiment 1 is that polycaprolactam (recycled polycaprolactam) is replaced by polybutyrolactam (recycled waste polybutyrolactam), 10 g of polybutyrolactam, 30.4 g of tetradecanedioic acid, and 13.7 g of hexamethylenediamine, and the mass ratio of polybutyrolactam, tetradecanedioic acid, and hexamethylenediamine is 1:3.04:1.37;

[0065] Other details are the same as in Example 1.

[0066] The viscosity-average molecular weight of the recycled polyamide obtained in this example is 25 kDa.

[0067] Example 4:

[0068] The only difference between this embodiment and embodiment 1 is that tetradecanedioic acid is replaced by terephthalic acid, polycaprolactam 10g, terephthalic acid 14.6g, hexamethylenediamine 10.3g, and the mass ratio of polycaprolactam, terephthalic acid, and hexamethylenediamine is 1:1.46:1.03;

[0069] Other details are the same as in Example 1.

[0070] The viscosity-average molecular weight of the recycled polyamide obtained in this example is 31 kDa.

[0071] Example 6:

[0072] The only difference between this embodiment and embodiment 1 is that tetradecanedioic acid is replaced by hydrogenated dimer acid, 10 g of polycaprolactam, 49.8 g of hydrogenated dimer acid, and 10.3 g of hexamethylenediamine. The mass ratio of polycaprolactam, hydrogenated dimer acid, and hexamethylenediamine is 1:4.98:1.03.

[0073] Other details are the same as in Example 1.

[0074] The viscosity-average molecular weight of the recycled polyamide obtained in this example is 19 kDa.

[0075] Example 7:

[0076] The only difference between this embodiment and embodiment 1 is that hexamethylenediamine is replaced by diamine, polycaprolactam 10g, tetradecanedioic acid 22.8g, diamine 15.2g, and the mass ratio of polycaprolactam, tetradecanedioic acid, and diamine is 1:2.28:1.52;

[0077] Other details are the same as in Example 1.

[0078] The viscosity-average molecular weight of the recycled polyamide obtained in this example is 25 kDa.

[0079] Example 8:

[0080] The only difference between this embodiment and embodiment 1 is that hexamethylenediamine is replaced by p-phenylenediamine, polycaprolactam 10g, tetradecanedioic acid 22.8g, p-phenylenediamine 9.6g, and the mass ratio of polycaprolactam, tetradecanedioic acid, and p-phenylenediamine is 1:2.28:0.96;

[0081] Other details are the same as in Example 1.

[0082] The viscosity-average molecular weight of the recycled polyamide obtained in this example is 28 kDa.

[0083] Example 9:

[0084] The one-pot method of this embodiment is used to prepare recycled polyester amide, which is prepared from polycaprolactam (waste polycaprolactam), tetradecanedioic acid, butanediol and antimony trioxide. The specific steps are as follows:

[0085] 10 g of polycaprolactam (recycled waste polycaprolactam PA6), 22.8 g of tetradecanedioic acid, 8.0 g of butanediol, and 0.0924 g of antimony trioxide were placed in a 250 mL three-necked flask. The mixture was first passed through argon and gradually heated to 220° C. with stirring at 200 rpm for reaction for 5 h. Then, the mixture was polymerized at 250° C. with stirring at 200 rpm under vacuum conditions (pressure less than 100 Pa) for 5 h to obtain regenerated polyester amide.

[0086] The mass ratio of polycaprolactam, tetradecanedioic acid and butanediol is 1:2.28:0.8, and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and butanediol.

[0087] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 27 kDa.

[0088] Comparative Example 2:

[0089] The two-step regenerated polyester amide in this comparative example is prepared from polycaprolactam (waste polycaprolactam), tetradecanedioic acid, butanediol and antimony trioxide. The difference between this comparative example and Example 9 is that the two-step method is adopted. The raw materials, amounts and process conditions are the same. The specific steps are as follows:

[0090] 10g of polycaprolactam (waste polycaprolactam) and 22.8g of tetradecanedioic acid were first placed in a 250mL three-necked flask, first purged with argon, and gradually heated to 220°C with stirring at 200rpm for 5 hours to depolymerize the polycaprolactam. 8.0g of butanediol and 0.0924g of antimony trioxide were then added, and polymerization was carried out at 250°C for 5 hours with stirring at 200rpm under vacuum conditions (pressure less than 100Pa) to obtain regenerated polyesteramide.

[0091] The mass ratio of polycaprolactam, tetradecanedioic acid and butanediol is 1:2.28:0.8, and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and butanediol.

[0092] The viscosity-average molecular weight of the regenerated polyester amide obtained in this comparative example is 18 kDa, the tensile strength is 12 MPa, the tensile strength is 108%, and the recovery rate of cyclic caprolactam is 40%.

[0093] By comparing the above-mentioned Example 1 with Comparative Example 1 and Example 9 with Comparative Example 2, it is found that the viscosity-average molecular weight, tensile strength and tensile strength of the recycled polyamide prepared by the two-step method are lower than those of the recycled product prepared by the one-pot method. The reason is that after the diprotic acid depolymerizes the polycaprolactam into low molecular weight oligomers, the diamine / diol is added, and the acid and amine amidation reaction or the acid and ester esterification reaction generates byproduct water, which further depolymerizes the low molecular weight oligomers into caprolactam at high temperature, increasing the proportion of caprolactam in the reaction system. Excess caprolactam will remain in the recycled polyamide, hindering the forward progress of the polymerization reaction. Moreover, the excess caprolactam cannot be completely removed, ultimately affecting the viscosity-average molecular weight, tensile strength and tensile strength of the recycled product. In contrast, when the one-pot method is used to recycle polycaprolactam, the molecular weight of the polycaprolactam is higher in the initial stage of the reaction, and the byproduct water is weak in its ability to depolymerize it into caprolactam. The proportion of depolymerized caprolactam is small, so the impact on the reaction process and the performance of the recycled product is relatively small. In addition, the one-pot method has a higher utilization rate for directly recycling waste polycaprolactam into recycled products.

[0094] Example 10:

[0095] The only difference between this example and Example 9 is that polycaprolactam (recycled polycaprolactam) is replaced by polyvalerolactam (recycled waste polyvalerolactam), with 10 g of polyvalerolactam, 26 g of tetradecanedioic acid, and 9.1 g of butanediol. The mass ratio of polyvalerolactam, tetradecanedioic acid, and butanediol is 1:2.6:0.91, and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and butanediol.

[0096] Other details are the same as in Example 9.

[0097] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 28 kDa.

[0098] Example 11:

[0099] The only difference between this embodiment and embodiment 9 is that polycaprolactam (recycled polycaprolactam) is replaced by polybutyrolactam (recycled waste polybutyrolactam), 10 g of polybutyrolactam, 30.4 g of tetradecanedioic acid, and 10.6 g of butanediol, with a mass ratio of polybutyrolactam, tetradecanedioic acid, and butanediol of 1:3.04:1.06; and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and butanediol.

[0100] Other details are the same as in Example 9.

[0101] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 25 kDa.

[0102] Example 12:

[0103] The only difference between this example and example 9 is that tetradecanedioic acid is replaced with terephthalic acid, 10 g of polycaprolactam, 14.6 g of terephthalic acid, and 8.0 g of butanediol are used; the mass ratio of polycaprolactam, terephthalic acid, and butanediol is 1:1.46:0.8; and the amount of antimony trioxide used is 0.3% of the total mass of terephthalic acid and butanediol.

[0104] Other details are the same as in Example 9.

[0105] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 28 kDa.

[0106] Example 13:

[0107] The only difference between this example and example 9 is that tetradecanedioic acid is replaced with hydrogenated dimer acid, 10 g of polycaprolactam, 49.8 g of hydrogenated dimer acid, and 8.0 g of butanediol are used. The mass ratio of polycaprolactam, hydrogenated dimer acid, and butanediol is 1:4.98:0.8, and the amount of antimony trioxide used is 0.3% of the total mass of hydrogenated dimer acid and butanediol.

[0108] Other details are the same as in Example 9.

[0109] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 16 kDa.

[0110] Example 14:

[0111] The only difference between this embodiment and embodiment 9 is that butanediol is replaced by dodecanediol, the polycaprolactam is 10 g, the tetradecanedioic acid is 22.8 g, and the dodecanediol is 17.9 g. The mass ratio of polycaprolactam, tetradecanedioic acid, and dodecanediol is 1:2.28:1.79, and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and dodecanediol.

[0112] Other details are the same as in Example 9.

[0113] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 24 kDa.

[0114] Example 15:

[0115] The only difference between this embodiment and embodiment 9 is that butanediol is replaced by terephthalic acid, polycaprolactam 10g, tetradecanedioic acid 22.8g, terephthalic acid 12.2g, the mass ratio of polycaprolactam, tetradecanedioic acid, and terephthalic acid is 1:2.28:1.22, and the amount of antimony trioxide used is 0.3% of the total mass of tetradecanedioic acid and terephthalic acid;

[0116] Other details are the same as in Example 9.

[0117] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 28 kDa.

[0118] Example 16:

[0119] The only difference between this embodiment and embodiment 9 is that antimony trioxide is replaced by zinc acetate;

[0120] Other details are the same as in Example 9.

[0121] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 22 kDa.

[0122] Example 17:

[0123] The only difference between this example and Example 9 is that antimony trioxide is replaced by p-toluenesulfonic acid;

[0124] Other details are the same as in Example 9.

[0125] The viscosity-average molecular weight of the regenerated polyester amide obtained in this example is 22 kDa.

[0126] The mechanical properties of the recycled polyamide and recycled polyester amide obtained in Example 1, Comparative Example 1, Example 9 and Comparative Example 2 were tested using a universal testing machine. The tensile curves obtained from the test are shown in FIG. Figure 1 As shown, the tensile strength of recycled polyamide and recycled polyester amide can reach 26MPa and 33MPa respectively, and the tensile strength can reach 676% and 886% respectively.

[0127] The thermal stability of the recycled polyamide and recycled polyester amide obtained in Example 1 and Example 9 was tested using a thermogravimetric analyzer (TGA). Figure 2 As shown in the figure, the decomposition temperatures of recycled polyamide and recycled polyester amide can reach 385℃ and 388℃ respectively.

[0128] The degradation of polyester amide under simulated composting conditions was determined according to ISO 20200-2015 standards. The samples were processed into standard samples, landfilled in a simulated composting environment according to standard requirements, and tested at a constant temperature of 58±2°C. The changes in the molecular weight of the samples were measured at fixed intervals. From the above examples, it can be seen that the molecular weights of the recycled polyamide and recycled polyester amide generated by the reaction of waste lactam polyamide, dibasic acid and diamine / diol provided by the present invention can reach 30kDa and 27kDa, respectively, the decomposition temperature can reach 385°C and 388°C, respectively, the tensile strength can reach 26MPa and 33MPa, respectively, and the tensile strength can reach 676% and 886%, respectively, with excellent thermal stability and mechanical properties. In particular, recycled polyester amide, such as Figure 3 As shown in the figure, the viscosity-average molecular weight of the recycled polyester amide decreased by 61.8% after 5 weeks, and the introduction of ester bonds made it biodegradable.

[0129] Given the numerous embodiments of the present invention, the raw materials and amounts involved can be selected within a limited range according to actual needs. The experimental data for each embodiment is voluminous and it is not suitable to list and explain them one by one here. However, the content required for verification and the final conclusions obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be described one by one here.

[0130] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, based on the ideas provided by the present invention, there may be changes in the specific implementation methods, and these changes should also be considered as the scope of protection of the present invention.

Claims

1. A one-pot chemical recovery method for lactam polyamides, characterized in that: include: The process comprises the following steps: feeding lactam polyamide, dibasic acid, diamine or diol; then carrying out a depolymerization reaction under an inert atmosphere at a reaction temperature of 100 to 250° C. and a reaction time of 0.5 to 12 hours; and finally carrying out a polymerization reaction under vacuum at a reaction temperature of 150 to 280° C. and a reaction time of 0.5 to 12 hours.

2. The one-pot chemical recovery method of lactam polyamide according to claim 1, characterized in that: The molar ratio of the lactam polyamide, dicarboxylic acid, diamine or diol is 1:(0.1-3):(0.1-3).

3. The one-pot chemical recovery method of lactam polyamide according to claim 1, characterized in that: The reaction formula of the lactam polyamide, dibasic acid and diamine is: Wherein, R1 is an alkane having 3 to 13 carbon atoms; R2 is an aliphatic hydrocarbon having 3 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000; R3 is an aliphatic hydrocarbon or an aromatic hydrocarbon having 2 to 36 carbon atoms.

4. The one-pot chemical recovery method of lactam polyamide according to claim 1, characterized in that: The reaction of the lactam polyamide, dibasic acid and diol is carried out under the condition of a catalyst, and the reaction formula is: Wherein, R1 is an alkane having 3 to 13 carbon atoms; R2 is an aliphatic hydrocarbon having 3 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000; R4 is an aliphatic hydrocarbon having 2 to 36 carbon atoms, an aromatic hydrocarbon, or an ether having a repeating unit of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- and an average molecular weight of 200 to 6000.

5. The one-pot chemical recovery method of lactam polyamide according to claim 4, characterized in that: The catalyst is one or more of antimony trioxide, antimony acetate, antimony glycol, zinc acetate, stannous chloride, stannous octoate, and p-toluenesulfonic acid; The amount of the catalyst used is 0.01-5wt% of the total mass of the dibasic acid and the diol.

6. The one-pot chemical recovery method of lactam polyamide according to any one of claims 1 to 5, characterized in that: The lactam polyamide is one or more of polypropiolactam, polybutyrolactam, polyvalerolactam, polycaprolactam, polyheptylamide, polyoctylamide, polynonylamide, polycaprolactam, polyundecanolactam, polydodecylamide, polytridecanamide.

7. The one-pot chemical recovery method of lactam polyamide according to any one of claims 1 to 5, characterized in that: The dibasic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, methylmalonic acid, 2-butyl suberic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methylhexanedioic acid, maleic acid, fumaric acid, itaconic acid, isopropylmalonic acid, 2,3-dibromosuccinic acid, terephthalic acid One or more of 1,2-dimethyl-2-nitropropene, 1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, dimeric acid, hydrogenated dimeric acid, hydrogenated dimeric oleic acid, dimeric linoleic acid, dimeric linolenic acid, dimeric myristic acid, polyethylene glycol terminated with carboxyl groups at both ends, polypropylene glycol terminated with carboxyl groups at both ends, and polytetrahydrofuran terminated with carboxyl groups at both ends.

8. The one-pot chemical recovery method of lactam polyamide according to any one of claims 1 to 5, characterized in that: The diamine is one or more of ethylenediamine, propylenediamine, butylenediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, dodecanediamine, 1,2-pentanediamine, 1,2-propylenediamine, 1,4-pentanediamine, 1,3-pentanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluenediamine, naphthalene-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, and dimeramine.

9. The one-pot chemical recovery method of lactam polyamide according to any one of claims 1 to 5, characterized in that: The diols include one or more of ethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, dodecanediol, tetradecanediol, terephthalylidene alcohol, isophthalylidene alcohol, o-phthalylidene alcohol, furan dimethanol, furan dimethanol, pyridine dimethanol, cyclohexanedimethanol, catechol, resorcinol, hydroquinone, 1,3-adamantanediol, phenyl glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran.

10. The one-pot chemical recovery method of lactam polyamide according to any one of claims 1 to 9 to synthesize regenerated polyamide or regenerated polyester amide.

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