Fast cooling of (non)-nucleated virgin and recycled poly(propylenes): Effect of processing conditions on structural and mechanical properties

• The effect of cooling rate and pressure on the structure and properties for (non-) nucleated i-PP was investigated.
• The nucleated and non-nucleated i-PP originated from virgin and recycled sources.
• Under ambient pressure and fast cooling the mesomorphic phase was formed as confirmed by WAXD.
• Nucleated samples form more γ-phase and less mesomorphic phase.
• At high cooling rates, the yield stress is reduced leading to stable deformation and a ductile behavior for recycled i-PP.

In this study, the effect of processing parameters, i.e., the cooling rate and pressure, on the structure-property relationships for nucleated and non-nucleated i-PP from virgin and recycled sources was investigated. Special attention was given to the brittle-to-ductile transition of nucleated i-PP from plastic packaging waste. Differential fast scanning calorimetry and dilatometry were used to mimic industrial process conditions. From the calorimetric experiments, it was observed that under ambient pressure the mesomorphic phase was formed upon fast cooling, which was confirmed by WAXD analysis. The dilatometry results showed that by applying pressure also γ-phase crystals are formed. Nucleated samples showed an increased tendency for the γ-phase formation and a decreased tendency for mesomorphic phase formation. Up to now, recycled i-PP showed a brittle behavior, but this study showed that by applying a sufficiently high cooling rate, the yield stress can be reduced and a stabilization of the deformation can be obtained leading to a ductile behavior for recycled i-PP.