Formation of fibrous crystals in flowing blends of polyethylene melts

Abstract

Flow induced crystallization of high density polyethylene has been studied in a two-phase flow system using low density polyethylene as the carrier phase. Extensional stresses were generated under slow flow conditions by either of two methods: one involving flow past a stationary seed, the other involving a droplet deformation and bursting mechanism. In both cases, oriented, fibrillar crystallization of the high density phase was observed optically and correlated with calculations indicating the presence of flow-induced extensional gradients. Morphological, thermal, and birefringence data indicate that the crystalline fibers produced are oriented and superheatable, and consist of a multifibrillar substructure. For fibers produced by the droplet bursting process a semi-quantitative agreement was found between fiber melting point and birefringence based on a simplified analysis for the bursting induced extensional flow. These results demonstrate that two-phase flows of crystallizable systems are a convenient means for studying the phenomenon of flow induced crystallization in polymer melts.

Multiscale and Multistep Ordering of Flow-Induced Nucleation of Polymers

“…PE is the simplest semicrystalline polymer and often serves as a model material to study phase transitions such as crystallization, melting, and so on. ,, PE can crystallize in various modifications depending on crystallization conditions. For instance, mobile hexagonal crystals may appear under high pressure and then transform to orthorhombic crystals with increasing thickness. − Here we discuss the formation and evolution of locally ordered trans-rich structure in the early stage of crystallization studied with Raman and FTIR spectroscopy. ,,, …”

Crystallization and Precursors during Fast Short-Term Shear

“…Flow can increase the crystallization rate by decades [10][11][12][13][14][15] and, in addition, can dramatically change the crystalline morphology. [16][17][18][19][20][21] In quiescent or quasi-quiescent conditions, morphology is dominated by spherulites, three-dimensional assemblies of randomly oriented folded chain lamellae. 22 For strong enough flows, spherulites are replaced by shish-kebabs, composite crystallites with an extended chain fibrillar core (shish) dressed with disklike folded chain lamellae (kebabs).…”

Reinforcement of the interface in drawn polymer blends PS/PA‐12

“…Depending on interfacial characteristics, the thickness of this layer can reach tens of nanometers; therefore, its total volume in a blend cannot be ignored. [11][12][13][14] Keeping in mind that characteristics of the interphase layer differ from those of the bulk components, one may expect a noticeable influence of its presence on final properties of compositions. 3,6,7,9,10,[12][13][14] Stretching of blend films resulting in molecular orientation of bulk polymers and the interface introduces additional possibilities in development of novel materials with new qualities.…”

“…[11][12][13][14] Keeping in mind that characteristics of the interphase layer differ from those of the bulk components, one may expect a noticeable influence of its presence on final properties of compositions. 3,6,7,9,10,[12][13][14] Stretching of blend films resulting in molecular orientation of bulk polymers and the interface introduces additional possibilities in development of novel materials with new qualities. 1,3,5,6,[15][16][17][18] In our previous paper, 17 the reinforcement of crystalline matrices with glassy particles of polystyrene (PS) has been detected.…”

“…It is an interphase layer formed at the surface of contact of alternative phases. Depending on interfacial characteristics, the thickness of this layer can reach tens of nanometers; therefore, its total volume in a blend cannot be ignored 11–14. Keeping in mind that characteristics of the interphase layer differ from those of the bulk components, one may expect a noticeable influence of its presence on final properties of compositions 3, 6, 7, 9, 10, 12–14…”