Draw-ratio-dependent morphology of biaxially oriented polypropylene films as determined by atomic force microscopy

Using atomic force microscopy we have examined the surface morphology of se quentially biaxially oriented polypropylene (BOPP) films. The surface was s hown to be dominated by a nanometer-scale fiber-like network structure, the configuration of which was found to be determined by the relationship betw een the draw ratios used in the bi-directional stretching processes [machin e draw (MD) and transverse draw (TD)]. For the film fabricated with MD and TD ratios of 5.2:1 and 9:1, respectively, preferential orientation of fine fibers to the TD direction and larger veins to the MD direction were observ ed. When MD and TD ratios became similar, no predominant TD direction fiber alignment and no larger veins were observed. We have shown that the residu al effects of the first stretching of the film surface can provide informat ion on the way in which morphological development of the BOPP occurs. (C) 1 999 Elsevier Science Ltd. All rights reserved.