WO2022146325A1

WO2022146325A1 - A production method for polyethylene terephthalate (pet) comprising use of polymethylmethacrylate (pmma) in order to reduce the amount of acetaldehyde, carboxylic end group and diethylene glycol generated in the industrial use of polyethylene terephthalate (pet)

Info

Publication number: WO2022146325A1
Application number: PCT/TR2021/051250
Authority: WO
Inventors: Bilal DEMIREL
Original assignee: Erciyes Universitesi
Priority date: 2020-12-30
Filing date: 2021-11-22
Publication date: 2022-07-07
Also published as: EP4271724A1; TR202022457A2

Abstract

The present invention relates to the use of Polymethylmethacrylate (PMMA) during preform production step in injection molding in order to reduce the amount of Acetaldehyde, Carboxylic end group and Diethylene Glycol generated in the industrial use of Polyethylene Terephthalate (PET).

Description

A PRODUCTION METHOD FOR POLYETHYLENE TEREPHTHALATE (PET) COMPRISING USE OF POLYMETHYLMETHACRYLATE

(PMMA) IN ORDER TO REDUCE THE AMOUNT OF ACETALDEHYDE, CARBOXYLIC END GROUP AND DIETHYLENE GLYCOL

GENERATED IN THE INDUSTRIAL USE OF POLYETHYLENE TEREPHTHALATE (PET)

Field of the Invention

The present invention relates to the use of Polymethylmethacrylate (PMMA) to reduce the amount of Acetaldehyde, Carboxylic end group and Diethylene Glycol generated in the industrial use of Polyethylene Terephthalate (PET).

Background of the Invention

Today, a wide variety of food packagings such as films, boxes, bottles are widely used. These packagings are manufactured in different processes and forms according to the type of food, usage and storage conditions. Non-carbonated beverages such as water, fruit juice, buttermilk (ayran), milk, and carbonated beverages such as sparkling water and fizzy drinks are consumed in abundance and sold in markets. It is of great importance in terms of food safety that the said foods are delivered to the customer in a healthy way, from production to final consumption, without being spoiled. For this reason, academic studies on the subject continue increasingly. Studies on packaging materials mainly focus on improvement of barrier properties, recycling, environmental degradation, migration and improvement of mechanical properties. Recently, studies have been encouraged in the packaging industry, which focus on deterioration of taste in drinking water packages, development of packaging with recycling barrier properties in PE packages, usage of polymer-based packages instead of aluminum-coated cardboard beverage boxes in milk packages, and development of hot-fill PET packaging. Acetaldehyde, Carboxylic end group and Diethylene Glycol generated in the industrial uses of PET emerge as an important problem. The thermal degradation of PET chains generally originates from the carboxyl end groups and the presence of acetaldehyde. In studies carried out by Sami Al- AbdulRazzak and Saleh A. Jabarin [1], it is shown that the increase in carboxyl end groups in PET increases the moisture holding capacity of the resin. This is due to hydrogen bonds between carboxyl end groups and water. The said hydrogen bonds cause the water to exist there longer after it is attached to the resin. This case leads the resin to hold more moisture, and thus enabling a medium more suitable for the realization of hydrolysis reaction to be prepared. Accordingly, the increase in number of the carboxyl end groups in PET reduces the resistance of PET against the hydrolysis. The content of the carboxyl end groups also affects the thermal stability of the PET.

It is also known that carboxyl end groups are one of the parameters that affect the reaction rate and, in parallel with its increase; it causes degradation of PET and losses in molecular weight.

Acetaldehyde has a characteristic taste and odor. They can cause smell and taste changes even in trace amounts. In addition, its detection threshold is very low. There is normally less than 2.5 ppm of residual Acetaldehyde (AA) in bottle resins. Acetaldehyde migration may cause taste and smell changes in foods put in PET bottles. Many researchers and institutions have stated that the acetaldehyde in PET can negatively affect the organoleptic characteristics of the product inside the bottle. Furthermore, it has been found that acetaldehyde is among the compounds which are likely to show carcinogenic effects on human health.

DEG (Diethylene glycol) is formed in the side reaction of ethylene glycol and causes the melting point of PET to decrease. DEG, which is a byproduct of polymerization reaction, is a comonomer which decreases the melting temperature. However, it is not effective in crystallization rates. DEG comonomer is added in ratio of 5% by mole into PET in order to prevent crystallization during preform injection molding and blowing. Diethylene glycol, which is toxic to humans and animals, is a substance that damages the kidneys and liver, among its other effects.

A commercial product is available in the market for inhibiting said substances that are harmful to the PET industry. However, no study has been carried out about its content.

International patent application no WO2019098979 A2 discloses Mg2B2O5 in order to eliminate harmful chemicals formed in the PET product.

Summary of the Invention

The main objective of the invention is to inhibit the by-products (Acetaldehyde, Carboxylic end group and Diethylene Glycol) which cause chemical degradation of the PET material and threaten human health in the process from the raw material to the final product. In the studies carried out within the scope of the invention, it has been determined that the formation of harmful chemicals such as Acetaldehyde, Carboxylic end group and Diethylene Glycol is prevented at certain rates by adding PMMA polymer in ratio of 0.05-0.1% by mass into the PET material at the step of preform with injection. On the other hand, it also has provided an increase in viscosity, allowing PET to be processed more easily.

Detailed Description of the Invention

The present invention relates to a method comprising a process step of adding Polymethylmethacrylate into the PET material at the preform stage in order to reduce or eliminate Acetaldehyde, Carboxylic end group, and Diethylene Glycol, which are generated as a result of thermal and mechanical induced chemical degradation during production of Polyethylene Terephthalate (PET), which is used in the packaging of beverages. The produced PET material is turned into a bottle in two stages in the state of the art. In the first stage, it is preformed by injection method, while in the second stage, the final product, which is the bottle, is obtained by blow molding method. In the injection stage, PET is molten at a temperature in the range of 260-280°C and compressed into the preform mold with the help of a screw. Then, in the blow molding process, the bottle is blown into the mold with the help of both tension rod and air. In both processes, the PET material undergoes chemical degradation due to both mechanical and thermal factors and releases several chemicals that are harmful to human health. These harmful chemicals such as Isophthalic Acid (IP A), Acetaldehyde (AA) and Diethylene Glycol (DEG) that are released pass into the human body upon transferring to the food carried in the packaging and harm human health over time. On the other hand, as a result of breaking of polymer chains due to this chemical degradation, situations such as changes in the glass transition temperature (Tg) and the color of PET, and decreases in viscosity and yield strength values thereof occur. Among these harmful chemicals, Acetaldehyde (AA), which has a characteristic taste and odor, causes taste and odor changes in the product inside the PET bottle [2, 3], On the other hand, it is known that Acetaldehyde has a carcinogenic effect on human health [4], Diethylene Glycol, which is another by-product of PET degradation, causes the melting temperature of PET to decrease and it is added to the PET resin in a ratio of around 5% so that PET does not crystallize during injection molding [5], There are 4 types of degradation of PET; namely oxidative, thermal, hydrolytic and mechanical. The first of these is oxidative degradation. Oxidative degradation is the most common type of degradation in polymers, since the temperature of PET rises to an average of 260 °C in the injection and extruder. It can also be called thermo-oxidative degradation. In this type of degradation, PET begins to degrade upon formation of free radicals and unstable peroxy radicals are formed due to the desire of the resulting radicals to react with O2. These peroxy radicals in the medium cause the emergence of unstable hydrogens. Ultimately, free radicals and unstable hydroxy peroxides in the medium lead to an autocatalytic cycle. Reactions stop when the reactants in the process medium are exhausted or propagation is inhibited by their by-products [6], As a result of oxidative degradation, CO2 and H2O are formed as reaction products [7], The degradation mechanism is as follows:

Initiation:

RH + O2 — R- + HO2 (Activation energy (Ea)=126-189 kj/mol) 2RH — 2R- + H2 (bimolecular; Ea=28-410 kj/mol) 2RH + O2 — ► 2R- + H2O2 (trimolecular)

Propagation:

R- + O2 RO2 (Ea=0) RO2 + RH — ROOH + R (Equation 1)

Termination:

RO2 + RO2 — R- + R- — R- + RO2— ► (Equation 2)

Ions of some metals such as Cu⁺², Fe⁺³ and Co⁺² in the injection or extruder medium also act as catalysts and decompose hydroxy peroxides as seen in Equation 2 [7],

Due to oxidative degradation in polymers, polymer chains are broken and groups such as -OOH, -OH and -COOH are formed. As a result, decreases in mechanical properties are observed. On the other hand, oxidation reactions having high activation energies are temperature dependent and these reactions increase at high temperatures. It has also been reported in the literature that high amount of diethylene glycol (DEG) accelerates the oxidation of PET. In a study carried out by Korshak and Vinogradova, it was stated that the molecular weight of polyesters also plays an important role in the degree of degradation [8], In this study, it was observed that after a polyester with an initial molecular weight of 9540 was heated at 250 °C for 10 hours, its molecular weight decreased to 6130 with a decrease of 36%, and the molecular weight of another polyester with an initial molecular weight of 6810 decreased to 5500 with a decrease of 19% after the same process.

Another degradation type of PET is thermal degradation. Thermal degradation is divided into two groups as intramolecular thermal degradation and chain end thermal degradation. In thermal degradation, a result of thermal degradation of PET is viscosity decrease. The reason for this has been shown to be the breaking of the ester bonds in the molecule. On the other hand, chain ends accelerate thermal degradation. Accordingly, molecular weight loss also accelerates [9], As a result of thermal degradation of PET at 282-323 °C, volatile substances such as CO, CO2, H2O, CH3CHO (acetaldehyde), methane, CeEfc, C2H4; and several compounds such as CH3CH2C6H4COOCH3 (methyl paraethylbenzoate), CH3C6H4COOCH3 (methyl paratoluate), CH3COCC6H4C6H4COOCH3 (dimethyldiphenyl 4.4 carboxylate) are generated [10],

As a result of thermal degradation, the color of PET also deteriorates and it is believed that Acetaldehyde causes this. On the other hand, as a result of thermal degradation, the molecular weight of PET decreases, and accordingly, decreases also in viscosity values are observed [11],

PET granules must be dried very well before processing. H2O remaining in the structure causes hydrolytic degradation. High temperature and high pressure are factors that accelerate the hydrolysis reaction. After hydrolytic degradation, PET decomposes to PTA and MEG [12],

There are studies in the literature about the mechanical degradation occurring during extrusion processes [13, 14], What is meant by mechanical degradation is molecular splits during screw movements (shear and longitudinal stresses). Mechanical degradation of PET can generally occur in solid and molten form [6], It can be said that the mechanical degradation of PET mostly occurs during the preform injection stage. During the injection, friction occurs between the molten material and the screw, which causes the emergence of free radicals. Mechanical degradation of PET depends on the magnitude of mechanical stress in the injection, temperature, O2 concentration, type of additives and particle size. Mechanical degradation can be prevented by adding some plasticizers and chemicals (inhibitors) to PET during injection [15], During the processing of PET, all of the above-mentioned degradation types can occur simultaneously. There is a disagreement as to which of the mechanical, thermal and chemical degradations is dominant. Springer et al. [16] and Holmstrom et al. [17] claim that thermal degradation is dominant, while Ford et al. [18] and Folt et al. [19] claim that the mechanical degradation is the fundamental one.

Within the scope of the invention, PMMA was added and blended in certain ratios into the PET resin with the help of a twin screw extruder before injection. As a result of the examination conducted, it was determined that the addition of PMMA in a ratio of 0.05-0.1% prevented the chemical degradation of PET, especially inhibited the formation of Acetaldehyde. In the same process, as a result of the degradation in pure PET, 9-12 ppm Acetaldehyde is formed therein. However, it was determined that this rate decreased to 2-3 ppm levels in mixed PET.

REFERENCES

[1]. Sami Al-AbdulRazzak and Saleh A Jabarin, 2002. “Processing characteristics of polyethylene terephthalate): hydrolytic and thermal degradation”, Polymer International, 51, 164-173.

[2]. State Planning Organization, 2001. “Eighth Five-Year Development

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[3]. Villain, F., Coudane, J. And Vert, M., 1995, Thermal Degradation of

Polyethylene Terephtalate: Study of Polymer Stabilization, Polymer Degradation and stability, 49, 393-397.

[4]. NTP, 2003, National Toxicology Programme, Tenth Report on

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[10]. Goodings, 1961. Soc. Chem. Ind. London Monograph, 13, 211.

[11]. Ehrig, R. J. 1992. Plastics Recycling. Hanser Publishers, Munich. 281.

[12]. Anonymous, 1994. The Fiber Spinning Research Group School of

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[19]. Folt, V. L. 1969. Rubber Chem. Techol. 42, 1294.

Claims

CLAIMS A Polyethylene Terephthalate (PET) production method for reducing or eliminating Acetaldehyde, Carboxylic end group and Diethylene Glycol generated during the production of Polyethylene Terephthalate (PET), comprising the steps of

- preforming by injection method and

- obtaining the final product, which is the bottle, by blow molding method, and characterized in that it comprises the process step of adding Polymethylmethacrylate into the PET material at the preform stage. A Polyethylene Terephthalate (PET) production method according to Claim 1, characterized in that it comprises the process step of adding Polymethylmethacrylate in the range of 0.05-0.1%. A Polyethylene Terephthalate (PET) production method according to Claim 1, characterized in that it comprises the process step of adding Polymethylmethacrylate by injection.