Crystallization studies of LLDPE during tubular blown film processing

The final physical properties of semi-crystalline blown films are highly de pendent on the crystalline morphology and orientation of polymer chains wit hin the film. Simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements were successfully used to study crys tallization during tubular blown film extrusion of LLDPE. SALS patterns wer e recorded at various vertical positions along the bubble. For LLDPE, an un deformed spherelulitic structure is formed if the stress level during proce ssing is not too high. The change in average scattered intensity with axial position cart be described using multiple step Avrami kinetic processes in parallel. The first step accounts for crystal growth and corresponds to th e well-known temperature plateau. The later processes start with the imping ement of the growing spherulites and may reflect secondary crystallization and orientation processes. Because the magnitude of the average intensity i s responsive to changes in process conditions, the on-line SALS system is p otentially a useful tool for monitoring process-properties interactions.