Interfacial slip reduces polymer-polymer adhesion during coextrusion
(a) Schematic drawing of the coextrusion die. The rectangular flow after the feed block is shaped into a square, which is transformed into a sheet in a fish-tail sheeting die. After the die land, the melt is picked up by a double chill-roll. (b) Optical micrograph of about half of a 20 layer PS/PMMA extrudate. The scale bar represents .
Schematic drawing of measurement of interfacial adhesion by the ADCB test: (a) at even-numbered interface; (b) at odd-numbered interface (the top PMMA layer was peeled away before measurement). is the crack length. The sample was glued to the glass slide with cyano-acrylate adhesive.
Interfacial adhesion after coextrusion vs interface number. is the PS/PMMA interface closest to the surface; 10 is at the center. for the laminated PS/PMMA interface, (엯), from Brown et al. (1993) and Cole et al. (2003).
Schematic drawing of the velocity profile inside and outside of the die. The no-slip boundary condition is assumed between polymer melt and die wall. Slip occurs at the interface between PS and PMMA. Outside of the die, full-slip boundary condition is assumed at the melt/air interface. Thus the layer next to the wall must accelerate dramatically.
(a) Pressure drop for PS, PMMA homopolymers and 32 layers flowing through a slit die. The dashed line is calculated assuming no interfacial slip. The solid lines through the homopolymers and 32 layer data are fitted using Ellis parameters and the slip velocity in (b). (b) The slip velocity of PS/PMMA calculated by assuming a sigmoidal functional and fitting the pressure drop shown in (a). The shear stress is divided into three regimes based on . [replotted from Zhao and Macosko (2002)].
Comparison between interfacial adhesion (∎) at different interfaces and shear stress (—) for the multilayer sample. The three regimes are defined by the two critical shear stresses [ and , see Fig. 5(b)] for the slip at PS/PMMA interface. The stress distribution at flow rate of is also plotted ( – – –).
Comparison of interfacial adhesion for extrudates at different flow rates vs interface number, . for the laminated interface is from Brown et al. (1993) and Cole et al. (2003).
Interfacial adhesion vs shear stress for multilayer samples extruded at different flow rates. values for all the flow rates converge to a master curve which is only a function of shear stress.
Adhesion vs layer position. (∎) quenched after coextrusion at ; (◆) same sample annealed ; (●) quenched after coextrusion at but with of the chain functional enabling reactive coupling at the interface.
Adhesion vs annealing time for the second interface of a 20 layer PS/PMMA at
Characteristics of polymers used in this work.
Ellis model parameters at .
values vs layer number at various condition.
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