Injection moulding of α- and β-polypropylenes: Morphology consequences

The specific effects of mould temperature (MT) and holding pressure (HP) on the structure of neat and β-nucleated isotactic polypropylenes have been studied. Commercially available isotactic polypropylene was modified by 0.03 wt.% of β-specific nucleator. From both original (α-iPP) and β-nucleated (β-iPP) materials test specimens were injection-moulded using two sets of processing parameters. In the T-set the MT was varied within a range of 40-120 °C by 10 °C steps, while in the P-set the HP was changed from 5 to 13 MPa in 1 MPa steps. Polarized-light microscopy showed a strong effect of MT but minute influence of HP on the morphology of α- and β-iPP specimens. The increase of MT positively influenced the crystallinity and the β-form content, particularly in the skin of specimens as wide-angle X-ray scattering displayed. On the contrary, the rising HP depressed the crystallinity within the bulk of specimens proportionally