Anywhere incidental contact with people, food or animals is possible. That covers heat transfer systems in breweries, dairies and food plants where a leak into product would mean a recall, pharmaceutical and cosmetic formulation, e-liquids, and any application where a spill could be ingested. The performance difference is small; the toxicological difference is decisive.
2
What is the difference between USP and industrial grade MPG?
Purity specification. USP or EP grade meets pharmacopoeial limits on identity, water, acidity, residue and, critically, diethylene glycol and ethylene glycol content, and is required for food, pharmaceutical and cosmetic use. Industrial grade has looser limits and is used for unsaturated polyester resin, de-icing and antifreeze. The grade must be stated at enquiry.
3
Why must every container of MPG be identity tested?
Because of the history of diethylene glycol substitution. DEG is cheaper, looks and tastes similar, and has repeatedly been substituted for MPG and glycerine in medicines, causing mass poisonings with hundreds of deaths. Pharmacopoeias now require identity testing of every container received rather than reliance on the certificate of analysis alone.
4
Is MPG less effective than MEG as an antifreeze?
Marginally. Being the larger molecule, it contributes fewer particles per unit mass, so it depresses the freezing point slightly less and a somewhat higher concentration is needed for equivalent protection. It is also more viscous at low temperature, which affects pumping. Those are manageable differences, and where toxicity matters they are not the deciding factor.
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