We tested some N550 carbon black collected from our plant day bin following ASTM 2414. Those black was unload from a trailer truck to a silo, then delivered to day bin by air (They look finer than freshly sampled black from truck). The OAN number we obtained from those N550 was around 8-10 numbers lower than usually. We also tested some daybin sampled N220, N330, an N660. So far the results are within QA spec.
From what I read mechanical force on carbon black will reduce its secondary structure which is measured with OAN, but not sure if it is the case here. I am wondering if anyone else has experience with this OAN reducing phenomenon before?