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A reference with more on Film Shrinkage, etc.
March 24, 2008
While looking through my reference materials this weekend for heat shrinkage data for films, I used a fine reference which is focused heavily on oriented films and a special focus on shrink and stretch films. The book is “Plastic Films For Packaging”, Calvin J. Benning, Technomic Publishing Co., Inc., Lancaster, (1983).
Dr. Benning worked, among other places, at W.R. Grace, where he focused on shrink films and foams. The book has several good chapters on the stretching process as well as the properties which are developed, and while the book was published in 1983, its information is still useful and the understanding it supplies is timeless.
For instance, I am working on a project to improve a film barrier and aside from polymer selection I can improve it by orientation, but how much? Generally form my OPP experience, I know that I cut the WVTR in half or two thirds with PP orientations, but is this a general rule of thumb as I seem to think?
Well a nice table from this book (page 109) shows:
|
Polymer |
Degree of orientation, % |
Oxygen permeability cc/mil/100in^2/day @ 73oF |
|
polypropylene |
0 |
150 |
|
300 |
80 |
|
|
polystyrene |
0 |
420 |
|
300 |
300 |
|
|
polyester |
0 |
10 |
|
300 |
5 |
|
|
Acrylonitrile/styrene (70/30) copolymer |
0 |
1.0 |
|
300 |
0.9 |
Because oxygen barrier is generally controlled by size of the permeating molecule, we see clearly that the barrier is controlled by the orientation for the first three polymers where it is cut by 1/3 to ½ by the orientation. But for the Acrylonitrile/styrene copolymer there appears to be an overriding control relating to the chemical interaction between the polymer and the oxygen molecule. So for the WVTR improvement, I will consider polymers which do not interact with moisture to follow a conservative rule of thumb of cutting the WVTR by 1/3 to ½, but I will have to be a little careful of polymers which absorb moisture. Of course, to really know we have to measure the final WVTR improvement.
Posted by Eldridge M. Mount on March 24, 2008 | Comments (0)