Douglas Harper's Etymology Dictionary
protectant
1660s, irregularly formed from protect + -ant. As a noun from 1935.
Wiktionary
protectant
n. Something which gives protection.
Usage examples of "protectant".
When I wasn't on chemo, I was attached to a 24-hour IV drip of saline and a chemical protectant to shield my immune system from the most toxic effects of ifosfamide, which is particularly damaging to the kidneys and the bone marrow.
My Acepan noses, conveniently located in the front third of my feet and two even more sensitive spots near my posterior segment for physiological reasons no longer significant in an extinct species, detected volatile hydrocarbons and a tinge of musk: the tug's protectants against corrosion, I guessed, since it was hardly necessary to grease a starship.