vmelkon
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Glass cola bottles and metal caps
This is perhaps not a chemistry question. Perhaps it has to do with physics or economics.
Why do glass cola bottle have a steel cap and PET bottles have a polyethylene cap?
Can't they make a steel cap for PET bottles or polyethylene cap for glass bottles?
For the glass, can't they mold a screw thing at the top? I know they can because hard liquor bottles and orangine glass bottles do have it.
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Boffis
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I presume by steel caps you mean Crown caps like you get on beer bottles? These require a ridgid corbelled rim that on a plastic bottle would require
a lot of extra plastic. Molding screw threads on glass bottle is more expensive than forming a simple corbelled rim for crown caps.
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vmelkon
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Yes, beer bottles have the same steel caps.
PET is cheep and plastics like polyethylene, polypropylene, polystyrene is cheep. The value is 5 cents per bottle (well, at least that's how much they
charge us when we buy it and when you return the bottle, you get your 5 cents back).
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Refinery
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Steel caps have PE liner inside of them.
The crimp cap needs to be metal in order to hold the crimp. It (was) cheaper to make than threads back then and apparently also seals better.
And glass bottles.. They're old school anyways. Glass is very bulky and fragile compared to pretty much any plastic.
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vmelkon
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I suppose it is due to economics. It is cheaper to melt and reshape plastic than steel and glass.
But why do they make beer bottles the old fashioned way?
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We must attach the electrodes of knowledge to the nipples of ignorance and give a few good jolts.
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Refinery
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Probably because customers prefer glass. Drinks are perceived colder and tasting different when draught from glass.
In where I live, though, all bulk beverages are sold in aluminum cans nowadays. Only small brewery and specialty beers are glass. Bulk wine is sold in
bag-in-box with a tap.
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