A method for preparing recycled functional polyester using waste polyester

Abstract

The present invention belongs to the technical field of waste polyester recycling and relates to a method for preparing regenerated functionalized polyester from waste polyester. The method comprises first capping functional monomers with an excess of diol to produce a functional depolymerizing agent. The residual diol, functional depolymerizing agent, and waste polyester are then placed in a polymerization kettle for depolymerization to produce a functional depolymerized product. The functional depolymerized product undergoes a polycondensation reaction to produce the regenerated functionalized polyester. The functional monomers are functional monomers with carboxyl groups at both ends and a benzene ring. The molar ratio of diol to functional monomer is (3-12):1, and the ratio of the amount of functional depolymerizing agent added to the molar number of repeating units in the waste polyester is (0.05-0.3):1. The melting point of the functional depolymerizing agent is less than the depolymerization temperature, and the melting point of the waste polyester is less than the depolymerization temperature. The regenerated functionalized polyester prepared by the method has a molecular weight distribution of less than 2.0, and the functional monomers are evenly distributed throughout the molecular chains of the regenerated functionalized polyester, resulting in excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste polyester and relates to a method for preparing regenerated functional polyester by utilizing waste polyester. Background Art

[0002] Polyester is a widely used thermoplastic polyester material. Due to its excellent mechanical properties, heat resistance and chemical stability, it is widely used in various fields. However, the large-scale use and non-degradability of polyester have led to a large accumulation of waste, causing serious environmental pollution. Therefore, the recycling of polyester is of vital importance. Currently, polyester recycling methods are mainly divided into physical recycling and chemical recycling. Physical recycling is carried out through processes such as cleaning, crushing and melting, but its recycling effect is limited by the purity of the raw materials and the impurity content. Chemical recycling, on the other hand, converts waste polyester into its raw material monomers through chemical reactions, has high recycling efficiency, and plays a positive role in reducing the environmental burden.

[0003] In the existing technology, PET alcoholysis recovery is mainly carried out through the depolymerization of PET in an ethylene glycol solution. The depolymerization temperature is usually between 190 and 210°C. Below the melting point of PET, the entire depolymerization process is heterogeneous depolymerization. Because the depolymerization efficiency varies from the outside to the inside, in order to achieve uniform depolymerization of the alcoholysis solution and increase the reaction rate, the depolymerization is usually carried out using an excess of diol as a medium. The final target product of the alcoholysis is mainly monomers such as BHET. The problems brought by the above existing technologies include high solvent usage, long reaction time, high energy consumption, and complex process. At the same time, the price of recycled polyester is much higher than that of virgin polyester, which limits its application range. Therefore, the introduction of functional monomers can be used to achieve high-value modification of recycled polyester.

[0004] There are two ways to introduce functional monomers in the prior art. The first way, as shown in CN119331228A, is to react the functional monomer directly with the depolymerization product. In this case, during the entire reaction process, there is not only an esterification reaction between the functional monomer terminal carboxyl group and the depolymerization product terminal hydroxyl group, but also an ester exchange reaction between the depolymerization products. Even if a functional monomer with higher reactivity is used, the ester exchange reaction between the depolymerization products themselves cannot be avoided, which ultimately causes the functional monomer to be unevenly distributed in the molecular chain, resulting in a wide molecular weight distribution of the regenerated functional polyester. The second way, as shown in patent CN119331228A, is to co-esterify the functional monomer, dibasic alcohol, and depolymerization product. In this case, the dibasic alcohol can end-cap the functional monomer to obtain an alcohol-terminated functional ester. Subsequently, an ester exchange reaction occurs between the functional ester and the depolymerization product. Although this process can use the same dibasic alcohol as the depolymerization product to reduce the activity difference, due to the different degrees of polymerization between the depolymerization product and the functional ester, the length of the molecular chain still affects the end group activity, and an activity difference is inevitable between the two.

[0005] Therefore, it is of great significance to study a method for preparing recycled functional polyester using waste polyester to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing regenerated functional polyester by utilizing waste polyester.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing regenerated functionalized polyester using waste polyester comprises: first, capping a functional monomer with a slightly excess of diol to obtain a functional depolymerizing agent; then, placing the residual diol, the functional depolymerizing agent, and the waste polyester in a polymerization kettle for depolymerization to obtain a functional depolymerized product; and then, introducing the functional depolymerized product into a polymerization reactor for polycondensation to obtain a regenerated functionalized polyester.

[0009] The functional monomer is a functional monomer with carboxyl groups at both ends and a benzene ring; a slight excess means that the molar ratio of diol to functional monomer is (3-12):1, and the ratio of the amount of functional depolymerizing agent added to the molar number of waste polyester repeating units is (0.05-0.3):1; the melting point of the functional depolymerizing agent is less than the depolymerization temperature and less than the thermal decomposition temperature of the functional depolymerizing agent, and the melting point of the waste polyester is less than the depolymerization temperature and less than the thermal decomposition temperature of the waste polyester;

[0010] The melting point of the functional depolymerizer is 155~200℃, and the melting point of waste polyester is 220~250℃. The depolymerization temperature is 5~10℃ higher than the melting point of waste polyester.

[0011] In the prior art, when preparing recycled functional polyester, depolymerization is first performed to obtain a depolymerization product, and then the depolymerization product is polymerized with a functional monomer or a functional ester through ester exchange to obtain the recycled functional polyester. However, there is a difference in activity between the depolymerization product and the functional monomer or the functional ester, which will lead to uneven distribution of the functional monomer in the molecular chain, a wide molecular weight distribution of the recycled functional polyester, and ultimately affect the performance of the copolymer product.

[0012] The present invention firstly performs alcohol end-capping on a functional monomer with a diol to prepare a functional depolymerization agent, then performs ester exchange on waste polyester with the functional depolymerization agent to obtain a functional depolymerization product, and then performs a polycondensation reaction on the functional depolymerization product to obtain a regenerated functional polyester, thereby overcoming the problem of activity difference between the above-mentioned depolymerization product and the functional monomer or functional ester.

[0013] Since the regularity of the molecular chain is destroyed after copolymerization modification, it usually leads to a decrease in the intermolecular force of the copolymer and a decrease in the mechanical properties of the copolymer. Therefore, in order to enable the copolymer to maintain good mechanical properties while giving the copolymer functional properties, functional monomers containing rigid rings such as benzene rings are used to modify the polyester. The rigidity, high thermal stability and chemical stability of the benzene ring are used to maintain the heat resistance, mechanical strength, dimensional stability, chemical resistance and hydrolysis stability and barrier properties of the polyester; at the same time, flame retardant, cationic flammable, antibacterial and other functional monomers containing benzene rings can give polyester corresponding functional properties, but due to the high steric hindrance of the benzene ring, the terminal group reaction activity of such monomers is low, and effective copolymerization cannot be achieved at high addition amounts. At the same time, the molecular weight of the prepared recycled copolyester is low and cannot be used. Therefore, in the preparation process of functionalized polyester, the amount of functional monomer introduced is very small, and the corresponding amount of functional depolymerizer used is also very small. The amount of functional depolymerizer added should not be higher than 30% of the molar number of the waste polyester repeating unit, which leads to insufficient content of terminal hydroxyl groups in the depolymerization process. During the depolymerization process, the terminal hydroxyl groups attack the ester bonds on the polyester molecular chain to break them, which is the main mode of depolymerization reaction. Therefore, when the terminal hydroxyl groups are insufficient (that is, there is no residual diol of the present invention), the limited terminal hydroxyl groups can only randomly attack the ester bonds they can contact, resulting in an insufficient depolymerization reaction process. In addition, the distribution of the breaking points is highly uneven, resulting in a wide molecular weight distribution of the functional depolymerization product. The wide molecular weight distribution of the functional depolymerization product will still lead to a wide molecular weight distribution of the regenerated functionalized polyester, which ultimately affects the performance of the copolymer product.

[0014] To address this issue, the present invention uses a slight excess of diol when preparing the functional depolymerization agent. The residual diol compensates for the lack of terminal hydroxyl groups in the depolymerization reaction system. This slight excess, rather than a large amount of diol, is because small-molecule diols are more active than the functional depolymerization agent. Before reaching the final depolymerization temperature, the temperature of the depolymerization system continues to rise. The higher the temperature, the higher the depolymerization activity of the small-molecule diol. Therefore, during this heating process, the small-molecule diol will primarily depolymerize the waste polyester. A large amount of diol would completely depolymerize the waste polyester, preventing the functional depolymerization agent from participating in the depolymerization reaction and preventing the production of a functional depolymerization product, thus failing to address the problems of the prior art. Therefore, the present invention uses a slight excess of diol, allowing the residual diol to pre-depolymerize the waste polyester (i.e., reduce the molecular weight of the polyester).

[0015] However, this design introduces a new problem: the residual diol cannot achieve uniform pre-depolymerization of the waste polyester because the diol only contacts the surface of the waste polyester and cannot reach the interior. The present invention further designs depolymerization conditions, namely, the melting point of the functional depolymerizer < the depolymerization temperature < the thermal decomposition temperature of the functional depolymerizer, and the melting point of the waste polyester < the depolymerization temperature < the thermal decomposition temperature of the waste polyester. This setting ensures that the temperature of the depolymerization system will continue to rise before reaching the final depolymerization temperature. The higher the temperature, the higher the depolymerization activity of the small molecule diol. Therefore, during the heating process, the small molecule diol will first undergo pre-depolymerization on the surface of the waste polyester. As the temperature rises further, the waste polyester will gradually melt, and the small molecule diol will also depolymerize within the waste polyester, thus achieving uniform pre-depolymerization. Afterwards, the functional depolymerization agent and the waste polyester are both in a molten state during depolymerization, and the molecular chains can be evenly mixed, so that the molecular weight distribution of the functional depolymerization product is narrow, that is, high-temperature melting homogeneous depolymerization is achieved; wherein, in this process, the residual diol pre-depolymerizes the waste polyester (that is, reduces the molecular weight of the polyester), which can make the viscosity of the polyester melt lower, which is conducive to the diffusion and mixing between the functional depolymerization monomer and the waste polyester melt. The reaction will proceed more evenly in the entire system, and the degree of molecular chain breakage at different positions is small, so that the molecular weight distribution of the functional depolymerization product finally obtained is more uniform.

[0016] In order to achieve a slight excess of diol, the molar ratio of diol to functional monomer in this application is 3 to 12:1, which is theoretically calculated and analyzed as follows:

[0017] When the theoretical molar ratio of the added diol to the repeating units of the waste polyester is 1:1, depolymerization to monomers similar to BHET is possible. However, considering the chemical equilibrium of the depolymerization reaction, the added diol amount should be slightly higher than 1:1. However, because the final depolymerization temperature of the present invention is above the melting point of the waste polyester, the melt mixing of the depolymerizing agent and the waste polyester is more thorough. Furthermore, in order to ensure that the functionally modified monomer is evenly distributed throughout the molecular chains of the depolymerized product, depolymerization to monomers is not necessary. Instead, the depolymerized product must have a certain molecular chain length, i.e., a dimer or longer. Therefore, the theoretical molar ratio of the sum of the moles of the residual diol and the functional depolymerizing agent in the depolymerization system to the repeating units of the waste polyester is up to 0.5:1 (two waste polyester repeating units correspond to one diol, or one functional depolymerizing agent).

[0018] Assuming that the repeating unit of waste polyester is 1 mol, the sum of the moles of residual diol and functional depolymerizer required in the entire depolymerization system is up to 0.5 mol. According to the "ratio of the amount of functional depolymerizer added to the mole of waste polyester repeating unit is 0.05:1~0.3:1", the mole of functional depolymerizer is 0.05~0.3 mol, and an additional 0.45~0.2 mol of diol is required, that is, the residual diol is 0.45~0.2 mol of diol. alcohol; and when preparing 0.05~0.3mol of functional depolymerizer, 0.1~0.6mol of diol is required. Therefore, 0.55~0.8mol of diol is required in the preparation process of regenerated functional polyester, so the molar ratio of diol to functional monomer is 2.67~11:1 (0.55 / 0.05=11, 0.8 / 0.3=2.67). Considering the chemical equilibrium of the depolymerization reaction, the molar ratio of diol to functional monomer is set to 3~12:1.

[0019] As the preferred technical solution:

[0020] As described above, a method for preparing recycled functionalized polyester using waste polyester, wherein the waste polyester is any one of waste polyethylene terephthalate (waste PET), waste polybutylene terephthalate (waste PBT), waste polypropylene terephthalate (waste PTT) and waste polyethylene terephthalate-1,4-cyclohexanedimethanol (waste PETG).

[0021] In the method for preparing recycled functional polyester using waste polyester as described above, the intrinsic viscosity of the waste polyester is 0.55-1.20 dL / g.

[0022] In the method for preparing recycled functionalized polyester using waste polyester as described above, the diol is any one of ethylene glycol, 1,4-butanediol, 1,3-propylene glycol, 1,5-pentanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, isosorbide, tricyclodecane dimethanol or spirodiol.

[0023] As described above, a method for preparing recycled functionalized polyester using waste polyester, wherein the functional monomer is any one of 2-carboxyethylphenylphosphite (CEPPA), 5-sodium sulfoisophthalate (5-SSIPA) or [(6-oxy-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6)-one-methyl]-succinic acid (DDP).

[0024] In the method for preparing recycled functional polyester from waste polyester, the specific process of preparing a functional depolymerizing agent by alcohol-capping a functional monomer with a diol is as follows: under nitrogen protection, the functional monomer, the diol and the catalyst are placed in a polymerization reactor for esterification reaction; wherein the reaction pressure is 0.01-0.2 MPa, the reaction temperature is 180-220°C, and the reaction time is 1-4 hours.

[0025] In the method for preparing regenerated functional polyester using waste polyester as described above, the catalyst is any one or two of titanium ethylene glycol, tetrabutyl titanate, antimony ethylene glycol, antimony acetate, zinc acetate and zinc oxide, and the mass of the catalyst is 100-500 ppm of the mass of the functional monomer.

[0026] In the method for preparing recycled functional polyester using waste polyester as described above, the depolymerization temperature is 225-260°C, the depolymerization time is 2-10 minutes, the polycondensation temperature is 260-280°C, and the polycondensation reaction time is 1.5-2.5 hours.

[0027] The method for preparing recycled functional polyester using waste polyester as described above has an intrinsic viscosity of 0.6-0.90 dl / g and a melting point of 210-246°C.

[0028] In the method for preparing recycled functionalized polyester using waste polyester as described above, the molecular weight distribution of the functional depolymerization product is <2.5, the molecular weight distribution of the obtained recycled functionalized polyester is <2.0, and the randomness of the different alcohol units of the recycled functionalized polyester is 0.90~1.15; the randomness of the copolyester essentially describes the uniformity of the arrangement order of different monomer units in its molecular chain. It is quantitatively characterized by analyzing the sequence length distribution, namely the randomness (mainly measured by NMR). When the randomness value of a monomer unit is 1, it means that the monomer unit is randomly distributed and evenly distributed in the copolyester. Therefore, the closer the randomness of a monomer unit is to 1, the more evenly the monomer unit is distributed in the copolyester. Regenerated functionalized polyester is also a copolyester. Because in the nuclear magnetic spectrum, the hydrogen atoms on the rigid ring structure in the functional monomer are usually used as its characteristic hydrogen atoms, and the ring structure restricts molecular motion. Therefore, the coupling constants of the characteristic hydrogen atoms of the functional monomer phases connecting different diols are too small, and the splitting peaks cannot be clearly distinguished. Adjacent small peaks overlap, and it looks like a wider "single peak" or a The packages cannot be distinguished (diols can be distinguished, so the peak areas corresponding to different peaks can be calculated to calculate the randomness of diols). Therefore, the randomness of the functional monomer unit cannot be directly characterized. Since the functional monomer of the present application reacts with diols to generate functional depolymerizers, ester exchange occurs when the functional depolymerizer depolymerizes the waste polyester. Therefore, the functional monomer not only forms an ester bond with the added diol, but also forms an ester bond with the ethylene glycol in the waste polyester after ester exchange. That is, the functional monomer will have a connection relationship with the added diol and the ethylene glycol in the waste polyester. Therefore, by simultaneously detecting the randomness of the diol unit and the ethylene glycol unit in the regenerated functional polyester, the randomness of the functional monomer can be indirectly reflected. According to Reference 1 (Synthesis of Thermal-Resistant Polyester-Polycarbonate withFully Rigid Structure from Biobased Isosorbide[J].Macromolecules, 2024, 57(13):11.) It can be seen that the randomness of the two alcohol units can indicate whether the functional monomers in the copolyester are evenly distributed.

[0029] Beneficial effects:

[0030] (1) The present invention provides a method for preparing recycled functional polyester using waste polyester, wherein the waste polyester is depolymerized under the combined action of residual diol and a functional depolymerizing agent, thereby achieving uniform distribution of functional monomers in the functional depolymerization product, and the molecular weight distribution of the depolymerization product is relatively narrow.

[0031] (3) The present invention provides a method for preparing recycled functionalized polyester using waste polyester. The prepared functionalized depolymerizer terminates the functional monomer with a diol, thereby reducing the difference in end group activity among different components and avoiding uneven dispersion of the functional monomers due to differences in reaction activity, thereby improving the uniform distribution of the functional monomers in the molecular chain. The obtained recycled functionalized polyester has a narrow molecular weight distribution and excellent performance.

[0032] (3) The present invention provides a method for preparing recycled functional polyester using waste polyester. The depolymerization and repolymerization process of the recycled functional polyester is simple and can be prepared in an existing polymerization device. It has high production efficiency and low cost, and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the H-NMR spectrum of the regenerated functionalized polyester corresponding to Example 1. DETAILED DESCRIPTION

[0034] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0035] The test methods involved in the performance indicators of the present invention are as follows:

[0036] Intrinsic viscosity: Use an Ubbelohde viscometer with a capillary diameter of 0.8 mm for testing. Use an electronic balance to take 0.25 g of the sample to be tested and dissolve it in a mixed solvent of phenol and tetrachloroethane with a mass ratio of 1:1 in a 60°C water bath to obtain a test solution with a concentration of 0.005 g / ml. Then, place the test solution in a constant temperature water bath at 25±0.1°C for 10 minutes. Observe and record the time it takes for the test solution to pass through the upper and lower scale lines of the Ubbelohde viscometer (a control group is also set up, which differs from this test only in that the test sample is not added). Perform three parallel tests and take the average value as the final result. The calculation process is based on the following formula:

[0037] ;

[0038] ;

[0039] ;

[0040] Where η r is the relative viscosity, is the flow time of the solution to be tested (s), is the flow time of the mixed solvent of phenol and tetrachloroethane in the control group (s), ηsp To increase the specific viscosity, is the intrinsic viscosity (dL / g).

[0041] Molecular weight distribution: tested by gel permeation chromatography (GPC), the instrument is Agilent 1260 gel permeation chromatography, the chromatographic column is Agilent HFIP series, the mobile phase is hexafluoroisopropanol, some sodium trifluoroacetate is added, the concentration of sodium trifluoroacetate is 0.02 mol / L, and the test temperature is 35°C.

[0042] Randomness: 5 mg of the sample to be tested was dissolved in 0.6 mL of deuterated chloroform (CDCl3) to obtain a test solution, which was tested using an Avance-600 Hz nuclear magnetic resonance spectrometer (NMR); wherein the number of scans was 64 times, and the peaks corresponding to the TAT, XAX, TAX, and XAT structural units were integrated using the integration tool of Mestrenova software, with the peak area of ​​the characteristic peak of terephthalic acid as the standard, to obtain the relative areas of different peaks. The relative areas of the corresponding peaks were divided by the sum of the relative areas of the peaks corresponding to the TAT, XAX, TAX, and XAT structural units to obtain the sequence content of the corresponding peaks. The randomness of different alcohol units in the regenerated functionalized polyester was then calculated using the following general formula:

[0043] ;

[0044] ;

[0045] ;

[0046] ;

[0047] ;

[0048] In the formula, A represents a certain diol in the recycled functional copolyester (hereinafter referred to as diol A), X represents a certain functional monomer (hereinafter referred to as functional monomer X); AT is a structural unit in which diol A is connected to terephthalic acid, AX is a structural unit in which diol A is connected to functional monomer X, TAT is a structural unit in which both ends of diol A are connected to terephthalic acid, TAX and XAT are structural units in which both sides of diol A are connected to terephthalic acid and functional monomer respectively, and XAX is a structural unit in which both ends of diol A are connected to functional monomer; f AT is the sequence content of AT units; f AX is the sequence content of AX unit; f TAX + f XAT is the sum of the sequence content of the TAX unit and the sequence content of the XAT unit; f XAX is the sequence content of XAX units; f TATis the sequence content of TAT units; L AT is the number average sequence length of AT units; L AX is the number-average sequence length of AX units; R A is the randomness of diol A in the regenerated functional polyester.

[0049] Example 1

[0050] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0051] (1) Preparation of raw materials:

[0052] Diol: 1,4-cyclohexanedimethanol;

[0053] Functional monomer: sodium 5-sulfoisophthalate;

[0054] Catalyst: tetrabutyl titanate;

[0055] Waste polyester: waste polyethylene terephthalate, the intrinsic viscosity of the waste polyester is 0.67 dL / g, and the melting point is 250°C.

[0056] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0057] Under nitrogen protection, functional monomers, diols and catalysts were placed in a polymerization reactor to undergo esterification reaction to obtain a functional depolymerizing agent with a melting point of 175°C.

[0058] The reaction pressure is 0.01 MPa, the reaction temperature is 180° C., and the reaction time is 4 h. The molar ratio of the diol to the functional monomer is 3:1, and the mass of the catalyst is 100 ppm of the mass of the functional monomer.

[0059] (3) placing the diol, functional depolymerizing agent and waste polyester remaining from step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2.2;

[0060] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.30:1; the depolymerization temperature is 260°C, and the depolymerization time is 10 minutes;

[0061] (4) The functional depolymerization product was subjected to polycondensation at 260°C for 2.5 h to obtain regenerated functional polyester.

[0062] The intrinsic viscosity of the finally prepared recycled functional polyester is 0.65 dl / g, the melting point is 246° C.; and the molecular weight distribution of the recycled functional polyester is 1.5.

[0063] pass Figure 1The relative integrated areas of the corresponding peaks in the NMR spectrum shown in the figure indicate that the molar ratio of the functional components in the recycled functional polyester to the repeating units of the waste polyester is 0.3:1, which is consistent with the design. The randomness of the two units based on 1,4-cyclohexanedimethanol and ethylene glycol in the recycled functional polyester is calculated to be 0.90 by the following formula;

[0064] Comparative Example 1

[0065] A method for preparing recycled functional polyester using waste polyester is basically the same as Example 1, except that the molar ratio of diol to functional monomer is 2:1.

[0066] The final recycled functional polyester has an intrinsic viscosity of 0.65 dl / g and a melting point of 246°C; the molecular weight distribution of the recycled functional polyester is 3.0, and the randomness of the two units based on 1,4-cyclohexanedimethanol and ethylene glycol in the recycled functional polyester is 0.85 and 0.87, respectively.

[0067] Comparing Comparative Example 1 with Example 1 reveals that the molecular weight distribution of the regenerated functionalized polyester in Comparative Example 1 broadens and its randomness decreases, indicating that the functional components are unevenly distributed within the copolymer molecular chain, and the molecular weight distribution of the copolymer is uneven. This is because the reduced amount of diol leads to insufficient terminal hydroxyl groups. The limited terminal hydroxyl groups can only randomly attack the ester bonds they can access, resulting in an incomplete depolymerization reaction process. In addition, the distribution of breakpoints is highly uneven, resulting in a broad molecular weight distribution of the functionalized depolymerization product. This broad molecular weight distribution of the functionalized depolymerization product also leads to a broad molecular weight distribution of the regenerated functionalized polyester, ultimately affecting the performance of the copolymer product. Furthermore, the uneven distribution of breakpoints prevents the functional components from being evenly distributed, resulting in a decrease in the randomness of the copolymer.

[0068] Comparative Example 2

[0069] A method for preparing recycled functional polyester using waste polyester is basically the same as Example 1, except that the molar ratio of diol to functional monomer is 13:1.

[0070] The final recycled functional polyester has an intrinsic viscosity of 0.63 dl / g and a melting point of 210°C; the molecular weight distribution of the recycled functional polyester is 3.2, and the randomness of the two units based on 1,4-cyclohexanedimethanol and ethylene glycol in the recycled functional polyester is 0.86 and 0.88, respectively.

[0071] Comparing Comparative Example 2 with Example 1, it can be found that the randomness of the regenerated functionalized copolyester obtained in Comparative Example 2 decreases. This is because the activity of the small molecule diol is higher than that of the functional depolymerizing agent, and the excess diol provides sufficient terminal hydroxyl groups, which can fully depolymerize the waste polyester, resulting in the functional depolymerizing agent being unable to participate in the depolymerization reaction, and the functional components cannot be evenly distributed in the molecular chain, which ultimately affects the uniform dispersion of the functional components in the regenerated functionalized polyester, resulting in a decrease in the randomness of the copolyester.

[0072] Comparative Example 3

[0073] A method for preparing recycled functional polyester using waste polyester is basically the same as Example 1, except that the depolymerization temperature is 220° C., that is, the melting point of the waste polyester is greater than the depolymerization temperature.

[0074] The final recycled functional polyester has an intrinsic viscosity of 0.65 dl / g and a melting point of 244°C; the molecular weight distribution of the recycled functional polyester is 3.1, and the randomness of the two units based on 1,4-cyclohexanedimethanol and ethylene glycol in the recycled functional polyester is 0.85 and 0.86, respectively.

[0075] Comparing Comparative Example 3 with Example 1, it can be found that the molecular weight distribution of the recycled functional polyester obtained in Comparative Example 3 becomes wider. This is because the melting point of the waste polyester is greater than the depolymerization temperature, the waste polyester is in a solid state, and the entire depolymerization system is a heterogeneous system. The depolymerizer can only depolymerize the surface of the waste polyester, and the molecular chains cannot be depolymerized uniformly, resulting in some depolymerizers being unable to effectively depolymerize the interior of the waste polyester, and the functional monomers being unable to effectively enter the molecular chains. The molecular weight distribution of the obtained functional depolymerization product is wide, which ultimately leads to a wide molecular weight distribution of the recycled functional polyester obtained after the polycondensation reaction, a decrease in randomness, and the inability of the functional components to be evenly distributed in the recycled copolyester molecular chains.

[0076] Example 2

[0077] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0078] (1) Preparation of raw materials:

[0079] Diol: 1,3-propylene glycol;

[0080] Functional monomer: sodium 5-sulfoisophthalate;

[0081] Catalyst: titanium glycolate;

[0082] Waste polyester: waste polybutylene terephthalate, the intrinsic viscosity of the waste polyester is 0.55 dL / g, and the melting point is 220°C.

[0083] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0084] Under nitrogen protection, functional monomers, diols and catalysts are placed in a polymerization reactor to undergo esterification reaction to obtain a functional depolymerizing agent with a melting point of 200°C.

[0085] The reaction pressure is 0.05 MPa, the reaction temperature is 190° C., and the reaction time is 3 h. The molar ratio of the diol to the functional monomer is 6:1, and the mass of the catalyst is 200 ppm of the mass of the functional monomer.

[0086] (3) placing the diol, functional depolymerizing agent and waste polyester remaining in step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2.3;

[0087] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.15:1; the depolymerization temperature is 225°C, and the depolymerization time is 8 minutes;

[0088] (4) The functional depolymerization product was subjected to polycondensation at 270 °C for 2 h to obtain regenerated functional polyester.

[0089] The final recycled functional polyester has an intrinsic viscosity of 0.6 dl / g and a melting point of 215°C; the molecular weight distribution of the recycled functional polyester is 1.5, and the randomness of the two units based on 1,3-propylene glycol and 1,4-butanediol in the recycled functional polyester is 0.90 and 0.91, respectively.

[0090] Example 3

[0091] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0092] (1) Preparation of raw materials:

[0093] Diol: 2,2,4,4-tetramethyl-1,3-cyclobutanediol;

[0094] Functional monomer: [(6-oxo-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6-one)-methyl]-butanedioic acid;

[0095] Catalyst: antimony glycol;

[0096] Waste polyester: waste poly(trimethylene terephthalate), the intrinsic viscosity of the waste polyester is 0.9 dL / g, and the melting point is 230°C.

[0097] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0098] Under nitrogen protection, functional monomers, diols and catalysts were placed in a polymerization reactor for esterification reaction to obtain a functional depolymerizing agent with a melting point of 173°C.

[0099] The reaction pressure is 0.1 MPa, the reaction temperature is 200° C., and the reaction time is 2.5 h. The molar ratio of the diol to the functional monomer is 4:1, and the mass of the catalyst is 300 ppm of the mass of the functional monomer.

[0100] (3) placing the diol, functional depolymerizing agent and waste polyester remaining in step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2;

[0101] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.05:1; the depolymerization temperature is 235°C, and the depolymerization time is 5 minutes;

[0102] (4) The functional depolymerization product was subjected to polycondensation at 280°C for 1.5 h to obtain regenerated functional polyester.

[0103] The final recycled functional polyester has an intrinsic viscosity of 0.7 dl / g and a melting point of 226°C; the molecular weight distribution of the recycled functional polyester is 1.6, and the randomness of the two units based on 2,2,4,4-tetramethyl-1,3-cyclobutanediol and 1,3-propylene glycol in the recycled functional polyester is 0.94 and 0.98, respectively.

[0104] Example 4

[0105] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0106] (1) Preparation of raw materials:

[0107] Diol: ethylene glycol;

[0108] Functional monomer: 2-carboxyethylphenyl hypophosphite;

[0109] Catalyst: antimony acetate;

[0110] Waste polyester: waste polyethylene terephthalate-1,4-cyclohexanedimethanol ester, the intrinsic viscosity of the waste polyester is 1.2 dL / g, and the melting point is 225°C.

[0111] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0112] Under nitrogen protection, functional monomers, diols and catalysts were placed in a polymerization reactor to undergo esterification reaction to obtain a functional depolymerizing agent with a melting point of 155°C.

[0113] The reaction pressure is 0.15 MPa, the reaction temperature is 210° C., and the reaction time is 2 h. The molar ratio of the diol to the functional monomer is 7:1, and the mass of the catalyst is 300 ppm of the mass of the functional monomer.

[0114] (3) placing the diol, functional depolymerizing agent and waste polyester remaining from step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2.2;

[0115] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.24:1; the depolymerization temperature is 260°C, and the depolymerization time is 2 minutes;

[0116] (4) The functional depolymerization product was subjected to polycondensation at 270°C for 2.25 h to obtain regenerated functional polyester.

[0117] The final recycled functional polyester has an intrinsic viscosity of 0.9 dl / g and a melting point of 210°C; the molecular weight distribution of the recycled functional polyester is 1.7, and the randomness of the two units based on 1,4-cyclohexanedimethanol and ethylene glycol in the recycled functional polyester is 1.00 and 1.02, respectively.

[0118] Example 5

[0119] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0120] (1) Preparation of raw materials:

[0121] Diol: Isosorbide;

[0122] Functional monomer: sodium 5-sulfoisophthalate;

[0123] Catalyst: zinc acetate;

[0124] Waste polyester: waste poly(trimethylene terephthalate), the intrinsic viscosity of the waste polyester is 0.9 dL / g, and the melting point is 230°C.

[0125] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0126] Under nitrogen protection, functional monomers, diols and catalysts are placed in a polymerization reactor to undergo esterification reaction to obtain a functional depolymerizing agent with a melting point of 180°C.

[0127] The reaction pressure is 0.2 MPa, the reaction temperature is 220° C., and the reaction time is 1 h. The molar ratio of the diol to the functional monomer is 9:1, and the mass of the catalyst is 400 ppm of the mass of the functional monomer.

[0128] (3) placing the diol, functional depolymerizing agent and waste polyester remaining in step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2.1;

[0129] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.26:1; the depolymerization temperature is 240°C, and the depolymerization time is 9 minutes;

[0130] (4) The functional depolymerization product was subjected to polycondensation at 270 °C for 2 h to obtain regenerated functional polyester.

[0131] The final recycled functionalized polyester has an intrinsic viscosity of 0.7 dl / g and a melting point of 224°C. The molecular weight distribution of the recycled functionalized polyester is 1.8, and the randomness of the recycled functionalized polyester based on isosorbide and 1,3-propylene glycol units is 1.09 and 1.12, respectively.

[0132] Example 6

[0133] A method for preparing recycled functional polyester using waste polyester, comprising the following steps:

[0134] (1) Preparation of raw materials:

[0135] Diol: spirodiol;

[0136] Functional monomer: [(6-oxo-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6-one)-methyl]-butanedioic acid;

[0137] Catalyst: zinc acetate and zinc oxide in a mass ratio of 1:1;

[0138] Waste polyester: waste polyethylene terephthalate, the intrinsic viscosity of waste polyethylene terephthalate is 0.67 dL / g, and the melting point is 250°C;

[0139] (2) Prepare functional depolymerizing agent by alcohol-capping functional monomers with diols:

[0140] Under nitrogen protection, functional monomers, diols and catalysts were placed in a polymerization reactor to undergo esterification reaction to obtain a functional depolymerizing agent with a melting point of 190°C.

[0141] The reaction pressure is 0.1 MPa, the reaction temperature is 200° C., and the reaction time is 2.5 h. The molar ratio of the diol to the functional monomer is 12:1, and the mass of the catalyst is 500 ppm of the mass of the functional monomer.

[0142] (3) placing the diol, functional depolymerizing agent and waste polyester remaining from step (2) in a polymerization kettle for depolymerization to obtain a functional depolymerized product with a molecular weight distribution of 2.4;

[0143] The ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating unit is 0.17:1; the depolymerization temperature is 260°C, and the depolymerization time is 3 minutes;

[0144] (4) The functional depolymerization product was subjected to polycondensation at 275°C for 1.75 h to obtain regenerated functional polyester.

[0145] The final recycled functional polyester has an intrinsic viscosity of 0.65 dl / g and a melting point of 232°C; the molecular weight distribution of the recycled functional polyester is 1.9, and the randomness of the recycled functional polyester based on spirodiol and ethylene glycol units is 1.12 and 1.15, respectively.

Claims

1. A method for preparing recycled functional polyester using waste polyester, characterized in that: First, a functional monomer is capped with alcohol using a slightly excess amount of diol to prepare a functional depolymerizing agent, and then the residual diol, functional depolymerizing agent and waste polyester are placed in a polymerization kettle for depolymerization to obtain a functional depolymerization product, and the functional depolymerization product is subjected to a condensation reaction to obtain a regenerated functional polyester; The functional monomer is any one of 2-carboxyethylphenyl hypophosphite, sodium 5-sulfoisophthalate, or [(6-oxo-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6-one)-methyl]-butanedioic acid; the slight excess means that the molar ratio of the diol to the functional monomer is (3-12):1, the ratio of the amount of the functional depolymerizing agent added to the molar number of the waste polyester repeating units is (0.05-0.3):1; the melting point of the functional depolymerizing agent is less than the depolymerization temperature, and the melting point of the waste polyester is less than the depolymerization temperature; The melting point of the functional depolymerizer is 155~200℃, the melting point of waste polyester is 220~250℃, and the depolymerization temperature is 5~10℃ higher than the melting point of waste polyester.

2. The method for preparing recycled functional polyester from waste polyester according to claim 1, wherein: The waste polyester is any one of waste polyethylene terephthalate, waste polybutylene terephthalate, waste polypropylene terephthalate and waste polyethylene terephthalate-1,4-cyclohexanedimethanol ester.

3. The method for preparing recycled functional polyester from waste polyester according to claim 2, wherein: The intrinsic viscosity of waste polyester is 0.55~1.20dL / g.

4. The method for preparing recycled functional polyester from waste polyester according to claim 3, wherein: The diol is any one of ethylene glycol, 1,4-butanediol, 1,3-propylene glycol, 1,5-pentanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, isosorbide, tricyclodecane dimethanol, or spirodiol.

5. The method for preparing recycled functional polyester from waste polyester according to claim 4, characterized in that: The specific process of preparing a functional depolymerizing agent by alcohol-capping a functional monomer with a diol is as follows: under nitrogen protection, the functional monomer, diol and catalyst are placed in a polymerization reactor for esterification reaction; wherein, the reaction pressure is 0.01~0.2MPa, the reaction temperature is 180~220℃, and the reaction time is 1~4h.

6. The method for preparing recycled functional polyester from waste polyester according to claim 5, characterized in that: The catalyst is any one or two of titanium glycolate, tetrabutyl titanate, antimony glycolate, antimony acetate, zinc acetate and zinc oxide, and the mass of the catalyst is 100-500ppm of the mass of the functional monomer.

7. The method for preparing recycled functional polyester from waste polyester according to claim 6, characterized in that: The depolymerization temperature is 225~260℃, and the depolymerization time is 2~10min; the condensation temperature is 260~280℃, and the condensation reaction time is 1.5~2.5h.

8. The method for preparing recycled functional polyester from waste polyester according to claim 7, characterized in that: The obtained recycled functional polyester has an intrinsic viscosity of 0.6-0.90 dl / g and a melting point of 210-246°C.

9. The method for preparing recycled functional polyester from waste polyester according to claim 8, characterized in that: The molecular weight distribution of the functional depolymerization product is less than 2.5, the molecular weight distribution of the obtained regenerated functional polyester is less than 2.0, and the randomness of different alcohol units in the regenerated functional polyester is 0.90-1.15.

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