Highly transparent polypropylene cast films: Relationships between optical properties, additives, and surface structure

Abstract Polypropylene homopolymer and ethylene/propylene‐random‐copolymer cast films formulated with various amounts of slip and antiblocking aids as well as acid scavengers and produced under different processing conditions were characterized with respect to surface structure and optical properties. The topographical analysis was done by atomic force microscopy (AFM). Optical properties were determined using a hazemeter and an UV/Vis/NIR spectrophotometer. AFM height images revealed a significant influence of processing conditions on the development of surface structures. Besides the occurrence of scratches displaying the replica of the metallic chill roll, particularly characteristic eight‐shaped superlamellar crystalline features were affected by the cooling conditions. Relationships between surface enrichment of additives and vertical and lateral roughness parameters were established. In general, film types formulated without additives exhibit better optical properties. For film types formulated with polymer‐processing aids, the diffuse‐scattering power is reduced by low molecular weight, high amounts of acid scavenger aid, and antiblocking agents with low porosity. A separation of haze into its bulk and surface components indicated that total haze is dominated by surface haze. The comparison of haze and the vertical roughness parameters exhibited a tendency of a linear correlation. POLYM. ENG. SCI., 47:1021–1032, 2007. © 2007 Society of Plastics Engineers