Blown Film Modeling Quiz

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A blown film is to be produced with high density polyethylene for a study for a high moisture barrier food packaging application.  It is well know in the literature that orientation in the film is directly related to the performance of the film.  The development engineers would like to characterize the operating parameters that are occurring in the process to relate that to orientation measurements determined by SAXS, WAXS, and IR Dichroism.  The conditions measured during the blown film trial are as follows: production rate = 14 kg/hr, density of the melt = 0.8 g/cm3, viscosity = 3*104 newton-second/m2, the die diameter is 5 cm, the film layflat width is 25 cm, the die opening is 200 microns, and the final film gauge is 25 microns.

1.      Calculate the blow up ratio with the given machine conditions.

2.      Calculate the draw ratio in the z-direction (machine direction).

3.      Comment on how changes in the blow up ratio and the draw down ratio would influence the orientation of the film.  What would be the optimum conditions to maximize the barrier properties of the film. 

4.      Calculate the force of the winder at the draw ratio determined in Problem 1.  Hint: Use figure 10-3 from Middleman’s text.

5.      Calculate the internal pressure of the bubble at the draw ratio determined in Problem 1.  Hint: Use figure 10-3 from Middleman’s text.

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