Maya Ellison
Plastics are categorized based on their resin type, thickness, and foaming. The seven main types of plastic are polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and 'other'. The 'other' category includes plastics such as acrylics, nylon, fiberglass, and BPA (bisphenol A). The resin type of plastic is important as it determines its use and recyclability. For example, PET is commonly used for food and drink containers, while PVC is used for vinyl flooring, shower curtains, and plumbing pipes. The thickness and foaming of plastic affect its degradation rate, with thick polyethylene sheets exhibiting a heterogeneous and depth-dependent degradation profile. The generation, recycling, and disposal of plastic materials are measured and classified by organizations such as the US EPA, which found that in 2018, 35.7 million tons of plastic were generated in the United States, with only 9% recycled and 16% incinerated, while the remaining majority was disposed of in landfills.
| Characteristics | Values |
|---|---|
| Plastic resins used in | PET beverage bottles, HDPE bottles for milk and water, plastic containers, bags, sacks, wraps and lids |
| Generation of plastics in 2018 | 35.7 million tons in the US, which was 12.2% of MSW generation |
| Percentage of plastic waste in landfills in 2018 | 18.5% of all MSW landfilled |
| Projection of MSW by 2050 | 3.4 billion tons worldwide |
| Percentage distribution of plastic and multilayer packaging waste within the MSW stream | Kaunas (40.16%), Daugavpils (36.83%), and Tallinn (35.09%) |
| Percentage distribution of plastic and multilayer packaging waste within the separately collected packaging waste stream | Multi-family residential buildings (62.05% to 74.7%), single-family residential buildings (44.66% to 56.89%) |
| Factors that affect the gasification process | Reactor temperature, pressure, and reactor types |
| Plastic with the highest chlorine content | Polyvinyl chloride (PVC) at about 55% |
| Plastics with the highest heating value | PE, PP, and PS |
| Plastics that are challenging to recycle | Polystyrene and polyvinyl chloride |
| Number 1 PET plastics used for | Food and drink containers |
| Number 2 HDPE plastics used for | Milk and juice containers |
| Number 3 PVC plastics used for | Vinyl flooring, shower curtains, plumbing pipes, shrink wrap, and toys |
| Number 4 LDPE plastics used for | Food and beverages, plastic bags, shopping bags, and disposable packaging |
| Number 5 PP plastics used for | Reusable, durable, and rigid food and beverage containers |
| Number 6 PS plastics used for | Egg cartons, shipping “peanuts,” and meat and poultry trays |
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What You'll Learn
Plastic resins and their uses
Plastic resins are a key component of plastics, which have become a staple of most products we use and purchase. The versatility of plastic resins makes them widely used in manufacturing, packaging, and many other applications.
The terms plastic and resin are defined by two different sets of physical and chemical properties, and a particular material may meet the definition of one or the other or both. The main base of all plastics is plastic resins, but these resins are transformed to fit specific needs. First, they go through the cracking process, where high heat breaks down and cracks the hydrocarbons. Then, the different compounds created are formed into a chain, also known as a polymer.
Resins are generally categorized as a group of solid or semi-solid amorphous compounds, and they are usually mixtures of organic compounds. Many resins are naturally occurring, plant-based compounds, but some are derived from insects. They possess adhesive qualities and are used in products like varnishes and sealing waxes.
There are several types of plastic resins, each with its own unique characteristics and uses. Polyethylene (PE), including High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE), is the most widely used plastic resin. LDPE is softer, naturally translucent, and has a shinier finish. It is used in products that require flexibility, such as plastic beverage rings, shampoo bottles, and food storage containers. On the other hand, HDPE is used in food plastic packaging, bottles, and grocery bags due to its excellent resistance to chemicals and moisture. Polyethylene terephthalate (PET) is another type of plastic resin that is lightweight and durable, making it suitable for food and beverage packaging. Polypropylene (PP) is a type of resin that shares characteristics with polyethylene but has a higher melting point, making it suitable for applications requiring higher temperature resistance. It is used in pumps due to its cost-effectiveness, resistance to stress-induced damage, and lightweight. Other types of plastic resins include Polyvinyl chloride (PVC), which is used in pipes and household items, and polystyrene, which is used in packing material, insulation, and sporting goods.
In summary, plastic resins are an essential component of plastics, with each type of resin offering unique characteristics that cater to specific applications. The versatility and widespread use of plastic resins make them a significant aspect of modern life.
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Plastic waste composition
Plastic waste is a significant contributor to environmental and public health issues. The global annual production of plastic is more than 359 million tons, with 35.7 million tons generated in the United States alone in 2018. Plastic waste composition within municipal solid waste (MSW) varies across regions, but the largest amount typically comes from the packaging sector.
In the Kaunas, Daugavpils, and Tallinn municipalities, plastic and multilayer packaging waste accounted for 40.16%, 36.83%, and 35.09% of MSW, respectively. However, when examining separately collected plastic and multilayer packaging waste streams, the proportion of these materials within the total packaging waste stream ranged from 44.66% to 56.89% for single-family residences and 62.05% to 74.7% for multi-family residential buildings.
The composition of plastic waste discarded by households in Watamu, Kenya, was found to be dominated by low-density polyethylene, polyethylene terephthalate, high-density polyethylene, and polypropylene. Similarly, in a study by Krüger et al. (2020), sorted municipal plastic waste (MPW) was found to contain high levels of PE (28.5 wt%) and PP (22.2 wt%), with lower levels of PS (4 wt%) and impurities (16.5 wt%).
The MPW composition, with its high content of PE and PP plastics, aligns with studies defining MPW composition in developed countries. Plastic waste can be managed through recycling, reprocessing, incineration with energy recovery, modification reuse, value addition, and landfilling. However, in Watamu, open dumpsites, burning, and discards were the most common disposal methods, with only 0.7% of respondents recycling their plastic waste.
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Plastic recycling
The plastic recycling process typically begins with sorting the plastic waste into different categories. This sorting can be done manually or using technologies like near-infrared (NIR) spectroscopy. The sorted plastic is then baled into compressed rectangular blocks and sold to recyclers. These recyclers will process the plastic into recycled content.
There are two main types of plastic recycling: mechanical recycling and feedstock recycling. Mechanical recycling involves melting and reforming plastic into new items. This method is used for the majority of plastic recycling. Feedstock recycling, on the other hand, converts waste plastic back into its starting chemicals, which can then be used to create fresh plastic. This process is more costly in terms of energy and capital.
In the United States, the plastic recycling process is measured and classified by the EPA (Environmental Protection Agency). The EPA considers factors such as the generation, recycling rate, composting, combustion with energy recovery, and landfilling of plastic materials in municipal solid waste (MSW). In 2018, landfills in the US received 27 million tons of plastic, accounting for 18.5% of all MSW landfilled.
Despite the efforts and benefits of plastic recycling, there has been criticism and controversy surrounding the effectiveness of these programs. The plastics industry has been accused of lobbying for the expansion of recycling programs, even when research indicated that most plastic could not be economically recycled. Additionally, there is the challenge of "wishcycling," where people place non-recyclable materials into recycling bins, hoping they will be recycled.
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Plastic waste management
The Basel Convention, an international agreement, provides guidance on better managing plastic waste. It is the first agreement to directly address plastic pollution. The UNEP Global Waste Management Outlook highlights the lack of access to controlled disposal services and regular waste collection for many people worldwide, leading to plastic littering and inadequate disposal. As a result, about 80% of all plastics produced since the 1950s have ended up in the environment or landfills.
The US EPA measures the generation, recycling, composting, combustion with energy recovery, and landfilling of plastic materials in municipal solid waste (MSW). In 2018, plastics generation in the US was 35.7 million tons, with 27 million tons landfilled, contributing to 12.2% and 18.5% of MSW generation and landfilled waste, respectively. EPA data sources include the American Chemistry Council, the National Association for PET Container Resources, and the Association of Plastic Recyclers.
Plastic waste composition analysis within MSW reveals that plastic and multilayer packaging waste make up a significant portion, ranging from 35% to 40% in certain municipalities. The thickness, foaming, and resin type of plastics impact degradation rates, with polyethylene sheets exhibiting depth-dependent degradation. Strategies for plastic waste disposal include materials recycling and controlled breakdown methods such as biological, thermal, or chemical degradation.
To promote sustainability, the EPA advocates for a systemic approach to using and reusing plastic materials throughout their lifecycle, aiming for environmental, economic, and social benefits. Additionally, waste-to-methanol technologies have been explored to mitigate the increasing demand for methanol. However, addressing the plastic waste challenge requires global cooperation and a commitment to implementing environmentally sound management practices.
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Eco-friendly alternatives
Plastics are a significant contributor to waste, with 35.7 million tons generated in the United States in 2018, and 27 million tons of plastic ending up in landfills the same year. To reduce plastic waste, individuals can switch to eco-friendly alternatives. One of the most effective ways to reduce plastic waste is to adopt reusable and refillable packaging. Consumers can bring their own containers when shopping and opt for unpackaged products. For example, instead of using plastic bags, one can bring their own reusable bags made from materials like cotton, linen, or hemp. Similarly, reusable containers can be used for bulk bin shopping, eliminating the need for single-use plastic containers.
In the bathroom, liquid soaps, shampoos, and detergents contribute significantly to plastic waste. Switching to bar soaps, shampoo bars, and powdered products packaged in recyclable containers can help reduce this waste. Glass, metal, or unlined paper packaging are also more environmentally friendly alternatives to plastic. Upcycling glass jars from food items like jam, honey, or pickles into food storage containers is a cost-effective way to reduce plastic waste.
For clothing, traditional alternatives to polyester and nylon, which shed microplastic fibres, include cotton, wool, linen, and hemp. However, the production of cotton has environmental and human costs, and bamboo, while a newer alternative, poses concerns due to the chemicals used in its fabrication. Linen and hemp are considered more sustainable choices.
When it comes to food packaging, compostable plastics and plant-based bioplastics are emerging as eco-friendly alternatives. However, it is important to note that compostable plastics require specific conditions, such as industrial anaerobic composting facilities, to break down effectively. Bioplastics, like bio-PET, are recyclable, but public collection facilities for recycling bioplastics are limited.
Looking to the future, algae-based compounds show promise as a large-scale replacement for plastic, offering similar properties without the negative environmental impact.
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Frequently asked questions
Thermoplastics and thermosets. Thermoplastics can be molded and remolded repeatedly, while thermosets can’t be reprocessed once heated.
Polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and ‘other’.
Vinyl flooring, shower curtains, plumbing pipes, shrink wrap, and toys.
Egg cartons, shipping peanuts, and meat and poultry trays.
