The polymorphic composition of long-chain branched polypropylene processed by injection and compression molding

The impact of injection molding processing parameters, including mold temperature, injection speed, and holding pressure, on the supermolecular structure of long-chain branched polypropylene (LCB-PP) was investigated. Commercial LCB-PP was processed under different conditions, with four sets of processing parameters applied. Holding pressure was varied from 30–70 MPa by 10 MPa in the P-SET, mold temperature was raised from 40 to 120°C in 20°C steps in the T-SET,and injection speed increased from 20 to 140 mm/s in 30 mm/s steps in S-SET1 and S-SET2, with mold temperatures at 40 or 120 °C. The polymorphic composition of the specimens was analyzed using wide-angle X-ray scattering, demonstrating a strong dependence on the processing parameters. The skin of the specimens showed an increase in β-phase content with higher mold temperature and injection speed. Conversely, growing holding pressure slightly suppressed β-phase content and promoted the formation of the γ-phase, which was predominantly manifested in the core of the specimens. The polymorphic composition, with both β- and γ-phases present in notable amounts, had a beneficial effect on the impact strength of the specimens.