Determination of polyolefin film properties from refractive index measurements. II. Birefringence

The use of refractive index data for studying changes in oriented polyolefin films has been demonstrated. Application of this technique to oriented polypropylene and polyethylene films showed that the birefringence is a linear function of the refractive index in the direction of maximum orientation. By utilizing refractive index, density, and crystallinity data the crystalline refractive indices n c and ( n a + n b )/2 and polarizabilities α ∥ and α ⊥ could be estimated for polypropylene and polyethylene.