Sofia Martinez
Plastics are a significant contributor to global waste, with over 350 million tons generated in 2019 alone, and very little of it recycled. To combat this, scientists are developing new techniques to recycle and upcycle plastic waste into useful products. This process, known as biorecycling or chemical recycling, uses microbes and enzymes to break down plastics into their basic building blocks, which can then be used to create new, higher-value products. This approach not only reduces plastic waste but also promotes a circular economy, where resources are reused and recycled instead of discarded, conserving natural resources and reducing the environmental impact of incineration and landfill. While biorecycling is currently limited to certain types of plastics and faces challenges such as high costs, it shows promise in mitigating the adverse effects of plastic waste on the environment and human health.
| Characteristics | Values |
|---|---|
| Recycling method | Mechanical recycling, chemical recycling, biorecycling |
| Benefits of recycling | Conserving natural resources, saving energy, reducing greenhouse gas emissions, reducing health risks, reducing dependence on fossil fuels |
| Recycling process | Sorting, reprocessing (melting plastics and returning to solid form or converting to liquid/gas building blocks), converting to new products |
| Biorecycling process | Using microbes to convert plastic waste into new products of equal or better quality |
| Upcycling | Recombining monomers into more desirable materials, such as biodegradable plastics or high-value chemicals |
| Novel techniques | Converting waste plastic into high-value products through homogenous hydroformylation catalysis |
| Global plastic waste | Over 350 million tons generated in 2019, with most sent to landfills or incinerated |
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What You'll Learn
Plastic production history: From Bakelite to modern times
Plastic is everywhere in our modern world, from toys and computers to sports equipment and clothing. However, the story of plastic began over a century ago with the creation of Bakelite—the world's first fully synthetic plastic.
The Birth of Bakelite
In 1907, Leo Baekeland, an immigrant living in Yonkers, New York, invented the world's first completely synthetic plastic, which he named Bakelite after himself. Bakelite is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde. By controlling the pressure and temperature applied to these components, Baekeland produced a hard, mouldable material. The resulting plastic was extremely hard, infusible, and insoluble, with high resistance to electricity, heat, and chemicals.
The Rise of the Plastic Industry
Bakelite revolutionised the emerging electrical and automobile industries, as it was perfect for electrical insulators and automobile distributor caps. It also found its way into jewellery, pipe stems, children's toys, and even firearms. The ability to quickly mould Bakelite into various shapes gave rise to mass production processes, and its versatility and low cost made it a popular choice for consumers.
World War II and Beyond
The plastics industry received a significant boost during World War II, as synthetic plastics became essential for parachutes, ropes, body armour, helmet liners, and aircraft windows. After the war, Americans eagerly spent their money on plastic products, which were seen as inexpensive, safe, and versatile. Plastic replaced steel in cars, paper and glass in packaging, and wood in furniture.
Environmental Concerns and Recycling
However, the public perception of plastic began to shift in the postwar years, as the environmental impact of plastic waste became evident. The presence of plastic debris in the oceans and the growing concern about the potential health threats posed by plastics led to a decline in the reputation of the plastics industry. Recycling emerged as a proposed solution, with the industry encouraging municipalities to collect and process recyclable materials. While mechanical recycling has its limitations and biorecycling is still costly and applicable to only certain types of plastic, these methods offer potential pathways to reduce plastic waste and promote a circular economy.
Today, the quest for sustainability has led to the development of bioplastics, which are made from plant crops instead of fossil fuels, and the exploration of chemical recycling methods, such as conversion to feedstock, to turn plastic waste into new products.
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Extraction and refinement of raw materials
The first step in plastics manufacturing is the extraction and refinement of raw materials. The primary raw materials used in plastics manufacturing are hydrocarbons, derived from natural resources like coal, natural gas, and petroleum. Crude oil, a complex mixture of thousands of compounds, is a key raw material. It is extracted by drilling holes through rocks underground or drilling beneath the ocean with support from platforms. Different-sized pumps produce between 5 and 40 litres of oil per stroke. The oil is then transported to an oil refinery via pipelines, which can be thousands of miles long.
The refining process transforms crude oil into different petroleum products, which are then converted into useful chemicals, including monomers, the basic building blocks of polymers. Crude oil is heated in a furnace and sent to a distillation unit, where it separates into lighter components called fractions. One of these fractions, naphtha, is crucial for plastic production.
Naphtha is a mixture of hydrocarbons obtained from the distillation of crude oil. It is further broken down into products such as propylene and heptane, which are then used to make poly(propylene). Other raw material molecules are converted into monomers such as ethylene, propylene, and butene. These monomers have double bonds, allowing their carbon atoms to react and form polymers.
The process of breaking down hydrocarbons is called cracking, and it can be performed in two ways: steam cracking and catalytic cracking. Steam cracking uses high temperature and pressure to break hydrocarbon chains, while catalytic cracking uses a catalyst to allow the process to occur at lower temperatures and pressures.
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Polymerisation and polycondensation
Polymerisation
Polymerisation is the process of connecting monomers into chains or networks. This process is also known as polymer synthesis.
Polycondensation
Polycondensation is a polymer formation process that links small molecules (monomers) together, accompanied by the elimination of byproducts such as water and alcohols. This process is also known as condensation polymerization or condensative chain polymerization. The current definition of polycondensation embraces both the earlier term "condensation polymerization" and the term "condensative chain polymerization".
Condensation Polymerization
Condensation polymerization is a form of step-growth polymerization. Linear polymers are produced from bifunctional monomers, i.e. compounds with two reactive end-groups. Common condensation polymers include polyesters, polyamides such as nylon, polyacetals, and proteins.
Polycondensation Methods
To overcome the disadvantage of low molecular weight and low quality in direct polycondensation, new polycondensation methods have been proposed. Azeotropic polycondensation (AP) and solid-state polymerization (SSP) are two main directions. The AP approach efficiently removes water by using appropriate azeotropic solvents, manipulating the equilibrium between the monomer and polymer in an organic solvent to produce a polymer with a relatively high molecular weight in one step.
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Compounding and additives
Plastic recycling is essential to creating a circular economy where plastics are sustainably produced, designed, used, reused, and recycled instead of being discarded. Mechanical reprocessing and chemical reprocessing are two methods used to convert plastics into materials for new products. Mechanical re-processors use heat and pressure to melt plastics and reform them into solid form, usually pellets. On the other hand, chemical re-processors break down plastics into liquid or gas building blocks, which are then converted back into solid-form plastics by plastic material makers. These re-processed materials, known as "recycled plastics," are sold to companies that create plastic products and packaging.
Biorecycling, or upcycling, is another approach that uses microbes and enzymes to convert plastic waste into new products of equal or better quality. This process can produce more biodegradable plastics or valuable chemicals like vanillin, found in vanilla flavorings. While biorecycling has the potential to benefit the environment and economy, it currently faces limitations in applicability and higher costs.
To address the limitations of biorecycling, researchers have developed novel techniques to turn low-value waste plastic into high-value products. One such process, led by Professor George Huber, involves recovering olefins from pyrolysis oil and using homogenous hydroformylation catalysis to convert them into aldehydes. These aldehydes can be further reduced to produce high-value industrial alcohols, which are essential ingredients in soaps, cleaners, and other polymers.
Another method, known as "conversion to feedstock," breaks down mixed plastic waste into oil or gas-like feedstock, which is then used to produce chemicals, including new plastics. These recycling methods not only reduce the environmental impact of plastic waste but also contribute to energy savings, reduced greenhouse gas emissions, and the development of a more sustainable economy.
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Plastic pellets and the supply chain
Plastic pellets are a key part of the plastic supply chain. Pellets are small, uniform pieces of plastic that are easy to transport and melt down into new products. They are the most common form of resin, the raw material used to create plastic products.
The plastic recycling chain involves recovering used plastic products and packaging and reprocessing the material for use in new products and packaging. Mechanical reprocessors use heat and pressure to melt down plastic waste and reform it into pellets. Chemical reprocessors, on the other hand, convert plastics into their liquid or gas building blocks, which are then converted into solid-form plastics (usually pellets). These recycled plastics are then sold to companies that make plastic products and packaging.
The benefits of recycling plastic include reducing the need for fossil resources and keeping plastic waste out of the environment. Recycling plastic also conserves natural resources, saves energy, and reduces greenhouse gas emissions. However, recycling plastic can be more expensive than creating new plastics, and it currently only works with certain types of plastic.
There are also emerging technologies that can turn plastic waste into high-value products. For example, a team at UW-Madison has developed a process that converts olefins from pyrolysis oil into industrial alcohols, which can be used to make soaps and cleaners. Another process is "conversion to feedstock," where mixed plastic waste is broken down into oil- or gas-like feedstock, which is then used to produce chemicals, including plastics.
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Frequently asked questions
Plastic recycling is the process of recovering plastic products and packaging at the end of their useful life and reprocessing the material for use in new products and packaging.
There are two main types of plastic recycling: mechanical and chemical. Mechanical recycling uses heat and pressure to melt plastics and then return them to their original solid form, typically small pellets. Chemical recycling, on the other hand, converts plastics into their liquid or gas building blocks, which are then converted back into solid-form plastics.
Plastic recycling has several benefits. It conserves natural resources, saves energy, reduces greenhouse gas emissions, and promotes a circular economy. Additionally, it reduces dependence on fossil fuels for new plastics and keeps plastic waste out of the environment.
