The effect of metals on the processing of LLDPE through a slit die

The effect of surfaces on the rheology and processing of polymers is a newly developing area of research. In this work, a stainless steel slit die was used with a variety of inserts of other metals, at the exit. The viscosity measured with the slit die was well predicted by the generalized Maxwell model containing a damping function with parameters determined from separate shear experiments. The viscosity was not affected by different metal type at the die exit. However, there was a marked increase in exit pressures for flow over brass inserts at the die exit. This effect coincided with the production of a porous, copper-rich brass surface and it was shown that this was the result of surface dezincification. This was postulated to cause increased adhesion between the LLDPE and the brass via physical interlocking at the porous surface which subsequently increased the exit pressure.