Die lip build-up in the extrusion of highly filled low density polyethylene

摘要

It is common that a highly filled master batch (MB) contains a low molecular weight (LMw) lubricant as a filler dispersion agent and compounding processing aid. Sometimes, the presence of such a lubricant in the MB creates a die build-up problem in the extrusion process of a let-down formulation. Several MBs with a laboratory Banbury mixer were produced to investigate the effect of the amount of aluminum stearate (as a lubricant) on dispersion and die build-up. When the MB containing the stearate below the critical amount is used, die build-up decreases and filler dispersion improves with increased amounts of stearate. At the critical amount of the stearate, the MB shows good dispersion as well as minimum build-up. Above the critical amount, dispersion is still good. But, build-up increases with further increase in the amount of stearate added up to 3.0%. This observation results from the different mechanisms of the die build-up, which depends on whether the stearate level is below or above the critical amount. We confirmed such a mechanism in the commercial extrusion process of the MBs. This observation leads to the conclusion that in the use of the stearate (as a dispersion agent) for highly filled MB, the amount of the stearate need to be optimized to minimize a die build-up of the MB with good filler dispersion.