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Crystal rotation during film orientation
July 21, 2008
During orientation, as stretching continues the tie molecules pull on the lamella crystals in which they are embedded, and the crystal begins to rotate in the direction of the forces. The resistance to the rotation of the crystal is the mechanism of strengthening of a polymer by the crystal phase and gives rise to the polymers stiffness. However, once the polymer begins to draw the lamella are rotated and realigned by the forces applied to them by the elongating tie molecules. Here is the drawing I promised in an earlier posting.
What is very interesting (at least to me) is that the A, B and C axis align in particular orientation relative to the film surface, C axis in the plane of the film and then the A and B axis perpendicular to parallel or the film surface. If I recall correctly the B axis is generally parallel to the film surface but I do not know that this is always true.
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Unstretched semicrystalline polymer showing tie molecules between various crystalline lamellas randomly oriented in the polymer spherulite with the A, B and C crystal axis unaligned |
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Stretched semicrystalline polymer (applied force represented by large arrows) showing elongated tie molecules between various crystalline lamellas oriented in the polymer spherulite with the A, B and C axis aligned more uniformly |
Posted by Eldridge M. Mount on July 21, 2008 | Comments (0)