Direct correlation between modulus and the crystalline structure in isotactic polypropylene

Abstract

Mechanical properties and crystalline structure of isotactic polypropylene (iPP) types were studied using polymers, which were polymerized differently in order to obtain diverse molecular architectures. The objective of this work is to describe quantitative correlation between the crystalline structure and the elastic modulus in order to predict structures with expectably advantageous properties. The molecular mass was measured by gel permeation chromatography (GPC) and the regularity of molecular structure was investigated by Fourier transform infrared spectroscopy (FTIR) and stepwise isothermal segregation technique (SIST). The chain regularity of the studied samples is varying in a wide range according to the results of SIST and FTIR measurements. The crystalline structure was characterized by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The tensile properties were determined by standardized tensile tests. The results indicate clearly that the increased chain regularity is accompanied by a proportional advancement in crystallinity and consequently proportionally larger stiffness. Moreover, the results of this work were compared to those obtained on other previously produced iPP samples and it can be established that the correlations found during this work are valid generally. An empirical model was developed also, which connects the stiffness to the structural parameters of iPP and makes possible the design and prediction of materials with targeted molecular structure and properties.

Keywords

• Mechanical properties
• Modeling and simulation
• crystalline structure
• structure-property correalatio