CN115490839B - Method for preparing PETG/PCTG copolyester by depolymerizing waste PET through mixed alcohol - Google Patents

Method for preparing PETG/PCTG copolyester by depolymerizing waste PET through mixed alcohol Download PDF

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CN115490839B
CN115490839B CN202211149046.0A CN202211149046A CN115490839B CN 115490839 B CN115490839 B CN 115490839B CN 202211149046 A CN202211149046 A CN 202211149046A CN 115490839 B CN115490839 B CN 115490839B
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petg
alcoholysis
polycondensation
waste pet
mixed alcohol
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CN115490839A (en
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赵玲
郑伟中
孙伟振
魏鑫
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East China University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
    • C08G63/16—Dicarboxylic acids and dihydroxy compounds
    • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
    • C08G63/199—Acids or hydroxy compounds containing cycloaliphatic rings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/82—Preparation processes characterised by the catalyst used
    • C08G63/85—Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/82—Preparation processes characterised by the catalyst used
    • C08G63/85—Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof
    • C08G63/86—Germanium, antimony, or compounds thereof
    • C08G63/866—Antimony or compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
    • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
    • C08J11/24—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/62—Plastics recycling; Rubber recycling

Abstract

The invention discloses a method for preparing PETG/PCTG copolyester by depolymerizing waste PET with mixed alcohol, which belongs to the field of PET recovery, ethylene Glycol (EG) and 1, 4-Cyclohexanedimethanol (CHDM) are used as mixed alcohol, the waste PET is subjected to alcoholysis under the action of a catalyst, and depolymerization products BHET/BHCT monomers and oligomers thereof are obtained through filtration and separation; and (3) taking the depolymerized product as a raw material, and preparing PETG/PCTG copolyester through pre-polycondensation and final polycondensation under the action of a polycondensation catalyst. By regulating and controlling the proportion of the fed alcohol and the depolymerization degree, the controllable preparation of PETG/PCTG copolyester with different chain structures and copolymerization components can be realized.

Description

Method for preparing PETG/PCTG copolyester by depolymerizing waste PET through mixed alcohol
Technical Field
The invention relates to the technical field of PET recovery, in particular to a method for preparing PETG/PCTG copolyester by mixing alcoholysis polymerization of waste PET.
Background
Polyethylene terephthalate (poly (ethylene terephthalate), PET) is the most predominant species in thermoplastic polyesters, and is commonly used in the fields of food packaging, textile fibers, electronics and the like, and the production market thereof has been increasing over the years. However, PET has stable chemical properties, is difficult to decompose under natural conditions, and can cause white pollution and generate harmful gases by direct landfill incineration. Therefore, recycling of waste PET is becoming more and more important.
At present, there are physical and chemical methods for recycling PET. Physical recycling is to melt and re-granulate waste PET, and is the treatment mode of most of the regenerated PET at present. The method has the advantages of simple process, low investment cost and fast income, but the performance of the regenerated product is reduced compared with that of the original PET, and the regenerated product cannot be used continuously after being physically recovered for many times. While chemical recycling may utilize depolymerizing agents to depolymerize PET into small molecules that may be reused for polymerization or to produce other chemical products. The chemical recovery can realize the closed cycle of PET, and is a real environment-friendly recovery mode. The chemical recovery method mainly comprises an alcoholysis method, a hydrolysis method, an ammonolysis method and the like, wherein the alcoholysis (especially ethylene glycol alcoholysis) has high efficiency, the reaction condition is relatively mild, and the method is the most industrially applied method at present.
Publication number CN110818886a discloses a method for preparing regenerated food-grade PET polyester from waste PET polyester, which uses waste PET polyester as raw material to prepare food-grade regenerated PET by four steps of methanolysis, DMT rectification, glycol transesterification and BHET repolymerization. Publication No. CN11321448B discloses a method for preparing regenerated polyester by high-efficiency alcoholysis of waste polyester, which comprises the steps of mixing waste polyester with depolymerization solution, carrying out depolymerization reaction to obtain BHET, and carrying out esterification reaction and polycondensation reaction to obtain regenerated polyester. Publication No. CN114656684A discloses a method for preparing high-purity recycled PET polyester by using waste PET polyester, which is characterized in that the treated waste PET polyester is depolymerized by glycol and purified to obtain high-purity BHET monomer, and the high-purity recycled PET polyester is prepared by further pre-polycondensation and final polycondensation. Most of the current processes need to be separated and purified to obtain the dihydroxyethyl terephthalate (BHET), and the BHET is used as a raw material to further prepare the regenerated polyester, so that the steps are complicated and the cost is high.
Polyethylene terephthalate-1, 4-cyclohexanedimethanol ester (PETG) is a transparent amorphous copolyester obtained by taking 1, 4-Cyclohexanedimethanol (CHDM) as a comonomer to replace part EG and destroy the regularity of PET molecular chains. When CHDM is present at 50% or less (molar ratio), it is referred to as PETG; when CHDM is present in an amount of 50% or more (molar ratio), it is referred to as PCTG. The glass has the performances of high light transmittance, environmental protection, heat resistance, easy molding and processing and the like, and is increasingly applied to the fields of 3D printing materials, card-based materials, high light transmittance bottles and the like. However, the catalytic system of the esterification or transesterification process is still kept secret and cannot be studied intensively.
Disclosure of Invention
Aiming at the technical problems, the invention provides a method for preparing PETG/PCTG copolyester by depolymerizing waste PET with mixed alcohol, which takes EG/CHDM as mixed alcohol and carries out alcoholysis on the waste PET under the action of a catalyst; only filtering and separating to obtain depolymerized products (BHET/BHCT monomer and oligomer thereof); the depolymerization product is used as a raw material, and PETG/PCTG copolyester is prepared by polycondensation under the action of a polycondensation catalyst, so that the high-value recycling of waste PET is realized.
In order to achieve the above object, the present invention provides the following solutions:
a method for preparing PETG/PCTG copolyester by depolymerizing waste PET with mixed alcohol uses EG/CHDM mixed alcohol as an alcoholysis agent, and the waste PET is subjected to alcoholysis under the action of an alcoholysis catalyst, and depolymerization products BHET/BHCT monomer and oligomer thereof are obtained through filtration and separation; and (3) taking the depolymerized product as a raw material, and preparing PETG/PCTG copolyester through pre-polycondensation and final polycondensation under the action of a polycondensation catalyst.
Further, the method for preparing PETG/PCTG copolyester by depolymerizing waste PET through mixed alcohol specifically comprises the following steps:
(1) Alcoholysis of waste PET: taking washed and dried waste PET, sequentially adding an alcoholysis catalyst and mixed alcohol EG/CHDM, catalyzing alcoholysis to obtain a depolymerization product, and cooling and filtering to obtain BHET/BHCT monomers and oligomers thereof;
(2) Preparation of PETG/PCTG: mixing the depolymerization product obtained in the step (1), a polycondensation catalyst and a stabilizer, uniformly stirring, gradually heating to 250-260 ℃, establishing low vacuum, performing pre-polycondensation, and removing excessive ethylene glycol; continuously heating to 260-285 ℃, and obtaining PETG/PCTG copolyester, wherein the pressure is less than 60pa, and the reaction time is 1-3 h.
Further, the waste PET is one or more of waste PET bottle chips, PET films and PET fiber fabrics.
Further, the catalytic alcoholysis of step (1) is carried out in a nitrogen atmosphere.
Further, the catalytic alcoholysis reaction temperature of the step (1) is 180-240 ℃ and the reaction time is 0.5-10 h.
Further, the alcoholysis catalyst in the step (1) is one or more of zinc acetate, tetrabutyl titanate, choline acetate, urea and creatinine, and the dosage of the alcoholysis catalyst is 0.05-5% of the mass of the waste PET.
Further, the amount of the mixed alcohol in the step (1) is 100-800% of the mass of the waste PET.
Further, the molar ratio of EG to CHDM in the mixed alcohol of step (1) is 0:1 to 1:0, which may be specifically 1: 0. 9: 1. 8: 2. 7: 3. 6: 4. 5: 5. 4: 6. 3: 7. 2: 8. 1:9 and 0:1.
further, the polycondensation catalyst in the step (2) is SbO 3 、Sb(Ac) 3 And titanate, the dosage of which is 50-200 ppm of the theoretical PETG/PCTG copolyester mass.
Further, the pre-polycondensation time in the step (2) is 45-60 min, the low vacuum is 10kpa, the final polycondensation time is 60-180 min, and the pressure is less than 60pa.
Further, the stabilizer is trimethyl phosphate or triethyl phosphate, and the dosage of the stabilizer is 50-100 ppm of the theoretical PETG/PCTG copolyester.
The invention discloses the following technical effects:
(1) The raw material is PET waste, so that the cost of the raw material of the PETG/PCTG copolyester is reduced;
(2) The waste PET alcoholysis process replaces the esterification or transesterification process of PETG/PCTG production, and bypasses the technical blockage of the esterification or transesterification catalyst;
(3) The preparation of PETG/PCTG copolyester with different chain structures is realized by regulating and controlling the depolymerization degree and the feeding alcohol proportion, and the PETG/PCTG copolyester with different qualities is obtained, so that a new thought is provided for the chemical upgrading recovery of PET and the synthesis of PETG/PCTG, and the method has a larger economic value.
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
Example 1
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 190 ℃ in a nitrogen atmosphere, reacted for 3 hours to obtain a depolymerized product, cooled and filtered to obtain BHET/BHCT monomers and oligomers thereof.
(2) Preparation of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 2 hours, thus obtaining the PETG copolyester.
Example 2
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =60:40) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 190 ℃ in a nitrogen atmosphere, reacted for 3 hours to obtain a depolymerized product, cooled and filtered to obtain BHET/BHCT monomers and oligomers thereof.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 1h, thus obtaining the PETG copolyester.
Example 3
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =50:50) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 190 ℃ in a nitrogen atmosphere, reacted for 3 hours to obtain a depolymerized product, cooled and filtered to obtain BHET/BHCT monomers and oligomers thereof.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 1.5h, thus obtaining the PETG copolyester.
Example 4
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =40:60) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 190 ℃ in a nitrogen atmosphere, reacted for 3 hours to obtain a depolymerized product, cooled and filtered to obtain BHET/BHCT monomers and oligomers thereof.
(2) Synthesis of PCTG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 2 hours, thus obtaining the PCTG copolyester.
Example 5
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of tetrabutyl titanate and 30 parts of mixed alcohol (n (EG): n (CHDM) =20:80) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 190 ℃ in a nitrogen atmosphere, reacted for 3 hours to obtain a depolymerized product, cooled and filtered to obtain a BHET/BHCT monomer and an oligomer thereof.
(2) Synthesis of PCTG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 2 hours, thus obtaining the PCTG copolyester.
Example 6
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, the pressure is less than 60pa, and the reaction time is 2 hours, thus obtainingPETG copolyester.
Example 7
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of choline acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 240 ℃ under the nitrogen atmosphere, reacted for 2 hours to obtain a depolymerized product, cooled and filtered to obtain BHET/BHCT monomers and oligomers thereof.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 280 ℃, wherein the pressure is less than 60pa, and the reaction time is 1.5h, thus obtaining the PETG copolyester.
Example 8
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.001 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 280 ℃, wherein the pressure is less than 60pa, and the reaction time is 1h, thus obtaining the PETG copolyester.
Example 9
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of urea and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with mechanical stirring, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.002 part of SbO 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 45min, and excessive ethylene glycol is removed; continuously heating to 280 ℃, wherein the pressure is less than 60pa, and the reaction time is 45min, thus obtaining the PETG copolyester.
Example 10
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 Placing 0.0005 part of triethyl phosphate in a polycondensation reaction kettle, uniformly stirring, gradually heating to 260 ℃, establishing low vacuum of 10kpa, pre-condensing for 45min, and removing excessive ethylene glycol; continuously heating to 280 ℃, wherein the pressure is less than 60pa, and the reaction time is 1.5h, thus obtaining the PETG copolyester.
Example 11
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of creatinine and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
depolymerizing the depolymerized product obtained in the step (1) to 0.0005 part of SbO 3 And 0.001 part of triethyl phosphate are placed in a polycondensation reaction kettle, stirred uniformly and gradually raisedHeating to 260 ℃ and establishing low vacuum for 10kpa, and performing pre-polycondensation for 45min to remove excessive ethylene glycol; continuously heating to 280 ℃, wherein the pressure is less than 60pa, and the reaction time is 1h, thus obtaining the PETG copolyester.
Example 12
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
0.0005 part of Sb (Ac) is added to the depolymerized product obtained in the step (1) 3 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 60min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 2 hours, thus obtaining the PETG copolyester.
Example 13
(1) Alcoholysis of waste PET:
10 parts of PET bottle flakes after washing and drying, 0.005 part of zinc acetate and 30 parts of mixed alcohol (n (EG): n (CHDM) =80:20) are taken, added into a four-neck flask with a mechanical stirring device, a thermometer and a condensing device, heated to 220 ℃ under the nitrogen atmosphere, reacted for 2.5 hours, and depolymerized products are obtained, and the BHET/BHCT monomers and oligomers thereof are obtained through cooling and filtering.
(2) Synthesis of PETG:
the depolymerized product obtained in the step (1) was subjected to a reaction to obtain 0.0005 parts of Ti (OC 4 H 9 ) 4 And 0.0005 part of trimethyl phosphate is placed in a polycondensation reaction kettle, uniformly stirred, gradually heated to 260 ℃ and low vacuum of 10kpa is established, pre-polycondensation is carried out for 55min, and excessive ethylene glycol is removed; continuously heating to 275 ℃, wherein the pressure is less than 60pa, and the reaction time is 80min, thus obtaining the PETG copolyester.
1. Intrinsic viscosity
According to GB/T14189-93, mixed solution of phenol and tetrachloroethane (the mass ratio of the phenol to the tetrachloroethane is 1:1) is used as a solvent for dissolving PETG or PCTG, the outflow time of the solvent and the copolyester PETG or PCTG solution (the mass concentration is 0.005 g/mL) is respectively measured by adopting an Ubbelohde viscometer in a constant temperature water bath with the temperature of (25.00+/-0.05), and the intrinsic viscosity of the polymer is calculated according to the measured data and the mass concentration of the known solution.
2. Hue of color
A sample of 0.5g was placed in a measuring cup and placed on a stage, and the hue of the sample was measured by using a Color 35 type automatic Color difference meter.
3. Melting point
0.1g of the sample was taken and heat treated at 90℃for 1 hour, cooled and then placed in an MP-S3 type micro-melting point apparatus and rapidly warmed to 100℃and then warmed to 120℃at a rate of 10℃per minute and then warmed to 2℃per minute. The temperature at which the sample geometry disappeared (final melting point, T m )。
4. Differential scanning calorimetric analysis
The change in enthalpy of the sample during this process was determined using a DSC analyzer.
5. Tensile yield strength
The yield strength of the standard specimen was measured by applying a unidirectional static load to the standard specimen under an environmental condition of a temperature of (23.+ -. 2) DEG C and a relative humidity of (50.+ -. 5)% using an electronic universal material tester.
6. Flexural Strength
The bending strength of PETG samples was measured using a three-point method using an electronic universal material tester under ambient conditions of temperature (23±2) °c and relative humidity (50±5)%. Test specimens were injection molded from PETG to a specification of 127mm x 13mm x 3mm. During testing, a sample with a rectangular cross section area is placed on 2 fulcrums with a span of 10mm, and a load wheel pressure head is used for applying force to the sample between the 2 fulcrums, so that the outside of the sample is longitudinally bent. When the sample is bent to the appearance fracture or directly reaches the maximum strain of 5.0%, the bending strength is determined by drawing a load deflection curve, and the quantity is expressed by the area under the deflection curve.
7. Transmittance of light
The light transmission properties of PETG clear flat sheets were measured using a spectrophotometer at ambient conditions of temperature (23±2) °c, relative humidity (50±5)%, and samples were compression molded from PETG clear flat sheets, specification: the thickness is 0.0025mm-0.25mm. A circle of 50mm diameter or a square of the same size. The testing process is the same as the plastic transmittance testing method.
The above measured values are shown in Table 1.
TABLE 1 PETG/PCTG Performance
It can be seen from a combination of the values in Table 1 and experimental conditions that the high performance PETG/PCTG copolyester products obtained by the process of the present invention. Through changing the technological parameters, the feeding ratio of EG and CHDM in the mixed alcohol is found to have great influence on the structure and performance of the copolyester. As CHDM content increases, the regularity of the molecular chain is destroyed, and the glass transition temperature and melting point thereof show a certain rule; the tensile yield strength and the bending strength of the injection molding sample show a decreasing trend; the light transmittance of the sample increases. The type of the polycondensation catalyst not only affects the polycondensation reaction rate, but also has a certain influence on the color and the transparency of the copolyester, for example, the titanium catalyst has high reaction activity, but the polymer color phase is poor; sbO (SbO) 3 、Sb(Ac) 3 The reactivity is lower than that of titanium, but the hue meets the process requirements. The method can be used for preparing the PETG copolyester meeting the product requirement, provides a new thought for upgrading and recycling PET and synthesizing PETG, and has a certain industrial prospect.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.

Claims (2)

1. The method for preparing PETG/PCTG copolyester by depolymerizing waste PET through mixed alcohol is characterized by comprising the following steps:
(1) Alcoholysis of waste PET: taking washed and dried waste PET, sequentially adding an alcoholysis catalyst and mixed alcohol EG/CHDM, catalyzing alcoholysis to obtain a depolymerization product, and cooling, filtering and separating to obtain BHET/BHCT monomers and oligomers thereof;
(2) Preparation of PETG/PCTG copolyester: mixing the depolymerization product obtained in the step (1), a polycondensation catalyst and a stabilizer, uniformly stirring, gradually heating to 250-260 ℃, establishing low vacuum of 10kpa, performing pre-polycondensation, and removing excessive ethylene glycol; continuously heating to 260-285 ℃, and carrying out final polycondensation under the pressure of less than 60pa for 1-3 h to obtain PETG/PCTG copolyester;
the alcoholysis catalyst is one or more of zinc acetate, choline acetate, urea and creatinine;
the catalytic alcoholysis reaction temperature is 180-240 ℃ and the reaction time is 0.5-10 h;
the dosage of the alcoholysis catalyst in the step (1) is 0.05-5% of the mass of the waste PET;
the consumption of the mixed alcohol in the step (1) is 100% -800% of the mass of the waste PET;
the molar ratio of EG to CHDM in the mixed alcohol in the step (1) is 8: 2-2: 8, 8;
the polycondensation catalyst in the step (2) is SbO 3 、Sb(Ac) 3 Or titanate, the dosage of which is 50-200 ppm of the theoretical PETG/PCTG copolyester mass;
the pre-polycondensation time in the step (2) is 45-60 min, and the final polycondensation time is 60-180 min;
the stabilizer is trimethyl phosphate or triethyl phosphate, and the dosage of the stabilizer is 50-100 ppm of the theoretical PETG/PCTG copolyester.
2. The method for preparing PETG/PCTG copolyester by depolymerizing waste PET with mixed alcohol according to claim 1, wherein the catalytic alcoholysis in the step (1) is performed in a nitrogen atmosphere.
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