Customers continue to ask us for assurances that our PE films do not contain BHT. The reason they ask is that BHT makes film printed white turn yellow. When exposed to light, the yellow turns white again.
We just got another one of these inquiries. To understand it chemically and to have it explained in 10 year old English, I asked our guru - Mr. Rudy Bourgeois of the M Holland company.
"BHT especially makes white print turn yellow due to the iron content in the white masterbatch which acts as an accelerant to the reaction described below:
BHT was used years ago as an A/O agent. It has a low molecular weight and a relatively low melt point, which made it ideal for protecting PE resin during extrusion. The downfall of this phenolic A/O is that it migrates and reacts with the lignins in paperboard and also with the exhaust gas from forklifts to form a compound called stilbene quinone. This compound is crimson color in concentrated amounts and yellow in diulted amounts.
It is a reversible reaction and will go clear again when placed in sunlight for a while."
So now we know. Thanks, Rudy !