Hierarchical Structure of iPP During Injection Molding Process with Fast Mold Temperature Evolution

Area of Science:

• Polymer Science and Engineering
• Materials Science

Background:

• Injection molding is a key polymer processing technique.
• Mold surface temperature significantly affects polymer morphology and molecular orientation.
• Understanding these effects is vital for tailoring material properties.

Purpose of the Study:

• To investigate the influence of modulated mold surface temperature on isotactic polypropylene morphology during injection molding.
• To correlate the observed polymer structures with the thermo-mechanical histories experienced.
• To analyze the formation of different morphological structures based on flow and temperature fields.

Main Methods:

• Injection molding of isotactic polypropylene into a rectangular mold with controlled cavity surface temperature.
• Utilizing polarized optical microscopy and atomic force microscopy for morphological analysis.
• Analyzing the interplay between flow fields, cooling rates, and temperature gradients.

Main Results:

• High flow fields and temperatures promote a shish-kebab structure aligned with flow.
• Weak flow fields lead to the formation of beta-phase structures (cylindrites).
• Hierarchical structure formation is dictated by the combined flow and cooling conditions.

Conclusions:

• Mold surface temperature modulation is a critical factor in controlling polymer morphology.
• Distinct structures (shish-kebab, beta-phase) arise from specific combinations of flow and thermal conditions.
• The study provides insights into tailoring injection molded polymer microstructures for desired properties.