More than 300 billion beverage cans and 75 billion food cans are produced globally each year. About 90% of the beverage cans were made of aluminum; the remaining 10% consisted of steel. Most of them are lined with plastic.
Plastic began the canned marriage in the 1950s with epoxy resins coating aluminium (think soda tin) and steel cans (think food can). About a million tons of can coatings are now producted globally to line cans and most cans are coated internally and externally with films of 1 to 10 µm thickness.
The reason for coating a can in plastic is essentially to protect the contents of the can from enagaging chemically with the metal container. Some foods are highly acidic for instance and other manufactured 'food / drinks' are highly corrosive. If you have ever used CocaCola as a toilet cleaner, you will know how powerful it is. Soft drinks are acidic and would literally eat through a thin walled metal tin in a few days if there was no plastic protection liner.
Want to see a plastic liner in action? In a recent vid Chem Teacher Phil, dissolved the metal on a CocaCola tin to expose the plastic sleeve.
The are a couple of issues, and probably the biggest is that much of this plastic is still BPA based. Bisphenol A (BPA) is an industrial chemical used in the production of polycarbonate plastics and epoxy resins. BPA is an endocrine disruptor - meaning that it's a chemical that can interfere with the hormonal system. Endocrine disruptors can cause cancerous tumours, birth defects and other developmental disorders.
BPA has been associated with breast and prostate cancers, genital defects in males, early onset of puberty in females, obesity and behavioural problems such as attention-deficit hyperactivity disorder. It has been banned across the world in baby food and in some countries universally. (Not Australia.)
In the 1950s, Bisphenol A (BPA) epoxy resins were introduced as coatings for aluminum and steel cans. Their stability, protective function, and technical properties made them the most commonly used coating material. Most epoxy coatings are synthesized from bisphenol A (BPA, CAS 80-05-7) and epichlorohydrin forming bisphenol A-diglycidyl ether epoxy resins.
If you, like me, used to pick up a can of organic tomatoes and saw the little label saying, "BPA Free', you might have thought that was because you were holding a can. Not so. BPA Free means that can is still lined with plastic, just not BPA based plastic.
But BPA-free doesn’t mean bisphenol-free. It might just mean it is Bisphenol S (BPS), a BPA substitute. It's not unusual for the food or cosmetics industries to replace one hazardous chemical with another. It's like a crazy merry go round where you get off one poison horse and get a new untested one and until that new one is proven poisonous and then you swap horses again. The BPS horse, for instance, is known to be as estrogenic and toxic to embryos as its predecessor.
You can quickly reduce your exposure to BPA by simply limiting your purchase of canned anything.
Aluminium cans are infinitely recyclable as it 'claims on the can', despite being lined with plastic. The plastic liners in and on tins and cans - referred to as lacquer in the industry - don't impact recycling. When the tins are heated to thousands of degrees for recycling, what is left of the plastic liner, the inks and UV materials; is separated and basically skimmed off, leaving the metal.