why does some plastic tupperware type containers still look & feel greasy after washing even with name brand soap (dawn, ajax ect.)
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Anything acidic or corrosive can break down the smooth outer surfaces of plastic over time, this could be acidic foods like tomatoes (pasta sauce), fruit acid, bleach and other abrasive/corrosive cleaners and simply tough scrubbing with scouring sponges.
Once the sealed coating of the plastic wears away then it allows the ingress of oil and as others have mentioned, oil and plastic are pretty similar at a molecular level, so it is easy for them to bond together.
Cheaper containers (e.g dollar store, takeaway tubs you reuse) break down more quickly because of the quality of the materials and the finish, but even high-quality plastic kitchen wear will breakdown over time with enough exposure to acidic foods, corrosive cleaners, mechanical scrubbing and extreme heat/cold.
On a chemical/molecular level, plastics and oil/grease are very similar in structure and composition.
So when a grease molecule comes up next to a plastic molecule, long sections of it fit neatly and stick together. (Think like long Lego blocks snapping together)
Things like metal or ceramic are very different materials from grease, so the grease molecules only stick to the other surface on a few places here and there. This makes it easier for the surfaces to be separated when washed.
Fun fact: When professional pastry chefs make egg white meringues, for the best fluffiness results there should not be even a hint of fat/grease in the egg whites. Hence, they do not use plastic or plastic-coated utensils to whip the egg-whites, since the utensils likely harbour traces of fat on their surfaces.
Plastic is solid but when you zoom in you can see that there are little gaps. Plastic comes in many different types with different materials. Grease can get into those gaps if it’s left in these plastics for too long. It can work itself in so deep that using soap can’t quite reach it to break it down, kinda like having a kernel stuck in your teeth even after you brush.
These answers above also explain why I can’t get marinara red out of my plastic stuff and have to toss it.
Lol why would name brand soap be any better?
Plastic tupperware is like the borg, it assimilates everything thats ever been contained in it.
Never heard of the brand “Ect”. Which country is it sold in?
Plastic is made from oil (basically, oil mixed with salt) so will bond with other oils in a process called “polymerization”.
There is an easy solution. Washing with a baking soda solution will remove the “greasy” feel, although this is not as effective if you’ve used your “tupperware” as a microwave container.
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