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Orientation and haze
July 2, 2008
Film optics and especially haze are important usually, but not always with a desire for clearer films. In most semicrystalline polymers the difference between the density of the crystal and the amorphous phase drives light scattering which is a primary source of internal haze. Earlier blog postings spoke to the formation of surface haze and matte films. As light passes through matter it is slowed relative to its speed in vacuum and in the case of water you will remember that the position of something under water is not where it seems due to the bending of the light ray coming from the water into the air. This is due to the density difference of the air and water. The same thing happens when light passed from a polymer crystal to the amorphous phase. But because the spacing and the orientation of crystals in an unoriented film is so small the light is scattered and this is what makes it hazy.
As a film is oriented the stretching aligns the amorphous phase increasing its density while rearranging the crystals with no density change in this phase. The decrease if density difference is the source of the decreased scattering and therefore the improved haze
Posted by Eldridge M. Mount on July 2, 2008 | Comments (0)