@cholash This is new information for me. If you are willing to look for further research, I will gladly look at it, because PLA is also one of the primary materials used in 3D printing, which is becoming ubiquitous.

In the meanwhile, why not but bulk Mullein tea and steep it in unbleached muslin bags that close with a drawstring? Or an old-fashioned metal tea ball? Both of these have the advantage of being reusable. I have made my own in the past to be sure of the material, but the last ones my husband ordered clearly had cotton draswstrings as well.