Studies on multilayer film coextrusion I. The rheology of flat film coextrusion

Abstract

Multilayer flat film coextrusion was studied, both experimentally and theoretically. For the experimental study, a sheet-forming die with a feedblock MGIS designed, and plastic films of three and five layers were coextruded. The die was provided with three pressure transducers in thc axial direction in order to determine the pressure gradient in the die, allowing the dc+ermination of the reduction in pressure drop when different combinations of two polymer melts were coextruded. Polymers used for coextrusion were: (1) low density polyethylene and ethylene-vinyl acetate; (2) low density polyethylene and high density polyethylene; (3) low density polyethylene and polystyrene. For the theoretical study, the z-component of the equations of motion for steady fullydcucloped flow were solved using a power law non-Newtonian model. (hnpirisons were made ljctween the experimental ;ind the thcorctically predicted volumetric flow rates. Predictions ofthe velocity distriljutions, shear rate profiles, arid shear stress distrihutions n w c x made :is fiinctions of the processing conditions and the rheological properties of the individual polymers concerned

Convective linear stability analysis of two-layer coextrusion flow for molten polymers

“…In the first one, the transition between stable and unstable processing conditions is investigated by examining the extrudate obtained at die exit on industrial or prototype industrial devices. This approach has been followed by Han and Shetty [5][6][7], Antukar et al [8] and Valette et al [9,10] for commercial polymers. The authors have tried to point out a connection between observations and thickness ratio, viscosity or first normal stress difference ratios at the interface.…”

Numerical investigations of polyester coextrusion instabilities

“…When decreasing the temperature the viscosity of PET2 increases much more than the viscosity of PET1 and so the gap between viscosities of both polymers decreases and the shear rate for which the viscosities are equivalent decreases towards the range of processing conditions. Following the literature ( [1,2,3,4]) one may believe a strong influence of temperature and flow rate on the defect appearance. Figure 4 shows that the mean relaxation time is much more important for PET1 than for PET2 in the extrusion processing range.…”

“…-In the first approach, the transition between stable and unstable processing conditions is investigated by examining the aspect of the extrudate obtained with different couples of commercial polymers (Han and coworkers [1,2,3], Antukar et al [4], Valette et al [5]). The authors related stable and unstable processing conditions to thickness ratio as well as viscosity and first normal stress difference ratios at the interface.…”

Numerical modeling of multilayer film coextrusion with experimental validation

“…In the coextrusion process, the different melt layers must remain distinct but well bonded (or compatible) when in contact [5,6]. Assuming that a desirable final coextrusion structure is obtained, coextrusion can combine the properties of different polymers into a single structure with improved features [1][2][3][4]7]. There are many aspects that one must consider to obtain a successful coextruded product.…”