Alexei Volkov
Plastic waste is a pressing environmental concern, with the vast majority of plastics being disposed of in non-environmentally friendly ways. Recycling plastic is critical to improving the environment and waste management solutions. However, not all plastics are created equal, and some are incredibly hard to recycle. Before being recycled, plastics are sorted according to their resin type, and there are two main ways to recycle them: mechanical recycling, where plastic is washed, ground, and melted, and chemical recycling, where plastic is broken down into monomers to form new polymers. The numbers within the recycling symbol on plastic containers, known as SPI or resin identification codes, indicate the type of plastic and provide information about its safety and biodegradability. These codes help determine how the plastic can be recycled, with some plastics being easier to recycle than others due to their structure and composition.
| Characteristics | Values |
|---|---|
| Plastic resin codes | Numbers ranging from 1-7, with 7 being 'other' |
| Recyclability | The lower the resin code, the more likely the plastic type is to be easily recyclable |
| Types of plastic | Thermoset plastics, thermoplastics, bioplastics, composite plastic, plastic-coated wrapping paper, polycarbonate, PET, HDPE, rPP, rHDPE, rLDPE |
| Plastic recycling process | Sorting, shredding/crushing, washing/cleaning, melting, moulding into new products |
| Plastic recycling challenges | Economical, environmental, and technical factors; difficulty recycling certain plastics like polypropylene |
| Plastic recycling benefits | Reduced natural resource extraction, decreased energy use, job creation, reduced greenhouse gas emissions |
| Plastic recycling rates | India, Europe, and South Korea have rates higher than 50%; the US and China are lower |
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What You'll Learn
Sorting plastics by resin type
Before recycling, plastics are sorted according to their resin type, either manually or through mechanised automated processes, or even by colour. Sorting plastics by resin type ensures that similar plastics are processed together, increasing their value and improving the efficiency of the recycling process.
Resin identification codes are usually found on plastic products inside a triangle of arrows. These codes help recycling facilities identify the polymer structure of the plastic and determine the most suitable recycling method. For example, thermoset plastics with irreversible chemical bonds cannot be recycled, while thermoplastics can be remelted and remoulded.
Some plastics, such as bioplastics, composite plastics, plastic-coated wrapping paper, and polycarbonate, are not recyclable. Flexible packaging, like chip bags, can be challenging to recycle as they are made of multiple layers of different plastics. Small plastic items, such as bread bag clips and pill packaging, can also cause issues for recycling equipment due to their size.
To facilitate effective sorting and recycling, it is important to separate different types of plastics and ensure they are free of residue. Additionally, providing technical specifications, such as Melt Flow, Resin Number, and Extrusion Grade, can assist recycling companies in identifying and processing specific types of plastics.
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Mechanical recycling methods
Mechanical recycling is a process that turns plastic waste into secondary raw materials or products without significantly altering the material's chemical structure. This method can be applied to all thermoplastics with little to no impact on quality. The process begins with the collection of end-of-life plastic products from separate and mixed waste streams. Once at the recycling plant, the plastics are sorted by colour or thickness, shredded into smaller pieces, and washed to remove dust, dirt, food residue, drink residue, or labels. The clean, shredded plastic is then ready to be melted down and repurposed into new products.
Mechanical recycling is one of the two main ways to recycle plastic, the other being chemical recycling. In chemical recycling, plastic is broken down into monomers to form new polymers to be reused. Mechanical recycling is a more straightforward process that does not alter the chemical structure of the plastic.
The recyclability of plastic types depends on how they are made. Thermoset plastics, for example, contain polymers that form irreversible chemical bonds and cannot be recycled, whereas thermoplastics can be remelted and remoulded. Plastic waste can often be repurposed or reused, diverting it from landfills. However, some plastics are incredibly challenging to recycle, such as crisp packets, salad bags, plastic wrap, bioplastics, composite plastic, plastic-coated wrapping paper, and polycarbonate.
To improve the recyclability of plastics, it is essential to separate and sort them properly. Small plastic items, such as bread bag clips, pill packaging, and single-use condiment pouches, can cause problems for recycling equipment by getting caught or falling between belts and gears. Additionally, flexible packaging, like potato chip bags, which are made from layers of different types of plastic and often lined with aluminium, can be challenging to recycle.
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Chemical recycling methods
Plastic waste is a critical environmental concern, with the majority of plastic waste in the US ending up in landfills, causing polluted oceans, overextended landfills, and ecological damage. While mechanical recycling is the dominant technology for recycling plastics, chemical recycling is emerging as a promising alternative for hard plastics that are otherwise difficult to recycle.
Chemical recycling is a broad term for a range of technologies that use heat, chemical reactions, or both, to break down plastic polymers into monomers or simpler molecules, which can then be used as raw materials for manufacturing new products. This process is also known as feedstock recycling. By breaking down the polymers, chemical recycling can produce recycled plastic with virgin plastic properties, making it suitable for demanding applications such as food packaging. Additionally, chemical recycling can create a closed-loop system, where plastics are reused instead of being discarded in landfills or incinerated, contributing to a circular economy.
There are three general categories of chemical recycling technologies: conversion, decomposition, and purification. Conversion techniques, such as pyrolysis and gasification, convert mixed or sorted plastics into smaller molecules. Pyrolysis, or "plastics to fuel," involves heating plastic waste to high temperatures in the absence of oxygen, resulting in a synthetic crude oil that can be refined into fuel products. Other chemical recycling technologies include hydro-cracking, depolymerisation, methanolysis, glycolysis, and hydrolysis.
Chemical recycling is particularly useful for hard-to-recycle plastic products, such as films, multi-layered containers, and epoxy resin wind turbine blades. It can also be used for food packaging and medical applications where mechanical recycling may not be suitable. However, chemical recycling faces challenges such as high startup costs and the need for further investments and policy frameworks to support its adoption.
Overall, chemical recycling methods offer a promising approach to addressing the problem of plastic waste, reducing reliance on landfills, and promoting a more sustainable circular economy for plastics.
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Non-recyclable plastics
While recycling plastic has specific benefits, such as extending the lifetime of non-renewable resources like petroleum, conserving limited natural resources and energy, and improving waste management solutions, it is important to note that not all plastics are recyclable. The recyclability of plastic types depends on various factors, including their composition, size, shape, and level of contamination. Here is a detailed overview of non-recyclable plastics:
Thermoset Plastics:
Thermoset plastics, also known as thermosetting plastics, are characterized by their ability to form irreversible chemical bonds during the curing process. These bonds lock chemical chains into new configurations, resulting in strong materials with high heat resistance and mechanical strength. Examples of thermoset plastics include epoxy, phenolic, unsaturated polyester, and urethane. Due to the irreversible nature of the chemical bonds, thermoset plastics cannot be recycled or reused.
Bioplastics and Composite Plastic:
Bioplastics and composite plastics are often non-recyclable. Bioplastics, such as compostable plastic, require special treatment and are typically designed to be composted at commercial composting facilities rather than recycled. Composite plastics, on the other hand, are made from multiple layers or types of plastic, making them challenging to recycle.
Plastic-Coated Materials:
Materials coated in plastic, such as plastic-coated wrapping paper, plastic-coated paper cups, and plastic-lined aluminum packaging, are generally non-recyclable. The coating process makes it difficult to separate the plastic from the underlying material, and the resulting mixture may not be recyclable.
Contaminated Plastics:
Plastics heavily contaminated with food or other substances, such as plastic food trays, containers, cups, straws, and tubes, are often non-recyclable. The contamination can affect the quality and integrity of the recycled material, rendering it unsuitable for reuse.
Small and Thin Plastics:
Small plastics, such as bread bag clips, pill packaging, and single-use condiment pouches, can cause issues in recycling equipment by getting caught or falling between the belts and gears. Thin plastics, such as plastic bags, cling film, and plastic wrap, can also pose problems by clogging recycling machines if not properly separated. Therefore, many recycling programs do not accept these items.
It is important to note that the recyclability of plastics can vary depending on local regulations and the capabilities of specific recycling facilities. While some plastics may be challenging to recycle, advancements in recycling methods and technologies are constantly being made to improve the recyclability of various plastic types.
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Recycling symbols and resin identification codes
Plastic waste is a pressing environmental concern, and recycling is critical to improving the environment and waste management. Recycling symbols and resin identification codes are essential for sorting and recycling plastic waste.
The Resin Identification Code (RIC) is a technical standard with a set of symbols that appear on plastic products. These symbols identify the plastic resin used to make the product. The RIC was developed in 1988 by the Society of the Plastics Industry (now the Plastics Industry Association) in the United States. The original RIC symbols consisted of arrows that cycle clockwise to form a triangle enclosing a number, resembling the universal recycling symbol. However, subsequent revisions replaced the arrows with a solid triangle to address consumer confusion, as the presence of a RIC on an item does not necessarily indicate recyclability.
The numbers within the RIC, ranging from 1 to 7, identify the polymer structure of the plastic and facilitate the sorting and recycling process. The lower the resin code, the more likely the plastic is to be easily recyclable. Each number represents a different type of plastic and specific recycling instructions:
- 1: Polyethylene Terephthalate (PETE)—Beverage bottles, cups, and other packaging.
- 2: High-Density Polyethylene (HDPE)—Bottles, cups, milk jugs, and plastic shopping bags.
- 3: Polyvinyl Chloride (PVC)—Pipes, siding, flooring, etc.
- 4: Low-Density Polyethylene (LDPE)—Plastic bags, six-pack rings, tubing, etc.
- 5: Polypropylene (PP)—Auto parts, industrial fibers, food containers, etc.
- 6: Polystyrene (PS)—Plastic utensils, Styrofoam, cafeteria trays, etc.
- 7: Polycarbonate and other plastics—Clear, hard plastic with potential hormone-disrupting properties.
It is important to note that the acceptability of plastic items for recycling has evolved, and some areas can now collect and recycle most plastic products regardless of their RIC. Additionally, different localities may have varying recycling guidelines, so it is essential to refer to local guidelines or packaging instructions when determining the recyclability of a plastic item.
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Frequently asked questions
There are seven unique plastic types, ranging from numbers 1 to 7, with 7 being 'other'.
The number within the recycling symbol on plastic containers, known as an SPI Code, provides information about the safety and biodegradability of each plastic type. However, just because something has the chasing arrows symbol with a number on it doesn’t mean it’s recyclable — it’s just a way of showing what type of plastic it is.
Examples of non-recyclable plastics include bioplastics, composite plastic, plastic-coated wrapping paper, polycarbonate, cling film, blister packaging, and plastic bags.
Plastics #1 and #2 are the most common types of plastic containers and the most easily recyclable. Bottles used for laundry detergent and personal care products such as shampoo and soap are all recyclable.
The two main ways to recycle plastic are mechanical recycling, where plastic is washed, ground, and melted, and chemical recycling, where plastic is broken down into monomers to form new polymers to be reused.
