Hello Rolfe,
You are not alone in your interest to locate thermal paper without phenol developers. Many organizations are searching for thermal paper that does not contain chemicals like bisphenol A, bisphenol S, diaminodiphenyl sulfone etc. There are several thermal paper makers or thermal paper converters that say they have safer thermal paper alternatives. You may want to contact thermal paper makers directly and ask them to provide detailed information related to the chemical replacements in their products. I am a chemist with deep understanding of the chemistries related to thermal paper. You mentioned citric acid. Citric or ascorbic acid is not likely by itself to be an effective developer. If it is used in thermal paper then it is likely to be there in relatively small amounts. It is also likely that there will be at least one additional developer chemical used at higher levels in conjunction with the citric or ascorbic acid. My advice is to be cautious and verify the chemistry and ask the company offering the thermal paper to validate to you that the thermal paper being offered does not in fact contain any of these chemicals of concern. We want to avoid regrettable substitutions. You may also want to pursue thermal paper that does not contain developers at all. I am aware of at least one company that claims to offer a thermal paper that does not contain a developer. I am not at liberty to share the name of that company but you should be able to locate them with a little research. Maybe one of our GC3 colleagues may be in a position to be able to share that information.
Roger
