Reader Feedback
I recently received an e-mail from Steven Brunner, Applications Chemist at WPC Technologies, offering some feedback on an article we published in October by Emerald Performance Materials, titled “Optimizing Performance in Low- and Zero-VOC Coatings with New Resins and Additives”. I would like to share Steven’s comments with you, as well as the response I received from Emerald.
In reading the article, I feel compelled to comment on Question 14. In the question you have left out two of the big regulations: EPA RM 24 (the VOC regulation), which mirrors ASTM D3960, and SCAQMD (the South Coast Air Quality Management District). EPA RM 24 calls for a collection of numerous ASTM test methods to derive a paint’s VOC. In essence, RM 24 defines VOC as anything evolved from the paint during a 1 hour bake at 110 °C. This regulation includes exempt solvents that are quantified by GC. Herein lies a problem: given low-molecular-weight reactive materials, testing these components individually may yield results too high to consider for use in a low-VOC material; however, when placed in a coating matrix they react as intended and are not evolved. An example is benzyl alcohol; when tested by itself it is a 100% VOC, but when placed in an epoxy coating it is about 25% volatile.
EPA RM 24, in particular the ASTM D2369 portion, has come under fire in recent years. This is a thermogravimetric method to determine the percent of volatiles in the paint. It was developed in the early 80s when VOCs were high and this test method worked fairly well. With the decrease in VOC levels this method has evolved to five sections in an effort to account for paint matrix variability – the latest for very high solids multi-component coatings. Basically the method has been revised to allow the reactive ingredients to react, as they would in a paint, prior to placing in an oven – thus a more accurate depiction of the actual VOC level.
ISO 11890-2, a GC method, places a boiling point marker in the sample. Anything that eludes before this marker, 250-260 °C, is considered to be a VOC. Texanol is on the borderline.
ASTM D6886 is a GC method to speciate the volatile components in a coating. The SCAQMD has been using this test method for VOC calculations of very low-VOC paints. They use a marker that I believe is dimethyl adipate.
The bottom line is a formulator needs to be well versed in the VOC test methodology and how components within the paint behave under test conditions, which are often outside of service conditions. Formulation and theorization of VOC without testing can prove difficult.
Emerald’s Response
When our team considered the question on VOCs, with two members on the ASTM D01.21 committee and methods continually evolving, we agreed we could literally devote an entire article to that topic! We instead sought to shed light on only certain aspects of VOC reporting that have been areas of confusion.
The writer makes a good point that the VOCs of individual components do not always carry through to a corresponding proportional level in the final paint, as illustrated by the example of benzyl alcohol in epoxy coatings. This point certainly should be re-emphasized. Our scientists have observed this as well – resulting from interaction and compatibility of a component with others in the formulation. For this reason in our development work, we evaluate both the VOCs of the components as well as the final product.
Thank you to both Steven Brunner and Emerald for helping to further define VOC testing. I encourage feedback on our articles. If you have a comment, feel free to share it with me at kristin@pcimag.com.
