The Friction of Structurally Modified Isotactic Polypropylene

The purpose of studies was to analyse an impact of heterogeneous nucleation of modified isotactic polypropylene (iPP) on its tribological properties. The iPP injection molded samples, produced by mold temperature of 20 and 70 degrees C, were modified with compositions of two nucleating agents (NA's), DMDBS creating alpha-form and mixture of pimelic acid with calcium stearate (PACS) forming beta-phase of iPP, with a total content 0.2 wt.% of NA's. A polymorphic character of iPP, with both, monoclinic (alpha) and pseudo-hexagonal (beta) crystalline structures, depending on the NA's ratio, was verified. The morphology observation, DSC, hardness and tribological measurements as test in reciprocating motion with pin on flat method, were realized, followed by microscopic observation (confocal and SEM) of the friction patch track. It was found that Shore hardness rises along with DMBDS content, independent on mold temperature. The friction coefficient (COF) depends on NA's content and forming temperature-for upper mold temperature (70 degrees C), its value is higher and more divergently related to NA's composition, what is not the case by 20 degrees C mold temperature. The height of friction scratches and the width of patch tracks due to its plastic deformation, as detected by confocal microscopy, are related to heterogeneous nucleation modified structure of iPP.

Automated summary

The study aimed to analyze the impact of heterogeneous nucleation on the tribological properties of modified isotactic polypropylene. It was found that hardness increased with higher nucleating agent content, while the friction coefficient depended on the nucleating agent content and forming temperature.