We have studied the effect of ageing on the efficiency of fine fiber Melt Blown.

Two grades have been selected for this study: One grade ePM1 75% and another one use in masks with BFE efficiency 98%.

These grades have been stored during 3 years in different shapes (rolls and A4 sheets) in different environments. The two environments are standard conditions (heated warehouse) and extreme conditions (in a trailer protected from weather but exposed to a large span of temperature and relative humidity).

Temperature and relative humidity have been recorded during the study. Mechanical properties and filtration properties have been measured regularly during the ageing. Whatever the conditions of storage and the shape of the samples, level of efficiency remains close to its initial value and remain well above the minimum efficiency obtained when exposing the samples to Isopropyl Alcohol vapor for 24 hours (discharge method used in ISO 16890).

This stability can be explained by....