The idea of a plastic tea bag might be unpalatable for folks for a number of reasons, the most clear-cut being the contribution to landfill waste, but
additionally because heating plastic can rouse alarm in consumers. That's probably why tea companies like to describe their silken sachets as a quality compromise for loose leaf lovers who "are switching
to [mesh tea bags] as their lives get more hectic," instead of emphasizing "get the plastic hot and then drink the thing it was in." For these reasons,
some tea companies like Numi even use their lack of plastic tea bags as a selling point.
Could plastic tea bags also be bad for our health? They are most commonly made from food
grade nylon or polyethylene terephthalate (PET), which are two of the safest plastics on the scale of harmful leaching potential. Both have very high melting points, which offer some
assurance to consumers, as one would think the melting point of plastic is the temperature at which one would need to worry about accidentally eating it.
There is another temperature point for plastics, though, that we may need to worry about, called the "glass transition" temperature (Tg) . That is the temperature at which the molecule in certain materials such as polymers begin to break down. As a rule, the Tg of a material is always lower than the melting point. In the case of PET and food grade nylon (either nylon 6 or nylon
6-6), all have a Tg lower than the temperature of boiling water. For example, while the melting point of PET is 482 degrees Fahrenheit,
the Tg is about 169 degrees. Both nylons have a lower glass transition temperature than PET. (Remember that water boils at 212 degrees.) This
means the molecules that make up these plastic tea bags begin to break down in hot water.
"If the question is, 'As the polymer goes through that transition state, is it easier for something to leach out?', the answer is yes," said Dr. Ray
Fernando, professor and director of polymers and coatings at Cal Poly San Luis Obispo. "However, just because it makes it easier for something to leach
out, it doesn't mean it will." There seems to be something in the plastic collective consciousness that says there are inherently toxins in all plastics,
and when they begin to break down, they will naturally gravitate toward food. "This would only happen if there are potential materials trapped in the
substance. What we don't know is what FDA requirements manufacturers have to meet before they go to market," said Dr. Fernando.
There is also a matter of whether or not the leachate is hydrophobic or hydrophilic. If hydrophobic pollutants were potentially in the plastic tea bag
materials, their nature would be to stay in the bag and not go frolicking into the water and into your mouth.
So polymers will only leach out harmful chemicals, like cancer causing phthalates, at their glass transition temperature if there are said phthalates to
begin with. It almost seems silly to think that either of these materials would have toxins to begin with, considering we eat off of them and in
them. That's what food standards are for, right? The Lipton website reassures us their Pyramid Tea
Bags made of PET are "the same food grade material clear water and juice bottles are made of and ... are microwave safe." That sounds, well ... safe.