Chloe Zhang
Plastic is a polymer, a long, repeating chain of atoms made by combining monomers, or shorter chains of atoms such as hydrogen, carbon, and oxygen. The current method of plastic recycling involves shredding, melting, and remoulding plastic waste, which weakens the plastic as the process breaks the polymers, and impurities and additives are hard to separate. This means that most plastic can only be recycled two or three times before becoming unusable. However, recent developments in chemical recycling, which breaks down plastic into its original monomers, and new types of plastic polymers that allow for easier removal of additives, could allow for the infinite recycling of plastics.
| Characteristics | Values |
|---|---|
| Recyclability of plastic | Plastic can be recycled one to 10 times, depending on the type, although most can be recycled only once. |
| Plastic recycling process | Plastic is usually recycled mechanically by sorting, cleaning, shredding, melting, and remoulding. |
| Challenges of mechanical recycling | The process breaks the polymers, resulting in weaker recycled plastic with decreased tensile strength and viscosity. |
| Chemical recycling | Chemical recycling is an alternative process that turns plastic back into oil, allowing for infinite recycling. |
| PDK plastic | A new type of plastic called poly(diketoenamine) or PDK can be easily and cheaply recycled into its original monomers with minimal energy input. |
| Benefits of PDK | PDK plastic can be recycled indefinitely, is not made from petroleum, and has potential for carbon neutrality. |
| Applications of PDK | PDK can be used in a variety of consumer products, such as car parts and water bottles, and in industries with product take-back programs. |
| Improving recyclability | Scientists are working on new types of plastic polymers that allow for easier removal of additives and contaminants, improving recyclability. |
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What You'll Learn
- Plastic polymers are prone to degradation, becoming brittle and losing viscosity
- Chemical recycling could see all types of plastic fed into an infinite recycling system
- PDK plastics can be recycled indefinitely and are not made from petroleum
- Recycled plastics are mixed with virgin material to make them usable
- Glass and aluminium can be recycled endlessly
Plastic polymers are prone to degradation, becoming brittle and losing viscosity
Plastic polymers are prone to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment, and recycling. The major factors contributing to the degradation of plastic polymers are heat, light, air, and water.
Heat treatments, such as incineration, pyrolysis, and gasification, cause thermal degradation, which can lead to the release of harmful gases like dioxins and furans. At low temperatures, the polymer melt is more viscous and prone to mechanical degradation through shear stress. Higher temperatures reduce viscosity but increase thermal degradation. Friction at points of high shear can cause localized heating, resulting in additional thermal degradation. Mechanical degradation can be minimized by adding lubricants, also known as processing aids or flow aids, which reduce friction between polymer chains and lower melt viscosity.
The degradation of plastic polymers can also be caused by chemical changes such as oxidation and chain scission, leading to a reduction in molecular weight and degree of polymerization. These changes affect physical properties like strength, malleability, melt flow index, appearance, and colour. The changes in properties are often referred to as "aging".
Biodegradation, facilitated by microorganisms like bacteria and fungi, also contributes to the degradation of plastic polymers. Certain enzymes, such as lipase-type enzymes, accelerate the biodegradation process by breaking specific ester bonds. Additionally, hydrolysis can degrade polymers by autocatalyzing the carbon end-groups of polymers, leading to oligomer formation and enzymatic reactions on the polymer surface.
The degradation of plastic polymers during recycling is a significant issue. The mechanical recycling process of shredding, melting, and remoulding plastic waste weakens the material. This is because the process breaks the polymers, and impurities or additives are challenging to separate, resulting in reduced tensile strength and viscosity. Recycled plastics are often mixed with virgin material to improve their quality, but they can typically only be recycled a limited number of times before becoming unusable.
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Chemical recycling could see all types of plastic fed into an infinite recycling system
Plastic is made of polymers – long, repeating chains of atoms that are created by combining building blocks called monomers. The current mechanical process of recycling plastic involves shredding, melting, and remoulding plastic waste. However, this process weakens the plastic as it breaks the polymers and leaves impurities that are challenging to separate. Consequently, recycled plastics are often mixed with virgin materials to be usable, but even then, they can only be recycled a few times before becoming unusable.
Chemical recycling, on the other hand, has emerged as a promising alternative to conventional recycling methods. This process aims to recycle the unrecyclable by breaking down plastics into their original monomer state through a process called depolymerization. Chemical recycling can accommodate all types of plastic, regardless of colour or composite, and create an "infinite" recycling system. For instance, PDK plastics can be easily broken down into individual monomers when mixed with an acid, allowing for the creation of new plastics without any loss of quality.
Recent advances in sorting technology, such as artificial intelligence, can further enhance the efficiency of chemical recycling. Additionally, chemical recycling can promote a closed-loop system, also known as a circular economy, where plastics are reused instead of being discarded in landfills or incinerated. This process can be achieved through conversion, decomposition, and purification methods.
While chemical recycling offers exciting possibilities, it also faces challenges. One significant hurdle is the high energy requirement for the process, which, combined with volatile oil prices, can make it cheaper to produce new plastic than to recycle existing plastic. Additionally, if the end product of chemical recycling is oil used for fuel, burning such fuels would release greenhouse gases. Furthermore, the adoption of chemical recycling faces obstacles such as high startup costs and limited incentives for innovation.
Despite these challenges, chemical recycling technologies have made significant progress, with companies like Berkeley Lab and Eastman demonstrating efficient and eco-friendly processes. These advancements offer hope in tackling the urgent problem of plastic waste and environmental leakage.
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PDK plastics can be recycled indefinitely and are not made from petroleum
Plastic is notoriously difficult to recycle, and only 9% of all plastic ever made has been recycled into new plastics. The process of mechanical recycling, which is the most common method, shreds and melts plastic waste before remoulding it. However, this weakens the plastic as the process breaks the polymers, and impurities and additives are difficult to separate from the rest of the material. This means that recycled plastic usually contains virgin resin to make up for the dip in quality, and can usually only be recycled two or three times before becoming unusable.
However, a team of scientists from Berkeley Lab has developed a new type of plastic called poly(diketoenamine) or PDK, which can be recycled indefinitely and is not made from petroleum. PDK plastic is engineered to easily break down into individual monomers when mixed with an acid. The monomers can then be separated from any additives and gathered to make new plastics without any loss of quality. This "chemical recycling" process is light on energy and carbon dioxide emissions, and it can be repeated indefinitely, creating a completely circular material lifecycle.
The scientists also plan to develop a process to create the initial PDK resin using microbe-fermented plant material, which would make the entire lifecycle of a PDK plastic product low-carbon or even carbon neutral. Once the infrastructure for large-scale PDK production and recycling is developed, PDK could replace traditional plastics in a variety of consumer products, from car parts to water bottles.
In the future, chemical recycling is expected to play a bigger role in the recycling industry as it prioritizes the recovery of high-value materials that can be reused in manufacturing. However, with current technology, very few polymers can be efficiently recycled chemically. PDKs are designed to require only small amounts of energy to be recycled back into their original monomers with high yields, so the carbon in PDKs can be recirculated across limitless cycles of remake-and-reuse.
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Recycled plastics are mixed with virgin material to make them usable
Plastic is made of polymers, which are long, repeating chains of atoms created by combining monomers. During the manufacturing process, chemical additives such as pigments, fire retardants, and antioxidants are added, giving the plastic desirable characteristics like colour, heat resistance, or durability.
The traditional way of recycling plastic involves shredding, melting, and remoulding it. However, this process results in weaker recycled plastic due to the breaking of polymers and the difficulty of separating impurities or additives. As a result, recycled plastics often need to be mixed with virgin material to be usable. Virgin plastics are new, pristine materials with a sturdier molecular structure, ensuring precision and high performance in manufacturing.
The need to mix recycled plastics with virgin material arises from the challenges inherent in the traditional recycling process. The mixing compensates for the decrease in quality and performance of recycled plastics, making them suitable for specific applications. However, even with the addition of virgin material, recycled plastics can usually only be recycled two to three times before their quality becomes too poor for use.
To address these limitations, scientists are exploring chemical methods, such as "depolymerisation," to return waste plastics to their original monomer state. This process involves breaking down the resin polymers into individual monomers, separating them from additives, and using them to create new plastics without any loss of quality. Additionally, new types of plastic polymers are being developed to allow for easier removal of additives and contaminants, potentially enabling repeated recycling.
While the traditional mechanical recycling process has its limitations, innovative approaches like chemical recycling and the development of new plastic polymers offer hope for more sustainable practices. These advancements could revolutionise the way we recycle plastics, creating a truly circular material lifecycle.
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Glass and aluminium can be recycled endlessly
Plastic is notoriously difficult to recycle, and less than 10% of plastic is mechanically recycled more than once. This is because the process of shredding and melting plastic waste before remoulding it breaks down the polymers and leaves the recycled plastic weaker. Additives and impurities in the plastic are also extremely challenging to separate from the rest of the material.
However, glass and aluminium are both infinitely recyclable materials. Glass is 100% recyclable, although it is often sent to landfills instead of being recycled. Glass does not deteriorate, corrode, stain or fade, and it can be recycled endlessly without losing quality. Aluminium is also continually recycled in closed loops and can be recycled repeatedly without changing its fundamental properties. Aluminium is one of the most recycled and recyclable materials in use today, and the process of recycling it requires far less energy than creating new aluminium, reducing carbon emissions and saving money for businesses and consumers.
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Frequently asked questions
No, plastic is not infinitely recyclable. The current way plastic is recycled is a downward spiral of waste and degraded materials. Each time plastic is recycled, its quality is degraded as the heating process shortens polymer chains. However, scientists are working on chemical methods that can return waste plastics to their original monomer state, allowing for indefinite recycling.
Most plastic recycling plants shred plastic waste, melt it down, and remould it. However, this process weakens the plastic as it breaks the polymers, and impurities or additives are challenging to separate from the rest of the material. Recycled plastics are often mixed with virgin materials to make them usable.
Chemical recycling, also known as "depolymerization," is a process that breaks down plastics into individual monomers, which can then be separated from additives and used to make new plastics without losing quality. Another alternative is the development of new types of plastic polymers that allow for easier removal of additives and contaminants, enabling repeated recycling.
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