Yes, milk freezes well in plastic containers. The plastic bottles milk is sold in are perfectly fine to freeze milk in after they’ve been opened, so long as they have a secure, airtight lid and are not full.
It’s important to never freeze a full container of milk. When it freezes, milk expands – which puts pressure on the container and causes it to burst.3 If this happens, frozen milk will likely adhere to other things inside your freezer, which can be a pain to clean up.
One to two inches of space at the top of your bottle or other container is sufficient to allow the milk to expand as it freezes.
You could also decant milk into a different plastic bottle, or other container made of plastic. Ziploc-type bags work well for freezing milk if you’ve not got room in the freezer for full bottles.
You could try freezing milk in an ice cube tray – we find that having milk ice cubes as opposed to a solid block inside a bottle makes the process of defrosting quicker.
Just remember – don’t fill the ice cube tray to the brim to allow for liquid expansion!