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Interfacial Instabilities (interfacial + instability)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Interfacial instabilities in coextrusion flows of low-density polyethylenes: Experimental studies

POLYMER ENGINEERING & SCIENCE, Issue 5 2000
Costas Tzoganakis
A fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well-characterized low-density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the "zig-zag" instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the "wave" instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the "wave" type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development. [source]

Role of the interphase in the flow stability of reactive coextruded multilayer polymers

POLYMER ENGINEERING & SCIENCE, Issue 4 2009
Khalid Lamnawar
Coextrusion technologies are commonly used to produce multilayered composite sheets or films for a large range of applications from food packaging to optics. The contrast of rheological properties between layers can lead to interfacial instabilities. Important theoretical and experimental advances regarding theses defects have, during the last decades, been made using a mechanical and numerical approach. This study deals with the influence of the physicochemical affinity between the neighboring layers on interfacial instabilities for functionalized incompatible polymers. It was experimentally confirmed, in this case, that weak disturbance can be predicted by considering an interface of nonzero thickness (corresponding to an interdiffusion/reaction zone interphase) instead of a purely geometrical interface between the two reactive layers. According to the rheological investigations, an experimental strategy was here formulated to investigate the parameters that controlled the stability of the reactive multilayer flows. The role of the viscosity ratio, elasticity ratio, and layer ratio of the stability of the interface was also investigated coupling to the reaction rate/compatibilization phenomenon. Hence, based on this analysis, guidelines for a stable coextrusion of reactive functionalized polymers can be provided coupling the classical parameters and the physicochemical affinity at the polymer/polymer interface. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Interfacial instabilities in coextrusion flows of low-density polyethylenes: Experimental studies

POLYMER ENGINEERING & SCIENCE, Issue 5 2000
Costas Tzoganakis
A fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well-characterized low-density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the "zig-zag" instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the "wave" instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the "wave" type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development. [source]

Surface Structures in Thin Polymer Layers Caused by Coupling of Diffusion-Controlled Marangoni Instability and Local Horizontal Temperature Gradient

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005
Lothar Weh
Abstract Summary: Surface tension-driven Marangoni convection causes the formation of regular surface structures in drying polymer layers. The shape of the surface structures formed during solvent evaporation depends on layer and interfacial dynamic parameters as well as external factors. The influence of a horizontal radial temperature gradient produced by a point heat source below the polymer layer on the diffusion-controlled Marangoni instability has been studied. In the region of the lateral temperature gradient, radial surface flow coupled with the interfacial instability leads to stripe, ladder, chevron and/or labyrinthine surface structures. Stepped ladder structures in a poly(vinyl butyral) layer produced by interfacial instability and heating with an ultrasonic sonotrode below the layer substrate. [source]

Interfacial instabilities in coextrusion flows of low-density polyethylenes: Experimental studies

POLYMER ENGINEERING & SCIENCE, Issue 5 2000
Costas Tzoganakis
A fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well-characterized low-density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the "zig-zag" instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the "wave" instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the "wave" type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development. [source]