Are PET Bottles Biodegradable?

First of all, PET bottles are not biodegradable, this artical will try to show you the reasons, difficulities and solutions in details.

I. The Wide Application of PET Plastic Bottles

PET plastic bottles have a wide range of applications in modern society and play an important role in multiple fields.

In the field of packaging, PET plastic bottles are undoubtedly star products. It is widely used in the packaging of carbonated beverages, drinking water, fruit juice, enzymes, and tea drinks. Whether on the shelves of supermarkets or in small shops on the street, you can see PET plastic bottles of various shapes and sizes containing various beverages.

At the same time, it also performs well in food packaging, with the majority of commonly used bottles for edible oils, soy sauce, snacks, dried fruits, and candied fruits being made of PET material. Food grade PET packaging bottles use high-quality raw materials and are not allowed to use recycled materials, ensuring the safety and hygiene of food.

In addition, PET plastic bottles also play an important role in various industries such as chemical and pharmaceutical packaging. Over 3,000,000 tons of PET will be used annually for the manufacturing of PET plastic bottles in the next few years, indicating a huge demand in the packaging field.

In short, PET plastic bottles occupy an important position in various fields due to their excellent performance and wide applications, bringing great convenience to people’s lives and industrial production.

II. Characteristics of PET Plastic Bottles

PET plastic, also known as polyethylene terephthalate, is a material widely used in multiple fields. It has several characteristics.

1. Lightweight: PET bottles have the characteristic of being lightweight, which makes transportation and use more convenient and reduces costs.
2. High Strength: It has high tensile strength and modulus, with a bending strength of up to 200MPa and an elastic modulus of up to 4000MPa. For example, in the field of electronic appliances, it can be used to manufacture components such as connectors, coil winding tubes, integrated circuit housings, etc., which can withstand certain external forces without damage.
3. High and Low Temperature Resistance: It has excellent high and low temperature resistance, can be used for a long time within the temperature range of 120 ℃, can withstand high temperatures of 150 ℃ for short-term use, can withstand low temperatures of -70 ℃, and has little effect on its mechanical properties at high and low temperatures. In some special environments, such as the automotive parts field, it can adapt to different temperature changes.
4. Chemical Corrosion Resistance: non-toxic, weather resistant, stable against chemical drugs, resistant to oil, fat, dilute acid, dilute alkali, and most solvents. Excellent performance in packaging food, drugs, chemicals, etc., ensuring the safety of the contents.
5. Good Insulation Performance: Good electrical insulation performance, less affected by temperature, widely used in the field of electronic appliances, such as manufacturing transformer casings, capacitor casings, etc., ensuring the safe operation of electrical equipment.
6. High Transparency: PET is a transparent polymer with good transparency and glossiness. In the field of packaging, especially in beverage packaging, consumers can clearly see the status of the contents, increasing the attractiveness of the product. For example, the plastic bottles of mineral water, fruit juice, and carbonated drinks that we usually drink are made of PET, which has high transparency and makes the products more aesthetically pleasing.

In summary, PET plastic plays an important role in various fields such as packaging, electronic appliances, automotive parts, and mechanical equipment due to its unique chemical structure and excellent performance characteristics.

III. The Degradation Problem of PET Plastic Bottles

PET plastic bottles face severe degradation challenges in natural environments due to their chemical structure and characteristics.

A. Reasons For Difficult Degradation

1. Strong Chemical Inertness: PET is composed of a large number of ethylene terephthalate basic units connected in a chain structure, which makes the molecular structure of PET highly symmetrical and has strong chemical inertness. Under natural conditions, PET is difficult to react with other substances and is not easily degraded by air or microorganisms.
2. Biodegradable: Although some microorganisms can produce enzymes that decompose PET, the conditions for this type of bacteria to act are relatively harsh and their quantity is limited in natural environments. Meanwhile, the chemical structure of PET makes it difficult to serve as a source of nutrients for microorganisms, resulting in a very slow biodegradation rate. For example, a bacterium that parasitizes on PET bottles can decompose PET, but the decomposition rate is slow, taking about a month to consume 0.2 millimeters thick PET film.

B. Pressure On The Environment And Ecology

1. Waste Accumulation: Due to the difficulty in degrading PET plastic bottles, a large amount of discarded PET plastic bottles, if not recycled, will continue to accumulate in the environment. These discarded plastic bottles are scattered on the streets, tourist areas, Rivers and Lakes, roads and railways of the city, which will not only cause visual pollution, but also occupy a lot of space.
2. Soil Pollution: The large amount of plastic debris entering the soil can seriously affect the productivity of the land. PET has strong chemical inertness and can exist in the natural environment for a long time. It is difficult to decompose in soil and hinders the circulation of water and air in the soil, affecting the growth of plant roots and the activity of soil microorganisms.
3. Marine Pollution: Every year, a large number of PET plastic bottles are discarded into the ocean, becoming an important source of marine pollution. According to statistics, millions of tons of plastic waste flow into the ocean every year, including a large number of PET plastic bottles. These discarded PET plastic bottles pose a threat to marine life and may be ingested or entangled by birds, fish, etc., causing them to be injured or even killed. Meanwhile, plastics may also decompose into microplastic particles, which are ingested by organisms and ultimately affect human health through the food chain. The United Nations Environment Programme has pointed out that a large amount of plastic waste in the ocean is threatening the safety of marine life, and conservatively estimates that it causes economic losses of up to 13 billion US dollars annually. Marine plastic pollution has been listed as one of the top ten pressing environmental issues worth paying attention to in the past decade.
4. Resource Waste: The production of PET plastic bottles requires a large amount of crude oil and other fossil fuels, and its difficult to degrade nature makes it impossible to effectively recycle and reuse these resources after use, resulting in huge waste of resources.

In summary, the degradation problem of PET plastic bottles has brought severe pressure to the environment and ecology, and solving this problem requires the joint efforts of the whole society.

IV. Magical Biodegradation Methods

A new enzyme proposed by a team from the University of Toulouse in France can hydrolyze 90% of plastic bottle PET within 10 hours. The research team first conducted an “exam” on several different hydrolytic enzymes and selected the “chosen one” LCC. This hydrolytic enzyme showed the best thermal stability in the competition and its reaction efficiency was also very high. However, the ability of LCC enzyme in its original state is not enough to become a “plastic killer” and still needs to be refined by scientists.

The LCC improved by replacing divalent metal binding sites with disulfide bonds can survive in high-temperature environments, with only a partial reduction in activity. The newly modified variant of hydrolytic enzyme not only retains similar or higher specific activity than the original LCC, but also increases the survival temperature. With the help of this enzyme, the hydrolysis efficiency of PET is greatly improved. The plastic products prepared from LCC hydrolysis products have very similar mechanical properties and transparency, meeting the standards for the use of PET bottles.

The team from the University of Texas at Austin has created a novel enzyme called FAST PTEase. Researchers used machine learning systems to predict mutations in PET degrading enzymes, identifying an enzyme that contains five mutations compared to wild-type PETase and has higher PET degradation activity compared to wild-type and engineered alternatives. FAST PET can completely depolymerize PET under relatively “mild” conditions, amorphous PET can be directly depolymerized, and PET with a crystallinity exceeding 25% requires thermal pretreatment.

This enzyme can degrade samples of 51 untreated PET products previously used by consumers, demonstrating its ability to handle various raw materials. FAST PET can be used for closed-loop recycling to produce colorless PET from colored PET. This result demonstrates a feasible approach for enzymatic plastic recycling on an industrial scale.

V. Factors Affecting the Biodegradation of PET Plastic Bottles

1. Temperature: Temperature has a significant impact on the biodegradability of PET plastic bottles. Generally speaking, the higher the temperature, the faster the degradation rate may be. This is because higher temperatures can provide more energy for the biodegradation process, promote microbial activity, and catalyze related enzymes. Within the appropriate temperature range, the metabolic activity of microorganisms will accelerate, thereby accelerating the decomposition of PET plastic bottles. For example, some studies have found that as the temperature increases, the activity of PET hydrolytic enzymes also increases, leading to an accelerated degradation rate of PET plastics. However, excessively high temperatures may also have adverse effects on microorganisms and enzymes, even leading to their inactivation. Therefore, determining an appropriate temperature range is crucial for improving the biodegradation efficiency of PET plastic bottles.
2. PH Value: The pH value also plays an important role in the biodegradation process of PET plastic bottles. When the pH value is moderate, the biodegradation rate of PET plastic bottles is faster. This is because different microorganisms and enzymes have optimal activity within a specific pH range. If the pH value of the environment is too high or too low, it may affect the survival of microorganisms and the catalytic function of enzymes, thereby reducing the degradation rate of PET plastic bottles. For example, certain microorganisms are better able to secrete enzymes that degrade PET in neutral or slightly alkaline environments, thereby accelerating the decomposition of PET plastics. Therefore, maintaining a suitable pH environment is crucial for promoting the biodegradation of PET plastic bottles.
3. Moisture: Moderate moisture content has a significant impact on the degradation rate of PET plastic bottles. Water plays multiple key roles in the process of biodegradation. Firstly, water is essential for the survival and metabolism of microorganisms. Moderate water can provide a favorable growth environment for microorganisms, promoting their reproduction and activity. Secondly, water can serve as a medium for certain enzyme catalyzed reactions and participate in the degradation process of PET plastics. When the moisture content is moderate, microorganisms can fully exert their degradation effect, and related enzymes can also catalyze reactions in suitable environments, thereby improving the degradation rate of PET plastic bottles. However, if the moisture content is too high or too low, it may have adverse effects on the biodegradation process. Excessive moisture content may lead to insufficient oxygen, affecting the activity of aerobic microorganisms; However, a low water content may cause microorganisms to be in a state of dehydration, inhibiting their metabolic activity.
4. Light Intensity: The light intensity is closely related to the photodegradation rate of PET plastic bottles. Light exposure can trigger the photodegradation reaction of PET plastic, mainly through the mechanism of free radical reactions. The higher the light intensity, the faster the photodegradation rate of PET plastic bottles. This is because stronger light can provide more energy, stimulate PET molecules to produce free radicals, thereby accelerating the breakage and degradation of molecular chains. For example, in a sunny environment, the photodegradation rate of PET plastic bottles will significantly accelerate. In addition, the wavelength of light can also affect the photodegradation rate of PET plastic bottles. Generally speaking, the shorter the wavelength of light, the higher its energy and the stronger its degradation effect on PET plastic. However, the higher the light intensity, the better. Excessive light exposure may cause the surface of PET plastic bottles to overheat, thereby affecting their physical properties and degradation process.
5. Additives: Additives play an important role in the degradation rate of PET plastic bottles. Some specific additives can promote the biodegradation process of PET plastic bottles. For example, certain biodegradable additives can be blended with PET plastic to enhance its biodegradability. These additives can stimulate the growth and activity of microorganisms, or promote the catalytic degradation of PET plastics by enzymes. In addition, some additives can also improve the physical properties of PET plastic, making it more easily decomposed by microorganisms. For example, by adding certain compatibilizers, the compatibility between different types of polymers can be increased, improving the uniformity and stability of the recycled plastic system, thereby facilitating the process of biodegradation. However, the use of additives also needs to be cautious, as excessive additives may have a negative impact on the environment or affect other properties of PET plastic bottles. Therefore, when selecting additives, it is necessary to comprehensively consider their promoting effect on degradation rate and their impact on the environment and product performance.

VI. Prospects and Challenges of Biodegradation of PET Plastic Bottles

A. Vast Prospects

1. Promotion of environmental protection demand: With the increasing global attention to environmental protection, reducing plastic pollution has become an urgent task. PET plastic bottles, as a widely used plastic product, have attracted much attention for their biodegradability. Biodegradation technology provides a sustainable solution to solve PET plastic bottle pollution, which is in line with the trend of environmental protection development.
2. Continuous technological progress: Research institutions and enterprises are making new progress in the field of PET plastic bottle biodegradation. For example, the new enzymes developed by the team from the University of Toulouse in France and the team from the University of Texas at Austin in the United States have brought new hope for the biodegradation of PET plastic bottles.
3. Huge market potential: With the increasing awareness of environmental protection among consumers, the demand for biodegradable materials continues to grow. The biodegradable products of PET plastic bottles are expected to replace traditional PET plastic bottles in various fields such as packaging, electronics, and automobiles, with huge market potential. It is predicted that the future bottle grade PET market will develop towards a more environmentally friendly, high-performance, and multifunctional direction, providing a broad market space for PET plastic bottle biodegradable products.

B. Challenges Coexist

1. Cost issue: Currently, the cost of biodegradation technology is relatively high. For example, the use of biodegradable additives and other additives can promote the biodegradation process of PET plastic bottles, but it also increases production costs. In addition, the research and production of some new enzymes also require significant financial investment. According to relevant reports, the cost of manufacturing the new enzyme may be $25 per kilogram, which makes the cost of biodegradable PET plastic relatively high. Compared to petrochemical raw materials, the cost of using recycled PET, although sustainable, may not be as cheap as petrochemical products. Taking bio film as an example, about 250000 tons of film are used annually in Xinjiang. If all of them are replaced with bio film, the cost per ton will increase by 20000 yuan, which will greatly increase production costs.
2. Difficulties in technology promotion: The promotion of biodegradation technology faces some difficulties. Firstly, the complexity of technology poses challenges for its large-scale application. For example, the use of novel enzymes requires specific conditions and technical support, which may be difficult for some small businesses to achieve. Secondly, consumers’ awareness and acceptance of biodegradable products need to be improved. At present, consumers find it difficult to identify which are reliable biodegradable plastic products, and there are pseudo degradable products such as photo degradable and oxygen degradable plastics in the market, which poses certain difficulties for the promotion of biodegradable plastics. In addition, the incomplete standard labeling of biodegradable plastics and inadequate market supervision have also affected the promotion of technology.
3. Performance needs to be improved: Some of the properties of biodegradable plastics are still insufficient compared to traditional plastics such as PET, such as tensile strength, water resistance, and so on. This may prevent biodegradable plastics from completely replacing traditional plastics in some application scenarios. In addition, biodegradable plastics may deteriorate during the inventory period. For example, biodegradable plastic bags can be easily torn into small pieces with a light tear after being left in the air for a long time, which undoubtedly increases the difficulty of sales and inventory management for enterprises.

In summary, although the biodegradation of PET plastic bottles has broad prospects, it also faces challenges in terms of cost, technology promotion, infrastructure, and performance. Solving these challenges requires joint efforts from the government, enterprises, and research institutions to increase research and development investment, improve standard labeling and market supervision, strengthen infrastructure construction, enhance consumer awareness and acceptance, in order to promote the development and application of PET plastic bottle biodegradation technology.