Uploaded November 2024 | Updated September 2026, 2 weeks ago
About 5000 paper coffee cups are thrown into garbage cans in the world every minute and given that paper is both recyclable and compostable, how come we are not directed to deposit these cups in recycling or compost bins instead of garbage cans? The answer lies in the thin layer of polyethylene that coats the inside of the cup to prevent the liquid from soaking into the paper and destroying its rigidity. While that layer of plastic prevents leakage, and maintains the cup’s structure, it is not compostable and can contaminate a compost pile preventing the compost from being sold as fertilizer. The polyethylene also prevents recycling of the paper because it mucks up the equipment that is used to break paper down into the pulp that is needed to make recycled paper. While it is possible to separate the polyethylene from the paper, most recycling facilities are not equipped to do this. Another issue is that polyethylene is made from non-renewable fossil fuels and there is also concern that on contact with coffee, polyethylene breaks down and releases micro and nanoparticles into the beverage. Then there is the matter of the catalysts, stabilizers and UV absorbers that are used in the manufacture of polyethylene that may leach out.
The search is therefore on for safe coatings that can be made from renewable resources and also allow paper coffee cups to be recycled or composted. That is a significant chemical challenge! Polylactic acid (PLA) can be produced from corn starch or sugarcane, has good barrier properties, and is compostable in an industrial composting facility. It is also recyclable, however, the coating interferes with recycling processes for paper coated with polyethylene. And there is the cost problem. PLA-lined cups are anywhere from 30-50% more expensive than polyethylene-lined cups.
The industry is now looking at “water-based coatings” in which the major ingredient is not a plastic although there are minor plastic components. These are not actually coatings, since they do not form an impervious layer that coats the paper, but rather diffuse into the paper and strengthen it while plugging up the microscopic holes through which liquid can leak out. Formulations are understandably proprietary because a lot of money is at stake, but the main ingredients are waxes made from cellulose, which is a renewable resource, calcium carbonate and an emulsion of an acrylic polymer. Cups with water-based coatings can be composted or recycled and leave a smaller environmental footprint but cost more to produce.
Lids are another problem. They are usually made of polypropylene or polystyrene both of which are produced from raw materials derived from petroleum. In theory they are recyclable but are too small and light to be sorted properly at the recycling facility and end up contaminating other recyclables. One company, SOFi Paper Products, solves this problem by having a folding top, eliminating the lid altogether. And their paper cup is formulated with a water-based-coating making for an environmentally more friendly product. Obviously, a great deal of science goes into that coffee cup before any coffee goes in.
About 5000 paper coffee cups are thrown into garbage cans in the world every minute and given that paper is both recyclable and compostable, how come we are not directed to deposit these cups in recycling or compost bins instead of garbage cans? The answer lies in the thin layer of polyethylene that coats the inside of the cup to prevent the liquid from soaking into the paper and destroying its rigidity. While that layer of plastic prevents leakage, and maintains the cup’s structure, it is not compostable and can contaminate a compost pile preventing the compost from being sold as fertilizer. The polyethylene also prevents recycling of the paper because it mucks up the equipment that is used to break paper down into the pulp that is needed to make recycled paper. While it is possible to separate the polyethylene from the paper, most recycling facilities are not equipped to do this. Another issue is that polyethylene is made from non-renewable fossil fuels and there is also concern that on contact with coffee, polyethylene breaks down and releases micro and nanoparticles into the beverage. Then there is the matter of the catalysts, stabilizers and UV absorbers that are used in the manufacture of polyethylene that may leach out.
The search is therefore on for safe coatings that can be made from renewable resources and also allow paper coffee cups to be recycled or composted. That is a significant chemical challenge! Polylactic acid (PLA) can be produced from corn starch or sugarcane, has good barrier properties, and is compostable in an industrial composting facility. It is also recyclable, however, the coating interferes with recycling processes for paper coated with polyethylene. And there is the cost problem. PLA-lined cups are anywhere from 30-50% more expensive than polyethylene-lined cups.
The industry is now looking at “water-based coatings” in which the major ingredient is not a plastic although there are minor plastic components. These are not actually coatings, since they do not form an impervious layer that coats the paper, but rather diffuse into the paper and strengthen it while plugging up the microscopic holes through which liquid can leak out. Formulations are understandably proprietary because a lot of money is at stake, but the main ingredients are waxes made from cellulose, which is a renewable resource, calcium carbonate and an emulsion of an acrylic polymer. Cups with water-based coatings can be composted or recycled and leave a smaller environmental footprint but cost more to produce.
Lids are another problem. They are usually made of polypropylene or polystyrene both of which are produced from raw materials derived from petroleum. In theory they are recyclable but are too small and light to be sorted properly at the recycling facility and end up contaminating other recyclables. One company, SOFi Paper Products, solves this problem by having a folding top, eliminating the lid altogether. And their paper cup is formulated with a water-based-coating making for an environmentally more friendly product. Obviously, a great deal of science goes into that coffee cup before any coffee goes in.
