Relationship Between Volume Volatiles and Volume Solids

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Q:  Within the next few months we expect to see the Miscellaneous Metal Parts and Products (MMPP) NESHAP published in the Federal Register.  To the best of my knowledge, the regulations will require most companies that are subject to this regulation to report emissions as lbs HAP/gal of solids.  If an MSDS provides the %volume volatiles (in other words, all the components that will evaporate) will it be valid to calculate % volume solids by the following equation? 

% Volume solids = 100 - % Volume volatiles

A:  We need to consider at least two general scenarios:

Air/Force Dry Liquid Coatings

These are coatings that dry and cure at room temperature, or at elevated temperatures that do not exceed 194F (by EPA definition).  By far the majority of coatings used by military installations and OEMs that manufacture large machines, fall into this category.  Radiation curable coatings cure at these temperatures, but I am not including in this category for reasons that I’ll discuss later. On the other hand it does include two component coatings such as epoxies and polyurethane’s.

The relationship given above is essentially true.  For calculation purposes we can assume that the only chemicals that will evaporate after a coating has been applied are the volatile liquid ingredients that are added to the coating; namely solvents, diluents, thinners and perhaps some small quantity chemical additives.

In the real world not all of these will leave the coating, because some will remain entrapped in the solid film.  However, as far as the EPA is concerned, all of the volatiles will evaporate, and hence we are probably safe in assuming that the above relationship between volatiles and solids is true.  That will not relieve us of the responsibility to perform the ASTM test for determining % volume solids in borderline cases, but for all practical purposes the relationship can be assumed to hold.

Thermoset Liquid Coatings that Cure in High Temperature Ovens, and Radiation Curable Coatings

Many of the coatings used by the steel fabrication industry fall into this category.  These are coatings that create brand new volatiles as a result of chemical reactions that take place when the coating is subjected to temperatures exceeding 250F.  (The 250F value is not absolute.  We simply use this lower limit as an approximate temperature below which the reactions probably do not take place.)

When a coating is "baked" in a high temperature oven not only the solvents, diluents and thinners that formed part of the original formulation are emitted.  Additional volatiles, usually amines, formaldehydes, and others are also emitted. Many of these volatiles are VOCs and possibly also HAPs.

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