Why do the paper cups that places like fast food restaurants not get soggy and weak like paper straws do?
In: Chemistry
As already stated there’s usually a wax lining to prevent the paper from absorbing any liquid.
Obvious question is why not coat the straw? Well the wax coating makes the cup unrecyclable and harder to biodegrade. The average coffee cup is actually not recyclable despite being made of paper.
They coat the inside with a special chemical that repels water.
I looked into starting a paper cup manufacturing business at one stage and this is where the bulk of the BOM (bill of materials) comes from because that chemical isn’t cheap.
The paper cups have a wax or plastic lining that prevents liquids from soaking the paper.
Paper straws don’t have this lining and get saturated fairly quickly.
They do get soggy, it just takes longer. As others have said there is a water repellent coating of some sort on the inside, usually wax. But eventually the water can leak through.
Paper cups only come into contact with liquid on the inside surface, which has a protective wax coating, while the outside surface of a cup stays dry.
Straws are totally immersed and contact the liquid on all surfaces. If you submerged a paper cup into water the same way as you do a straw, it would also get soggy.
It would require an all-around wax coating of a paper straw to protect it, which would make them too expensive and maybe not as environmentally friendly.
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