KR20210058560A - Preparation method for polyester having excellent transferency from recylced polyethylene terephthalate - Google Patents

Abstract

Disclosed is a method for producing polyester having properties similar to properties of virgin PETG by using waste PET without separation, purification, and recovery of monomers and oligomers. The present invention provides the method for producing the polyester, which comprises a step of melting a mixture containing a polyethylene terephthalate component and a diol component containing cyclohexanedimethanol and proceeding a glycolysis reaction.

Description

Manufacturing method of polyester with improved transparency using waste polyethylene terephthalate {PREPARATION METHOD FOR POLYESTER HAVING EXCELLENT TRANSFERENCY FROM RECYLCED POLYETHYLENE TEREPHTHALATE}

The present invention relates to a method for producing recycled polyester, and more particularly, to a method for producing polyester with improved transparency using waste polyethylene terephthalate.

Polyethylene terephthalate (PET) is a polymer produced through a condensation polymerization reaction through an esterification reaction using terephthalic acid (TPA) or dimethyl terephthalate (DMT) and ethylene glycol (EG) as the main raw materials. It is environmentally friendly and is used in food and beverage containers and packaging, textiles for clothing, films, and a wide range of other fields.

As such PET is the most widely used among general synthetic resins, a large amount of PET waste is generated every year, and due to its nature not easily decomposed, it has become a major cause of serious environmental pollution in recent years. Accordingly, recycling of waste such as waste PET, such as beverage bottles that are discarded after use, is emerging as a great concern.

Overseas, studies on the recovery and recycling of useful resources from waste are already being promoted in various fields under a long-term plan, and as public opinion about environmental pollution has begun to rise in Korea, economic recovery and recycling plan for waste resources has been established. As a result, research related to this is in progress.

There are largely two methods of recycling waste PET: physical recycling and chemical recycling.

The physical recycling method, for example plastic bottles, is a method of collecting and separating used plastic bottles, cutting them into small pieces and effectively cleaning them, melting these pieces to make a new bottle again. However, physically recycled PET has a disadvantage in that purity and physical properties are not stably secured in mass production of products. Also, it cannot be used as a food container, which is the main application field of PET. According to the manufacturing standards of'Standards and Standards for Equipment and Containers/Packaging' of the Ministry of Food and Drug Safety, recycled PET can be used as a food container only when it has undergone chemical regeneration methods such as heating/decomposition/polymerization, and is simply crushed/heated. /This is because it cannot be used if it has undergone physical methods such as molding.

In the chemical recycling method, the polymer chain of PET is decomposed by a chemical reaction, and through a separation and purification process, monomers or oligomers such as TPA, DMT, and EG are made, and this material is used to synthesize PET again. It is a method of chemically converting waste PET, which is discarded after use, and is very important in terms of the environment, but it is hardly applied in the actual market because the profitability for large-scale factories is limited due to high plant operating costs.

On the other hand, when PET is molded with a crystalline resin, cooling is insufficient, or when it is molded with a thick thickness, the rapid cooling efficiency per unit area is lowered due to the fast crystallization rate, resulting in white turbidity due to crystallization, and thus the transparency is greatly reduced. In order to prevent such cloudiness, the modified polyester is prepared so that crystallization does not occur under general molding conditions by lowering the crystallization rate of the resin itself. As a study to satisfy this, DMT or TPA, one of the monomers used in PET polymerization, is substituted with Diacid or Diacidester, or EG is substituted with 1,4-cyclohexanedimethanol (CHDM). Thus, modified PET (PETG) through copolymerization has been developed, but as a polyester using waste PET, a polyester having similar physical properties to PETG has not been suggested.

International Patent Publication No. WO2017/006217 discloses a method of preparing glycol-modified polyethylene terephthalate (PETG) from waste PET, but as a neopentyl glycol-based recycled PETG, the physical properties of virgin PETG are different. There is.

Japanese Patent Laid-Open No. 2009-524731 discloses a method of recycling waste PET, but it does not mention about PETG production other than the method of preparing polybutylene terephthalate (PBT) using 1,4-butanediol as a diol component. Without.

An object of the present invention is to provide a method of manufacturing a polyester having similar physical properties to virgin PETG using waste PET without the need for separation, purification, and recovery of monomers and oligomers.

In order to solve the above problems, the present invention provides a method for producing a polyester comprising the step of melting a mixture including a polyethylene terephthalate component and a diol component including cyclohexanedimethanol to proceed with a glycolysis reaction.

In addition, the polyethylene terephthalate component provides a polyester production method, characterized in that the waste polyethylene terephthalate flakes.

In addition, the cyclohexanedimethanol provides a polyester production method, characterized in that it is contained in an amount of 5 to 40 mol% of the diol component.

In addition, the polyester has a glass transition temperature (Tg) of 75 to 85°C and a carboxylic end group (CEG) content of 12 to 18 Eq/ton as measured according to the following method. Provides.

[Method of measuring CEG]

According to ASTM D7409, dissolve the polyester in Benzyl Alcohol/Chloroform and analyze the CEG content using a potentiometric titrator, but using a 0.05 N KOH solution as a titration reagent, a suitable point at which the potential value reaches -40 to -60 mV. CEG content is calculated through Equation 1 below.

[Equation 1]

CEG=(V × 0.05) × 1000)/M

V: Amount of KOH solution required for titration (ml)

M: sample amount (g)

According to the present invention, a mixture containing cyclohexanedimethanol as a diol component in a polyethylene terephthalate component is melted and polycondensed as it is without a recovery process of a monomer, etc. It is possible to provide a method for easily obtaining a polyester having similar physical properties to PETG.

This has the advantage of not only being able to manufacture high value-added products beyond simple recycling of waste PET, but also developing new recycling technologies and solving environmental problems.

Hereinafter, a preferred embodiment of the present invention will be described in detail. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted. Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In the conventional method of chemical recycling of waste PET in which the polymer chain of waste PET is decomposed, converted into a monomer or oligomer state through separation and purification, and then synthesized into PET again, the process is complicated and the manufacturing cost As a result of repeated research, facing the fact that this has risen and has not been widely applied in the actual market, and that polyester with physical properties similar to PETG has not yet been proposed as polyester using waste PET. Cyclohexanedimethanol (CHDM) is added to PET to carry out the glycolysis reaction, and the reaction product is directly polymerized without separation, purification, and recovery of monomers and oligomers, thereby simplifying the existing process and shortening the reaction time. It was confirmed that it was possible to manufacture high value-added products with improved transparency, such as PETG, rather than recycling, and the present invention was reached.

Accordingly, the present invention discloses a method for producing a polyester comprising the step of performing a glycolysis reaction by melting a mixture including a polyethylene terephthalate component and a diol component including cyclohexanedimethanol.

The polyethylene terephthalate component may be waste polyethylene terephthalate flakes. For example, recycled PET bottles can be prepared by washing, crushing, dehumidifying and drying, and the size of the flakes may vary slightly depending on the pulverization process for recycling waste PET, but the average particle size is usually 1 cm or less. It is used, and preferably those having an average particle size of 0.1 to 1 cm may be used. Here, the'particle size' of the flake may be viewed as the longest particle diameter irrespective of the orientation of the particles to be measured.

In waste PET, since PET containers of various uses and colors from Homo-PET to Co-PET are recycled, the waste PET flakes can be used through a series of washing processes to improve the quality and color of polyester. For example, it can be prepared by washing a PET bottle in an aqueous sodium hydroxide solution, separating foreign substances other than PET such as film, paper, metal, adhesive, etc. on the surface, pulverizing it into flakes having a size of 1 cm or less, washing with water and drying dehumidification. have.

In the present invention, a part of the diol component is replaced with CHDM (1,4-Cyclohexanedimethanol) in order to recycle waste PET into polyester with improved transparency. Even if the mixture is melted and subjected to a polycondensation reaction immediately after the glycolysis reaction proceeds, polyester having similar physical properties to PETG can be produced.

The content of CHDM for producing regenerated polyester having similar physical properties to PETG is preferably 5 to 40 mol%, and more preferably 20 to 40 mol% of the total diol component. When the CHDM content is less than 5 mol%, amorphousness does not appear and the reaction time may be lengthened, and when it exceeds 40 mol%, it may be disadvantageous in terms of cost.

In the present invention, the diol component other than CHDM may be, for example, an aliphatic diol, an aromatic diol, or a mixture thereof.

The aromatic diol may include an aromatic diol compound having 8 to 40 carbon atoms, preferably 8 to 33 carbon atoms. Examples of such aromatic diol compounds include polyoxyethylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(2.0)-2,2-bis(4-hydroxyphenyl) Propane, polyoxypropylene-(2.2)-polyoxyethylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene-(2.3)-2,2-bis(4-hydroxyl Phenyl) propane, polyoxypropylene-(6)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(2.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxy Propylene-(2.4)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene-(3.0)- Bisphenol A derivatives added with ethylene oxide and/or propylene oxide such as 2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene-(6)-2,2-bis(4-hydroxyphenyl)propane (Polyoxyethylene-(n)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(n)-2,2-bis(4-hydroxyphenyl)propane or polyoxypropylene-( n)-polyoxyethylene-(n)-2,2-bis(4-hydroxyphenyl)propane may be mentioned, but specific examples of the aromatic diol compound are not limited thereto, wherein n is polyoxyethylene. Or it means the number of polyoxypropylene units (unit).

In addition, the aliphatic diol may include an aliphatic diol compound having 2 to 20 carbon atoms, preferably 2 to 12 carbon atoms. Examples of such aliphatic diol compounds include ethylene glycol, diethylene glycol, triethylene glycol, propanediol (1,2-propanediol, 1,3-propanediol, etc.), 1,4-butanediol, pentanediol, hexanediol ( 1,6-hexanediol, etc.), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedi Linear, branched or cyclic aliphatic diol components such as methanol, 1,3-cyclohexanedimethanol, and tetramethylcyclobutanediol may be mentioned, but ethylene glycol may be preferably used.

Diols other than CHDM, such as EG, used together with CHDM, have a molar ratio of a dicarboxylic acid component: a diol (based on all diols including CHDM) component in the glycolysis reaction of 1:1.05 to 1:2.0. Can be mixed with PET ingredients.

In the present invention, a step of melting the mixture may be performed prior to the glycolysis reaction. The mixture can be melted by adding PET components such as waste PET flakes to the mixture of EG and CHDM, and then stirring the mixture at 50 to 200 rpm for 60 to 90 minutes at 100 to 220°C while flowing nitrogen in the reactor. have.

In the glycolysis reaction performed after melting the mixture as described above, CHDM is replaced at the EG position of the PET polymer chain, and when the amount of CHDM is replaced, the reaction is terminated, and the reaction conditions are Although it may be appropriately adjusted according to specific properties, molar ratio, process conditions, etc., in the present invention, it is preferable to perform at 200 to 240°C, 200 to 400 minutes, and 50 to 300 rpm conditions, and to produce polyester having similar physical properties to virgin PETG More suitably to 200 to 230 ℃, it may be carried out in the conditions of 240 to 300 minutes and 100 to 200 rpm.

Thereafter, a step of polymerizing under reduced pressure by adding a catalyst to the reaction product according to the glycolysis reaction is performed, and at this time, a thermal stabilizer may be further added together with the catalyst.

The polycondensation reaction is terminated when the intrinsic viscosity (IV) of the final PETG reaches a target value, and the reaction conditions may be appropriately adjusted according to specific properties, viscosity, and process conditions of the polyester to be produced, but in the present invention, 260 to 290 ℃, 30 to 200 minutes, preferably carried out under conditions of 10 to 150 rpm and 1 torr or less, more suitably to produce a polyester having similar physical properties to virgin PETG 270 to 280 ℃, 60 to 120 minutes, It can be carried out under conditions of 40 to 80 rpm and 0.5 torr or less.

Here, in the present invention, unlike the conventional chemical recycling method of waste PET, the reactant obtained by glycolysis is directly polymerized without separation, purification, and recovery of monomers or oligomers. PET is a crystalline resin, and when there are impurities, the impurities act as crystal nuclei during molding, and the transparency decreases due to clouding caused by crystallization, so separation and purification are important in the manufacturing process of recycled PET. On the other hand, since PETG is an amorphous resin and has less effect of clouding due to crystallization of impurities than PET, impurities of the glycolic acid reactant in the present invention do not need to be removed through a filter while being transferred to the polymerization reactor.

As the catalyst used in the polymerization step, a known commercial titanium compound may be used without limitation. However, in the case of the catalyst content, the content of the catalyst is 2 to 100 ppm based on the central metal atom in the total polyester resin prepared according to the present invention. Can be included.

Examples of the titanium-based compound include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate , Triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, titanium dioxide/silicon dioxide copolymer, titanium dioxide/zirconium dioxide copolymer, and the like.

On the other hand, in the polyester manufacturing process according to the present invention, a phosphorus stabilizer may be used, and in particular, the step of adding a phosphorus stabilizer to the polycondensation reaction may be further included. In this case, the phosphorus stabilizer is based on phosphorus atoms in the total resin. It may be included in an amount of 5 to 100 ppm.

Specific examples of the phosphorus stabilizer include phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triethylphosphonoacetate, or a mixture of two or more thereof.

Unlike virgin PETG, the polyester produced through the above process is composed of various constituents depending on the recycled PET used. However, even though the constituents are slightly different from virgin PETG, if some physical properties such as viscosity and thermal properties are similar, they can be used for the same purposes as virgin PETG because they have mechanical properties and processing properties that are very similar to virgin PETG. The viscosity of the polyester according to the present invention has an intrinsic viscosity (IV) of 0.6 to 0.8 dl/g level, preferably 0.6 to 0.7 dl/g level, and its thermal properties are 75 to 85°C, preferably 78 to 82 Although it shows a glass transition temperature (Tg) of ℃, but crystallization temperature (Tc) and melting temperature (Tm) are not observed, it has properties very similar to virgin PETG in terms of viscosity and thermal properties. , CEG) content also has a carboxyl terminal content of 12 to 18 Eq/ton, preferably 13 to 17 Eq/ton, similar to virgin PETG, based on the measurement method described later.

Hereinafter, the present invention will be described in more detail through specific examples and comparative examples.

Example 1 to 3

Waste PET flakes that have undergone washing and drying (washing the PET bottle in 1.0 wt% NaOH aqueous solution, separating foreign substances other than PET such as film, paper, metal, adhesive, etc. on the surface, crushing into flakes having an average particle size of 0.1 to 1 cm, washing with water) After, dehumidification and drying), EG and CHDM were mixed so that the content of CHDM in the final polyester became the content of Table 1 below. Nitrogen (N ₂ ) in the reactor was flowed and the mixture was melted while slowly raising the temperature to 200° C. while stirring at 70 rpm for 60 minutes, and the reaction was carried out while stirring at 220° C. for 280 minutes at 150 rpm. Thereafter, the reaction product was transferred to a polycondensation reactor, and 230 ppm of a titanium-based catalyst (12 ppm based on a central metal atom) and 160 ppm of TEPA (Triethyl phosphonoacetate) as a thermal stabilizer (22 ppm based on a phosphorus atom) were added based on the final polyester. . Thereafter, while raising the internal temperature to 275°C, the pressure was gradually reduced from normal pressure to 0.1 torr over 30 minutes, polycondensation reaction was performed under high vacuum until the desired intrinsic viscosity was reached, and the final polyester was prepared by discharging it and cutting it into chips. .

Comparative example One

A commercial virgin PETG was prepared.

Comparative example 2

A commercial virgin PET was prepared.

Test example

Intrinsic viscosity, carboxyl terminal content, thermal properties and components were analyzed by the following method for resins prepared or prepared according to the Examples and Comparative Examples, and the results are shown in Table 1 below.

[Measurement and Analysis Method]

(1) Intrinsic Viscosity (I.V.)

After dissolving at a ratio of 0.5 parts by weight in a solution containing 60 parts by weight of phenol and 40 parts by weight of 1,1,2,2-tetrachloroethane with respect to the polyesters obtained in Examples and Comparative Examples, a Cannon-Ubbelohde microviscometer was used. The intrinsic viscosity was measured at 30°C.

(2) Carboxylic End Group (CEG) content

According to ASTM D7409, the polyester obtained in Examples and Comparative Examples was dissolved in Benzyl Alcohol/Chloroform, and the CEG content was analyzed using a potentiometric titrator. 0.05 N KOH solution was used as a titration reagent, and the CEG content was calculated through Equation 1 below at the titration point at which the potential value reached -40 to -60 mV.

[Equation 1]

CEG=(V × 0.05) × 1000)/M

V: Amount of KOH solution required for titration (ml)

M: sample amount (g)

(3) thermal properties

Thermal properties of the polyesters obtained in Examples and Comparative Examples were measured using a Differential Scanning Calorimeter (DSC). The sample is heated from 30°C to 300°C to remove the heat history for 5 minutes, then rapidly cooled, and heated again at a rate of 10°C/min and cooled while the glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tcc) Was confirmed.

(4) Component analysis (nuclear magnetic resonance, NMR)

After dissolving the polyester obtained in Examples and Comparative Examples at a concentration of 0.5% by weight in a mixed solution of Deuterated Chloroform/Trifluoroacetic acid, after analysis using an Agilent DD2 500MHz Spectrometer, the constituent components were calculated.

Referring to Table 1, in the case of melting a mixture containing CHDM as a diol component in a PET component according to the present invention and polycondensing the reaction product produced after the glycolysis reaction without a recovery process such as a monomer, virgin PETG (Comparative Example 1) It can be seen that it is possible to prepare a polyester having physical properties very similar to (Examples 1 and 2).

However, when the added CHDM content does not reach a certain level (Example 3), there is a difference in thermal properties from PETG properties. Therefore, in the case of producing polyester using CHDM according to the present invention, CHDM is used. It can be seen that it is desirable to use it within a certain content range.

The preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to understand that other specific forms can be easily modified without changing the technical spirit or essential features of the present invention.

Therefore, the scope of the present invention is indicated by the claims to be described later rather than the detailed description, and all changes or modified forms derived from the meaning, scope and equivalent concepts of the claims are included in the scope of the present invention. It must be interpreted.

Claims (4)

A method for producing a polyester comprising the step of melting a mixture including a polyethylene terephthalate component and a diol component including cyclohexanedimethanol to undergo a glycolysis reaction. The method of claim 1,
The polyethylene terephthalate component is a polyester manufacturing method, characterized in that the waste polyethylene terephthalate flakes. The method of claim 1,
The cyclohexane dimethanol is a polyester manufacturing method, characterized in that contained in an amount of 5 to 40 mol% of the diol component. The method according to any one of claims 1 to 3,
The polyester has a glass transition temperature (Tg) of 75 to 85°C and a carboxylic end group (CEG) content of 12 to 18 Eq/ton measured according to the following method:
[Method of measuring CEG]
According to ASTM D7409, dissolve the polyester in Benzyl Alcohol/Chloroform and analyze the CEG content using a potentiometric titrator, but using a 0.05 N KOH solution as a titration reagent, a suitable point at which the potential value reaches -40 to -60 mV. CEG content is calculated through Equation 1 below.
[Equation 1]
CEG=(V × 0.05) × 1000)/M
V: Amount of KOH solution required for titration (ml)
M: sample amount (g)