Bill Hammack is a chemical engineer with a YouTube channel (The Engineer Guy). This recent video on the development of plastic bottles is well worth watching.
Bill explains how the two-liter plastic soda bottle begins as a plastic tube, called a preform, which is heated and inflated with air in a bottle-shaped mold. He explains how the stretching of the preform creates a crystalline regions in the bottle’s plastic (polyethylene terephthalate) that create a bottle with great strength, low permeability to carbon dioxide, but which is also lightweight—some 35 times lighter than a glass bottle of the same size. Bill explains key features of the bottles design, including: why the bottle looks like it does, why the neck has gaps in its threads, and how the tamper-proof ring works. He also discusses “hot-fill bottles” used for sports drinks and plastic juice bottles, noting the panels molded into the bottles to accommodate temperature changes. Lastly, he discusses briefly the recycling of PET bottles, although noting that about 75% of the 500 billion PET bottles manufactured annually end up in landfills or are incinerated.
I remember when bottles changed to a shape that no longer required a cap at the bottom as well as the not-so-long ago (to me) change to smaller lids. At the time both changes just seemed like obvious reductions in plastic but learning about the many tests and years of litigation to make them happen is a fascinating look at the rest of the story.
The other thing that struck me about this video was learning about the bottle shapes for products that need to be heated. For a long time I’ve been annoyed at the shape of apple sauce bottles because of how hard the ridges make getting the last scraps out but seeing why they have that shape makes me slightly less annoyed. Now I’ve unlocked a new fear about what super heated apple sauce plastic is doing to our bodies.
(via Dr. Drang)
