Abstract:

The plasticization and crystallization behaviors of three types of melt blown PP plastics and four types of PP melt blown fibers for mask filter layer were investigated by DSC and hot stage polarizing microscopy. In the DSC thermograms， the sample 3^# showed a single melting peak， whereas the sample 1^#， sample 2^#， sample 4^#， sample 6^# and sample 7^# revealed a bimodal melting behavior. Moreover， the sample 5^# showed three peaks in its DSC thermogram. Compared to the PP melt blown plastic samples， the crystal plasticization of the PP melt blown fabric samples for mask filter layer started at a lower initial temperature with a wider temperature range for completing the plasticizing process. The presence of such a temperature range also shifted to a lower temperature zone. The initial crystallization temperature of the PP melt blown plastic samples was higher than that of the PP melt blown fabric ones. These results are consistent with their crystal plasticization temperatures and plasticization completion temperatures. This may due to the fact that the PP melt blown fabric samples for the mask filter layer have higher number average molecular weights， resulting in higher crystallization and plasticization temperatures. The crystallization temperature range of the PP melt blown plastic samples is narrower than that of the PP melt blown cloth ones for the mask filter layer， indicating different evolution mechanisms in their crystalline morphology.

Key words: polypropylene, melt blown fabric, plasticizing behavior, crystallization behavior, evolution mechanism