Blown film

Assume that a plastic shopping bag, made from blown film, has a lateral (width) dimension of 300 mm. (a) What should be the extrusion die diameter? (b) These bags are relatively strong. How is this strength achieved?

Question

Blown film

Assume that a plastic shopping bag, made from blown film, has a lateral (width) dimension of 300 mm. (a) What should be the extrusion die diameter? (b) These bags are relatively strong. How is this strength achieved?

Accepted Answer

(a) The perimeter of the bag is (2) (300)= 600 mm. Since the original cross section of the film was round, the blown diameter can be calculated from [latex]\pi D=600[/latex], or D = 190 mm. Recall that in this process a tube is expanded 1.5 to 2.5 times the extrusion die diameter. Selecting the maximum value of 2.5, the die diameter is calculated as 190/2.5 = 76 mm.

(b) Note in Fig. 10.25 that, after being extruded, the bubble is being pulled upward by the pinch rolls. Thus, in addition to diametral stretching and the resulting molecular orientation, the film is stretched and oriented in the longitudinal direction as well. The biaxial orientation of the polymer molecules significantly improves the strength and toughness of the blown film.

Question 10.6: Blown film Assume that a plastic shopping bag, made from blo...

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