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How unhealthy are teflon / non-stick coating chips that end up eaten? What role does the primer coating play?

Existing similar threads that don't go into enough detail: 1, 2

I understand that there is a lot of concern about PFAS and its analogs. However, most sources discuss the enviromental pollution inherent to the production of non-stick coatings; there is also the danger of them decomposing when overheated.

Both of these issues aside, how dangerous is it if you ingest non-stick coating? Particularly, how significant in this is the primer coating?

  1. Teflon is pretty inert, so my thought is that it should just pass the digestive system (alleged EPA corroboration). Based on this, teflon is resistant to both the hydrochloric acid in the stomach and to the alkaline conditions in the intestine. I assume this holds true for all non-stick coatings, right?

  2. As I understand it, coating metal with teflon can be done in various ways (none of them tremendously effective); this and this DuPont patent provides some overview. Basically, the metal surface is eroded and coated with a primer of PTFE, PFA $\ce{(C2F4)_n}$ and polyamide imide, which is applied at 5-10 um dry film thickness; it is then baked, and subsequent coats of PTFE are baked on top of it. Table 1 below shows the example composition from the patent.

    Now, from what I can tell, the solvents used, like NMP, are basically irrelevant, as they are volatile and will all evaporate during baking. I was not able to find an SDS sheet or equivalent for the PAI referenced (AI-10 polyamide imide resin); Solvay states This document is not available online, please contact us to request documentation. They do mention in their general PAI presentation that The polymer, however, may be attacked by saturated steam, strong bases, and some high-temperature acid systems, but that's neither here nor there; still, assuming that human digestive tract pH doesn't rise above 7.5, PAI should be pretty inert as well.

    So, long story short, would it be, then, safe to assume that non-stick coating flakes are not harmful when eaten, or is there some flawed logic here, or something that I have overlooked?

I understand that this forum is not meant to provide medical advice (actually, I would assume that, since medical advice needs some pretty rigorous published evidence to back it, in this case it really can't be had anyway, aside from general tips - studies and documentation on this issue are facing conflicts of interest at every turn). I am asking in terms of chemical logic and safety.

Table 1: 40% PFA/60% PTFE PRIMER (Tannenbaum / DuPont patent 1993)

 0.008  Zinc oxide
 0.050  "Afflair 153' titania coated mica from EM Industries
 6.936  Ultramarine Blue Pigment
 7.206  "T-30' PTFE from Du Pont
 1.038  "Ludox AM' colliodal silica from Du Pont
 4.930  Type 340 PFA from Du Pont
 4.959  Amoco AI-10 Polyamide imide resin from Anoco
65.38  Deionized Water
 0.47   "Triton X-100" octyl phenol polyether alcohol non-ionic surfactant from Rohm and Haas
 0.700  Diethylethanolamine
 1.399  Triethylamine
 3.859  Furfuryl Alcohol
 3.306  N-Methyl Pyrolidone

100    Total
Zubo
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    I closed your question using the "personal medical questions are not allowed" reason. Although your post does not violate this in an obvious way it's hard to know what kind of response you would be satisfied with, particularly when you ask "is it safe to assume that non-stick coating flakes are not harmful?" after writing that studies have shown it repeatedly. What could the answer be other than yes? On the other hand, the crowd at chem SE cannot be held accountable for decisions a visitor might make based on what they read here. – Buck Thorn Oct 19 '21 at 06:53
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    As you mention, the polymer coatings you refer to have been subjected to extensive experiments to check their toxicity under physiological conditions. It looks like you want information about degradation pathways that might lead to toxic compounds during the residence time of a polymer in your digestive tract. Rephrasing the question to indicate this more clearly would help readers. – Buck Thorn Oct 19 '21 at 06:55
  • You may find the following interesting: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4928218/ – Buck Thorn Oct 19 '21 at 07:16
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    @BuckThorn I can see your reasoning; I guess I was reluctant to accept the mentioned studies at face value, so I appreciate the neutral perspective. Thanks for the link! This reminds me of Olestra; weirdly enough, teflon is probably the better choice... – Zubo Oct 19 '21 at 14:38

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