Comparison of different β-nucleators for isotactic polypropylene, characterisation by DSC and temperature-modulated DSC (TMDSC) measurements

The nucleating efficiency and selectivity of different beta-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-gamma-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 beta-nucleated samples cooled down to room temperature: reversible partial melting of the beta-form, irreversible beta alpha- recrystallisation, and the melting of the alpha-modification formed during beta alpha- recrystallisation or being present in samples prepared with non-selective beta-nucleators. Melting of the alpha-phase contains both reversible and irreversible components.