The influence of molten fraction on the uniaxial deformation behavior of polypropylene: Real time mechano‐optical and atomic force microscopy observations

Abstract

In this study, we have coupled the real time mechano‐optical measurements with the off‐line structural characterization techniques including AFM, WAXS, and DSC to establish the quantitative relationships between the “true mechano‐optical behavior and developed morphology” as influenced by the fraction of molten phase present in the polypropylene films. Stretching PP in the solid state invariably leads to formation of fibrillar texture. The evolution of surface morphology in partially molten state was found to depend on the fraction of the molten phase present at the start of the deformation. If the samples are strained past the yielding in partially molten state, the birefringence begins a rapid rise. Concurrent with this, the equatorial zones of the spherulites begin to crack while meridional regions remaining intact. This leads to temporary reduction of crystallinity because of destruction of some of the crystals. If held in this strained state, the crystallite thickening was observed while the birefringence increases while the lost crystallinity is recovered. If the films are strained past the strain hardening point, the microfibrillar structure was found to dominate the surface morphology. When the films are stretched in the melting temperature range, they exhibit substantial nodular surface topology. These nodules that were absent in the solid state deformed samples are hard lamellae buried inside amorphous “soft matter”. The tangential lamellae increasingly become dominant as the processing temperature approaches substantially molten state leading to the observation of a* oriented crystallites in the X‐ray analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 925–941, 2006

Stretching Temperature Dependency of Fibrillation Process in Isotactic Polypropylene

“…Moreover, some part of initial crystallites in samples annealed at higher temperature transformed into amorphous phase after stretching. The low mobility of molecular chains at 30 °C constrained the movement of amorphous chains converting back to crystalline state. , …”

Evolution of Poly(propylene) Morphology in the Rubbery State under Uniaxial Strain

“…They consider the material as lamellar crystals separated from each other by a layer of amorphous polymer and held together by tie molecules through the amorphous phase. The role of the tie molecules on the crystalline phase orientation was broadly studied . These molecules and the amorphous phase are firstly oriented during uniaxial stretching while the crystalline phase remains only slightly oriented.…”

The deformation behavior of polypropylene film under high strain rates

“…Polypropylene (PP), for example, is well studied from many points of view, such as the characterization and the modeling of macroscopic deformation behavior of film using a uniaxial or biaxial stretcher [ 1–4], the observation, measurement, and modeling of the evolution of higher order structure during stretching [5–11], and the characterizing of stretched film [5, 12–17] have been conducted. Most of them, however, are basic studies because the phenomena during the TD stretching process are very complicated and experimental study using a pilot plant is expensive.…”