If plastic is inert, why does it have a taste and smell? Plastic bin bags have a strong smell when first opened and water left in plastic bottles can acquire a distinct taste.
Greg Cash, Goodna, Queensland, Australia
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Plastics in everyday use are usually made of artificial polymers that comprise a string of monomers derived from oil. The polymers consist of numerous, very long chains of atoms. In thermoplastics, these chain-like molecules aren鈥檛 chemically bonded to each other. In thermoset plastics, the polymer strands are cross-linked.
Any smell won鈥檛 come from these polymers, but must be from small molecules that are volatile at room temperatures. These could be additives, left over monomers from the polymerisation process or breakdown products.
Non-rigid PVC (polyvinyl chloride) contains plasticisers such as phthalates which have noticeable odours. They are added to make a rigid polymer flexible.
As a retired polymer chemist, I can smell the phthalates in the oxygen masks when I have minor procedures at my hospital.
The water in clear drinks bottles made of PET (polyethylene terephthalate) that are left in the sun can become contaminated with some of the starting products used to make the plastic of the bottle. One of these is bisphenol A and could be the source of the taste in the water.
鈥淲ater in clear drinks bottles left in the sun can get contaminated with the products used to make the plastic鈥�
I have a number of tubs at home made from LDPE (low density polyethylene) in which I store my PET bottles for recycling. Over time, these have developed an odour that I know as polyethylene oxide and which signifies the breakdown of the polymer by free radicals.
They will soon split and I will then need to put them in the rubbish bin. Sending them for recycling could contaminate clean polyethylene and cause it to degrade prematurely.
A fourth example I recalled after a trip to the dentist is acrylic. This is a clear rigid plastic with lots of applications. It is mainly PMMA (polymethyl methacrylate), but if you cut it with a saw you will get the sharp smell of methyl methacrylate (the starting material) which my dentist uses as part of the preparation for modern dental 鈥渇illings鈥�.
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Talia Morris, Cape Tribulation, Queensland, Australia
Plastics have a taste and smell because they aren鈥檛 as inert as we would like to think they are.
Common plastics exude their more-volatile components 鈥� plasticisers such as bisphenols, for example. These can be smelled and tasted by us, and can also mimic oestrogen.
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