Fundamental understanding and modeling of diffuse interphase properties and its role in interfacial flow stability of multilayer polymers

Abstract

This work aims to investigate the growth and structural evolution of a diffuse interphase generated in a flow field and to highlight its importance on controlling the final properties of compatible multilayer materials. The model polymers chosen are poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). Interdiffusion kinetics, geometrical, and rheological properties of the interphase decoupled and coupled to flow have been probed and quantified under fundamental conditions of rheological measurement and under real practical conditions of processing, respectively. Polymer chain orientation is shown to decelerate the interdiffusion coefficient. This phenomenon is demonstrated to be balanced by intermixing (i.e. flow effect) at the vicinity of the interface triggered from excess interfacial shear stress, thus favors development of the interphase. The diffuse interphase generated therein during the processing has been well characterized via scanning electron microscopy coupled with energy dispersive X‐ray analysis (SEM‐EDX) and transmission electron microscopy (TEM). Results indicate that the interphase is robust with a geometrical property of tens microns depending on processing conditions and the interfacial structure is shown to be smooth with continuous amorphous‐crystallization transition between neighboring layers without causing any interfacial disturbances. Finally, experimental studies concerning the interfacial flow instability and encapsulation in coextrusion process have been performed, taking into account some key classical decisive parameters such as viscosity ratio, thickness ratio and elasticity ratio, etc. Different from severe flow instability observed in incompatible multilayer systems, presence of the interphase at PMMA/PVDF multilayers plays a vital role in weakening (or even eliminating) the viscous instabilities and elastic instabilities despite of the very high rheological contrast. POLYM. ENG. SCI., 55:771–791, 2015. © 2014 Society of Plastics Engineers

Numerical modeling of multilayer film coextrusion with experimental validation

“…This is not always obtainable and certain coextrusion issues can have a negative impact on the final product performance [3]. Both viscous and elastic melt property differences can lead to an unwanted nonlinear interface, which would have deleterious effects upon the optical, physical, and mechanical film properties [15,16]. Such interfacial irregularity can be either spatial (caused by viscous effects) or temporal (elastic effects).…”

“…1 are produced when different polymers are extruded, producing separate polymer melt streams. These streams then come together for the first time in either an injector (or feed) block linked to a die or a multimanifold die [1,4,5,[8][9][10][11][12][13][14][15]. A thin, unified melt curtain sheet exits the die, which is then rapidly cooled by a casting drum before being stretched in both the machine and transverse directions, producing a biaxially oriented final film [5].…”

Fundamental studies of interfacial rheology at multilayered model polymers for coextrusion process

“…Besides, nonlinear rheology, which is closer to the processing situation, is even scarcer regarding multilayers despite of its high significance [7]. In our knowledge, few studies have, from fundamental and experimental aspects, been dedicated to the correlations between the interfacial rheology and the properties of coextruded multilayer polymers including the flow stability [2,3]. To have a better understanding, this study is focused on the interdiffusion decoupled and coupled to flow as well as the linear and nonlinear rheology of the triggered interphase before disclosing its role in the interfacial flow instability of coextrusion based on PMMA/PVDF asymmetrical bilayer structures.…”

“…Indeed, in multiphase polymer systems (blend/multilayer), interfacial phenomena like interdiffusion, interfacial slippage and/or interfacial reactions taking place at the polymer-polymer interface are very important considering that an interphase (a non-zero physicochemical affinity as opposed to a plane interface) may appear therein, which impacts the adhesion and properties [1][2][3][4][5][6]. So far, rheology /properties associated with such interphase as well its contributions persist as a hot issue.…”

“…Owning the advantage of combining separate features of different individual polymers together in a facile way, coextrusion has been widely used to fabricate multilayered composite sheets or films for various applications ranging from food package to reflective optics [1][2][3]. This technology is realized by a combination of two or three extruders using a multimanifold die or a feedblock within which polymer melts are brought together.…”