The Friction of Structurally Modified Isotactic Polypropylene.

Area of Science:

• Polymer Science
• Materials Science
• Tribology

Background:

• Isotactic polypropylene (iPP) exhibits polymorphism, with monoclinic (α) and pseudo-hexagonal (β) crystalline structures.
• Nucleating agents (NAs) are crucial for controlling iPP's crystalline morphology and properties.
• Understanding the influence of NAs on iPP's tribological behavior is essential for material applications.

Purpose of the Study:

• To analyze the impact of heterogeneous nucleation of modified iPP on its tribological properties.
• To investigate how different nucleating agents (DMDBS for α-form, PACS for β-phase) affect iPP's structure and performance.
• To determine the role of mold temperature in the relationship between iPP nucleation and tribology.

Main Methods:

• iPP samples were injection molded at 20 °C and 70 °C, modified with DMDBS and PACS (0.2 wt.%).
• Characterization included differential scanning calorimetry (DSC), Shore hardness testing, and tribological measurements (pin-on-flat reciprocating motion).
• Morphological analysis utilized confocal microscopy and scanning electron microscopy (SEM) of friction tracks.

Main Results:

• Shore hardness increased with DMDBS content, irrespective of mold temperature.
• Friction coefficient (COF) was dependent on NA composition and mold temperature; higher and more varied COF observed at 70 °C.
• Friction scratch height and track width correlated with the heterogeneous nucleation-modified iPP structure.

Conclusions:

• Heterogeneous nucleation significantly modifies iPP's crystalline structure, influencing its hardness and tribological properties.
• Mold temperature plays a critical role in the tribological response of nucleated iPP, affecting friction coefficient variability.
• The study demonstrates a clear link between iPP's polymorphic structure, induced by specific nucleating agents, and its wear behavior.