That’s a great question. In general, modern solvents are neither acid nor alkaline, they are neutral.
However, old-style chlorinated solvents like 1,1,1, TCE, perc, nPB and methylene chloride could literally turn acidic (into hydrochloric acid) if the solvents were exposed to too much water and heat. This always was a mess.
When a system “went acid” the solvent had to be completely emptied from the machine and disposed as a hazardous waste. In addition, the entire vapor degreaser needed to be re-passivated and could be off-line for weeks or months for heavy maintenance.
Brominated solvents also will degrade over time when catalyzed by water, certain metals, heat and oxygen. Degradation products include phosgene and bromic acid. These present worker safety concerns at elevated concentrations. Acidic solvent actually can destroy a vapor degreaser, requiring the solvent to be scrapped and potentially the entire machine to be rebuilt and repassivated. The use of stabilizers can avoid this disastrous situation.
To prevent systems from “turning acid” there are “acid acceptance” tests to measure the quantity of acid in the solvent. A simple calculation is all that is required to determine the amount of stabilizer that will be required to bring the system back into balance.
Going forward, the replacement solvents for nPB from MicroCare are thermally and hydrolytically stable. The MicroCare, Tergo and Opteon fluids will not turn acidic except under the most extreme conditions, specifically (1) exposed to a strong base or acid, or (2) exposed to extreme heat, such as when the heater elements become exposed and “burn” the solvent. These fluids do not require the stabilizers or scavengers or testing required of nPB and TCE.