Book 13, Question 97
Why Are Some Plastics Clear and Others Cloudy?
Clear plastics have molecules arranged so that light can pass through without much scattering. Cloudy plastics have tiny crystals or added particles that bounce light around. Soda bottles are clear, while milk jugs are cloudy.
More fun facts
- Many cheap plastics used for packaging, like polypropylene, are semicrystalline, which means parts of them are packed into tidy crystals.
- Those crystal parts scatter light a lot, which makes the plastic look hazy instead of clear.
- As this kind of plastic crystallizes, it builds tiny ball shaped structures called spherulites.
- Scientists at Budapest University of Technology and Economics showed that the size of the spherulites helps decide how hazy the plastic looks.
- Special additives called clarifiers can make polypropylene look clearer.
- An earlier study found that haze is closely linked to the temperature at which the plastic crystallizes.
- For packaging, how clear a plastic looks has become a big deal for selling products.
Sources: Journal of Polymer Science (Budapest University of Technology and Economics)
Questions kids ask
Why do plastic makers care about haze?
Shoppers like to see what is inside a package, so clear plastic helps products sell.
What is a spherulite?
A tiny ball of plastic that grows outward from its center, with crystal parts and less tidy parts mixed together.