posted on 2021-01-21, 18:33authored byGregory S. Larsen, Yongqiang Cheng, Luke L. Daemen, Tej N. Lamichhane, Dale K. Hensley, Kunlun Hong, Harry M. Meyer, Steven J. Monaco, Alan M. Levine, Richard J. Lee, Emma Betters, Kim Sitzlar, Jesse Heineman, Justin West, Peter Lloyd, Vlastimil Kunc, Lonnie Love, Merlin Theodore, Mariappan Parans Paranthaman
The
current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2)
pandemic has highlighted the need for personal protective equipment,
specifically filtering facepiece respirators like N95 masks. While
it is common knowledge that polypropylene (PP) is the industry standard
material for filtration media, trial and error is often required to
identify suitable commercial precursors for filtration media production.
This work aims to identify differences between several commercial
grades of PP and demonstrate the development of N95 filtration media
with the intent that the industry partners can pivot and help address
N95 shortages. Three commercial grades of high melt flow index PP
were melt blown at Oak Ridge National Laboratory and broadly characterized
by several methods including differential scanning calorimetry (DSC),
X-ray diffraction (XRD), and neutron scattering. Despite the apparent
similarities (high melt flow and isotacticity) between PP feedstocks,
the application of corona charging and charge enhancing additives
improve each material to widely varying degrees. From the analysis
performed here, the most differentiating factor appears to be related
to crystallization of the polymer and the resulting electret formation.
Materials with higher crystallization onset temperatures, slower crystallization
rates, and larger number of crystallites form a stronger electret
and are more effective at filtration.