Regenerated high-transparency copolyester material and preparation method thereof

Abstract

The invention discloses regenerated high-transparency copolyester and a preparation method thereof.The regenerated high-transparency copolyester is prepared by taking waste PET as a raw material, conducting ethylene glycol depolymerization and then conducting copolymerization with a modified composition, the material has the advantage of being low in crystallization rate, and good transparency and heat resistance can be kept when the material is processed into a thick-wall container; meanwhile, in the preparation process, a depolymerization reaction is carried out by adopting a relatively low mass ratio of ethylene glycol to waste PET, so that energy consumption is reduced and side reactions are few in the technological process; in the preparation process, diol A with a side group and CBDO are cooperatively added, so that the compatibility of CBDO and a PET alcoholysis product is greatly improved, and CBDO is almost completely embedded into macromolecules in the polymerization process; and the total mass ratio of the modified composition does not exceed 10%, so that the requirement of recoverable design is met, and good application value is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of PET recycling and regeneration, and particularly relates to a recycled highly transparent copolyester material and a preparation method thereof. Background Art

[0002] Plastics have been widely used in the fields of fibers, resins, films, etc. due to their low cost, light weight, and versatility. Among them, polyethylene terephthalate (PET) is one of the most widely used and versatile thermoplastics at present, and its presence can be seen everywhere from food, packaging, beverage bottles to synthetic fibers. As a commonly used polymer material, its output accounts for about 13% of the total world plastic output. However, PET is considered non-biodegradable, so the problem of plastic pollution caused by a large amount of PET waste has gradually attracted people's attention.

[0003] In recent years, more and more research has been carried out in the field of PET waste recycling. At present, the recycling of waste PET polyester materials mainly uses chemical methods, and the methods mainly include hydrolysis method, methanol depolymerization method, and ethylene glycol depolymerization method. The hydrolysis method requires high-pressure reaction of waste PET under the catalysis of strong acid or strong base, which has high requirements for equipment and there are few industrialized cases; the methanol alcoholysis method uses methanol as the alcoholysis agent to depolymerize waste PET into DMT (dimethyl terephthalate) and EG (ethylene glycol) under the action of a catalyst. The generated DMT is distilled and extracted to obtain refined DMT, and then regenerated PET is obtained through transesterification and polycondensation reactions with EG. The advantage of the methanol alcoholysis method is that the depolymerization product DMT is easy to refine, and high-quality recycled PET can be obtained by re-polymerization with this raw material. The disadvantages are that the energy consumption in the refining process is too high, and the recycling cost is too high to affect large-scale use. In addition, methanol is used in the depolymerization process, which requires higher safety and explosion-proof requirements for the factory; the advantage of the ethylene glycol alcoholysis method is that the reaction does not require high temperature and high pressure, and the depolymerization product bis(2-hydroxyethyl) terephthalate (BHET) can be directly used for re-polymerization to obtain recycled PET. However, since the obtained BHET contains impurities such as dimers and trimers, a large amount of excess EG needs to participate in the reaction to obtain high selectivity of BHET in the existing technology. The reaction process consumes a large amount of energy, and a large amount of diethylene glycol (DEG) is by-produced. The complex purification process also increases the equipment investment and manufacturing cost.

[0004] As a semi-crystalline polymer material, PET is suitable for textile fibers, films and container packaging fields. However, during the melting and cooling process, crystallization behavior occurs, resulting in poor transparency of the container when making thicker containers by injection molding or blow molding, which affects the appearance of the product. To solve this problem, companies such as Eastman in the United States and SK in South Korea have developed amorphous or low-crystallization-rate transparent polyester PETG with CHDM (1,4-cyclohexanedimethanol) as a modifier. However, PETG products are prone to adhesion during the recycling process, which affects the recycling of waste polyester products and thus does not meet the requirements of recyclable design. Eastman in the United States modified with two diols, 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and CHDM, and copolymerized with PTA and EG to obtain Tritan polyester with improved heat resistance. This modified polyester can be used for hot water cups, baby bottles, etc. However, both CHDM and CBDO are diols with chiral ring structures. Due to large steric hindrance during the synthesis of copolyesters, it is difficult to completely embed them into the polyester molecular chain, resulting in a longer polycondensation time and a small amount of monomers remaining in the polymer, which affects the processing performance. Summary of the Invention

[0005] In view of the above problems, the present invention provides a recycled highly transparent copolyester material and its preparation method. A highly transparent recycled polyester material is prepared using waste polyester bottles as raw materials. This material should have the characteristics of a low crystallization rate, good transparency and heat resistance when processed into thick-walled containers, and is an upgraded recycling technology. At the same time, a lower mass ratio of ethylene glycol to waste PET is used for the depolymerization reaction, and the process saves energy and has fewer side reactions. The specific technical solutions are as follows:

[0006] S1. The waste PET bottles are crushed, washed and dried to obtain PET fragments;

[0007] S2. The PET fragments and ethylene glycol are put into a reaction kettle according to a certain mass ratio, and an alcoholysis catalyst is added to the reaction kettle for alcoholysis reaction;

[0008] S3. A binary alcohol A with side groups and CBDO are mixed according to a certain mass ratio to obtain a composition. The composition is added to a flask, heated and stirred to obtain a modified composition;

[0009] S4. After the reaction in step S2 is completed, the modified composition obtained in step S3 is added to the reaction kettle for a transesterification reaction, and the ethylene glycol generated in the reaction is recovered;

[0010] S5. After the transesterification reaction in step S4 ends, a polycondensation catalyst is continuously added to the reaction kettle, and then it is transferred to a polycondensation reactor with a vacuum and condensation device, and a polycondensation reaction is carried out under certain conditions. After completion, a recycled highly transparent copolyester material is obtained.

[0011] As a preferred technical solution, the specific operation in step S1 is to crush the waste PET bottles into fragments of 5*5 mm with a small crusher, soak them in an aqueous solution of soda ash, and then rinse them with pure water to wash away impurities and oil. After washing, the fragments are dried in a vacuum oven to obtain PET fragments.

[0012] As a preferred technical solution, the mass ratio of the waste PET to ethylene glycol in step S2 is 1:0.3 to 1.0;

[0013] The reaction kettle is equipped with a reflux device;

[0014] The conditions for the alcoholysis reaction are: air pressure 0 to 100 KPa, temperature 180 to 220 °C, and reaction time 1 to 4 h.

[0015] As a preferred technical solution, the alcoholysis catalyst in step S2 is a metal acetate, including one or more of zinc acetate, manganese acetate, magnesium acetate, sodium acetate, and lithium acetate, and the addition amount is 0.05 to 0.1% of the mass of the PET fragments;

[0016] As a preferred technical solution, the diol A in step S3 is one of 1,2-propanediol, 2-methyl-1,3-propanediol, or neopentyl glycol, and the mass ratio of the diol A in the composition is 10 to 50%;

[0017] The heating temperature is 110 to 125 °C, and the time is > 20 min.

[0018] As a preferred technical solution, the addition amount of the modified composition in step S4 does not exceed 10% of the total mass in the recycled high-transparency copolyester material;

[0019] The conditions for the transesterification reaction are: the material is heated to 190 to 230 °C and maintained for 40 to 120 min; as a preferred technical solution, the conditions for the polycondensation reaction in step S5 are: after heating to 240 °C, a vacuum is established at a rate of -2 kPa / min and the temperature is continuously increased, the vacuum degree is ≤ 100 Pa, the internal temperature is controlled not to exceed 280 °C, and polycondensation is carried out for 1 to 4 h.

[0020] As a preferred technical solution, the polycondensation catalyst in step S5 is an oxide or organic chelate of titanium or germanium, and the addition ratio is 2 to 30 ppm of the mass of the PET fragments.

[0021] As a preferred technical solution, the recycled high-transparency copolyester material is the recycled high-transparency copolyester material prepared according to any one of the above technical solutions.

[0022] As a preferred technical solution, the intrinsic viscosity (IV) of the recycled highly transparent copolyester material is 0.60 to 1.2 dl / g (phenol: tetrachloroethane = 1), the melting point is 210 to 250 °C, and the glass transition temperature (Tg) ≥ 75 °C;

[0023] For the container sample with a wall thickness of 3 - 6 mm prepared using the recycled highly transparent copolyester material, the haze ≤ 1.5%.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) The present invention uses waste PET bottles as raw materials to prepare a recycled highly transparent polyester material. This material has the characteristic of a low crystallization rate and can maintain good transparency and heat resistance when processed into thick-walled containers, which is an upgraded recycling technology;

[0026] (2) During the preparation process of the recycled highly transparent polyester material of the present invention, a lower mass ratio of ethylene glycol to waste PET is used for the depolymerization reaction. The process saves energy and has fewer side reactions;

[0027] (3) During the preparation process of the recycled highly transparent polyester material of the present invention, the addition of diol A with side groups in combination with CBDO greatly improves the compatibility between CBDO and the PET alcoholysis product. CBDO is almost completely embedded in the macromolecules during the polymerization process. Particularly preferred is the synergy of MPO and CBDO;

[0028] (4) During the preparation process of the recycled highly transparent polyester material of the present invention, two diols are used as a modifier combination, and the total mass ratio of the modifiers does not exceed 10%, meeting the requirements of recyclable design. Description of the Drawings

[0029] Figure 1 is the differential scanning calorimetry (DSC) result of Comparative Example 4;

[0030] Figure 2 is the differential scanning calorimetry (DSC) result of Example 1. Detailed Embodiments

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0032] Example 1

[0033] This example is a preparation method for a recycled highly transparent copolyester material. The specific preparation steps are as follows:

[0034] S1. A certain amount of discarded PET bottles is crushed into 5*5 mm fragments using a small crusher, and then soaked in a soda ash aqueous solution. After completion, the fragments are rinsed with pure water to remove impurities and oil stains. The washed fragments are dried in a vacuum oven to obtain PET fragments;

[0035] S2, weigh 1500g of PET fragments and 750g of EG, add them into a 5L stainless steel reactor with a reflux device, add 1.2g of zinc acetate as an alcoholysis catalyst, stir and heat to 195°C, react under normal pressure, and the reaction time is 2.5h;

[0036] S3, weighing a composition of 22.5 g MPO and 120 g CBDO, placing it in a flask and heating it, controlling the heating temperature at 110-125° C. and stirring for more than 20 minutes to obtain a modified composition;

[0037] S4. After the reaction of step S2 is completed, the modified composition obtained in step S3 is added to the stainless steel reactor, the temperature is continued to be raised to 215° C., the reaction is carried out at normal pressure for 80 minutes, and the ethylene glycol distilled from the chain exchange reaction is condensed and received.

[0038] S5, after the reaction of step S4 is completed, add the polycondensation catalyst GeO 2 18 mg, then transferred into a polycondensation reactor with a vacuum and condensation device for polycondensation reaction, continued stirring and heated to 235°C, then began to evacuate to enter a low vacuum reaction, entered a high vacuum reaction after 40 minutes, controlled the reaction temperature to rise to 275°C, the residual pressure ≤100Pa, stopped stirring after 90 minutes of high vacuum reaction, introduced nitrogen to release the vacuum state and extruded the regenerated high transparent copolyester material, the regenerated high transparent copolyester material had an intrinsic viscosity (IV) of 0.705, a melting point of 220°C, a glass transition temperature of 78°C, and a crystallization peak temperature T C 156℃;

[0039] S6. The obtained recycled high-transparency copolyester material was cut into pellets, dried in a vacuum oven at 110° C. for 12 h, and then made into a container with a wall thickness of 5 mm using a Φ25 mm injection molding machine. The haze was measured to be 1.3%.

[0040] Example 2

[0041] Compared with Example 1, the only difference between this example and Example 1 is that the composition in step S3 is 37.5 g MPO and 100 g CBDO, and the other steps and raw materials are the same.

[0042] Example 3

[0043] Compared with Example 1, the only difference between this example and Example 1 is that the composition in step S3 is 15 g MPO and 120 g CBDO, and the other steps and raw materials are the same.

[0044] Example 4

[0045] Compared with Example 1, the only difference in this example is that the composition in step S3 is 60 g of MPO and 75 g of CBDO, and the other steps and raw materials are the same.

[0046] Example 5

[0047] Compared with Example 1, the only difference in this example is that the polycondensation catalyst in step S5 is 120 mg of the organic chelate AQ5800 of titanium, and the other steps and raw materials are the same.

[0048] Example 6

[0049] Compared with Example 1, the only difference in this example is that the composition in step S3 is 22.5 g of NG and 120 g of CBDO, and the other steps and raw materials are the same.

[0050] Comparative Example 1

[0051] Compared with Example 1, the only difference in this comparative example is that the composition in step S3 is 130 g of CBDO, and the other steps and raw materials are the same.

[0052] Comparative Example 2

[0053] Compared with Example 1, the only difference in this comparative example is that the composition in step S3 is 120 g of MPO, and the other steps and raw materials are the same.

[0054] Comparative Example 3

[0055] Compared with Example 1, the only difference in this comparative example is that the polycondensation catalyst in step S5 is 400 mg of antimony glycolate, and the other steps and raw materials are the same.

[0056] Comparative Example 4

[0057] Compared with Comparative Example 3, the only difference in this comparative example is that the composition in step S3 is 0 g, and the other steps and raw materials are the same.

[0058] The experimental results of the regenerated highly transparent copolyester materials prepared in each example and comparative example are shown in Table 1 below.

[0059] Table 1

[0060]

[0061]

[0062] From Table 1 combined with Figure 1 、 Figure 2It can be seen that the experimental results of the examples and the comparative examples show that the regenerated highly transparent copolyester material prepared by the regenerated highly transparent polyester material and its preparation method of the present invention has a high intrinsic viscosity and is not easily adhered during the recycling process; and due to its strong endothermic and exothermic capabilities and low glass transition temperature, the material has good heat resistance; at the same time, the difference between the melting point and the crystallization peak temperature is small, and there is little crystallization in the molten state. The products prepared using this material have low haze and good transparency, etc.

[0063] In summary, the present invention uses waste PET bottles as raw materials to obtain a regenerated highly transparent polyester material. This material has the characteristics of a low crystallization rate and can maintain good transparency and heat resistance when processed into thick-walled containers. It is an upgraded recycling technology; in the preparation process of the regenerated highly transparent polyester material of the present invention, a depolymerization reaction is carried out with a relatively low mass ratio of ethylene glycol to waste PET, and the process saves energy and has few side reactions; in the preparation process of the regenerated highly transparent polyester material of the present invention, a diol A with a side group is combined with CBDO and added, which greatly improves the compatibility of CBDO with the PET alcoholysis product. CBDO is almost completely embedded in the macromolecule during the polymerization process, and the synergy of MPO and CBDO is particularly preferred; in the preparation process of the regenerated highly transparent polyester material of the present invention, two diols are used as a modifier combination, and the total mass ratio of the modifiers does not exceed 10%, which meets the requirements of recyclable design and has good application value.

[0064] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. In addition, it should be understood that although this specification is described according to the embodiments, it does not only contain one technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a recycled highly transparent copolyester material, characterized in that: The steps include: S1, crushing, washing and drying the discarded PET bottles to obtain PET fragments; S2, putting the PET fragments and ethylene glycol into a reactor in a certain mass ratio, and adding an alcoholysis catalyst into the reactor to carry out an alcoholysis reaction; S3, mixing the diol A with a side group and CBDO in a certain mass ratio to obtain a composition, adding the composition into a flask, heating and stirring, to obtain a modified composition; S4, after the reaction in step S2 is completed, adding the modified composition obtained in step S3 into a reactor to carry out a chain exchange reaction, and recovering the ethylene glycol produced in the reaction; S5. After the chain exchange reaction in step S4 is completed, continue to add the polycondensation catalyst into the reaction kettle, and then move it into a polycondensation reactor with a vacuum and condensation device to carry out the polycondensation reaction under certain conditions, and after the polycondensation reaction is completed, a regenerated high-transparent copolyester material is obtained.

2. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: The specific operation in step S1 is to crush the discarded PET bottles into 5*5 mm fragments using a small crusher, soak them in a soda ash aqueous solution, rinse them with pure water to wash away impurities and oil stains, and dry the washed fragments in a vacuum oven to obtain PET fragments.

3. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: In step S2, the mass ratio of the waste PET to ethylene glycol is 1:0.3-1.0; the reactor is provided with a reflux device; The alcoholysis reaction conditions are: air pressure 0-100 KPa, temperature 180-220° C., and reaction time 1-4 h.

4. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: The alcoholysis catalyst in step S2 is a metal acetate, including one or more of zinc acetate, manganese acetate, magnesium acetate, sodium acetate, and lithium acetate, and the added amount is 0.05-0.1% of the mass of the PET fragments; According to the method for preparing a recycled high-transparency copolyester material according to claim 1, it is characterized in that: the diol A in step S3 is one of 1,2-propylene glycol, 2-methyl 1,3-propylene glycol or neopentyl glycol, and the mass ratio of the diol A in the composition is 10-50%; The heating temperature is 110-125° C., and the heating time is greater than 20 min.

5. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: The amount of the modified composition added in step S4 accounts for no more than 10% of the total mass of the recycled high-transparent copolyester material; The chain exchange reaction conditions are: the material temperature is raised to 190-230° C. and maintained for 40-120 minutes.

6. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: The polycondensation reaction conditions in step S5 are: heating to 240° C., then starting to establish vacuum at a rate of -2 kPa / min and continuously heating, the vacuum degree is ≤100 Pa, the internal temperature is controlled not to exceed 280° C., and the polycondensation is carried out for 1 to 4 hours.

7. The method for preparing a recycled high-transparent copolyester material according to claim 1, characterized in that: The polycondensation catalyst in step S5 is an oxide or an organic chelate of titanium or germanium, and the addition ratio is 2 to 30 ppm based on the mass of the PET fragments.

8. A recycled highly transparent copolyester material, characterized in that: The recycled high-transparency copolyester material is a recycled high-transparency copolyester material prepared by the method for preparing a recycled high-transparency copolyester material according to any one of claims 1 to 8.

9. A recycled high-transparency copolyester material according to claim 9, characterized in that: The recycled high-transparent copolyester material has an intrinsic viscosity (IV) of 0.60-1.2 dl / g (phenol:tetrachloroethane=1), a melting point of 210-250°C, and a glass transition temperature (Tg) ≥75°C; The container sample with a wall thickness of 3-6 mm made from the recycled high-transparency copolyester material has a haze of ≤1.5%.

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