Precursor of Shish-Kebab above the Melting Temperature by Microbeam X-ray Scattering

Abstract

Preparation of strong fiber with ultrahigh strength and modus is a dream of polymer scientists and engineers. It is believed that a shish-kebab is the structure origin of the ultrahigh strength and modulus fiber. This article presents our investigation on the inner structure of shish-kebab precursor of isotactic polystyrene in μm scale formed by shear flow above the nominal melting temperature T m using microbeam wide-and small-angle X-ray scattering (WAXS and SAXS). The microbeam WAXS experiments indicated that the precursor included crystallites with degree of crystallinity of ∼0.15%, which had higher melting temperature than normal lamellar crystals, meaning that its size (the length) was longer in the c-axis of crystals than the normal lamellar crystals. The microbeam SAXS experiments confirmed that approximately 1% of the crystallites in the precursor were rather long in the direction of c-axis. It is expected that such crystallites work as an initiator of a shish when it is below T m .

Flow-Induced Precursors of Isotactic Polypropylene: An in Situ Time and Space Resolved Study with Synchrotron Radiation Scanning X-ray Microdiffraction

“…The experiment result suggests the formation of flow-induced noncrystalline precursors. With SR-μSXRD, Kanaya et al 64 showed that shear-induced precursors contained limited crystallinity with higher thermal stability than normal lamellar crystals. The above two SR-μSXRD studies seem reaching contrary conclusion on the structure of precursors, which may be due to their different experimental procedures.…”

Effect of processing parameters on the morphology development during extrusion of polyethylene tape: An in-line small-angle X-ray scattering (SAXS) study

“…The route to crystallization during flow is generally accepted to be via the formation of 'shishkebab' morphology [6][7][8][9]. Proposed mechanisms and kinetics for the formation of shish-kebab morphology usually relate to data from shear flow conditions using custom made shearing devices [10][11][12][13][14][15][16]. However, during extrusion, the polymer melt exits the die head and begins to cool rapidly, and at the same time it is uniaxially elongated under constant force, between the die head and take-up device.…”

Fibrillar Morphology in Shear-Induced Crystallization of Polypropylene

“…Recent developments in shear‐induced crystallization (SIC) have demonstrated the existence of three regimes which, for the same polymer at the same temperature and pressure, occur on increasing the flow intensity: (i) the effect of flow upon the final morphologies and crystallization kinetics is negligible, (ii) the flow causes a strong enhancement of crystallization kinetics, increasing the number of nuclei and thus the average dimension decreases, but the spherulitic morphology is kept, (iii) the flow deeply influences both morphology and kinetics by causing the formation of fibrillar structures in the polymer melt. However, apart from a qualitative understanding of the phenomena, a quantitative description of the phenomena is still discussed and it is currently under investigation …”