It's been regulated since 2020 in Europe at least.

> As part of the EU’s REACH Regulation Annex XVII, a restriction banning Bisphenol A (BPA) content in thermal paper above 0.02% by weight came into effect on January 2, 2020. This prohibition was implemented due to health concerns associated with BPA exposure

bpa free thermal paper is pretty easy to source from anywhere now because of this.

This brand claims to be fully recyclable:

https://www.koehlerpaper.com/en/products/Thermal-paper/TH_Bl...

It supposedly works by using a layer of reflective bubbles that collapses when exposed to heat:

https://www.youtube.com/watch?v=pc1mlCThevg&t=20s

Of course, I don't know how those bubbles are made or how they are made to collapse from heat, so for all I know that layer still uses chemicals that currently slip through regulations. But I can also imagine that it is doable to create such a "functional layer" with safe materials.

Yeah I was excited about such a project concept until I saw it was thermal printer. Would love a little Polaroid type camera with inexpensive film for my kids to play with, but I don’t want them playing with thermal paper, kids put literally everything in their mouths.