One-pot chemical recovery method for lactam polyamides and its application

Abstract

This invention relates to a one-pot chemical recovery method for lactam polyamides and its application, comprising: feeding lactam polyamide, diacid, diamine, or diol; followed by a depolymerization reaction under an inert atmosphere at a temperature of 100–250°C for 0.5–12 h; and finally, a polymerization reaction under vacuum at a temperature of 150–280°C for 0.5–12 h. This invention is based on a one-pot method for directly chemically recovering lactam polyamides to recycled polyamide or recycled polyesteramide, saving the steps of traditional chemical recovery to monomers or prepolymers and reducing monomer purification costs. Simultaneously, the reaction process forms a portion of cyclic lactams that can be separated and reused to synthesize lactam polyamides, ultimately generating recycled polyamide or polyesteramide products. The mechanical properties of the recycled products are comparable to those of lactam polyamides, and the recycled polyesteramide, in particular, possesses biodegradability in soil due to the introduction of ester bonds.

Description

Technical Field

[0001] This invention belongs to the field of plastic recycling technology, specifically relating to a one-pot chemical recycling method for lactam polyamides and its application. Background Technology

[0002] With the continuous increase in plastic production, 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 valuable carbon resources and posing an irreversible and serious threat to the environment. Polyamide plastics alone account for 8 million tons of global production. Polyamide products possess excellent mechanical strength, thermal stability, wear resistance, and corrosion resistance. However, while these excellent properties grant them long-term stability, they also limit their biodegradability under natural conditions. The indiscriminate landfilling or incineration of large quantities 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 "circular plastics economy," methods for recycling waste polyamide have been developed, which can be divided into energy recovery, mechanical recovery, and chemical recovery. Energy recovery involves incinerating polyamide plastic waste to break the chemical bonds between molecules and recover the released energy for power generation and heating. Although this method has low technical barriers and is simple to operate, it has the lowest utilization rate and produces toxic and harmful gases, increasing the cost of post-processing. Mechanical recovery involves sorting, washing, crushing, melting, and granulating waste polyamide for direct molding and reprocessing. However, during processing, polyamide undergoes side reactions such as degradation or oxidation, leading to a decrease in molecular weight and a deterioration in material properties. It can only be converted into "equivalent or low-value" products, which is a "downgraded recycling" method, and the number of mechanical recycling cycles is limited.

[0004] Chemical recycling is the most promising method for solving plastic waste accumulation and achieving its reuse. It involves depolymerizing waste polyamide into oligomers or monomers, which are then repeatedly polymerized into recycled products for reuse. Chemical recycling enables closed-loop recycling of waste polyamide, representing a sustainable recycling model. Based on the chemical depolymerization pathway, it can be categorized into hydrolysis, ammonolysis, alcoholysis, hydrogenolysis, and ionic liquid depolymerization. Currently, the chemical recycling of waste polyamide follows a "polymer-monomer (prepolymer)-polymer" model. However, these recycling conditions are harsh (e.g., strong acids, strong alkalis, high pressure), monomer purification is cumbersome, and the cycle from waste polyamide to recycled products is long. These factors lead to high costs for chemical recycling, and recycled products lack a competitive advantage compared to virgin products. Summary of the Invention

[0005] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a one-pot chemical recovery method for lactam polyamides and its application that meets one or more of the aforementioned requirements.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A one-pot chemical recovery method for lactam polyamides includes: feeding lactam polyamide, diacid, diamine or diol into the feedstock; then carrying out a depolymerization reaction under an inert atmosphere at a temperature of 100–250°C for 0.5–12 h; and finally carrying out a polymerization reaction under vacuum at a temperature of 150–280°C for 0.5–12 h.

[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 for the lactam-type polyamide, diacid, and diamine is as follows:

[0010]

[0011] Among them, R1 is an alkane with 3 to 13 carbon atoms;

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

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

[0014] As a preferred embodiment, the reaction of the lactam-type polyamide, diacid, and diol is carried out under catalytic conditions, and the reaction formula is as follows:

[0015]

[0016] Among them, R1 is an alkane with 3 to 13 carbon atoms;

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

[0018] R4 is an ether consisting of aliphatic hydrocarbons, aromatic hydrocarbons, or repeating units of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- with 2 to 36 carbon atoms 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 catalyst used is 0.01 to 5 wt% of the total mass of the dicarboxylic acid and diol.

[0021] As a preferred embodiment, the lactam polyamide is one or more of the following: polypropyl lactam, polybutyrolactam, polyvalerolactam, polycaprolactam, polyheptamide, polyoctamide, polynonamide, polydecyl lactam, polyundecaprolactam, polydodecanamide, and polytridecylamide.

[0022] As a preferred embodiment, the dicarboxylic acid includes malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, methylmalonic acid, 2-butyloctanoic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyladacic acid, maleic acid, trans-butenedioic acid, itaconic acid, isopropylmalonic acid, 2,3-dibromosuccinic acid, and p-... One or more of the following: phthalic acid, isophthalic acid, phthalic acid, 5-methylisophthalic acid, phenyl succinic acid, benzyl malonic acid, furanyl dicarboxylic acid, pyridine dicarboxylic 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 with carboxyl groups at both ends, polypropylene glycol with carboxyl groups at both ends, and polytetrahydrofuran with carboxyl groups at both ends.

[0023] As a preferred embodiment, the diamine is one or more selected from ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, heptaethylenediamine, octanediamine, nonanediamine, decanediamine, dodecanediamine, 1,2-pentanediamine, 1,2-propanediamine, 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 dimelamine.

[0024] As a preferred embodiment, the diol includes one or more of the following: ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, dodecanediol, tetradecanediol, terephthalic acid, isophthalic acid, ophthalic acid, furanyl alcohol, furanyl alcohol, pyridinediethanol, cyclohexanediol, catechol, resorcinol, hydroquinone, 1,3-adamantanediol, phenylethylene glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran.

[0025] The present invention also provides a one-pot chemical recovery method for lactam polyamides as described in any of the preceding embodiments to synthesize recycled polyamides or recycled polyesteramides.

[0026] Compared with the prior art, the beneficial effects of this invention are:

[0027] This invention relates to a one-pot method for the direct chemical recovery of lactam polyamides into recycled polyamides or recycled polyesteramides using a melt polycondensation process. This method employs a "polymer-polymer" recovery model, saving the steps of traditional chemical recovery to monomers or prepolymers and reducing monomer purification costs. Simultaneously, the reaction process forms a portion of cyclic lactams that can be separated and reused in the synthesis of lactam polyamides. The diacid acts as a depolymerizing agent, with the carboxylic acid of the diacid dissociating to release protons (H). + The carbonyl oxygen of the amide is combined with the carbonyl oxygen, which enhances the positive charge of the carbonyl carbon and promotes the nucleophilic attack reaction between the carboxyl, hydroxyl and amino groups and the carbonyl carbon, depolymerizing into low molecular weight prepolymers. In addition, the water byproduct generated by the esterification reaction of diol and diacid or the amidation reaction of diamine and diacid can participate in the hydrolysis reaction of lactam polyamides to generate terminal carboxyl oligomers. Then the terminal carboxyl oligomers react with amino / hydroxyl groups. The introduction of inert gas and the formation of a vacuum negative pressure environment are to remove the byproduct water and a small amount of cyclic lactams, promote the forward polymerization reaction, and finally generate recycled polyamide or polyesteramide.

[0028] The mechanical properties of the recycled products of this invention are comparable to those of lactam polyamides. In particular, the recycled polyesteramide has the ability to be biodegraded in soil due to the introduction of ester bonds. Experimental results show that the molecular weights of recycled polyamide and recycled polyesteramide can reach 30kDa and 27kDa, respectively, the decomposition temperatures can reach 385℃ and 388℃, respectively, the tensile strengths can reach 26MPa and 33MPa, respectively, and the tensile strengths can reach 676% and 886%, respectively. They have excellent thermal stability and mechanical properties. Attached Figure Description

[0029] Figure 1 The above are stretch curves of the recycled products obtained in Example 1, Comparative Example 1, Example 9, and Comparative Example 2 of this invention.

[0030] Figure 2 The TGA diagrams are of the recycled products obtained in Examples 1 and 9 of this invention.

[0031] Figure 3 This is a graph showing the change in molecular weight of the recycled polyesteramide obtained in Example 9 of the present invention during composting degradation. Detailed Implementation

[0032] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0033] The present invention provides a one-pot chemical recovery method for lactam polyamides, utilizing the depolymerization and polymerization reactions of lactam polyamides, dicarboxylic acids, and diamines / diols to obtain recycled products. The depolymerization reaction of the lactam polyamides is carried out in an inert atmosphere, and the polymerization reaction is carried out under vacuum conditions. The reaction formula is as follows:

[0034]

[0035] Among them, R1 is an alkane with 3 to 13 carbon atoms;

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

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

[0038] R4 is an ether consisting of aliphatic hydrocarbons, aromatic hydrocarbons, or repeating units of -CH2CH2O-, -CH2CH2CH2O-, or -CH2CH2CH2CH2O- with 2 to 36 carbon atoms and an average molecular weight of 200 to 6000.

[0039] Specifically, the aforementioned lactam polyamide is preferably recycled waste lactam polyamide, used for recycling and reuse of waste lactam polyamide.

[0040] The aforementioned lactam polyamides preferably include one or more of polyacrylamide, polybutyrolactam, polyvaleramide, polycaprolactam, polyheptamide, polyoctamide, polynonamide, polydecylamide, polyundulalactam, polydodecanoamide, and polytridecylamide, and more preferably one or more of polybutyrolactam, polyvaleramide, polycaprolactam, polyheptamide, and polyoctamide. This invention limits the types of lactam polyamides to the above-mentioned range to enable the preparation of recycled products.

[0041] The aforementioned dicarboxylic acids preferably include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, methylmalonic acid, 2-butyloctanoic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyladacic acid, maleic acid, trans-butenedioic acid, itaconic acid, isopropylmalonic acid, 2,3-dibromosuccinic acid, terephthalic acid, isophthalic acid, phthalic acid, and 5-methylisophthalic acid. One or more of the following are preferred: phenylbutyric acid, benzylmalonic acid, furanyldicarboxylic 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 with carboxyl groups at both ends, polypropylene glycol with carboxyl groups at both ends, and polytetrahydrofuran with carboxyl groups at both ends. More preferably, one or more of the following are preferred: tetradecanoic acid, hexadecanoic acid, terephthalic acid, furanyldicarboxylic acid, hydrogenated dimer acid, and hydrogenated dimer oleic acid. This invention limits the types of dicarboxylic acids to the above range to prepare recycled products.

[0042] The aforementioned diamines preferably include one or more of the following: ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, heptaethylenediamine, octanediamine, nonanediamine, decanediamine, dodecanediamine, 1,2-pentanediamine, 1,2-propanediamine, 1,4-pentanediamine, 1,3-pentanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluenediamine, naphthyl-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, and dimelamine. More preferably, they include one or more of the following: hexanediamine, octanediamine, decanediamine, p-phenylenediamine, 1,4-cyclohexanediamine, and dimelamine. By limiting the types of diamines to the above range, this invention allows for the preparation of recycled products.

[0043] The aforementioned diols preferably include one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptahydrate, octanediol, nonanediol, decanediol, undecanediol, dodecanediol, tetradecanediol, terephthalic acid, isophthalic acid, o-phthalic acid, furanyl alcohol, furanyl alcohol, pyridinediethanol, cyclohexanediol, catechol, resorcinol, hydroquinone, 1,3-adamantanediol, phenylethylene glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran, and more preferably one or more of butanediol, dodecanediol, tetradecanediol, terephthalic acid, cyclohexanediol, and polyethylene glycol. This invention limits the types of diols to the above range to prepare recycled products.

[0044] The catalysts mentioned above preferably include one or more of antimony trioxide, antimony acetate, antimony glycolate, zinc acetate, stannous chloride, stannous octanoate, and p-toluenesulfonic acid, and more preferably one or more of antimony trioxide, stannous chloride, and p-toluenesulfonic acid. This invention limits the type of catalyst to the above range to prepare recycled products. The preferred amount of catalyst added is 0.01–5 wt% of the total mass of the diacid and diol, and more preferably 0.1–2 wt%. Limiting the catalyst content to the above range ensures the smooth and rapid progress of the reaction.

[0045] The preferred molar ratio of the above-mentioned lactam polyamide, diacid, and diamine / diol is 1:(0.1-3):(0.1-3), and more preferably 1:1:1. By limiting the molar ratio of lactam polyamide, diacid, and diamine / diol to the above range, this invention ensures that the recycled product has good performance.

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

[0047] Furthermore, the above-mentioned depolymerization reaction is preferably carried out under stirring conditions, with the stirring speed preferably >100 rpm, more preferably 150-500 rpm. The present invention promotes the reaction by stirring.

[0048] The above polymerization reaction is carried out under vacuum conditions, preferably <150 Pa, more preferably <30 Pa. The introduction of argon gas and the creation of a vacuum negative pressure environment in this invention can separate the byproducts water and cyclic lactams generated during the reaction from the polymerization system, promoting the forward polymerization reaction. Specifically, 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 0.5–12 h, more preferably 0.5–8 h. By limiting the temperature and time of the polymerization reaction to the above ranges, this invention ensures the reaction proceeds fully, resulting in a recycled product with higher molecular weight and superior performance.

[0049] Furthermore, the above polymerization reaction is preferably carried out under stirring conditions; the stirring speed is preferably >100 rpm, more preferably 150-500 rpm. The present invention promotes the repolymerization reaction through stirring.

[0050] The present invention synthesizes a recycled product from waste lactam polyamide based on the above-mentioned one-pot chemical recycling method, which has good mechanical properties and the polyesteramide has biodegradability.

[0051] Example 1:

[0052] This embodiment describes a one-pot method for preparing recycled polyamide, which is derived from polycaprolactam (recycled waste polycaprolactam), tetradecanoic acid, and hexamethylenediamine. The specific steps are as follows:

[0053] 10g of polycaprolactam (i.e., recycled waste polycaprolactam PA6), 22.8g of tetradecanoic acid, and 10.3g of hexamethylenediamine were added to a 250mL three-necked flask. Argon gas was first introduced, and the mixture was gradually heated to 220℃ for 5 hours under stirring at 200rpm. Then, under vacuum conditions (pressure less than 100Pa), the polymerization reaction was carried out at 250℃ for 5 hours under stirring at 200rpm to obtain recycled polyamide.

[0054] The recycled polyamide obtained in this embodiment 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 less polycaprolactam decomposes into caprolactam monomers, and most of the waste polycaprolactam directly participates in the reaction to form the recycled polymer.

[0055] Comparative Example 1:

[0056] This comparative example uses a two-step method to prepare recycled polyamide, which is prepared from polycaprolactam (recycled waste polycaprolactam), tetradecanoic acid, and hexamethylenediamine. The only difference between this and Example 1 is that it uses a two-step method. The raw materials, amounts, and process conditions are the same. The specific steps are as follows:

[0057] 10g of polycaprolactam (recycled waste polycaprolactam) and 22.8g of tetradecanoic acid were first added to a 250mL three-necked flask. Argon gas was first introduced, and the mixture was gradually heated to 220℃ for 5 hours under stirring at 200rpm to depolymerize the polycaprolactam. Then, 10.3g of hexamethylenediamine was added, and the mixture was polymerized at 250℃ for 5 hours under vacuum (pressure less than 100Pa) with stirring at 200rpm to obtain recycled polyamide.

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

[0059] Example 2:

[0060] The only difference between this embodiment and Example 1 is that polycaprolactam (recycled polycaprolactam) is replaced with polyvaleramide (recycled waste polyvaleramide). The composition is 10g polyvaleramide, 26g tetradecanoic acid, and 11.7g hexamethylenediamine, with a mass ratio of 1:2.6:1.17.

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

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

[0063] Example 3:

[0064] The only difference between this embodiment and Example 1 is that polycaprolactam (recycled polycaprolactam) is replaced with polybutyrolactam (recycled waste polybutyrolactam). The composition is 10g polybutyrolactam, 30.4g tetradecanoic acid, and 13.7g hexamethylenediamine. The mass ratio of polybutyrolactam, tetradecanoic acid, and hexamethylenediamine is 1:3.04:1.37.

[0065] The rest is the same as in Example 1.

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

[0067] Example 4:

[0068] The only difference between this embodiment and Example 1 is that tetradecanoic acid is replaced with terephthalic acid, and the ingredients are: 10g polycaprolactam, 14.6g terephthalic acid, and 10.3g hexamethylenediamine. The mass ratio of polycaprolactam, terephthalic acid, and hexamethylenediamine is 1:1.46:1.03.

[0069] The rest is the same as in Example 1.

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

[0071] Example 6:

[0072] The only difference between this embodiment and Example 1 is that tetradecanoic acid is replaced with hydrogenated dimeric acid. The composition is 10g polycaprolactam, 49.8g hydrogenated dimeric acid, and 10.3g hexamethylenediamine. The mass ratio of polycaprolactam, hydrogenated dimeric acid, and hexamethylenediamine is 1:4.98:1.03.

[0073] The rest is the same as in Example 1.

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

[0075] Example 7:

[0076] The only difference between this embodiment and Example 1 is that hexamethylenediamine is replaced with decanediamine. The ingredients are: 10g polycaprolactam, 22.8g tetradecanoic acid, and 15.2g decanediamine. The mass ratio of polycaprolactam, tetradecanoic acid, and decanediamine is 1:2.28:1.52.

[0077] Everything else is the same as in Example 1.

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

[0079] Example 8:

[0080] The only difference between this embodiment and Example 1 is that hexamethylenediamine is replaced with p-phenylenediamine. The ingredients are 10g polycaprolactam, 22.8g tetradecanoic acid, and 9.6g p-phenylenediamine. The mass ratio of polycaprolactam, tetradecanoic acid, and p-phenylenediamine is 1:2.28:0.96.

[0081] Everything else is the same as in Example 1.

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

[0083] Example 9:

[0084] This embodiment describes a one-pot method for preparing recycled polyesteramide, which is prepared from polycaprolactam (recycled waste polycaprolactam), tetradecanoic acid, butanediol, and antimony trioxide. The specific steps are as follows:

[0085] 10g of polycaprolactam (recycled waste polycaprolactam PA6), 22.8g of tetradecanoic acid, 8.0g of butanediol, and 0.0924g of antimony trioxide were added to a 250mL three-necked flask. Argon gas was first introduced, and the mixture was gradually heated to 220℃ for 5 hours under stirring at 200rpm. Then, under vacuum conditions (pressure less than 100Pa), the polymerization reaction was carried out at 250℃ for 5 hours under stirring at 200rpm to obtain recycled polyesteramide.

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

[0087] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 27 kDa.

[0088] Comparative Example 2:

[0089] This comparative example of two-step recycled polyesteramide is prepared from polycaprolactam (recycled waste polycaprolactam), tetradecanoic acid, butanediol, and antimony trioxide. The only difference between this example and Example 9 is the use of a two-step method; the raw materials, amounts, and process conditions are identical. The specific steps are as follows:

[0090] 10g of polycaprolactam (recycled waste polycaprolactam) and 22.8g of tetradecanoic acid were first added to a 250mL three-necked flask. Argon gas was first introduced, and the mixture was gradually heated to 220℃ for 5 hours under stirring at 200rpm to depolymerize the polycaprolactam. Then, 8.0g of butanediol and 0.0924g of antimony trioxide were added, and the mixture was polymerized at 250℃ for 5 hours under vacuum (pressure less than 100Pa) with stirring at 200rpm to obtain recycled polyesteramide.

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

[0092] The recycled polyesteramide obtained in this comparative example has a viscosity-average molecular weight of 18 kDa, a tensile strength of 12 MPa, a tensile strength of 108%, and a cyclic caprolactam recovery rate of 40%.

[0093] Comparing Example 1 with Comparative Example 1, Example 9, and Comparative Example 2, it was found that the recycled polyamide prepared by the two-step method had lower viscosity-average molecular weight, tensile strength, and tensile strength compared to the recycled product prepared by the one-pot method. This is because after the diacid depolymerizes polycaprolactam into low-molecular-weight oligomers, the addition of diamine / diol and the byproduct water generated by the acid-amine amidation reaction or the acid-ester esterification reaction further depolymerizes the low-molecular-weight oligomers into caprolactam at high temperatures, increasing the proportion of caprolactam in the reaction system. Excess caprolactam remains in the recycled polyamide, hindering the forward polymerization reaction. Furthermore, excess caprolactam cannot be completely removed, ultimately affecting the viscosity-average molecular weight, tensile strength, and tensile strength of the recycled product. In contrast, the one-pot method for recovering polycaprolactam initially results in a higher molecular weight of polycaprolactam and a weaker ability to depolymerize water into caprolactam. The lower proportion of depolymerized caprolactam thus has less impact on the reaction process and the performance of the recycled product. Moreover, 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 embodiment and Example 9 is that polycaprolactam (recycled polycaprolactam) is replaced with polyvaleramide (recycled waste polyvaleramide). The composition is 10g polyvaleramide, 26g tetradecanoic acid, and 9.1g butanediol. The mass ratio of polyvaleramide, tetradecanoic acid, and butanediol is 1:2.6:0.91, and the amount of antimony trioxide is 0.3% of the total mass of tetradecanoic acid and butanediol.

[0096] The rest is the same as in Example 9.

[0097] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 28 kDa.

[0098] Example 11:

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

[0100] The rest is the same as in Example 9.

[0101] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 25 kDa.

[0102] Example 12:

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

[0104] The rest is the same as in Example 9.

[0105] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 28 kDa.

[0106] Example 13:

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

[0108] The rest is the same as in Example 9.

[0109] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 16 kDa.

[0110] Example 14:

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

[0112] The rest is the same as in Example 9.

[0113] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 24 kDa.

[0114] Example 15:

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

[0116] The rest is the same as in Example 9.

[0117] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 28 kDa.

[0118] Example 16:

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

[0120] The rest is the same as in Example 9.

[0121] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 22 kDa.

[0122] Example 17:

[0123] The only difference between this embodiment and Embodiment 9 is that antimony trioxide is replaced with p-toluenesulfonic acid;

[0124] The rest is the same as in Example 9.

[0125] The viscosity-average molecular weight of the recycled polyesteramide obtained in this embodiment is 22 kDa.

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

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

[0128] The degradation of polyesteramide under simulated composting conditions was determined according to ISO 20200-2015 standard. Samples were processed into standard specimens and landfilled in a simulated composting environment according to standard requirements. Testing was conducted under a constant temperature of 58±2℃, and the molecular weight change of the samples was measured at fixed time intervals. As can be seen from the above examples, the recycled polyamide and recycled polyesteramide provided by this invention, generated from the reaction of waste lactam polyamide, diacid, and diamine / diol, have molecular weights of up to 30kDa and 27kDa, respectively; decomposition temperatures of up to 385℃ and 388℃, respectively; tensile strengths of up to 26MPa and 33MPa, respectively; and tensile strengths of up to 676% and 886%, respectively, exhibiting excellent thermal stability and mechanical properties. Especially the recycled polyesteramide, such as... Figure 3 As shown, the viscosity-average molecular weight of the recycled polyesteramide decreased by 61.8% after 5 weeks, and it acquired biodegradability due to the introduction of ester bonds.

[0129] Given that there are numerous embodiments of the present invention, and the raw materials and quantities involved can be selected within a limited range according to actual needs, and that the experimental data for each embodiment are extensive and numerous, it is not suitable to list and describe them one by one here. However, the content to be verified 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 merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for chemically recycling a lactam-based polyamide in one pot, characterized by, It comprises: feeding of a lactam-based polyamide, a dibasic acid and a dibasic amine or a dibasic alcohol; then performing a depolymerization reaction under an inert atmosphere, the reaction temperature being 100-250 DEG C and the reaction time being 0.5-12 h; and finally performing a polymerization reaction under vacuum, the reaction temperature being 150-280 DEG C and the reaction time being 0.5-12 h; the lactam-based polyamide is one or more of polypropionolactam, polybutyrolactam, polypentolactam, polycaprolactam, polyheptolactam, polyoctolactam, polynonolactam, polydecenolactam, polyundecenolactam, polydodecanolactam and polytridecanolactam; the molar ratio of the lactam-based polyamide, the dibasic acid, the dibasic amine or the dibasic alcohol is 1:(0.1-3):(0.1-3).

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

3. The method of one-pot chemical recovery of lactam-based polyamide according to claim 1, characterized in that, the reaction of the lactam-based polyamide, the dibasic acid and the dibasic alcohol is performed in the presence of a catalyst, and the reaction formula is: ； R1 is an alkane with 3-13 carbon atoms; R2 is an aliphatic hydrocarbon with 3-36 carbon atoms, an aromatic hydrocarbon or an ether with repeating units of -CH2CH2O-, -CH2CH2CH2O- or -CH2CH2CH2CH2O- and an average molecular weight of 200-6000; R4 is an aliphatic hydrocarbon with 2-36 carbon atoms, an aromatic hydrocarbon or an ether with repeating units of -CH2CH2O-, -CH2CH2CH2O- or -CH2CH2CH2CH2O- and an average molecular weight of 200-6000.

4. The process for one-pot chemical recovery of lactam-based polyamide according to claim 3, characterized in that, the catalyst is one or more of antimony trioxide, antimony acetate, ethylene glycol antimony, zinc acetate, stannous chloride, stannous octoate and p-toluene sulfonic acid; the amount of the catalyst is 0.01-5 wt% of the total mass of the dibasic acid and the dibasic alcohol.

5. The method of one-pot chemical recovery of lactam-based polyamide according to claim 1, characterized by, the dibasic acid comprises one or more of 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-butyloctanedioic acid, 2-propylmalonic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyladipic acid, maleic acid, fumaric acid, itaconic acid, 2,3-dibromosuccinic acid, terephthalic acid, isophthalic acid, phthalic acid, 5-methylisophthalic acid, phenylsuccinic acid, benzyllmalonic acid, furandicarboxylic acid, pyridinedicarboxylic acid, cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, dimer acid, hydrogenated dimer acid, carboxyl-terminated polyethylene glycol, carboxyl-terminated polypropylene glycol and carboxyl-terminated polytetrahydrofuran.

6. The method of one-pot chemical recovery of lactam-based polyamide according to claim 1, characterized in that, The diamines are one or more of ethylenediamine, propylenediamine, butylenediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, dodecanediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-toluylenediamine, naphthalene-2,6-diamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, dipropylenediamine.

7. The method of one-pot chemical recovery of lactam-based polyamide according to claim 1, characterized by, The diols include one or more of ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, undecylene glycol, dodecylene glycol, tetradecylene glycol, p-xylylene glycol, m-xylylene glycol, o-xylylene glycol, furan diol, pyridine diol, cyclohexane diol, o-resorcinol, m-resorcinol, p-resorcinol, 1,3-adamantanediol, phenylethylene glycol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran.

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