I don't know all the nitty-gritty, but the last Shellac record was "pressed" using an injection molding process that utilized recyclable PET (I can't find the interview with Albini[RIP] where this was discussed but if I find it I'll edit it into the comment).
Confused by this until I realized you meant "Shellac (band)" and not "Shellac - resin secreted by the female lac bug" which was used to press records in the 1920s.
The last shellac record was indeed made from shellac. And shellac is a natural (or at least non-manmade) material; does this make it more environmentally friendly than vinyl or PET?
I don't know all the nitty-gritty, but the last Shellac record was "pressed" using an injection molding process that utilized recyclable PET (I can't find the interview with Albini[RIP] where this was discussed but if I find it I'll edit it into the comment).