Effect of Material Structure and Additives on the Optical Properties of PP Cast Films

Polypropylene homopolymer and ethylene/propylene-random-copolymer cast films formulated with slip, anti-blocking, and acid scavenger aids were analyzed as to material structure and optical properties. The structural and topographical characterization was done by atomic force microscopy and by spectroscopic methods. Optical properties were determined using a hazemeter and an UV/VIS/NIR spectrophotometer. As to the effect of additives it was established that slip and anti-blocking aids migrate to and accumulate on the surface, resulting in increased surface roughness and larger scattering identities close to the surface. Acid scavenger additives were shown to contribute to less significant slip aid domains and hence to lower haze. In general, films without additives showed much better optical properties. The separation of haze into its bulk and surface components revealed that the total haze is dominated by surface haze.