Method for preparing degradable polyester plastic from polyethylene glycol terephthalate

Abstract

The invention provides a method for preparing degradable polyester plastic from polyethylene glycol terephthalate. The method comprises the following steps: reacting plastic containing polyethylene glycol terephthalate with hydrogen under the action of a catalyst, and after the reaction is finished, separating the obtained mixture to obtain a product containing the polyethylene glycol terephthalate-polyethylene-1, 4-cyclohexane diformate, and separating the product containing the polyethylene glycol terephthalate-polyethylene-1, 4-cyclohexane diformate, wherein the reaction temperature is 140 DEG C to 180 DEG C; the pressure of the hydrogen ranges from 2 MPa to 6 MPa. According to the method, the waste PET can be converted into the degradable PET-PECHD through a one-step hydrogenation process, the operation is simple, and the production cost is low; in addition, the PET-PECHD material with different proportions of benzene rings and aliphatic rings is obtained through accurate regulation and control of reaction conditions; pET-PECHD and PET have equivalent thermal performance and mechanical strength, but PET-PECHD has higher toughness and barrier property and has natural degradation capacity in mild acid / alkali aqueous solution and soil, and a new direction is created for recycling waste PET and economically and efficiently synthesizing degradable polyester plastic.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic chemistry, in particular to a method for preparing degradable polyester plastics from polyethylene terephthalate. BACKGROUND

[0002] Polyethylene terephthalate (PET) accounts for the largest share of the polyester plastics market, reaching 24.2 Mt in 2021 (about 6.2% of the total plastics market), second only to polyethylene and polypropylene. Due to its excellent tensile and barrier properties, it is widely used in packaging and textile fields. However, its rigid structure (consisting of benzene ring, high regularity and strong hydrophobicity) makes it difficult to degrade in hundreds of years. In order to deal with post-consumer PET waste, several strategies have been proposed, including mechanical recycling, chemical recycling, chemical upgrading and biotechnological degradation; but the PET recycling rate in most countries is still less than 30%, which means that more than half of the PET waste plastics will eventually enter the environment, posing a threat to the ecosystem. Therefore, developing new processes that can efficiently produce degradable plastic products will help the circular economy of the PET industry. SUMMARY

[0003] The purpose of the present application is to provide a method for preparing degradable polyester plastics from polyethylene terephthalate, which can convert waste polyethylene terephthalate (PET) into a degradable polyester plastic polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate (PET-PECHD) through a one-step hydrogenation process, which is simple to operate, low in production cost, and can obtain PET-PECHD materials with different benzene ring and aliphatic ring ratios by precise control of reaction conditions. The specific technical solutions are as follows:

[0004] The present application provides a method for preparing degradable polyester plastics, comprising: reacting plastics containing polyethylene terephthalate and hydrogen under the action of a catalyst; after the reaction is completed, the obtained mixture is separated to obtain a product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate; wherein the temperature of the reaction is 140-180℃; the pressure of the hydrogen is 2-6 MPa.

[0005] In some embodiments of the present application, the catalyst is selected from 5wt%-15wt% Pd / C and / or 5wt%-15wt% Ru / C.

[0006] In some embodiments of the present application, the reaction is carried out in the presence of an organic solvent.

[0007] In some embodiments of the present application, the organic solvent is selected from 1,4-dioxane.

[0008] In some embodiments of the present application, the mass-volume ratio of the plastic containing polyethylene terephthalate to the organic solvent is (0.05-0.2) g: 1 mL.

[0009] In some embodiments of the present application, the reaction time is 0.5 h-20 h.

[0010] In some embodiments of the present application, the reaction is carried out under stirring, and the stirring speed is 500 r / min-700 r / min.

[0011] In some embodiments of the present application, when the mixture is in a solid-liquid mixed state, the separation comprises: filtering the mixture, and evaporating the obtained liquid to obtain the product containing polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate.

[0012] In some embodiments of the present application, when the mixture is a solid or a gel, the separation comprises: adding water to the mixture, stirring, and after the polymer is completely precipitated, sequentially performing filtration, washing, and drying to obtain the product containing polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate.

[0013] In some embodiments of the present application, the washing agent used in the washing is water.

[0014] Advantages of the present application:

[0015] The present application provides a method for preparing degradable polyester plastics from polyethylene terephthalate, which can convert waste polyethylene terephthalate into a degradable polyester plastic polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate through a one-step hydrogenation process, which is simple to operate and low in production cost. In addition, the present application can obtain PET-PECHD materials with different benzene ring and aliphatic ring ratios by precise control of reaction conditions. PET-PECHD has comparable thermal performance and mechanical strength to PET, but has higher toughness and barrier properties, and has the ability to naturally degrade in mild acid / alkali aqueous solution and soil, which opens up a new direction for recycling waste PET and economically and efficiently synthesizing degradable polyester plastics.

[0016] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0018] Figure 1a Schematic diagram for preparing PET-PECHD and PECHD polyesters from controlled hydrogenation of PET;

[0019] Figure 1b TGA curves of the products of controlled hydrogenation of PET for different reaction times; 1 H NMR spectra;

[0020] Figure 1c Variation of the number average molecular weight (Mn) of the reaction products is shown;

[0021] Figure 1d GPC curves of the reaction products are shown;

[0022] Figure 1e TGA curves of the hydrogenation products with different a+b percentages obtained by controlled hydrogenation; 1 H NMR spectra;

[0023] Figure 2a Differential scanning calorimetry (DSC) analysis of the reaction products is shown in Figure 1;

[0024] Figure 2b Differential scanning calorimetry (DSC) analysis of the reaction products is shown in Figure 2;

[0025] Figure 2c The relationship between the heat transition temperature (Tm) and the glass transition temperature (Tg) of the reaction products is shown;

[0026] Figure 2d The stress-strain curves of the reaction products are shown;

[0027] Figure 2e The toughness, tensile strength and elongation at break of the reaction products are shown;

[0028] Figure 2f The oxygen and water vapor permeability of PET, PET-PECHD (a+b percentage ranging from 35% to 96%), PECHD and Mix 85% (PET and PECHD physically mixed in a mass ratio of 85:15) samples is shown;

[0029] Figure 3a Degradation characteristics of PET and PET-PECHD (a+b=87% and a+b=50%) in 1M NaOH solution at 25°C are shown.

[0030] Figure 3b Degradation properties of PET and PET-PECHD (a+b=87% and a+b=50%) in 1 M HCI solution at 25°C are shown;

[0031] Figure 3c Degradation properties of PET and PET-PECHD (a+b=87% and a+b=50%) in 1 M TFA solution at 25°C are shown;

[0032] Figure 3d Pictures of degradation products of PET and PET-PECHD (a+b=50% and a+b=87%) in 1 M NaOH solution; 1 H NMR spectra;

[0033] Figure 3e Biochemical oxygen demand (BOD) results of PET, PET-PECHD (a+b=35%, a+b=50%, a+b=87%, a+b=96%), PECHD and Mix 85% (PET and PECHD physically mixed in a mass ratio of 85:15) are shown;

[0034] Figure 3f Pictures of PET and PET-PECHD (a+b=50%) thin films during degradation process in natural soil. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0036] Existing research not only focuses on recycling reactions to recover terephthalic acid (TPA) or its derivative chemicals and ethylene glycol (EG), but also focuses on upgrading treatment through different reaction designs to produce other chemicals (such as 1,4-benzene dimethanol, cyclohexane dimethyl ester, methyl p-toluate, 1,4-cyclohexane dimethanol, aromatic hydrocarbon, ethylene, ethane, glycolic acid, formate, 1,2-dichloroethane, and formamide, etc.) and high-performance polymers (such as PEXT23, antibacterial PET24, fiber-reinforced plastic, dihydroxy terephthalate, and polyethylene-1,4-cyclohexane dicarboxylate). Functionalization or structural changes of PET into new polymers are usually avoided by direct reactions of different reagents (such as aliphatic diacid, diol, olefinic acid, diethyl ester, etc.) with PET chains to avoid the formation of monomers, but there are still some challenges, including the complexity and high cost of reagent preparation, polymerization difficulties, and the complexity of the overall synthesis process, etc. In addition, end-of-life products still face difficulties in recycling.

[0037] For the production of polymers, (bio)degradable materials have attracted the interest of a wide range of researchers as an option for managing the end-of-life of plastic waste. The present inventors have unexpectedly found that aliphatic polyesters have better chemical degradability, biodegradability and biocompatibility than aromatic polyesters; polyethylene-1,4-cyclohexane dicarboxylate (PECHD) obtained by polymerization of 1,4-cyclohexane dicarboxylic acid and ethylene glycol is (bio)degradable, and direct hydrogenation of the aromatic ring in PET without depolymerization is a direct method for producing (bio)degradable plastic material PECHD.

[0038] The present application provides a method for preparing degradable polyester plastics, comprising: reacting plastics containing polyethylene terephthalate and hydrogen under the action of a catalyst; after the reaction is completed, the obtained mixture is separated to obtain a product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate; wherein the temperature of the reaction is 140-180°C; the pressure of the hydrogen is 2-6 MPa.

[0039] The present application proposes a method for upgrading end-of-life PET into (bio)degradable polyester PET-PECHD (copolymer) by systematically optimizing the hydrogenation of PET aromatic ring without depolymerizing the ester bond. By controlling the ratio of benzene ring and aliphatic ring on the polymer backbone, the performance of the product can be adjusted. Partial hydrogenation of PET at 140-180℃ under 2-6 MPa hydrogen pressure can obtain high molecular weight pure PET-PECHD copolymer. Deep hydrogenation will lead to the formation of PET-PECHD / PECHD mixture or pure PECHD, and the relative molecular weight will be significantly reduced. The inventors surprisingly found that before the polymer backbone is broken, pure PET-PECHD exhibits similar mechanical strength and thermal properties to the original PET, but the elongation at break, toughness and barrier properties are significantly improved; and PET-PECHD shows excellent degradability in mild acidic / basic solutions and moist soil, indicating its potential application in degradable packaging materials.

[0040] In the present application, the reaction temperature can be 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃ or a value within the range formed by any two of the above values as endpoints. When the reaction temperature is lower than 140℃, the hydrogenation speed of PET is significantly reduced; when the reaction temperature is higher than 180℃, it is easy to cause the breakage of molecular chain, thus greatly reducing the molecular weight of the product. Controlling the reaction temperature within the above range is beneficial to effectively control the hydrogenation degree of PET and synthesize high molecular weight PET-PECHD polyester.

[0041] In the present application, the hydrogen pressure can be 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, 5.5MPa, 6MPa or a value within the range formed by any two of the above values as endpoints. When the hydrogen pressure is lower than 2MPa, the hydrogenation speed of PET is significantly reduced, and it takes longer reaction time to complete the above reaction, greatly increasing the production time cost; when the hydrogen pressure is higher than 6MPa, it is easy to cause excessive breakage of molecular chain, reducing the molecular weight of the product. Controlling the hydrogen pressure within the above range is beneficial to efficiently synthesize PET-PECHD polyester with high molecular weight.

[0042] In the present application, the separation can be carried out after the reaction is completed and the reaction product is cooled to room temperature.

[0043] In the present application, the plastic containing polyethylene terephthalate can be pure polyethylene terephthalate, or waste polyethylene terephthalate plastic products such as mineral water bottles, lunch boxes, transparent plastic coiled material, polyester fiber clothes, etc.

[0044] In the present application, the weight average molecular weight of polyethylene terephthalate in the plastic containing polyethylene terephthalate is not particularly limited as long as the purpose of the present application can be achieved, for example, the weight average molecular weight of polyethylene terephthalate can be 20kDa-100kDa.

[0045] In the present application, the size of the plastic containing polyethylene terephthalate as a raw material for reaction is not particularly limited as long as the purpose of the present application can be achieved. For example, the plastic containing polyethylene terephthalate is in the form of fragments or powder after crushing (such as passing through a 10 mesh-100 mesh screen) to facilitate the reaction.

[0046] In the present application, the product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate can be PET-PECHD / PECHD mixture or pure PECHD, which is different because of different hydrogenation degree.

[0047] In some embodiments of the present application, the catalyst is selected from 5wt%-15wt% Pd / C and / or 5wt%-15wt% Ru / C. The inventors of the present application used Pt / C and Rh / C as catalysts in the research, neither of which can effectively hydrogenate the aromatic ring of PET. The present application selects the above-mentioned catalysts which can more efficiently hydrogenate the aromatic ring of PET.

[0048] The present application does not have a particular limitation on the amount of catalyst used as long as the purpose of the present application can be achieved. For example, the mass ratio of catalyst to plastic containing polyethylene terephthalate is (0.04-0.2):1.

[0049] In some embodiments of the present application, the reaction is carried out in the presence of an organic solvent.

[0050] In some embodiments of the present application, the organic solvent is selected from 1,4-dioxane. The 1,4-dioxane used in the present application can be super-dry 1,4-dioxane (e.g., water content ≤ 50 ppm) or 1,4-dioxane containing a small amount of water. The use of super-dry 1,4-dioxane (e.g., water content ≤ 50 ppm) can avoid the depolymerization of PET under reaction conditions due to water, avoid the adverse effects of hydrolysis reaction on hydrogenation reaction, and thus facilitate the synthesis of PET-PECHD polyester with high molecular weight. The present inventors have found in their research that the use of tetrahydrofuran, cyclohexane, n-hexane, 1,3-dioxolane, N,N-dimethylformamide, and decalin as organic solvents is not conducive to the efficient hydrogenation of the aromatic ring of PET by catalysts such as 5wt%-15wt% Ru / C catalyst, and the conversion efficiency of PET is low; the use of 1,4-dioxane as an organic solvent is conducive to the efficient hydrogenation of the aromatic ring of PET by catalysts such as Ru / C catalyst, and is conducive to improving the conversion efficiency of PET.

[0051] In some embodiments of the present application, the mass-to-volume ratio of the plastic containing polyethylene terephthalate to the organic solvent is (0.05-0.2) g: 1 mL. In the present application, the mass-to-volume ratio of the plastic containing polyethylene terephthalate to the organic solvent can be 0.05 g: 1 mL, 0.06 g: 1 mL, 0.07 g: 1 mL, 0.08 g: 1 mL, 0.09 g: 1 mL, 0.1 g: 1 mL, 0.11 g: 1 mL, 0.12 g: 1 mL, 0.13 g: 1 mL, 0.14 g: 1 mL, 0.15 g: 1 mL, 0.16 g: 1 mL, 0.17 g: 1 mL, 0.18 g: 1 mL, 0.19 g: 1 mL, 0.2 g: 1 mL, or a value within a range formed by any two of the above values as endpoints. The present application controls the mass-to-volume ratio of the plastic containing polyethylene terephthalate to the organic solvent within the above range, which is conducive to accurately controlling the ratio of benzene ring to cyclohexane ring in PET-PECHD, thereby further adjusting the physical properties of PET-PECHD; in addition, a suitable PET / organic solvent ratio is conducive to achieving maximum conversion of PET, improving production efficiency, and saving solvent usage.

[0052] In some embodiments of the present application, the reaction time is 0.5h-20h. In the present application, the reaction time can be 0.5h, 1h, 3h, 5h, 7h, 9h, 10h, 12h, 14h, 16h, 18h, 20h, or a value within a range formed by any two of the above values as endpoints. The present application can easily achieve controlled hydrogenation of PET by adjusting the reaction time.

[0053] In some embodiments of the present application, the reaction is carried out under stirring at a speed of 500 r / min to 700 r / min. In the present application, the stirring speed can be 500 r / min, 520 r / min, 540 r / min, 560 r / min, 580 r / min, 600 r / min, 620 r / min, 640 r / min, 660 r / min, 680 r / min, 700 r / min, or a value within a range formed by any two of the above values as endpoints. Controlling the stirring speed within the above range is beneficial for the smooth progress of the reaction.

[0054] In some embodiments of the present application, when the mixture is in a solid-liquid mixed state, the separation comprises filtering the mixture, and evaporating the obtained liquid to obtain the product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate. The solid-liquid mixed state in the present application refers to a homogeneous liquid containing solid catalysts, which needs to be filtered to separate the catalysts.

[0055] The evaporation method in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, rotary evaporation can be used to remove the organic solvent.

[0056] In some embodiments of the present application, when the mixture is in a solid or colloidal state, the separation comprises adding water to the mixture, stirring, and then sequentially filtering, washing, and drying after the complete precipitation of the polymer to obtain the product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate.

[0057] In some embodiments of the present application, the washing agent used in the washing is water. Using water for washing can better remove impurities attached to the product containing polyethylene terephthalate-polyethylene-1,4-cyclohexane dicarboxylate, thereby improving the purity of the final product.

[0058] Before the reaction, hydrogen can be injected into the reactor multiple times, such as three times, to replace air and fill to a preset reaction pressure. During the reaction or after the reaction, an online gas chromatograph (Agilent 8890) with a thermal conductivity detector (TCD) and a hydrogen flame ionization detector (FID) can be used to analyze the gaseous products.

[0059] This application provides a simple and controllable hydrogenation method to convert waste PET into biodegradable polyester PET-PECHD. Pure PET-PECHD exhibits similar mechanical strength and thermal properties to virgin PET, but with significantly improved elongation at break, toughness, and barrier properties. Furthermore, PET-PECHD possesses the ability to degrade naturally in mild acidic / alkaline solutions and soil, paving the way for innovative recycling of waste PET and cost-effective synthesis of biodegradable polyester plastics.

[0060] In the PET-PECHD copolymer prepared in this application, the overall performance is superior when the percentage of a+b (the percentage of a+b ((a+b) / (a+b+c+d)) represents the proportion of aromatic groups in the polymer chain) is between 50% and 80%. For example, the percentage of a+b can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of the above values ​​as endpoints within a range. By adjusting reaction conditions such as temperature, pressure, time, and PET concentration, this application can easily obtain any polymer with an a+b percentage within the range of 50%-80%.

[0061] Example

[0062] The following examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Unless otherwise specified, "parts" and "%" are mass standards, "room temperature" is 25±5°C, and "about" is ±0.5.

[0063] Example 1

[0064] In a 250 mL stainless steel high-pressure reactor equipped with a mechanical stirrer, 3 g of pulverized PET bottle powder (weight-average molecular weight 53 kDa, passed through a 50-mesh sieve), 40 mL of ultra-dry 1,4-dioxane (moisture content ≤ 50 ppm), and 200 mg of 5 wt% Ru / C catalyst (purchased from Alfa Aesar) were added. Hydrogen was then injected into the reactor three times to displace air, and the reactor was filled to a reaction pressure of 4 MPa. The reactor was heated to 160 °C under constant stirring at 600 rpm and reacted for 20 h. Nuclear magnetic resonance (NMR) was used to monitor the reaction process. 1The progress of PET hydrogenation was monitored by1H NMR analysis (Bruker AVANCE III 500MHz NMR with maleic acid as an internal standard) and the change in number average molecular weight (Mw) of the sample was analyzed by gel permeation chromatography (GPC); after cooling to room temperature at the end of the reaction, the resulting mixture was filtered, the liquid was collected and rotary evaporation was performed, obtaining 2.91 g of oven-dried product containing polyethylene terephthalate-polyethylene-1,4-cyclohexanedicarboxylate. The gaseous products were analyzed using an online gas chromatograph (Agilent 8890) with TCD and FID detectors.

[0065] Figure 1a A schematic representation of the preparation of PET-PECHD and PECHD polyesters by controlled hydrogenation of PET, from which it can be seen that the chemical shifts located at 5.1 (a), 4.7 (d), 4.8 (b) and 4.9 (c) ppm can be attributed to the CH2-CH2protons of PET, PECHD and the intersection of PET and PECHD, respectively.

[0066] Figure 1b A GPC plot of the products of the controlled hydrogenation of PET for different reaction times, from which it can be seen that the Mwof the sample decreases slightly from the initial 53 kDa of pure PET to 43 kDa in the first hour of the reaction, at which time the proportion of a+b exceeds 86%. When the reaction time is extended to 2 h, the Mwdecreases sharply to approximately 32 kDa and remains relatively stable over the following 15 h. When the reaction is further extended to 20 h, the Mwdecreases significantly to 9 kDa and, in the case of the sample with the longest reaction time, to 6 kDa. 1 The1H NMR spectra, from which it can be seen that the d signal gradually increases with increasing reaction time, while the a signal gradually decreases, are consistent with the process of gradual hydrogenation of the benzene rings to aliphatic rings in the molecular chain. Due to the complexity of the aliphatic ring signal, the ratio between the aromatic and aliphatic rings is defined as the ratio between a+b and c+d; thus, the percentage of a+b ((a+b) / (a+b+c+d)) represents the proportion of aromatic groups in the polymer chain. According to the1H NMR spectra, controlled hydrogenation of PET can be easily achieved by adjusting the reaction time. 1 The1H NMR spectra, from which it can be seen that the d signal gradually increases with increasing reaction time, while the a signal gradually decreases, are consistent with the process of gradual hydrogenation of the benzene rings to aliphatic rings in the molecular chain. Due to the complexity of the aliphatic ring signal, the ratio between the aromatic and aliphatic rings is defined as the ratio between a+b and c+d; thus, the percentage of a+b ((a+b) / (a+b+c+d)) represents the proportion of aromatic groups in the polymer chain. According to the1H NMR spectra, controlled hydrogenation of PET can be easily achieved by adjusting the reaction time.

[0067] Figure 1c A plot showing the change in the number average molecular weight (Mw) of the reaction products, from which it can be seen that the Mwof the sample presents a gradual decreasing trend with increasing reaction time.

[0068] Figure 1d A GPC plot of the reaction products, from which it can be seen that the number average molecular weight of the sample decreases slightly from the initial 53 kDa of pure PET to 43 kDa in the first hour of the reaction, at which time the proportion of a+b exceeds 86%. When the reaction time is extended to 2 h, the Mwdecreases sharply to approximately 32 kDa and remains relatively stable over the following 15 h. When the reaction is further extended to 20 h, the Mwdecreases significantly to 9 kDa and, in the case of the sample with the longest reaction time, to 6 kDa. 1 No peaks of a+b were observed in the1H NMR spectra and C NMR spectra, indicating complete hydrogenation of PET. 13 No peaks of a+b were observed in the1H NMR spectra and C NMR spectra, indicating complete hydrogenation of PET.

[0069] Figure 1e hydrogenated products with different a+b percentages obtained by controlled hydrogenation 1 HNMR spectra, from which it can be seen that by adjusting the reaction conditions, such as temperature, pressure, time and PET concentration, polymers with a+b composition adjustable in the range of 100% to 0% can be obtained, the above results show that the method provided in the present application can controllably hydrogenate PET into novel polymers containing aliphatic groups, and a series of complete samples are obtained.

[0070] Material thermodynamic and mechanical property tests:

[0071] The reaction products were subjected to differential scanning calorimetry (DSC) analysis, and the results are shown in Figure 2a and Figure 2b The relationship between the thermal transition temperature (Tm) and the glass transition temperature (Tg) is shown in Figure 2c From the above figures, it can be seen that the melting points of all PET-PECHD polyesters with different a+b percentages are slightly lower than that of PET (Tm = 253°C), which is 234°C-246°C; PET-PECHD polyesters with a+b < 87% also exhibit high Tm (about 240°C), however, the glass transition temperature (Tg) decreases significantly as the a+b percentage decreases; at the same time, the crystallinity of the sample gradually decreases as the number of benzene rings in the molecular chain decreases, eventually leading to the complete loss of crystallinity of PECHD Figure 2b Therefore, the recycled PET-PECHD polyesters exhibit high Tm and low Tg in a wide range of working temperatures, having thermoplastic and elastic properties.

[0072] The reaction products were subjected to tensile testing to characterize the mechanical properties of the PET-PECHD polyesters. The test method is as follows: Instron 5567 (100N load sensor) and 3365 (50N load sensor) universal testing system was used, and the test sample was PET-PECHD polyester product evaporated into a dog bone shape. The test sample was stretched at room temperature at a strain rate of 10 mm / min, and the measurement was repeated 2 times, and the average value of the measured data was taken. The tensile test results are shown in Figure 2d and Figure 2e Figure 2d shows the stress-strain curve of the reaction product; Figure 2e ​The toughness (tensile stress), tensile strength and elongation at break of the reaction products were shown. As can be seen from the figure, the tensile strength slightly decreased with the decrease of a+b percentage; however, the elongation at break (sample with a+b = 60% > 400%) and toughness (sample with a+b = 80% > 600 MPa) were significantly increased compared with PET. The above results show that PET-PECH HD has excellent ductility while maintaining inherent mechanical strength.

[0073] Considering the potential application of PET-PECH HD in packaging materials, the reaction products were evaluated for oxygen and water vapor permeability, and the samples evaluated included PET, PET-PECH HD (a+b percentage ranging from 35% to 96%), PECH HD and Mix85% (PET and PECH HD physically mixed at a mass ratio of 85:15) samples (thickness about 0.1 mm). Water vapor transmission rate (WVTR) was measured using C360M equipment at 23°C and 51% relative humidity. Oxygen permeability was measured using MOCON 2 / 12R equipment at 25°C and 36% relative humidity. The test results are shown in Figure 2f As can be seen from the figure, PET-PECH HD with a+b content of 87% or more has similar oxygen permeability (about 1.7 barrer) compared with PET, lower water vapor transmission rate (WVTR) (about 0.5 g mm m -2 day -1 ), and comparable to other commercial polymers such as LDPE, PLA and PBAT, the above results show that the product prepared in the present application has superior barrier properties.

[0074] Material degradation performance test:

[0075] The partially hydrogenated PET-PECH HD polymers (a+b = 87% and a+b = 50%) obtained during the reaction process, PET were tested for their degradability under different conditions, including different acid / alkali aqueous solutions, specifically: 1M NaOH solution, 1M HCl solution and 1M TFA (trifluoroacetic acid) solution at 25°C. The test results are shown in Figure 3a 、 3b , 3c, as can be seen from the figure: within 91 days, the degradation mass loss of PET-PECH HD polymers (a+b = 50% and a+b = 87%) in 1M NaOH solution reached 99% and 84% respectively, which is much faster than the degradation rate of pure PET (11%). Figure 3a In addition, these polymers also slowly degrade in acidic solutions such as 1M HCl solution and 1M TFA solution Figure 3b and Figure 3c , but their degradation rate is significantly slower than that in alkaline solution.

[0076] The degradation products of PET and PET-PECHD (a+b=50% and a+b=87%) in 1M NaOH solution were analyzed by HPLC 1 HNMR spectrum analysis, the results are shown in Figure 3d As can be seen from the above graph, PET-PECHD polymers are successfully degraded into monomers, i.e. terephthalic acid (TPA), cyclohexane dicarboxylic acid (CHDA) and ethylene glycol (EG).

[0077] Biochemical oxygen demand (BOD) can be used as an important indicator to predict the biodegradability of polyesters in water environment. The BOD of PET, PET-PECHD (a+b=35%, a+b=50%, a+b=87%, a+b=96%), PECHD and Mix 85% (PET and PECHD are physically mixed in a mass ratio of 85:15) was determined. The test was carried out according to the International Organization for Standardization (ISO) 14851 method with some adjustments, and the specific test procedure is as follows: each kind of polyester to be tested was divided into three equal parts and placed in a 300ml BOD glass bottle, then 120mg of activated sludge from a sewage treatment plant and 200ml of aqueous medium containing KH2PO4 (170mg), K2HPO4 (435g), Na2HPO4 (668mg), NH4Cl (30mg), MgSO4·7H2O (45mg), CaCl2·2H2O (72.8mg) and FeCl3·6H2O (0.5mg) were added. The above test bottles were incubated at 25°C and 200rpm on a shaker for 14 days, and the BOD was determined by measuring the oxygen consumption using a pH / RDO / DO instrument. The BOD test results are shown in Figure 3e As can be seen from the above graph, under the same test conditions, the BOD of the polymer containing aliphatic ring is significantly higher than that of PET and Mix 85% (physical mixture). The above results show that not only the aliphatic chain is more easily biodegradable, but also its introduction activates the aromatic part; PET-PECHD has higher biodegradability than PET.

[0078] PET and PET-PECHD (a+b=50%) were made into thin films of equal thickness and used as agricultural mulch to test their degradability, the test method including: PET, PET-PECHD (a+b=50%) were made into thin films with a thickness of about 0.1mm, and cut into 5cm×10cm pieces, then the edges were buried in natural soil with a depth of 1cm to test their degradability. The degradation under natural conditions was tested in open air conditions, the test site was Haidian District, Beijing, China (longitude: 116.29, latitude: 39.95), and the test time was from May 2024 to July 2024. The test results are shown in Figure 3fThe results are shown in the following table. As can be seen from the above table, the PET-PECHD (a+b=50%) film sample first showed obvious cracks and holes at 35 days, and as the degradation time was extended to 63 days, significant pulverization occurred, and finally degraded into fragments at 82 days; in contrast, the PET film showed little change. The above results show that when PET-PECHD is exposed to soil for a long time, it will effectively degrade and will not accumulate in these environments for a long time.

[0079] Example 2

[0080] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to 1,4-dioxane, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0081] Example 3

[0082] Except that the reaction time in Table 1 is adjusted to 10 h, the rest is the same as Example 1.

[0083] Example 4

[0084] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to tetrahydrofuran, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0085] Example 5

[0086] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to cyclohexane, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0087] Example 6

[0088] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to 1,3-dioxolane, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0089] Example 7

[0090] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to N,N-dimethylformamide, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0091] Example 8

[0092] Except that the organic solvent super dry 1,4-dioxane (moisture ≤ 50 ppm) in Table 1 is changed to decaline, and the reaction time is adjusted to 10 h, the rest is the same as Example 1.

[0093] The preparation parameters and result parameters of each example are shown in Table 1.

[0094] Table 1

[0095]

[0096] As can be seen from Examples 1 to 3, when 1,4-dioxane or super-dry 1,4-dioxane is used as the organic solvent, the Ru / C catalyst can efficiently hydrogenate the aromatic ring of PET, and the percentage of a+b can be reduced to 50% or less; while when tetrahydrofuran, cyclohexane, n-hexane, 1,3-dioxolane, N,N-dimethylformamide and decalin are used as the organic solvent respectively in Examples 4 to 8, the conversion efficiency of PET is relatively low, and the percentage of a+b is all above 89%. The above results show that when 1,4-dioxane is used as the organic solvent and Rh / C is used as the catalyst, the aromatic ring of PET can be efficiently hydrogenated.

[0097] The preferred embodiments of the present application are described above with reference to the drawings, but the present application is not limited to the above examples. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing degradable polyester plastic, comprising: reacting plastic containing polyethylene terephthalate and hydrogen in the presence of a catalyst; and separating the obtained mixture after the reaction to obtain a product containing polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate. The temperature of the reaction is 140-180℃, and the pressure of the hydrogen is 2-6 MPa.

2. The method of claim 1, wherein, The catalyst is selected from 5wt%-15wt% Pd / C and / or 5wt%-15wt% Ru / C.

3. The method of claim 1, wherein, The reaction is carried out in the presence of an organic solvent.

4. The method of claim 3, wherein, The organic solvent is selected from 1, 4-dioxane.

5. The method of claim 3 or 4, wherein, The mass-volume ratio of the plastic containing polyethylene terephthalate to the organic solvent is (0.05-0.2) g: 1 mL.

6. The method of claim 1, wherein, The reaction time is 0.5-20 h.

7. The method of claim 1, wherein, The reaction is carried out under stirring at a speed of 500-700 r / min.

8. The method of claim 1, wherein, When the mixture is in a solid-liquid mixed state, the separation comprises filtering the mixture, evaporating the obtained liquid, and obtaining the product containing polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate.

9. The method of claim 1, wherein, When the mixture is in a solid or colloidal state, the separation comprises adding water to the mixture, stirring, and sequentially filtering, washing, and drying after the polymer is completely precipitated to obtain the product containing polyethylene terephthalate-polyethylene-1, 4-cyclohexane dicarboxylate.

10. The method of claim 9, wherein, The washing agent used in the washing is water.

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