Method for in-situ preparation of semi-aromatic polyamide from waste pet and application thereof

Abstract

The application relates to a method for preparing a semi-aromatic polyamide in situ from waste PET and application thereof, and the method comprises the following steps: performing an alcoholysis reaction on waste PET and an alcoholysis reagent to obtain an ester mixture; performing an ester-amine exchange reaction on the ester mixture and an amine compound to obtain a prepolymer of the semi-aromatic polyamide; and performing a solid-phase polycondensation reaction on the prepolymer of the semi-aromatic polyamide to obtain the semi-aromatic polyamide. The application does not need to separate and purify the alcoholysis intermediate, directly polymerizes in situ, realizes efficient conversion of all components of the waste PET, has a short process flow, high atomic economy, mild reaction conditions, low energy consumption, the number average molecular weight of the prepared PA10T is 4100-13000 g / mol, the initial decomposition temperature T d5% >400 DEG C, and low-value waste PET can be converted into high-end semi-aromatic engineering plastics.

Description

Technical Field

[0001] This application relates to the field of resource utilization technology of waste polymer materials, and in particular to a method for preparing semi-aromatic polyamide in situ using waste PET and its application. Background Technology

[0002] Polyethylene terephthalate (PET), a widely used general-purpose thermoplastic polyester material, is extensively applied in many core fields such as food packaging, chemical fiber textiles, electronics, and the automotive industry. However, with the large-scale development of the PET industry, the consumption of PET plastic products has increased dramatically year by year, generating a large amount of waste PET material. Due to the stable molecular structure of PET and its extreme difficulty in natural degradation, waste PET is difficult to decompose naturally. Large-scale accumulation not only causes serious white pollution and environmental pressure but also results in a significant waste of polyester resources. Therefore, the resource-based and high-value recycling of waste PET has extremely high research value and industrial application potential.

[0003] Semi-aromatic polyamides, as a type of specialty engineering plastic with significant application value, incorporate rigid benzene rings and flexible long-chain diamines into their molecular chains, endowing the material with exceptional comprehensive properties. PA10T, compared to ordinary polyesters, exhibits outstanding advantages such as low water absorption, good dimensional stability, high mechanical strength and rigidity, while also possessing superior high-temperature and heat resistance, making it suitable for various harsh environments. These superior properties enable PA10T to operate reliably under complex working conditions, significantly extending the service life of related components and products, and improving overall product reliability. However, the current industrial synthesis of PA10T heavily relies on fossil-based high-purity monomers, resulting in complex synthesis processes and high raw material costs, which greatly limits its wider adoption and application.

[0004] Existing technologies include studies on the preparation of semi-aromatic polyamides from PET raw materials, but significant technical shortcomings remain in the process systems. For example, existing chemical recycling processes for waste PET typically employ alcoholysis (such as methanol or glycol alcoholysis) to break down the polyester backbone. However, existing chemical recycling technologies generally suffer from severe resource utilization inefficiencies and the disconnect between alcoholysis and polymerization processes. Traditional processes prioritize the absolute purity of alcoholysis monomers. To obtain refined main products (such as dimethyl terephthalate) suitable for subsequent repolymerization, large amounts of solvents and energy must be consumed for cumbersome separation and purification operations. In actual alcoholysis reaction networks, monomethyl terephthalate, ethyl terephthalate, and dimethyl isophthalate byproducts are inevitably generated. In traditional process routes, these alcoholysis byproducts are considered "impurities" that must be removed and are directly discarded, resulting in extremely low atom economy for the overall process. Meanwhile, the "alcoholization" of waste polyester and the "recombination polycondensation" of high-performance polyamide are completely disconnected in terms of process, lacking a green catalytic reaction system that can synergistically activate multiple mixed functional groups (ester groups, hydroxyethyl esters, etc.).

[0005] Therefore, developing a process that breaks away from the traditional mindset of "purification before polymerization" and uses the main product and all by-product intermediates generated from the alcoholysis of waste PET as mixed monomer raw materials, directly and continuously constructing high-performance semi-aromatic polyamides in situ without cumbersome separation and purification, thereby achieving a full-component, zero-waste cross-category upgrade from low-value waste plastics to high-end engineering plastics, is a core technical problem that urgently needs to be solved in the field of resource utilization of waste polymer materials. Summary of the Invention

[0006] To address the aforementioned technical problems, the purpose of this application is to provide a method for in-situ preparation of semi-aromatic polyamides from waste PET and its application. By overcoming the technical shortcomings of existing technologies, such as low utilization rate of waste PET alcoholysis byproducts, fragmented alcoholysis and polymerization processes, low added value of recycled products, and difficulty in achieving cross-category upgrading, this application provides a method for in-situ preparation of semi-aromatic polyamides from waste PET. This method achieves high-value utilization of all components of waste PET alcoholysis intermediates under mild conditions, enabling continuous in-situ synthesis of high-performance semi-aromatic polyamides. The process is characterized by a short flow chart, high atom economy, and low energy consumption.

[0007] To achieve this objective, the following technical solution is adopted in this application: In a first aspect, this application provides a method for in-situ preparation of semi-aromatic polyamides using waste PET, the method comprising the following steps: (1) Waste PET and alcoholysis reagent are subjected to alcoholysis reaction to obtain an ester mixture; (2) An ester mixture and an amine compound undergo an ester-amine exchange reaction to obtain a prepolymer of a semi-aromatic polyamide; (3) The prepolymer of the semi-aromatic polyamide undergoes a solid-state polycondensation reaction to obtain the semi-aromatic polyamide.

[0008] Compared to existing processes for separating and purifying waste PET alcoholysis intermediates, the preparation method provided in this application directly replaces the alcoholysis reagent by performing an ester-amine exchange reaction on mixed esters and amine compounds, thereby obtaining a prepolymer of semi-aromatic polyamide, which is then subjected to a solid-state polycondensation reaction to prepare a semi-aromatic polyamide with a specific structure.

[0009] In some embodiments, the alcoholysis reagent in step (1) is methanol.

[0010] In some embodiments, the mass ratio of the alcoholysis reagent to waste PET is (0.25-5):1, for example, 0.75:1, 1.25:1, 1.75:1, 2.25:1, 2.75:1, 3.25:1, 3.75:1, 4.25:1 or 4.75:1, etc.

[0011] In some embodiments, the alcoholysis reaction is carried out under the catalysis of a catalyst, preferably 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0012] In some embodiments, the mass ratio of TBD to waste PET is (0.01-0.1):1, for example, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1 or 0.09:1, and more preferably (0.06-0.07):1.

[0013] In some embodiments, the temperature of the alcoholysis reaction is 20-70°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, and more preferably 40-60°C.

[0014] In this application, the temperature of the alcoholysis reaction is controlled within a mild range of 20-70℃, which eliminates the need for high-temperature conditions and has the advantages of reducing production energy consumption and ensuring safe and stable operation.

[0015] In some embodiments, the alcoholysis reaction time is 10-120 min, such as 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min or 110 min, and more preferably 50-100 min.

[0016] In some embodiments, the solvent for the alcoholysis reaction is 1,3-dioxapentane, and the mass ratio of 1,3-dioxapentane to waste PET is (1-7):1, for example 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1 or 6.5:1, etc., and more preferably (4-6):1.

[0017] In some embodiments, the ester mixture includes dimethyl terephthalate (DMT), monomethyl terephthalate (MMT), methyl hydroxy terephthalate (MHET), and dimethyl isophthalate (DMI).

[0018] In some embodiments, step (1) includes: mixing waste PET, methanol, 1,3-dioxapentane and TBD, and carrying out an alcoholysis reaction at 20-70°C for 10-120 min, and obtaining an ester mixture after the reaction, wherein the ester mixture includes dimethyl terephthalate (DMT), monomethyl terephthalate (MMT), ethyl terephthalate (MHET) and dimethyl isophthalate (DMI).

[0019] The alcoholysis method provided in this application utilizes methanol and 1,3-dioxapentane in conjunction with a TBD-based alcoholysis system, achieving 100% degradation and conversion at relatively low temperatures. This overcomes the limitations of traditional chemical recycling, which typically requires high temperatures and pressures, and significantly reduces energy consumption in industrial processes.

[0020] In some embodiments, the total molar ratio of ester groups in the ester mixture in step (2) to the molar ratio of amino groups in the amine compound is 1:(0.96-1.08), for example, 1:0.965, 1:0.970, 1:0.975, 1:0.980, 1:0.995, 1:1.000, 1:1.025, 1:1.040, 1:1.055 or 1:1.075, etc.

[0021] In this application, the total molar number of ester groups in the ester mixture can be calculated by analyzing the content of each component in the alcoholysis product using liquid chromatography. Specifically, the contents of dimethyl terephthalate (DMT), monomethyl terephthalate (MMT), methyl hydroxy terephthalate (MHET), and dimethyl isophthalate (DMI) in the alcoholysis product are tested by high performance liquid chromatography (HPLC), and the total molar number of ester groups in the system is calculated based on the number of ester groups contained in each component.

[0022] In some embodiments, the amine compound includes any one or a combination of at least two of 1,6-hexanediamine, 1,8-octanediamine, 1,10-decanediamine, and 1,12-dodecanediamine.

[0023] In some embodiments, the ester-amine exchange reaction further includes the addition of a stabilizer, preferably anhydrous sodium hypophosphite, and preferably the amount of anhydrous sodium hypophosphite used is 0.1-0.7 wt% of the mass of waste PET, such as 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.40 wt%, 0.45 wt%, 0.50 wt%, 0.55 wt%, 0.60 wt%, or 0.65 wt%.

[0024] In some embodiments, the temperature of the ester-amine exchange reaction is 50-80°C, such as 55°C, 60°C, 65°C, 68°C, 70°C, 72°C, 75°C, or 78°C.

[0025] In some embodiments, the time for the ester-amine exchange reaction is 180-300 min, such as 185 min, 200 min, 215 min, 230 min, 245 min, 260 min, 275 min, or 290 min.

[0026] In some embodiments, the stirring rate of the ester-amine exchange reaction is 50-300 rpm, such as 70 rpm, 100 rpm, 130 rpm, 180 rpm, 210 rpm, 240 rpm or 270 rpm.

[0027] In some embodiments, after the ester-amine exchange reaction, the process further includes a step of heating and vacuuming to remove the solvent. Preferably, the solvent removal temperature is 60-200°C, such as 65°C, 70°C, 85°C, 110°C, 135°C, 150°C, 175°C, or 190°C.

[0028] In some embodiments, the solvent removal time is 180-300 min, such as 185 min, 200 min, 215 min, 230 min, 245 min, 260 min, 275 min, or 290 min.

[0029] In some embodiments, the stirring rate for solvent removal is 50-150 rpm, such as 55 rpm, 70 rpm, 85 rpm, 100 rpm, 115 rpm, 120 rpm, 135 rpm, or 145 rpm.

[0030] In some embodiments, the vacuum level of the vacuum pump is controlled to be within 100 Pa.

[0031] In some embodiments, step (2) includes: adding 1,10-decanediamine to the ester mixture obtained in step (1), controlling the total molar number of ester groups in the ester mixture to the molar ratio of amino groups of the amine compound in the reaction system to 1:(0.96-1.08), carrying out an ester-amine exchange reaction at 50-80°C for 180-300 min, constructing polyamide segments in situ, and removing the solvent and small molecules of reaction byproducts after complete reaction to obtain a prepolymer of solid semi-aromatic polyamide.

[0032] This application directly performs ester-amine exchange reaction after alcoholysis, breaking the limitation of traditional chemical recycling that must rely on high-purity single monomers. By using byproducts such as MMT, MHET, and DMI in the alcoholysis system as polymerization monomers, both the main product and byproducts can fully participate in the ester-amine exchange reaction, achieving 100% utilization of waste PET components, greatly simplifying the process, and reducing purification energy consumption and production costs.

[0033] In some embodiments, the temperature of the solid-state polycondensation reaction in step (3) is 220-280°C, such as 225°C, 230°C, 245°C, 250°C, 260°C, 265°C, 270°C or 275°C, and more preferably 260-280°C.

[0034] This application further regulates the temperature of the solid-phase polycondensation reaction to 260-280℃. Within this temperature range, the solid-phase chain extension is sufficient, the product has a higher molecular weight, and the thermal stability is better.

[0035] In some embodiments, the solid-phase polycondensation reaction time is 120-480 min, such as 150 min, 205 min, 260 min, 315 min, 370 min, 425 min, 450 min or 475 min, and more preferably 120-360 min.

[0036] This application further regulates the solid-state polycondensation reaction time to 120-360 min. Within this time range, the thermal degradation of molecular chains can be reduced to a greater extent, and the high molecular weight and high initial decomposition temperature of the product can be stably maintained, thus balancing production efficiency and product quality.

[0037] In some embodiments, step (3) includes: placing the prepolymer of the semi-aromatic polyamide obtained in step (2) under high vacuum (-0.1MPa) and carrying out a high-temperature solid-state polycondensation reaction at 220-280°C for 120-480 min, so that the macromolecular chain grows linearly further, and finally obtaining a high molecular weight semi-aromatic polyamide.

[0038] This application couples a multi-step reaction of PET alcoholysis-ethanol exchange of alcoholysis products-polymerization, which simplifies the process and significantly reduces costs.

[0039] In some embodiments, the raw material PET comes from waste PET bottle flakes. These waste PET bottle flakes can include any commercially available PET material such as mineral water bottle flakes, purified water bottle flakes, soda water bottle flakes, and beverage bottle flakes, all of which can be used as raw materials for the preparation of semi-aromatic polyamides. In writing the embodiments of this application, only a specific type of waste mineral water bottle is used as an example for illustration, and this does not mean that this application can only use it as a raw material. Any waste PET similar to the waste mineral water bottles actually used in the embodiments can meet the application requirements of this application, and this application will not list them in detail here.

[0040] Secondly, this application provides a semi-aromatic polyamide, which is prepared by the method described in the first aspect.

[0041] In some embodiments, the number-average molecular weight of the semi-aromatic polyamide is 4100-13000 g / mol, such as 4500 g / mol, 6000 g / mol, 7000 g / mol, 8000 g / mol, 9000 g / mol, 10000 g / mol, 11000 g / mol, or 12500 g / mol.

[0042] In some embodiments, the initial decomposition temperature T of the semi-aromatic polyamide d5% >400℃, for example 404.81℃, 405.14℃, 405.44℃, 409.01℃, 411.71℃ or 413.43℃, preferably 420℃ or above.

[0043] Thirdly, this application provides an application of the semi-aromatic polyamide as described in the second aspect in specialty engineering plastics.

[0044] The special engineering plastics used in this application may be, for example, PA6T, PA9T, PA10T, or PA12T.

[0045] The semi-aromatic polyamide prepared in this application has high number-average molecular weight and weight-average molecular weight, and sufficient molecular chain length, thus endowing the material with excellent tensile strength; at the same time, the initial decomposition temperature T of the semi-aromatic polyamide prepared in this application is... d5% With a temperature of >400℃, it exhibits outstanding thermal stability and can be better applied to special engineering plastics. It has successfully transformed ordinary waste polyester PET into high-value-added semi-aromatic engineering polyamide, changing the traditional situation of PET downgrading and recycling and low-value reuse, and greatly improving the added value of solid waste resource utilization.

[0046] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0047] Compared with the prior art, this application has at least the following beneficial effects: (1) This application does not require the separation and purification of intermediates, and directly generates the final product through in-situ polymerization. This breaks the limitation that traditional chemical recycling must rely on high-purity single monomers, and achieves 100% utilization of waste PET components. It has high atom economy and low energy consumption.

[0048] (2) This application successfully converts ordinary waste PET into high-value-added semi-aromatic engineering polyamide, which changes the traditional status quo of PET downgrading and recycling and low-value reuse, greatly improves the added value of solid waste resource utilization, and realizes the cross-category high-value upgrade of low-value waste plastics.

[0049] (3) The overall conditions of this application are mild and the energy consumption is low, which breaks the limitation that traditional chemical recycling usually requires high temperature and high pressure, and can significantly reduce the heat energy consumption in the industrial process. Attached Figure Description

[0050] Figure 1 It is the semi-aromatic polyamide PA10T obtained in Example 1. 13 C-NMR.

[0051] Figure 2 It is the semi-aromatic polyamide PA10T obtained in Example 1. 1 H-NMR.

[0052] Figure 3 This is the infrared spectrum of the semi-aromatic polyamide PA10T obtained in Example 1.

[0053] Figure 4 The image shows the TGA curve of the semi-aromatic polyamide PA10T obtained in Example 1. Detailed Implementation

[0054] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0055] Unless otherwise specified, the raw materials involved in the following specific embodiments of this application are all conventional materials in the field and can be purchased from commercially available products. Some raw material information is as follows: The waste PET used comes from waste Nongfu Spring mineral water bottle flakes.

[0056] Example 1 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET, including the following steps: (1) Weigh 15.374 g of waste PET, 1.076 g of TBD, 38.435 g of methanol and 76.870 g of 1,3-dioxane into a reactor and react at 60°C for 90 min to obtain an ester mixture solution.

[0057] (2) Weigh 14.474 g of 1,10-decanediamine and 0.029 g of anhydrous sodium hypophosphite and add them to the ester mixture solution. React at 65 °C for 240 min under a nitrogen atmosphere to obtain a solution containing the prepolymer. Vacuum the solution containing the prepolymer to below -0.05 MPa to remove methanol for 120 min. Continue to heat to 100 °C and maintain for 60 min, reduce the pressure to below -0.1 MPa, then heat to 170 °C and maintain for 60 min, and then heat to 190 °C and maintain for 60 min to completely remove the solvent and byproducts to obtain powdered polyamide PA10T prepolymer.

[0058] (3) Transfer the prepolymer powder to a vacuum oven, evacuate to below 100 Pa, and carry out solid-state polycondensation reaction at 260°C for 240 min. After the solid-state polycondensation reaction is completed, the white powdered semi-aromatic polyamide PA10T is discharged.

[0059] Example 2 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the time for the ester-amine exchange reaction is shortened to 180 min.

[0060] Example 3 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the time for the ester-amine exchange reaction is extended to 300 min.

[0061] Example 4 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation temperature is reduced to 240°C.

[0062] Example 5 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation temperature is reduced to 250°C.

[0063] Example 6 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation temperature is increased to 270°C.

[0064] Example 7 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation time is shortened to 120 min.

[0065] Example 8 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation time is extended to 360 min.

[0066] Example 9 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The only difference between this method and Example 1 is that the solid-phase polycondensation time is extended to 480 min.

[0067] Example 10 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from that in Example 1 only in that the molar ratio of the total number of ester groups in the ester mixture to the molar ratio of the amino group in the amine compound is changed to 1:0.95.

[0068] Example 11 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from that in Example 1 only in that the molar ratio of the total number of ester groups in the ester mixture to the molar ratio of the amino groups in the amine compound is changed to 1:1.

[0069] Example 12 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET, including the following steps: (1) Weigh 15.374 g of waste PET, 0.769 g of TBD, 30.748 g of methanol and 15.374 g of 1,3-dioxane into a reactor and react at 70°C for 30 min to obtain an ester mixture solution.

[0070] (2) Weigh 1,10-decanediamine (total molar ratio of ester group to amino group is 1:0.96) and 0.077 g of anhydrous sodium hypophosphite and add them to the ester mixture solution. React at 80 °C for 300 min under a nitrogen atmosphere to obtain a solution containing the prepolymer. Vacuum the solution containing the prepolymer to below -0.05 MPa to remove methanol for 120 min. Continue to heat to 100 °C and maintain for 60 min, reduce the pressure to below -0.1 MPa, then heat to 170 °C and maintain for 60 min, and then heat to 190 °C and maintain for 60 min to completely remove the solvent and byproducts to obtain powdered polyamide PA10T prepolymer.

[0071] (3) Transfer the prepolymer powder to a vacuum oven, evacuate to below 100 Pa, and carry out solid-state polycondensation reaction at 260°C for 360 min. After the solid-state polycondensation reaction is completed, the white powdery semi-aromatic polyamide PA10T is discharged.

[0072] Example 13 This embodiment provides a method for preparing semi-aromatic polyamides in situ using waste PET, including the following steps: (1) Weigh 15.374 g of waste PET, 0.307 g of TBD, 76.870 g of methanol and 76.870 g of 1,3-dioxane into a reactor and react at 20°C for 120 min to obtain an ester mixture solution.

[0073] (2) Weigh 1,10-decanediamine (total molar ratio of ester group to amino group is 1:1.08) and 0.108 g of anhydrous sodium hypophosphite and add them to the ester mixture solution. React at 50 °C for 180 min under a nitrogen atmosphere to obtain a solution containing the prepolymer. Vacuum the solution containing the prepolymer to below -0.05 MPa to remove methanol for 120 min. Continue to heat to 100 °C and maintain for 60 min, reduce the pressure to below -0.1 MPa, then heat to 170 °C and maintain for 60 min, and then heat to 190 °C and maintain for 60 min to completely remove the solvent and byproducts to obtain powdered polyamide PA10T prepolymer.

[0074] (3) Transfer the prepolymer powder to a vacuum oven, evacuate to below 100 Pa, and carry out solid-state polycondensation reaction at 260°C for 120 min. After the solid-state polycondensation reaction is completed, the white powdered semi-aromatic polyamide PA10T is discharged.

[0075] Comparative Example 1 This comparative example provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from Example 1 only in that DMT is reacted directly with 1,10-decanediamine.

[0076] Comparative Example 2 This comparative example provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from Example 1 only in that MMT is used to react directly with 1,10-decanediamine.

[0077] Comparative Example 3 This comparative example provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from Example 1 only in that MHET is used to react directly with 1,10-decanediamine.

[0078] Comparative Example 4 This comparative example provides a method for preparing semi-aromatic polyamides in situ using waste PET. The method differs from Example 1 only in that DMI is directly reacted with 1,10-decanediamine.

[0079] Performance Test 1 The structure of the semi-aromatic polyamide PA10T provided in Example 1 was characterized, and the results are as follows: Figure 1 and Figure 2 The semi-aromatic polyamide PA10T obtained in Example 1 are respectively 13 C-NMR characterization and 1 H-NMR characterization, through Figure 1 and Figure 2 It can be demonstrated that the semi-aromatic polyamide PA10T was prepared by the method in Example 1.

[0080] Figure 3 The infrared spectral test results of the semi-aromatic polyamide PA10T obtained in Example 1 were obtained by... Figure 3 It can be seen that the 3200-3400 cm⁻¹ in the spectrum -1 A broad absorption peak appears at 1640 cm⁻¹ for the NH stretching vibration of the amide. -1 1530 cm -1 The presence of characteristic absorption peaks for amide I and amide II bands, along with vibrational peaks for long-chain methylene groups and the benzene ring skeleton, confirms that the product is a semi-aromatic polyamide PA10T. The spectrum does not show PET ester groups at 1720 cm⁻¹. -1 The presence of characteristic absorption peaks, as well as the absence of primary amine characteristic double peaks for free diamines, indicates that the waste PET raw materials have been fully converted and the residual amount of small molecule impurities in the product is low.

[0081] Performance Test 2 (1) The molecular weight of the semi-aromatic polyamide PA10T obtained in Examples 1-13 and Comparative Examples 1-4 was determined. The test method parameters were: gel chromatography (GPC) with polymethyl methacrylate as standard, and the mobile phase was hexafluoroisopropanol (containing 5 mmol / L sodium trifluoroacetate). The test results are shown in Table 1.

[0082] (2) The initial decomposition temperature of the semi-aromatic polyamide PA10T obtained in Examples 1-13 and Comparative Examples 1-4 was determined. The test method parameters were: TG-60H (heating rate of 10℃ / min). The test results are shown in Table 1. Figure 4 The TGA characterization of the semi-aromatic polyamide PA10T obtained in Example 1 was performed by... Figure 4 It can be seen that the initial decomposition temperature T of the semi-aromatic polyamide PA10T obtained in Example 1 is... d5% It can reach 422.92℃.

[0083] Table 1 The test results show that: (1) As can be seen from Examples 1 to 13, this application does not require separation and purification of waste PET alcoholysis intermediates. The related products prepared by direct in-situ polymerization have a number average molecular weight of 4100-13000 g / mol, preferably 4145-12741 g / mol, a weight average molecular weight of 10570-63130 g / mol, a dispersibility coefficient of 2.54-7.74, and an initial decomposition temperature T. d5% It can reach temperatures above 404℃.

[0084] (2) As can be seen from Examples 1 and 4-5, 9-10, by changing the solid-phase polycondensation temperature, when it is not in the further preferred range of 260-280℃, the solid-phase chain extension will be insufficient, resulting in a decrease in number-average molecular weight and weight-average molecular weight, and the initial decomposition temperature will also decrease. By changing the solid-phase polycondensation time, when it is not in the further preferred range of 120-360 min, the thermal degradation of molecular chains will be increased, which will also lead to a decrease in number-average molecular weight and a decrease in initial decomposition temperature. By changing the total molar number of ester groups in the ester mixture to the molar ratio of amino groups in the amine compound, when it is not in the range of 1:(0.96-1.08) of this application, the ester-amine exchange polymerization reaction of the product will be affected to a certain extent, resulting in a decrease in its initial decomposition temperature.

[0085] (3) As can be seen from Example 1 and Comparative Examples 1-4, this application can obtain a better initial decomposition temperature and a higher number-average molecular weight by directly preparing semi-aromatic polyamide in situ. It can achieve the same or even better results as existing separation processes.

[0086] In summary, this application uses the main product and all by-product intermediates generated from the alcoholysis of waste PET as mixed monomer raw materials to directly and continuously construct high-performance semi-aromatic polyamides in situ without cumbersome separation and purification, thus realizing a full-component, zero-waste cross-category upgrade from low-value waste plastics to high-end engineering plastics.

[0087] This application illustrates its technical solution through the above embodiments, but it is not limited to the above process steps, meaning that this application does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this application.

Claims

1. A method for in-situ production of semi-aromatic polyamide using waste PET, characterized by, The method includes the following steps: (1) Waste PET and alcoholysis reagent are subjected to alcoholysis reaction to obtain an ester mixture; (2) An ester mixture and an amine compound undergo an ester-amine exchange reaction to obtain a prepolymer of a semi-aromatic polyamide; (3) The prepolymer of the semi-aromatic polyamide undergoes a solid-state polycondensation reaction to obtain the semi-aromatic polyamide.

2. The method of claim 1, wherein, The alcoholysis reagent mentioned in step (1) is methanol; And / or, the mass ratio of the alcoholysis reagent to waste PET is (0.25-5):1; And / or, the alcoholysis reaction is carried out under the catalysis of a catalyst, preferably TBD.

3. The method according to claim 1 or 2, characterized in that, The alcoholysis reaction in step (1) is carried out at a temperature of 20-70°C, preferably 40-60°C, for a time of 10-120 min, preferably 50-100 min.

4. The method according to any one of claims 1 to 3, characterized in that, The total molar number of ester groups in the ester mixture described in step (2) is 1:(0.96-1.08) to the molar ratio of amino groups in the amine compound. And / or, the amine compound includes any one or a combination of at least two of 1,6-hexanediamine, 1,8-octanediamine, 1,10-decanediamine or 1,12-dodecanediamine.

5. The method according to any one of claims 1-4, characterized in that, The ester-amine exchange reaction described in step (2) also includes the addition of a stabilizer; Preferably, the stabilizer is anhydrous sodium hypophosphite; Preferably, the amount of anhydrous sodium hypophosphite used is 0.1-0.7 wt% of the mass of waste PET.

6. The method according to any one of claims 1-5, characterized in that, The temperature of the ester-amine exchange reaction in step (2) is 50-80℃ and the time is 180-300 min.

7. The method according to any one of claims 1-6, characterized in that, The temperature of the solid-state polycondensation reaction in step (3) is 220-280℃, preferably 260-280℃; And / or, the solid-phase polycondensation reaction takes 120-480 min, preferably 120-360 min.

8. A semi-aromatic polyamide, characterized in that, The semi-aromatic polyamide is prepared by the method according to any one of claims 1-7.

9. The semi-aromatic polyamide according to claim 8, characterized in that, The number-average molecular weight of the semi-aromatic polyamide is 4100-13000 g / mol; and / or the initial decomposition temperature T d5% > 400°C, preferably above 420°C.

10. The application of a semi-aromatic polyamide according to claim 8 or 9 in specialty engineering plastics.

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