The nucleating efficiency and selectivity of different
β-nucleating agents was characterised and compared by differential scanning
calorimetry, (DSC) and temperature-modulated DSC (TMDSC). The nucleating agents
were the calcium salts of pimelic and suberic acid (Ca-pim and Ca-sub), linear trans-γ-quinacridone (LTQ), a commercial nucleator
NJ Star (NJS) and an experimental product (CGX-220). The efficiency and the
selectivity of Ca-sub and Ca-pim are extremely high. NJS is efficient above
a critical concentration, which is connected with its partial dissolution
in polypropylene melt. LTQ and CGX-220 possess strong overall nucleating ability
and moderate selectivity. Using TMDSC, we found that three consecutive processes
take place during the heating of β-nucleated samples cooled down to room
temperature: reversible partial melting of the β-form, irreversible βα-recrystallisation,
and the melting of the α-modification formed during βα-recrystallisation
or being present in samples prepared with non-selective β-nucleators.
Melting of the α-phase contains both reversible and irreversible components.