Annealing of the β‐modification of polypropylene

Expressive memory effect has been proven in the course of the annealing of the β‐modification of polypropylene (β‐PP). The character of the structural changes taking place in β‐PP during annealing strongly depends on the thermal history. In dependence on the thermal history βα or ββ‐recrystallization takes place during thermal treatment. In case the annealing starts from the crystallization temperature β‐PP is recrystallized into a more perfect structure with higher melting point ‐ similarly to thermodynamically stable modifications. The samples cooled below a certain temperature before subjected to annealing transform partly or fully into the α‐modification. The βα‐recrystallization tendency prevalent on the effect of recooling can be reduced or eliminated with the aid of stepwise annealing with decreasing temperature steps.