Chain extender composition for recovering polyamide, regenerated spinning-grade polyamide and preparation method of regenerated spinning-grade polyamide

Abstract

The invention relates to the technical field of recycling and regeneration of polyamide, in particular to a chain extender composition for recycling polyamide, regenerated spinning-grade polyamide and a preparation method of the regenerated spinning-grade polyamide. The invention relates to a chain extender composition for recovering polyamide. The chain extender composition comprises a dioxazoline chain extender and an epoxy chain extender according to a mass ratio of (1.50-2.61): 1. When the chain extender composition for recovering polyamide is used for recovering and regenerating polyamide, molecular chains can be efficiently repaired, side reactions are inhibited, melt stability is kept, and the performance of the obtained regenerated polyamide is close to that of a native material.

Description

Technical Field

[0001] This invention relates to the field of polyamide recycling technology, and in particular to a chain extender composition for recycling polyamide, recycled spinning-grade polyamide, and a method for preparing the same. Background Technology

[0002] Nylon 66, as an important high-performance engineering plastic, is widely used in automobiles, electronics, industrial machinery, and textile fibers due to its excellent mechanical properties, heat resistance, and chemical resistance. In recent years, with increasing environmental awareness and the growing demand for resource recycling, the development of recycled polyamide materials has become a hot topic in the industry. The recycling and reuse of nylon 66 waste fibers and materials has significant economic and environmental benefits.

[0003] The recycling and regeneration technologies for nylon 66 are mainly divided into two categories: chemical methods and physical methods. Chemical methods reduce nylon 66 to monomers through depolymerization, which are then repolymerized to obtain recycled materials. While producing high-quality products, these methods are complex and costly, making large-scale industrial application difficult at present. Physical methods convert nylon 66 into recycled resin chips through melt extrusion granulation. These methods offer advantages such as simple processes, low cost, and ease of large-scale industrial application, and have become the mainstream technology for recycling and reusing nylon 66.

[0004] However, existing recycling technologies still have certain limitations: First, polyamide molecular chains are prone to breakage during the recycling process, leading to a decrease in molecular weight and affecting melt flowability; second, commonly used chain extenders are prone to triggering side reactions during the reaction, producing cross-linked gels or small molecule byproducts (such as water, CO2, etc.), resulting in poor melt uniformity, yellowing color, and insufficient processing stability; third, the performance of recycled resin chips is still significantly different from that of virgin resin chips, making it difficult to meet the requirements of high-speed spinning for material consistency and stability.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a chain extender composition for recycling polyamide, recycled spinning-grade polyamide, and a method for preparing the same. The chain extender composition for recycling polyamide of this invention can efficiently repair molecular chains, suppress side reactions, and maintain melt stability during the recycling and regeneration of polyamide, and the resulting recycled polyamide exhibits properties close to those of the virgin material.

[0007] To achieve the above-mentioned objectives of the present invention, a first aspect of the present invention provides a chain extender composition for recycling polyamide, comprising a dioxazoline chain extender and an epoxy chain extender in a mass ratio of (1.50 to 2.61):1.

[0008] Furthermore, the dioxazoline chain extender includes at least one of 2,2'-(1,3-phenylene)-dioxazoline and 2,2-bis(2-oxazoline).

[0009] Furthermore, the purity of the dioxazoline chain extender is 98% to 99.1%.

[0010] Furthermore, the epoxy chain extender includes at least one of ethylene-methyl acrylate-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate copolymer, bisphenol A epoxy resin, bisphenol A diglycidyl ether, and bisphenol F diglycidyl ether.

[0011] Furthermore, the molar fraction of glycidyl methacrylate component in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 5% to 12%, and the molar fraction of methyl acrylate component in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 20% to 30%.

[0012] Furthermore, the molar fraction of glycidyl methacrylate component in the ethylene-glycidyl methacrylate copolymer is 5% to 12%.

[0013] Furthermore, the number-average molecular weights of the ethylene-methyl acrylate-glycidyl methacrylate copolymer and the ethylene-glycidyl methacrylate copolymer are each independently 15000 g / mol to 30000 g / mol.

[0014] Furthermore, the preparation method of the 2,2'-(1,3-phenylene)-dioxazoline includes the following steps: (a) 1,3-Phenyl chloride reacts with ethanolamine in the presence of an acid-binding agent to give 1,3-bis(2-hydroxyethylcarbamoyl)benzene; (b) 1,3-Bis(2-hydroxyethylcarbamoyl)benzene was refluxed in a solvent in the presence of pyridine p-toluenesulfonate as a catalyst; the reactants were then cooled to room temperature and the organic phase was washed and collected. (c) Remove the solvent from the organic phase to obtain the crude product; recrystallize the crude product using a mixed solvent of ethanol and acetone.

[0015] Further, in step (a), the molar ratio of ethanolamine to the acid-binding agent is 1:(1 to 1.5), and the molar ratio of 1,3-benzoyl chloride to ethanolamine is 1:(2.0 to 2.4).

[0016] Furthermore, in step (b), the amount of pyridine p-toluenesulfonate used accounts for 0.5 wt% to 1 wt% of the reaction system.

[0017] Further, in step (c), the volume ratio of ethanol to acetone is 3:1.

[0018] Furthermore, the HPLC purity of the 2,2'-(1,3-phenylene)-dioxazoline is ≥99%.

[0019] The second aspect of the present invention provides a composition for recycled spinning-grade polyamide resin, comprising a main material and a chain extender composition for recycled polyamide provided in the first aspect of the present invention; The main ingredients include recycled polyamide, virgin polyamide, optional antioxidants, and optional thermal stabilizers.

[0020] Preferably, the difference between the peak filtration pressure and the initial filtration pressure of the melt of the recycled spinning-grade polyamide resin blend is <6.0 MPaG, more preferably <5 MPaG, more preferably <4 MPaG, and even more preferably <3 MPaG.

[0021] Furthermore, the initial filtration pressure of the melt of the recycled spinning-grade polyamide resin blend is ≤12MPaG, preferably ≤11MPaG.

[0022] Furthermore, the melt stability coefficient (CV) of the recycled spinning-grade polyamide resin blend is ≤7.1%, preferably ≤6.0%.

[0023] Furthermore, the recycled spinning-grade polyamide resin blend comprises the following components by weight percentage: 20%–80% of polyamide is recycled. Virgin polyamide 18%–78% Chain extender compositions for polyamide recycling: 0.9%–3% Antioxidant 0.02%~1.5% Heat stabilizer 0.08%~0.25%.

[0024] Furthermore, in the recycled spinning-grade polyamide resin blend, the mass percentage of dioxazoline chain extender is 0.76% to 1.32%, and the mass percentage of epoxy chain extender is 0.3% to 0.88%.

[0025] Furthermore, in the recycled spinning-grade polyamide resin blend, the mass percentage of the recycled polyamide is 65% to 75%, preferably 68% to 71%.

[0026] Furthermore, the antioxidant includes at least one of antioxidant 1010 and antioxidant 168.

[0027] Furthermore, the heat stabilizer includes at least one of cuprous iodide and potassium iodide.

[0028] Furthermore, the recycled polyamide fibers have a length of 0.3 to 0.8 cm.

[0029] Furthermore, the oil content of the recycled polyamide is ≤0.1%.

[0030] Furthermore, the relative viscosity of the virgin polyamide is 2.40 to 2.50.

[0031] Furthermore, the melt index of the virgin polyamide at 275°C and 2.16 kg is 68–80 g / 10 min.

[0032] The third aspect of the present invention provides a recycled spinning-grade polyamide resin, which is mainly prepared from a blend of the recycled spinning-grade polyamide resin provided in the second aspect of the present invention.

[0033] Furthermore, the relative viscosity of the recycled spinning-grade polyamide resin chips is 2.37–2.47.

[0034] Furthermore, the molecular weight distribution of the recycled spinning-grade polyamide resin chips is 1.50–1.70.

[0035] Furthermore, the melt index of the recycled spinning-grade polyamide resin chips at 275°C and 2.16 kg was 72–95 g / 10 min.

[0036] The fourth aspect of the present invention provides a method for preparing the recycled spinning-grade polyamide resin provided in the third aspect of the present invention, comprising the following steps: melt extruding the recycled spinning-grade polyamide resin with a composite material, granulating it, and obtaining the recycled spinning-grade polyamide resin. In the melt extrusion process, the main material is added through the main feed port, and the dioxazoline chain extender and the epoxy chain extender are added sequentially through the first side feed port and the second side feed port, respectively.

[0037] Furthermore, the temperature of the melt extrusion is 150–285°C.

[0038] Furthermore, the temperature corresponding to the first side feeding port is 260-270℃.

[0039] Furthermore, the temperature corresponding to the second side feeding port is 270-280℃.

[0040] The fifth aspect of the present invention provides a recycled polyamide fiber, which is made from the recycled spinning-grade polyamide resin provided in the third aspect of the present invention.

[0041] Furthermore, the regenerated polyamide fiber has a tensile strength of 3.7–4.7 cN / dtex.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The chain extender composition for recycling polyamide of the present invention can efficiently repair molecular chains, suppress side reactions, and maintain melt stability when recycling and regenerating polyamide, and the properties of the recycled polyamide are close to those of the original material. (2) When the chain extender composition of the present invention is used to regenerate recycled polyamide, a high proportion of recycled polyamide can be used, which greatly reduces the cost of raw materials. Moreover, the performance of the recycled polyamide obtained is close to that of the virgin material, which has significant potential for industrial application and promotion value. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 The HPLC chromatogram of 2,2'-(1,3-phenylene)-dioxazoline prepared in an embodiment of the present invention is shown. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0046] The first aspect of the present invention provides a chain extender composition for recycling polyamide, comprising a dioxazoline chain extender and an epoxy chain extender in a mass ratio of (1.50 to 2.61):1.

[0047] The chain extender composition for recycling polyamide of the present invention uses a dioxazoline chain extender and an epoxy chain extender in a certain proportion. The dioxazoline chain extender can efficiently and specifically consume the terminal carboxyl groups to achieve linear chain extension; while the epoxy chain extender can specifically remove the terminal amino groups that are harmful to the dioxazoline chain extender. This fundamentally eliminates the possibility of the dioxazoline chain extender forming crosslinking points and eliminates the source of microgels. It can efficiently repair molecular chains, inhibit side reactions, maintain melt stability, and has performance close to that of the original material.

[0048] In some embodiments, the mass ratio of dioxazoline chain extender to epoxy chain extender is (1.50–2.61):1, specifically 1.50:1, 1.60:1, 1.80:1, 2.00:1, 2.20:1, 2.40:1, 2.50:1, 2.61:1, or any combination thereof. Excessive dioxazoline chain extender can easily lead to residual oxazoline functional groups, potentially causing later hydrolysis or color deterioration; insufficient dioxazoline chain extender results in inadequate chain extension and insufficient molecular weight recovery.

[0049] In some embodiments, dioxazoline chain extenders include at least one of 2,2'-(1,3-phenylene)-dioxazoline and 2,2-bis(2-oxazoline). 2,2'-(1,3-phenylene)-dioxazoline (PBO) exhibits high selectivity, high reaction efficiency, and byproduct-friendly properties when used in the recycling and regeneration of polyamides. Specifically, PBO has a symmetrical aromatic structure, and its oxazoline ring exhibits extremely high selectivity for the terminal carboxyl groups, preferentially reacting with the terminal carboxyl groups of the polyamide chain, reducing the probability of reaction with the terminal amino groups, thereby minimizing the risk of crosslinking and ensuring uniform melt flow. During the chain extension reaction with the carboxyl groups at the polyamide chain ends, the byproduct is a single, stable, and easily removed monoethanolamine molecule under vacuum, without generating water or CO2, thus avoiding hydrolytic degradation and bubble generation. Furthermore, the aromatic ring structure of PBO makes it stable at the processing temperature of polyamides (e.g., 250–275°C), reducing decomposition and volatilization during processing.

[0050] In some embodiments, the purity of the dioxazoline chain extender is 98% to 99.1%.

[0051] This invention can use commercially available PBO directly, or it can use self-made PBO with higher purity.

[0052] This invention provides an optional method for preparing PBO, which can improve the purity of PBO and help avoid the influence of impurities on the performance of recycled polyamide. Specifically, it includes the following steps: (a) 1,3-Phenyl chloride reacts with ethanolamine in the presence of an acid-binding agent to give 1,3-bis(2-hydroxyethylcarbamoyl)benzene; (b) 1,3-Bis(2-hydroxyethylcarbamoyl)benzene was refluxed in a solvent in the presence of pyridine p-toluenesulfonate as a catalyst; the reactants were then cooled to room temperature and the organic phase was washed and collected. (c) Remove the solvent from the organic phase to obtain the crude product; recrystallize the crude product using a mixed solvent of ethanol and acetone.

[0053] In some embodiments, the volume ratio of ethanol to acetone is 3:1.

[0054] In some embodiments, the molar ratio of 1,3-phthaloyl chloride to ethanolamine is 1:(2.0–2.4), specifically within the range of 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, or any two thereof; the molar ratio of ethanolamine to the acid-binding agent is 1:(1–1.5), specifically within the range of 1:1, 1:1.2, 1:1.4, 1:1.5, or any two thereof. The acid-binding agent includes triethylamine.

[0055] In some embodiments, in step (a), the solvent of the reaction system includes tetrahydrofuran.

[0056] In some embodiments, in step (a), the reaction temperature is 20–30°C, such as 25°C; and the reaction time is 8–16 h, such as 12 h.

[0057] In some embodiments, step (a) further includes: after the reaction is completed, filtering to collect the filtrate, and collecting the solid by vacuum distillation, which is 1,3-bis(2-hydroxyethylcarbamoyl)benzene.

[0058] In some embodiments, in step (b), the solvent includes toluene. Further, the mass of toluene is 3 to 5 times that of 1,3-bis(2-hydroxyethylcarbamoyl)benzene.

[0059] In some embodiments, in step (b), the amount of pyridine p-toluenesulfonate used is 0.5% to 1% of the total mass of the reaction system.

[0060] In some implementations, in step (b), the reaction time is determined by TLC monitoring, and can be 5 to 10 hours.

[0061] In some embodiments, the HPLC purity of 2,2'-(1,3-phenylene)-dioxazoline obtained by the above method is ≥99%.

[0062] In some embodiments, the epoxy chain extender includes at least one selected from ethylene-methyl acrylate-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate copolymer, bisphenol A epoxy resin, bisphenol A diglycidyl ether, and bisphenol F diglycidyl ether. These epoxy chain extenders can specifically remove terminal amino groups that are harmful to dioxazoline chain extenders, fundamentally eliminating the possibility of crosslinking sites and removing the source of microgels.

[0063] When the epoxy chain extender is an ethylene-methyl acrylate-glycidyl methacrylate copolymer or an ethylene-glycidyl methacrylate copolymer, the ethylene segments have good compatibility with the polyamide matrix, which helps the epoxy chain extender to be uniformly dispersed in the melt and avoids localized reactions. Furthermore, as a polymer copolymer, its epoxy functional groups are uniformly distributed, the reaction is controllable, it can effectively remove terminal amino groups without causing excessive crosslinking, and reduces the possibility of increased filtration pressure due to branching or gelation.

[0064] In some embodiments, the molar fraction of glycidyl methacrylate component in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 5% to 12%, specifically 5%, 6%, 7%, 8%, 9%, 10%, 12%, or any combination thereof.

[0065] In some embodiments, the molar fraction of glycidyl methacrylate component in the ethylene-glycidyl methacrylate copolymer is 5% to 12%, specifically 5%, 6%, 7%, 8%, 9%, 10%, 12%, or any combination thereof.

[0066] In some embodiments, the number average molecular weight of the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 15,000 g / mol to 30,000 g / mol, specifically within the range of 15,000 g / mol, 18,000 g / mol, 20,000 g / mol, 22,000 g / mol, 25,000 g / mol, 28,000 g / mol, 30,000 g / mol, or any combination thereof.

[0067] When the amount of glycidyl methacrylate introduced through the copolymer is the same, and the content of glycidyl methacrylate in the copolymer is within the above-mentioned range, it helps to balance the chain extender composition between molecular chain repair efficiency, gel inhibition, and processing stability. When the content of glycidyl methacrylate in the copolymer is too low, it cannot effectively inhibit the crosslinking of dioxazoline chain extenders; when the content of glycidyl methacrylate in the copolymer is too high, it will itself become a source of crosslinking sites and lead to product color deterioration.

[0068] In some embodiments, the molar fraction of methyl acrylate in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 20% to 30%, specifically within the range of 20%, 22%, 25%, 28%, 30%, or any combination thereof. As a structural regulating unit, controlling the content of methyl acrylate within the above range can improve the flexibility and compatibility of the copolymer's molecular chains and enhance the segmental mobility of the molecular chains. When used for the recycling and regeneration of polyamides, it can rapidly migrate to reaction sites, improving reaction accessibility and indirectly but significantly enhancing the effectiveness of the glycidyl methacrylate functional groups, further contributing to its ability to inhibit gelation and stabilize the melt.

[0069] In some embodiments, the number average molecular weight of the ethylene-glycidyl methacrylate copolymer is 15,000 g / mol to 30,000 g / mol, specifically within the range of 15,000 g / mol, 18,000 g / mol, 20,000 g / mol, 22,000 g / mol, 25,000 g / mol, 28,000 g / mol, 30,000 g / mol, or any combination thereof.

[0070] Ethylene-methyl acrylate-glycidyl methacrylate copolymer can be prepared using conventional methods. This invention provides an optional preparation method, comprising: determining the appropriate monomer feeding ratio through preliminary experiments based on the required content of each monomer unit in the target ethylene-methyl acrylate-glycidyl methacrylate copolymer; adding methyl acrylate and glycidyl methacrylate to a high-pressure reactor, sealing, evacuating, and purging with nitrogen, then introducing ethylene and an initiator (such as tert-butyl peroxybenzoate, at a dosage of 0.01wt%–0.1wt% of the total monomers), maintaining a pressure of 120–200 MPa, and reacting at 160–200°C for 1–2 hours; then depressurizing, discharging, granulating, and analyzing by nuclear magnetic resonance (NMR)... 13 The molar fraction of each monomer unit in the copolymer was determined by C NMR.

[0071] Ethylene-glycidyl methacrylate copolymers can be prepared using conventional methods. This invention provides an optional preparation method, comprising: determining the appropriate monomer feeding ratio through preliminary experiments based on the required content of each monomer unit in the target ethylene-glycidyl methacrylate copolymer; adding glycidyl methacrylate to a high-pressure reactor, sealing it, evacuating it under vacuum, purging it with nitrogen, and then introducing ethylene and an initiator (such as tert-butyl peroxybenzoate, at a dosage of 0.01wt%–0.1wt% of the total monomer content), maintaining a pressure of 150–220 MPa, and heating it to 160–190°C for 1–2 hours; then depressurizing, discharging, granulating, and analyzing the results using nuclear magnetic resonance (NMR). 13 The molar fraction of each monomer unit in the copolymer was determined by C NMR.

[0072] The second aspect of the present invention provides a composition for recycled spinning-grade polyamide resin, comprising a main material and a chain extender composition for recycled polyamide provided in the first aspect of the present invention; The main ingredients include recycled polyamide, virgin polyamide, optional antioxidants, and optional heat stabilizers.

[0073] Currently, in the field of polyamide recycling, conventional research and practice focus primarily on the effect of chain extenders on improving the viscosity properties of materials, while neglecting a crucial indicator in actual processing (especially spinning, where process continuity and melt uniformity are highly demanding): the processing stability of the melt at high temperatures. This stability indicator can be intuitively characterized and monitored through the trend of melt filtration pressure changes. The inventors of this invention discovered that when using dioxazoline chain extenders alone, although they primarily react with terminal carboxyl groups, a small number of chain extender molecules still react with terminal amino groups in the complex high-temperature melt environment. If a single dioxazoline chain extender molecule simultaneously connects to both carboxyl and amino groups, cross-linking points are formed. While these micro-cross-linking points are insufficient to gel the entire system in a short period, they do form microgels. These microgels tend to accumulate and become trapped when passing through a filter, causing a gradual increase in filtration resistance, manifested as a continuous and slow rise in melt filtration pressure, thus affecting its processing stability at high temperatures (280℃~300℃). In contrast, when epoxy chain extenders are used alone, the initial melt filtration pressure is higher and the increase is more pronounced. The main reasons for this phenomenon include: epoxy chain extenders have large molecular weights and complex chain structures, which may introduce branched structures during the reaction; simultaneously, their reactivity and selectivity are relatively poor, and side reactions are more complex, easily causing uneven melt flow. These factors collectively result in poor melt rheological properties of epoxy chain extender systems, poor initial passability to the filter screen, and a greater susceptibility to degradation and complex side reactions during processing, leading to a sharp increase in melt filtration pressure. This invention controls the trend of melt filtration pressure changes to select the optimal blending ratio of dioxazoline chain extenders and epoxy chain extenders, as well as the blending ratio with recycled polyamide, virgin polyamide, optionally antioxidants, and optionally thermal stabilizers. By blending, the filtration pressure meets the requirements, not only efficiently repairing the molecular chains and ensuring or even improving the performance of the obtained recycled polyamide, but also maintaining a low initial melt pressure and high-temperature processing stability.

[0074] In some embodiments, the difference between the peak filtration pressure and the initial filtration pressure of the melt of the recycled spinning-grade polyamide resin blend is <5.0 MPaG, preferably <4 MPaG, more preferably <3 MPaG, and even more preferably <2 MPaG. Specifically, it can be a range of 4.9 MPaG, 4.7 MPaG, 4.5 MPaG, 4.2 MPaG, 4 MPaG, 3.7 MPaG, 3.2 MPaG, 3.0 MPaG, 2.7 MPaG, 2.3 MPaG, 2 MPaG, 1.5 MPaG, 1 MPaG, 0.5 MPaG, 0.3 MPaG, or any combination thereof.

[0075] In some embodiments, the initial filtration pressure of the melt of the recycled spinning-grade polyamide resin blend is ≤12MPaG, preferably ≤11MPaG, and can specifically be a range of 12MPaG, 11MPaG, 10MPaG, 9MPaG, 8MPaG, 7.5MPaG, or any combination thereof.

[0076] In some embodiments, the melt stability coefficient (CV) of the recycled spinning-grade polyamide resin blend is ≤7.1%, preferably ≤6.0%, and can specifically be a range of 7.1%, 6.5%, 6%, 5%, 4%, 3%, 2.5%, 1.9%, or any combination thereof.

[0077] In some embodiments, the recycled spinning-grade polyamide resin blend comprises the following components by weight percentage: 20%–80% of polyamide is recycled. Virgin polyamide 18%–78% Chain extender compositions for polyamide recycling: 0.9%–3% Antioxidant 0.02%~1.5% Heat stabilizer 0.08%~0.25%.

[0078] In some embodiments, the amount of recycled polyamide in the compound is 20% to 80%, specifically 20%, 30%, 40%, 50%, 60%, 70%, 80% or any combination thereof, preferably 65% ​​to 75%, more preferably 68% to 71%.

[0079] When using the chain extender composition of the present invention to regenerate recycled polyamide, a high proportion of recycled polyamide can be used, significantly reducing raw material costs. Furthermore, the properties of the obtained recycled polyamide are close to those of the virgin material, demonstrating significant potential for industrial application and widespread adoption. However, excessive use of recycled polyamide is detrimental to the physical properties of the recycled polyamide, such as affecting its spinnability; conversely, insufficient use results in a high amount of virgin polyamide, leading to increased material costs.

[0080] In some embodiments, the length of the recycled polyamide fibers is 0.3 to 0.8 cm, specifically 0.3 cm, 0.4 cm, 0.5 cm, 0.6 cm, 0.7 cm, 0.8 cm, or any combination thereof.

[0081] In some implementations, the oil content of the recycled polyamide is ≤0.1%.

[0082] In some embodiments, the amount of virgin polyamide in the compound is 18% to 78%, specifically it can be a range of 18%, 20%, 30%, 40%, 50%, 60%, 70%, 78% or any two of these.

[0083] In some embodiments, the relative viscosity of the virgin polyamide is 2.40 to 2.50, specifically a range of 2.40, 2.42, 2.45, 2.48, 2.50, or any combination thereof.

[0084] In some embodiments, the melt index of the virgin polyamide at 275°C and 2.16 kg is 68–80 g / 10 min, specifically 68 g / 10 min, 70 g / 10 min, 72 g / 10 min, 75 g / 10 min, 78 g / 10 min, 80 g / 10 min, or any combination thereof.

[0085] In some embodiments, the amount of the chain extender composition for recovering polyamide in the blend is 0.9% to 3%, specifically within the range of 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%, or any combination thereof. Controlling the amount of the chain extender composition in the blend within the above range is beneficial for repairing the molecular chains and ensuring melt uniformity and filtration pressure stability. If the amount of the chain extender composition in the blend is too low, it cannot effectively repair the molecular chains; if the amount of the chain extender composition is too high, it can easily cause branching or even cross-linking, leading to uneven melt flow and decreased spinnability.

[0086] In some embodiments, the amount of dioxazoline chain extender in the compound is 0.76% to 1.32%, specifically 0.76%, 0.8%, 1.0%, 1.2%, 1.32%, or any combination thereof; the amount of epoxy chain extender is 0.3% to 0.88%, specifically 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 0.88%, or any combination thereof.

[0087] In some embodiments, the amount of antioxidant in the compound is 0.02% to 1.5%, specifically it can be 0.02%, 0.1%, 0.35%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5% or any combination thereof.

[0088] Antioxidants and heat stabilizers are not absolutely necessary in the melt processing and post-treatment of polyamides, but they are recognized conventional additives in the art, used to improve the material's oxidation resistance, heat aging resistance, and color stability. This invention uses conventional antioxidants and heat stabilizers, and the amount added is sufficient to meet performance requirements without affecting processing and product performance.

[0089] The following are preferred options for antioxidants and heat stabilizers: In some embodiments, the antioxidant includes at least one of antioxidant 1010 and antioxidant 168.

[0090] In some embodiments, the amount of heat stabilizer in the compound is 0.08% to 0.25%, specifically 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.25%, or any combination thereof.

[0091] In some embodiments, the heat stabilizer includes at least one of cuprous iodide and potassium iodide.

[0092] The use of antioxidants and heat stabilizers effectively inhibits oxidative degradation caused by high temperatures during melt processing, further preventing yellowing and performance deterioration of the material.

[0093] The third aspect of the present invention provides a recycled spinning-grade polyamide resin, which is mainly prepared from a blend of the recycled spinning-grade polyamide resin provided in the second aspect of the present invention.

[0094] In some embodiments, the relative viscosity of the recycled spinning-grade polyamide resin chips is 2.37 to 2.47, specifically a range of 2.37, 2.40, 2.42, 2.45, 2.47, or any combination thereof.

[0095] In some embodiments, the molecular weight distribution of the recycled spinning-grade polyamide resin chips is 1.50 to 1.70, specifically a range of 1.50, 1.55, 1.60, 1.65, 1.70, or any two of these ranges.

[0096] In some embodiments, the melt index of the recycled spinning-grade polyamide resin chips at 275°C and 2.16 kg is 72–95 g / 10 min, specifically within the range of 72 g / 10 min, 75 g / 10 min, 78 g / 10 min, 80 g / 10 min, 82 g / 10 min, 85 g / 10 min, 88 g / 10 min, 90 g / 10 min, 92 g / 10 min, 95 g / 10 min, or any combination thereof.

[0097] In some embodiments, the number average molecular weight of the recycled spinning-grade polyamide resin is 19,000 to 29,000 g / mol, specifically 19,000 g / mol, 22,000 g / mol, 24,000 g / mol, 26,000 g / mol, 29,000 g / mol, or any combination thereof.

[0098] The fourth aspect of the present invention provides a method for preparing the recycled spinning-grade polyamide resin provided in the third aspect of the present invention, comprising the following steps: melt extruding the recycled spinning-grade polyamide resin with a composite material, granulating it, and obtaining the recycled spinning-grade polyamide resin. In melt extrusion, the main material is added through the main feed port, while the dioxazoline chain extender and the epoxy chain extender are added sequentially through the first side feed port and the second side feed port, respectively.

[0099] In some embodiments, the melt extrusion temperature is 150–285°C, specifically a range of 150°C, 180°C, 200°C, 220°C, 250°C, 285°C, or any combination thereof.

[0100] In some embodiments, the temperature corresponding to the first feeding port is 260-270°C, specifically 260°C, 262°C, 265°C, 268°C, 270°C, or any combination thereof.

[0101] In some embodiments, the temperature corresponding to the second feeding port is 270 to 280°C, specifically 270°C, 272°C, 275°C, 278°C, 280°C, or any combination thereof.

[0102] Injecting dioxazoline chain extenders and epoxy chain extenders at the aforementioned temperatures further ensures reactivity and uniform dispersion. Temperatures that are too low may lead to incomplete reactions; temperatures that are too high may cause decomposition or gelation of the chain extenders.

[0103] The fifth aspect of the present invention provides a recycled polyamide fiber, which is made from the recycled spinning-grade polyamide resin provided in the third aspect of the present invention.

[0104] In some embodiments, the breaking strength of the recycled polyamide fiber is 3.7 to 4.7 cN / dtex, specifically within the range of 3.7 cN / dtex, 3.9 cN / dtex, 4.1 cN / dtex, 4.5 cN / dtex, 4.55 cN / dtex, 4.6 cN / dtex, 4.65 cN / dtex, 4.7 cN / dtex, or any combination thereof.

[0105] In the following examples and comparative examples, the PBO used in Example 13 was commercially available (Maclean) with a purity of 98%; the others used PBO prepared in-house according to the present invention. The preparation method of the in-house PBO includes the following steps: (1) 1,3-Benzoyl chloride (1.0 mol) was dissolved in 500 mL of anhydrous tetrahydrofuran (THF) to obtain a 1,3-benzoyl chloride solution; ethanolamine (2.0 mol) and triethylamine (2.2 mol) were mixed in 800 mL of anhydrous THF cooled in an ice-water bath and stirred until homogeneous to obtain an ethanolamine mixture. The 1,3-benzoyl chloride solution was added dropwise to the ethanolamine mixture at -5±1℃. After the addition was complete, the mixture was reacted at 25℃ for 12 h. After the reaction was completed, the triethylamine hydrochloride precipitate was removed by filtration, and THF was removed by vacuum distillation to obtain a white solid, which was the intermediate 1,3-bis(2-hydroxyethylcarbamoyl)benzene.

[0106] (2) The intermediate obtained in step (1) was dissolved in 1200g of toluene, and then 9.6g of pyridine p-toluenesulfonate (PPTS) was added; the mixture was heated to 120±2℃ and refluxed for 7h, and the generated water was removed by a water separator. The reaction endpoint was monitored by TLC (the developing solvent was ethyl acetate and n-hexane in a volume ratio of 1:3, Rf=0.35).

[0107] (3) The reaction solution from step (2) was cooled to room temperature and washed successively with 5wt% sodium bicarbonate aqueous solution and deionized water. The organic phase was dried over anhydrous magnesium sulfate for 12 h, filtered, and then rotary evaporated to remove toluene, yielding the crude product. The crude product was recrystallized from an ethanol-acetone mixture (volume ratio 3:1, 300 mL) to obtain 170.7 g of white needle-like PBO crystals. The calculated yield was 78.9%, and the HPLC chromatogram is shown below. Figure 1 As shown, the HPLC purity of PBO is calculated to be 99.1%.

[0108] The preparation method of the ethylene-methyl acrylate-glycidyl methacrylate copolymer used in the following examples or comparative examples includes: adding liquid methyl acrylate and glycidyl methacrylate to a high-pressure reactor according to the molar ratio, sealing the reactor, evacuating it with vacuum and replacing it with nitrogen, then filling it with ethylene and 0.01wt% to 0.1wt% of tert-butyl peroxybenzoate according to the total mass of the monomers, initiating polymerization at a pressure of 120 to 200 MPa and a temperature of 160 to 200 °C for 1 to 2 hours, and obtaining the product after depressurization, discharge, and granulation.

[0109] In the raw materials for different products, based on a total monomer content of 100%, the molar percentage of methyl acrylate was 30%, and the molar percentages of glycidyl methacrylate were 5%, 8%, 10%, 15%, and 20%, respectively; the amount of initiator was 0.05 wt% of the total monomer mass; the obtained terpolymers are as follows: 72% ethylene-25% methyl acrylate-3% glycidyl methacrylate, number average molecular weight is 28000 g / mol; 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate, number average molecular weight is 25000 g / mol; 67% ethylene-25% methyl acrylate-8% glycidyl methacrylate, number average molecular weight is 22000 g / mol; 63% ethylene-25% methyl acrylate-12% glycidyl methacrylate, with a number average molecular weight of 18000 g / mol; The number-average molecular weight of 60% ethylene-25% methyl acrylate-15% glycidyl methacrylate is 16000 g / mol.

[0110] The preparation method of the ethylene-glycidyl methacrylate copolymer used in the following examples or comparative examples includes: adding liquid glycidyl methacrylate to a high-pressure reactor according to the molar ratio, sealing the reactor, evacuating it with vacuum and replacing it with nitrogen, then filling it with ethylene and 0.01wt% to 0.1wt% of tert-butyl peroxybenzoate according to the total mass of the monomers, initiating polymerization at a pressure of 150 to 200 MPa and a temperature of 160 to 190°C for 1 to 2 hours, and obtaining the product by depressurization, discharge, and granulation.

[0111] Of which, based on a total monomer content of 100%, glycidyl methacrylate accounted for 15% in molar proportion; the initiator amount was 0.05 wt% of the total monomer mass; the resulting binary copolymer is as follows: 94% ethylene-6% glycidyl methacrylate, number average molecular weight 30000 g / mol.

[0112] Example 1 Example 1 provides a recycled polyamide resin, the raw material of which comprises the following components by weight percentage: The composition includes 71% recycled polyamide, 27.2% virgin polyamide, 0.9% PBO, 0.4% 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate, 0.25% antioxidant 1010, 0.15% antioxidant 168, 0.05% cuprous iodide, and 0.05% potassium iodide.

[0113] The recycled polyamide has a length of 0.7±0.1cm and an oil content of 0.05%. The virgin polyamide has a relative viscosity of 2.45 and a melt index of 72g / 10min at 275℃ / 2.16kg.

[0114] Methods for preparing recycled polyamide resins include: (1) Waste fiber pretreatment: Nylon 66 waste fibers are coarsely crushed to 3-10cm by a cutting machine, washed 3 times with desalinated water at 25℃, and dried in a vacuum drying oven at 80℃ (vacuum degree is -0.095MPa) for 48h. Then the dried fibers are further finely crushed by a cutting machine to obtain short fibers with a length of 0.7±0.1cm, which are recycled polyamide.

[0115] (2) The recycled polyamide obtained in step (1) is mixed with virgin polyamide 66 chips, antioxidant and heat stabilizer in a high-speed mixer at 800 rpm for 15 min at room temperature.

[0116] (3) The mixture obtained in step (2) is melt-extruded through a twin-screw extruder with a screw speed of 270 rpm. The timing of the addition of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate (terpolymer) and the extruder temperature settings are shown in Table 1.

[0117] Table 1 Extruder parameter settings

[0118] (4) The melt from step (3) is cooled by a 40°C water bath, and then granulated to obtain recycled chips. The recycled chips are dried in a 90°C vacuum drying oven (vacuum degree is -0.095MPa) for 6 hours to obtain recycled spinning grade polyamide resin.

[0119] Example 2 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the raw materials for the recycled polyamide resin are different, as detailed below: The recycled polyamide resin in this embodiment comprises the following components by mass percentage: The composition includes 20% recycled polyamide, 77.89% virgin polyamide, 0.76% 2,2'-(1,3-phenylene)-dioxazoline, 0.3% 67% ethylene-25% methyl acrylate-8% glycidyl methacrylate, 0.80% antioxidant 1010, and 0.25% cuprous iodide.

[0120] Example 3 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the raw materials for the recycled polyamide resin are different, as detailed below: The recycled polyamide resin in this embodiment comprises the following components by mass percentage: The composition includes 68% recycled polyamide, 29.37% virgin polyamide, 1.32% 2,2'-(1,3-phenylene)-dioxazoline, 0.88% 94% ethylene-6% glycidyl methacrylate, 0.25% antioxidant 1010, 0.1% antioxidant 168, and 0.08% potassium iodide.

[0121] Example 4 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being the amount of recycled polyamide and virgin polyamide used in the raw materials of the recycled polyamide resin. The specific differences are as follows: In this embodiment, the raw materials of the recycled polyamide resin are 80% recycled polyamide and 18.2% virgin polyamide.

[0122] Example 5 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the total amount of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin is the same, but their respective amounts are different, as follows: In this embodiment, the raw materials of the recycled polyamide resin include 0.78% PBO, 69% ethylene, 25% methyl acrylate, 6% glycidyl methacrylate, and 0.52% glycidyl methacrylate.

[0123] Example 6 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the total amount of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin is the same, but their respective amounts are different, as follows: In this embodiment, the raw materials of the recycled polyamide resin include 0.94% PBO, 69% ethylene, 25% methyl acrylate, 6% glycidyl methacrylate, and 0.36% glycidyl methacrylate.

[0124] Example 7 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, the only difference being that: in the raw materials of the recycled polyamide resin, an equimolar amount of 2,2-bis(2-oxazoline) is used to replace PBO in Example 1.

[0125] Example 8 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that: in the raw materials of the recycled polyamide resin, bisphenol A diglycidyl ether (DGEBA) is used instead of 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1, and the number of moles of epoxy groups introduced by DGEBA is kept the same as the number of moles introduced by 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1.

[0126] Example 9 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that: in the raw materials of the recycled polyamide resin, equimolar amounts of 2,2-bis(2-oxazoline) are used to replace PBO in Example 1; bisphenol A diglycidyl ether (DGEBA) is used to replace 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1, and the number of moles of epoxy groups introduced by DGEBA is kept the same as the number of moles introduced by 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1.

[0127] Example 10 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that: in the raw materials of the recycled polyamide resin, 63% ethylene-25% methyl acrylate-12% glycidyl methacrylate is used instead of 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1, and the number of moles of epoxy groups introduced by 63% ethylene-25% methyl acrylate-12% glycidyl methacrylate is kept the same as the number of moles introduced by 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1.

[0128] Example 11 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that: in the raw materials of the recycled polyamide resin, 60% ethylene-25% methyl acrylate-15% glycidyl methacrylate is used instead of 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1, and the number of moles of epoxy groups introduced by 60% ethylene-25% methyl acrylate-15% glycidyl methacrylate is kept the same as the number of moles introduced by 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1.

[0129] Example 12 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that: in the raw materials of the recycled polyamide resin, 72% ethylene-25% methyl acrylate-3% glycidyl methacrylate is used instead of 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1, and the number of moles of epoxy groups introduced by 72% ethylene-25% methyl acrylate-3% glycidyl methacrylate is kept the same as the number of moles introduced by 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in Example 1.

[0130] Example 13 This embodiment refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the PBO is commercially available PBO (manufacturer: McLean, purity: 98%).

[0131] Comparative Example 1 Comparative Example 1 refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the total amount of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin is the same, but their respective amounts are different, as follows: In the raw materials of the recycled polyamide resin of Comparative Example 1, there are 0.975% PBO, 69% ethylene, 25% methyl acrylate, 6% glycidyl methacrylate, and 0.325% glycidyl methacrylate.

[0132] Comparative Example 2 Comparative Example 2 refers to the recycled polyamide resin and its preparation method in Example 1, with the only difference being that the total amount of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin is the same, but their respective amounts are different, as follows: In the raw materials of the recycled polyamide resin of Comparative Example 2, there are 0.75% PBO, 69% ethylene, 25% methyl acrylate, 6% glycidyl methacrylate, and 0.55% glycidyl methacrylate.

[0133] Comparative Example 3 Comparative Example 3 refers to the recycled polyamide resin and its preparation method in Example 1, except that the amounts of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin are different, as follows: In the raw materials of the recycled polyamide resin of Comparative Example 3, PBO was 1.3%, and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate was not added.

[0134] Comparative Example 4 Comparative Example 4 refers to the recycled polyamide resin and its preparation method in Example 1, except that the amounts of PBO and 69% ethylene-25% methyl acrylate-6% glycidyl methacrylate in the raw materials of the recycled polyamide resin are different, as follows: The raw materials of the recycled polyamide resin in Comparative Example 4 did not contain PBO, and consisted of 69% ethylene, 25% methyl acrylate, 6% glycidyl methacrylate, and 1.3% glycidyl methacrylate.

[0135] Test case The recycled spinning-grade polyamide resin chips obtained from different embodiments and comparative examples were tested as follows, and the test results are shown in Table 2.

[0136] (1) Relative viscosity: Tested according to the method in GB / T 12006.1; (2) Number-average molecular weight (Mn) and molecular weight distribution (Mw / Mn): Tested according to the method of GB / T 21863-2008; (3) Colorimetric YI value: Tested according to the method of GB / T 39822; (4) Melt flow index: Tested according to GB / T 3682.1-2018 at 275℃ and 2.16kg; (5) Filter pressure test: The filter pressure value refers to the pressure change of the melt on both sides of the filter screen. The specific test parameters are as follows: Test equipment: Model FCC-4 (Zibo Fangchen Machinery Technology Co., Ltd.). Process parameters: Fixed pore size filter screen (1600 mesh); 5-stage heating gradient, specifically Zone 1 / Zone 2 / Zone 3 / Zone 4 / Zone 5 / Die head temperature settings: 290℃ / 295℃ / 295℃ / 295℃ / 295℃ (Zone 5 heating delay 900s); Preset pump pressure: 6.5MPa, frequency: 20Hz; Preset die head pressure: 15MPa; Preset metering pump pressure: 16.5MPa.

[0137] Test duration: 500 minutes; Data acquisition: The test equipment automatically outputs the initial filtration pressure value and the peak filtration pressure value; in addition, filtration pressure data is taken from the real-time pressure curve every 20 minutes, for a total of 500 / 20=25 filtration pressure data points, and the filtration pressure variation coefficient is calculated.

[0138] The coefficient of variation (CV) for filtration pressure is calculated as follows: CV(%) = σ / μ × 100%; σ is the standard deviation of 25 filtration pressure values, and μ is the arithmetic mean of 25 filtration pressure values; Table 2 Test results of recycled spinning-grade polyamide resin chips

[0139] Application examples Regenerated spinning-grade polyamide resin chips obtained from different embodiments and comparative examples were spun. The spinning steps included: drying the chips at 100-110°C until the water content was below 600 ppm, and then performing melt spinning in a spinning machine; the temperatures of the four heating zones of the spinning machine were 278°C, 280°C, 282°C and 282°C respectively, the melt pipe temperature was 280°C, the box temperature was 282°C, the metering pump temperature was 280°C, the metering pump flow rate was 20 mL / min, the first drafting roller speed was 2500 m / min, the second drafting roller speed was 3500 m / min, and the draw ratio was 1.4.

[0140] Application Examples 1-13 correspond to the recycled spinning-grade polyamide resin chips of Examples 1-13, respectively, while Comparative Application Examples 1-4 correspond to the polyamide resin chips of Examples 1-4, respectively. The breaking strength of the recycled polyamide fibers obtained by spinning in different application examples was tested, and the spinning breakage rate of different resin chips was tested. The test results are shown in Table 3.

[0141] Fracture strength refers to GB / T 14344 The method from 2022 was tested.

[0142] The test methods for spinning breakage rate include: (1) Dry the slices at 105°C until the water content is below 600 ppm.

[0143] (2) Melt spinning is then performed in the spinning machine. The temperatures of the four heating zones of the spinning machine are 278℃, 280℃, 282℃ and 282℃ respectively. The temperature of the melt pipe is 280℃, the temperature of the box is 282℃, the temperature of the metering pump is 280℃, the flow rate of the metering pump is 20mL / min, the speed of the first drafting roller is 2500m / min, the speed of the second drafting roller is 3500m / min, and the traction ratio is 1.4. The spinneret has 24 holes, the winding method is dual rotor friction winding (POY), the spinning time is 6 hours of continuous operation, the ambient humidity is 55% RH, and the ambient temperature is 23℃.

[0144] (3) Calculate the spinning breakage rate according to the following formula: Spinning breakage rate (tons / cycle) = Actual spun fiber mass (tons) / Total number of breakages; A breakage is defined as the situation where any single filament breaks, causing the winding to stop, 30 minutes after the start of spinning.

[0145] Table 3 Results of spinning performance tests

[0146] The chain extender composition for recycling polyamide of the present invention can efficiently repair molecular chains, suppress side reactions, maintain melt stability, and obtain recycled polyamide with properties close to those of virgin material during the recycling and regeneration of polyamide.

[0147] Specifically, the test results from Examples 1 and 4, as well as the application example test results, show that when the chain extender composition of the present invention regenerates recycled polyamide, a high proportion of recycled polyamide can be used, and the performance of the obtained recycled polyamide is close to that of the virgin material. However, if the amount of recycled polyamide used is too high, the chain extension efficiency may decrease due to increased impurities, thereby reducing the resin and spinning performance.

[0148] The test results from Examples 1, 5-6, Comparative Examples 1-4, and application examples show that a proper blend of dioxazoline chain extenders and epoxy chain extenders can effectively repair molecular chains, suppress side reactions, maintain melt stability, and achieve performance close to that of the virgin material. When only dioxazoline chain extenders are used, or when excessive amounts are applied, cross-linking points easily form, leading to microgel formation, increased melt filtration pressure, decreased processing stability at high temperatures, increased spinning breakage rate, and increased product color (YI) due to increased amine residue. When only epoxy chain extenders are used, or when excessive amounts are applied, the byproducts such as water and CO2 generated by the epoxy chain extenders result in poor melt uniformity, increased carboxyl residue leading to increased product color (YI), and insufficient recovery of the molecular weight of the regenerated polyamide.

[0149] The test results from Examples 1, 7-9, and the application examples show that using PBO and a copolymer containing glycidyl methacrylate is more helpful in repairing molecular chains, suppressing side reactions, and maintaining melt stability.

[0150] The test results from Examples 1, 10-12, and the application examples show that when using ethylene-methyl acrylate-glycidyl methacrylate copolymer as an epoxy chain extender, under the premise of adding the same molar amount of glycidyl methacrylate in the composition, controlling the content of glycidyl methacrylate in the copolymer within a certain range is more conducive to achieving efficient repair of molecular chains, gel inhibition, and excellent processing stability. When the content of glycidyl methacrylate is low, the inhibition of gelation is not obvious, the gel content in the melt is high, and the filtration pressure value is unstable and rises rapidly. When the content of glycidyl methacrylate is high, it itself becomes a source of crosslinking sites, resulting in unstable and rapid rise of the filtration pressure value, and also leading to an increase in the product's color YI value.

[0151] The test results from Examples 1 and 13, as well as the application examples, show that the self-made PBO and commercially available PBO can achieve similar effects. However, the chain extender composition corresponding to the self-made PBO of this invention is superior in terms of repairing molecular chains, inhibiting side reactions, and maintaining melt stability.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chain extender composition for recycling polyamides, characterized in that, This includes dioxazoline chain extenders and epoxy chain extenders in a mass ratio of (1.50–2.61):

1.

2. The chain extender composition for recycling polyamide according to claim 1, characterized in that, The dioxazoline chain extender includes at least one of 2,2'-(1,3-phenylene)-dioxazoline and 2,2-bis(2-oxazoline); Preferably, the epoxy chain extender includes at least one of ethylene-methyl acrylate-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate copolymer, bisphenol A epoxy resin, bisphenol A diglycidyl ether, and bisphenol F diglycidyl ether. Preferably, the molar fraction of glycidyl methacrylate component in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 5% to 12%, and the molar fraction of methyl acrylate component in the ethylene-methyl acrylate-glycidyl methacrylate copolymer is 20% to 30%. Preferably, the molar fraction of glycidyl methacrylate component in the ethylene-glycidyl methacrylate copolymer is 5% to 12%; Preferably, the number-average molecular weights of the ethylene-methyl acrylate-glycidyl methacrylate copolymer and the ethylene-glycidyl methacrylate copolymer are each independently 15000 g / mol to 30000 g / mol.

3. The chain extender composition for recycling polyamide according to claim 2, characterized in that, The preparation method of the 2,2'-(1,3-phenylene)-dioxazoline includes the following steps: (a) 1,3-Phenyl chloride reacts with ethanolamine in the presence of an acid-binding agent to give 1,3-bis(2-hydroxyethylcarbamoyl)benzene; (b) 1,3-bis(2-hydroxyethylcarbamoyl)benzene was refluxed in a solvent in the presence of pyridine p-toluenesulfonate as a catalyst; the reactants were then cooled to room temperature and the organic phase was washed and collected. (c) Remove the solvent from the organic phase to obtain the crude product; recrystallize the crude product using a mixed solvent of ethanol and acetone; Preferably, in step (a), the molar ratio of ethanolamine to the acid-binding agent is 1:(1 to 1.5), and the molar ratio of 1,3-benzoyl chloride to ethanolamine is 1:(2.0 to 2.4). Preferably, in step (b), the amount of pyridine p-toluenesulfonate used is 0.5 wt% to 1 wt% of the reaction system; Preferably, in step (c), the volume ratio of ethanol to acetone is 3:1; Preferably, the HPLC purity of the 2,2'-(1,3-phenylene)-dioxazoline is ≥99%.

4. A blend of recycled spinning-grade polyamide resins, characterized in that, Includes the main ingredient and the chain extender composition for recycling polyamide as described in any one of claims 1 to 3; The main ingredients include recycled polyamide, virgin polyamide, optional antioxidants, and optional thermal stabilizers.

5. The compound for recycled spinning-grade polyamide resin according to claim 4, characterized in that, The difference between the peak filtration pressure value and the initial filtration pressure value of the melt of the recycled spinning-grade polyamide resin compound is <6.0 MPaG, preferably <4 MPaG, and more preferably <3 MPaG. Preferably, the initial filtration pressure of the melt of the recycled spinning-grade polyamide resin blend is ≤12MPaG, and more preferably ≤11MPaG; Preferably, the melt stability coefficient (CV) of the recycled spinning-grade polyamide resin blend is ≤7.1%, and more preferably ≤6.0%.

6. The composite material for recycled spinning-grade polyamide resin according to claim 4, characterized in that, Includes the following components by mass percentage: Recycle 20%–80% of polyamide. Virgin polyamide 18%–78% Chain extender compositions for polyamide recycling: 0.9%–3% Antioxidant 0.02%–1.5% Heat stabilizer 0.08%–0.25%; Preferably, the antioxidant includes at least one of antioxidant 1010 and antioxidant 168; Preferably, the heat stabilizer includes at least one of cuprous iodide and potassium iodide.

7. The compound for recycled spinning-grade polyamide resin according to any one of claims 4 to 6, characterized in that, In the recycled spinning-grade polyamide resin blend, the mass percentage of dioxazoline chain extender is 0.76%–1.32%, and the mass percentage of epoxy chain extender is 0.3%–0.88%. Preferably, the recycled polyamide has a mass percentage of 65% to 75%, more preferably 68% to 71%.

8. The compound for recycled spinning-grade polyamide resin according to any one of claims 4 to 6, characterized in that, The recycled polyamide fibers have a length of 0.3–0.8 cm; Preferably, the oil content of the recycled polyamide is ≤0.1%; Preferably, the relative viscosity of the virgin polyamide is 2.40 to 2.50; Preferably, the melt index of the virgin polyamide at 275°C and 2.16 kg is 68-80 g / 10 min.

9. A recycled spinning-grade polyamide resin, characterized in that, It is mainly prepared from the recycled spinning-grade polyamide resin blend as described in any one of claims 4 to 8; Preferably, the relative viscosity of the recycled spinning-grade polyamide resin chips is 2.37 to 2.47; Preferably, the molecular weight distribution of the recycled spinning-grade polyamide resin chips is 1.50 to 1.70; Preferably, the melt index of the recycled spinning-grade polyamide resin chips at 275°C and 2.16 kg is 72–95 g / 10 min.

10. The method for preparing the recycled spinning-grade polyamide resin according to claim 9, characterized in that, Includes the following steps: Recycled spinning-grade polyamide resin is melt-extruded with a composite material and granulated to obtain recycled spinning-grade polyamide resin. In the melt extrusion process, the main material is added through the main feed port, and the dioxazoline chain extender and the epoxy chain extender are added sequentially through the first side feed port and the second side feed port, respectively. Preferably, the temperature of the melt extrusion is 150–285°C; Preferably, the temperature corresponding to the first side feeding port is 260-270℃; Preferably, the temperature corresponding to the second side feeding port is 270-280℃.

11. Regenerated polyamide fiber, made from the recycled spinning-grade polyamide resin as described in claim 9; Preferably, the regenerated polyamide fiber has a breaking strength of 3.7 to 4.7 cN / dtex.

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