by Rebecca Zarmon, Sheridan College
Individual Parts are Recyclable
Polyethylene is one of the most prolific polymers in industry; it is used for plastic bags, food films, bottles, cutting boards, toys, insulation, and many other objects. Disposable coffee cups are a prolific source of waste throughout Canada and North America. These cups are typically constructed of paper with a Low-density polyethylene (LDPE) lining, and have lids made of high impact polystyrene (HIPS).
While paper, HIPS, and LDPE are individually considered recyclable, the three materials require different treatment to be recycled, and are not recyclable when they are mixed together, such as they are in a coffee cup. Most disposal coffee cups end up in landfills and the LDPE ends up as microplastics that have become pervasive throughout most of our ecosystem.
Generation
Polyethylene is a polymer—a chain of repeating compounds—of ethene, ????????# = ????????#, from the catalytic cracking of crude oil. Depending on the pressure used during the process, polyethylene can be categorised as low density or high density. LDPE is made under high pressure and has many branching chains, resulting in a flexible plastic. HIPS is made under low pressure and is very linear, with few branches and is more rigid. Polyethylene is resistant to degradation from food and most water based mixtures, which makes it very popular for use in the food industry.
Disposable paper cups are generated by restaurant industry, fast food industry, coffee shops, supermarkets, and food trucks, to name a few. It is also possible to buy a package of disposable coffee cups for personal use from retail stores. Disposable coffee cups are seen everywhere, and it is not uncommon for a customer to purchase multiple disposable cups from the food industry in a single day. It was estimated that 1.5 billion disposable coffee cups were used in Canada in 2010, with 1 million cups per day being sent to a landfill from the City of Toronto alone.
Material Handling and Recycling
Polyethylene can be sent to a recycling facility. To recycle LDPE and retain high quality plastic, the used LDPE must be separated from other materials, including other plastics and HDPE. The separated plastic must be cleaned and dried and formed back into pellets.
Separation of the LDPE is typically done manually, by humans. In some businesses, such as the cosmetics company LUSH, washing is also done manually. While these processes add to the cost of recycling plastics like LDPE, it is still often worth recycling, and many facilities dedicated to recycling plastics exist throughout the country. An example of a company that recycles plastic is Nexcycle Canada Ltd., located in Brampton, Ontario. Besides recycling glass, Nexcycle recycles LDPE, HDPE, and polypropylene (PP).
Disposable cups are often marketed as recyclable or compostable, due to the materials individually being recyclable or compostable. Paper is well known for being recyclable and compostable, but as with polyethylene, the paper must be separated from other materials cleaned to be recycled into new paper products. This presents a problem for disposable paper cups, as they are lined with LDPE, which must be removed before either component can be recycled. The process to separate the LDPE lining and the paper is very difficult and as a result, most coffee cups end up in landfill or being incinerated.
Environmental Impacts
Polymers, including polyethylene, require about 100 MJ of energy expenditure to produce 1 kg of product and release about 10,000,000 tonnes of carbon dioxide equivalents (CO2e) to the atmosphere annually. Paper and cardboard require about 30 MJ of energy to produce 1 kg of product and release about 10,500,000 tonnes of CO2e to the atmosphere annually.
The production of a disposal coffee cup has an impact on greenhouse gas emissions. Professor Michael F. Ashby at the University of Cambridge determined the production of an average disposable cup weighing about 18 grams can generate 28 grams of CO2 equivalents, effectively 1.5 times its mass.
There are potential human health impacts from the use of disposal coffee cups. When cups are used under excessive heat, such as the near boiling temperatures of coffee and tea, the LDPE lining breaks down and enters the liquid, which is then ingested.
If coffee cups enter the organics recycling stream, problems result. The paper in the cup degrades quickly. However, the polyethylene coating on the cup does not degrade and coffee cups that enter the organic waste or recycle streams end up contaminating the process.
When polyethylene ends up in a lake or ocean, the plastic begins to degrade into smaller pieces, but does not decompose. Once the piece of plastic become less than 5 mm in size, they are categorised as microplastics. These microplastics are easily ingested by aquatic life, which are ingested by other animals eating the aquatic animals. Because the microplastics do not decompose, they have managed to spread across the food chain, including humans.
Potential Solutions
The “Four R’s” of waste management is a hierarchal strategy to manage waste at all points of its life cycle. The first of the four is to reduce the amount of waste at the point of generation.
Replacements for polyethylene and other plastics have been studied, such as using guar gum and citric acid as a food grade lining, but the replacement does not produce as effective of a lining and the currently low cost and high durability of polyethylene prevents from any alternatives from becoming more popular. Some coffee shops have switched to cups labeled as biodegradable, but these cups still go to landfill as their lining is not biodegradable.
The second “R” is to reuse products. Disposable paper cups are intended for single use, but many coffee shops offer monetary incentives for bringing a reusable mug instead of purchasing a disposable cup. In 2008, less than 2% of Starbucks customers used reusable cups. Starbucks initiated a campaign to improve the reusable cup rate to 25% by 2015. Reusable cups were offered for sale in store at low prices and discounts were given to those who used reusable cups, but the percentage of customers using reusable cups stayed below 2% by 2015.
It is possible that Starbucks’ strategy did not work because it is not the pricing that influences people to use or not use disposable cups, but the lack of knowledge of the impacts disposable cups have. Many people are unaware that most disposable cups are not recyclable nor compostable.
The City of Toronto displays on their waste management page that disposable coffee cups go into the landfill stream, but still some jurisdictions claim to accept coffee cups into green or blue bins. Coffee shops also frequently have bins displaying coffee cups under the recycling sign.
In the UK, a study was done where signs explaining the impact of coffee cups were displayed in coffee shops in varying locations. In most locations, the percentage of customers using reusable cups went up, the highest increase going from 7.5% of customers using a reusable mug to 24.0% of customers using a reusable mug.
The third “R” is recycling. As previously discussed, recycling is not an ideal situation, as current technology to separate LDPE from paper is too expensive. A number of organizations in Ontario are working to reduce the amount of disposable cups that end up in landfill as well.
A project in the UK called CupCycling from James Cropper turns the paper from the cups into usable paper by soaking and softening the paper, skimming off the plastic film, filtering out the inpurities and reusing the material for other marketable products for other products and uses and sends the plastic to a plastic recycler.
The “R” at the bottom—hence the least effective at managing waste—is recovery. Recovery refers to the incineration of the waste, with the product of the incineration being used to fuel another process, thereby reducing energy generation. Most polyethylene lined paper cups that aren’t in a landfill end up being incinerated.
Conclusion
Polyethylene is a highly durable plastic that is capable of maintaining stability even when in contact with water and food, which makes it a highly valuable material in the food industry. These same characteristics lead polyethylene to being very difficult to eliminate from the environment and it often ends up as microplastics in the ocean and in the digestive systems of animals throughout the food chain. Although polyethylene is recyclable, it is often used as a lining in disposable cups, rendering otherwise recyclable materials as landfill waste. Alternatives to polyethylene are possible, but as of yet not stable or cheap enough for companies to make the switch.
Currently, the best option to reduce the amount of polyethylene in landfills and oceans is to educate customers on the impacts of disposable coffee cups and promote the use of reusable mugs.
