Effects of Pressure and Cooling Rates on Crystallization Behavior and Morphology of Isotactic Polypropylene

Abstract

Isotactic Polypropylene (iPP) is a widely used polymer due to its excellent mechanical and thermal properties, as well as its chemical resistance. The crystallization behavior of polypropylene is influenced by several factors, such as temperature, cooling rate, and pressure. The effect of pressure is significant for both scientific and technological points of view, since in important industrial processing techniques the polymer solidifies under high pressures. In this paper, the study of the effect of pressure on the crystallization kinetics of iPP was conducted using a dilatometer in the pressure range from 100 to 600 bar and under two cooling rates: 0.1 and 1 °C/s. The morphology of the samples was characterized using DSC, optical microscopy, and X-ray diffraction. The results showed that pressure had a larger effect on specific volume changes at higher temperatures (in the melt state) than at lower temperatures (in the solid state). The polymer crystallization, which determined the transition between the melt and solid state, occurred at higher temperatures with increasing pressure. The cooling rate affected the crystallization process, with higher cooling rates leading to crystallization at lower temperatures. The size of the spherulites decreased with increasing cooling rates. The crystallinity evolution curves showed a linear relationship between the crystallization temperature and pressure. The study used a Kolmogoroff–Avrami–Evans model to describe the evolution into isotropic structures, and the predictions of the model accurately described the effect of pressure and cooling rates on the final spherulite radii.

Evolution of the Deformation‐ and Flow‐Induced Crystallization and Characterization of the Microstructure of a Single Spherulite, Lamella, and Chain of Isotactic Polypropylene

“…Speranza performed specific volume measurements using a piston‐die dilatometer operated at pressures ranging from 100 to 600 bar and cooling rates of 0.1 and 1 °C s −1 . [ 127 ] Several factors, such as temperature, cooling rate, and pressure, influence polypropylene's crystallization behavior. The pressure effect is significant from both scientific and technological points of view since, in essential industrial processing techniques, the polymer solidifies under high pressure.…”

“…Reproduced under the terms of the CC‐BY license. [ 127 ] Copyright 2023, the Authors. Published by MDPI.…”

“…iPP is a frequently used polymer in industrial processing, and scientific research is used as a model material in that work. [ 126–128 ] The iPP samples with well‐defined microstructure are obtained by annealing or adding a nucleating agent. In‐situ synchrotron X‐ray scattering, among other measurements, is employed in characterizing structural evolution under uniaxial stretching, creep, and stress relaxation tests.…”

“…Specific volumes of polymer in melt and solid state are represented as solid and dashed lines, respectively. [ 127 ]…”

“…Specific volume of iPP measurement at 100 bar with 0.1°C/s.Specific volumes of polymer in melt and solid state are represented as solid and dashed lines, respectively. Reproduced under the terms of the CC-BY license [127]. Copyright 2023, the Authors.…”