# Why are these food stretch films (LLDPE) holding one one-thousandth of the weight in reality than what is expected from the datasheet values?

I am trying to reproduce analytically the results found in this experiment where a weight of 3 x 5 lbs (6,8 kgs total) breaks the cling wrap (LLDPE) which is stretched over a medium size cooking pot.

Let say the weight plate has a diameter of 20 cm, thus the flexural strength when the cling film breaks is about 2kPa (6,8 x 9,81 / (pi x 0.20² / 4)).

Yet for LLDPE this datasheet gives a flexural modulus of at least 16MPa.

The experiment does not seem to involve hot conditions where film flexural strength could be decreased. The only parameter that differs from the datasheet is film thickness (at least 25 microns in the datasheet whereas food wrap could be 12 microns).

The experimental value is about one eight-thousandths of the expected values from the datasheet.

Consequently following the datasheet (fluctal strength 16MPa) shouldn't we expect the film to hold 8000 x 15 lbs = 120 000 lbs (54 tons)? This sounds impossible even with thicker film (25 microns) so how to use the datasheet data to find the experimental weight that makes the film break ? Am I using the correct data, what did my reasoning miss ?

Any help greatly appreciated !

• What is the tensile strength of the wrap? Note that the elastic modulus is not the same as the flexural strength, though the units are the same.
– r13
Commented Aug 19, 2022 at 21:20
• @r13 according to the datasheet the tensile strength at yield in MD is 1.3MPa and 10.3 MPa in TD. In sciencing.com/calculate-flexural-strength-5179141.html they use the terms "modulus of rupture" for flexural strength. You are right it should not be confused with "elastic modulus". By the way do you mean the tensile strength could help find the experimental value ? Commented Aug 20, 2022 at 2:47
• Yes, you shall check against the modulus of rupture.
– r13
Commented Aug 20, 2022 at 11:24