THE EFFECT OF AGING ON THE IMPACT STRENGTH OF b-POLYPROPYLENES
Tomas Bata University in
Zlin
Faculty of Technology
Department of Polymer
Materials and Technology
TGM 275, 762 72 Zlin
Czech Republic
This
work focuses on the time stability of the b-phase and the impact
strength of b-nucleated
injection-molded polypropylenes. For the purposes of the study, various amounts
of a specific b
nucleating agent based on N, Nī-dicyclohexyl-2,6-naphtalenedicarboxamide have
been added to commercially available isotactic polypropylene. From the prepared
blends standard impact testing specimens have been injection-molded. The
structure has been characterized with the aid of wide-angle X-ray diffractometry,
differential scanning calorimetry and polarized light microscopy, and toughness
has been characterized by Charpy impact testing. At first, a measurement of
impact strength and b-phase
content was carried out immediately after injection molding, and as a second
step the same values were measured after 2 years. The results suggest that the b-phase
is time-stable, and that the notch impact strength of the samples does not
significantly change with time. Furthermore, it was confirmed that the b-phase
has a positive influence on impact strength but it is not the only one
important factor. There are other positive effects such as creation of structural heterogeneity,
elongated chains in the skin layer, specific size of spherulites and their
continuity with the amorphous phase.