A rheological model for the prediction of polyethylene blown film properties

Development of new or improved blown film products is an expensive and time-consuming exercise for converters. Often, many experiments and trial runs have to be performed, accompanied by evaluations of the resulting film samples. If no lab-scale blown film line is available, valuable production time is lost while seeking out optimum processing parameters. Utilization of model calculations relating polymer type and machine parameters to properties of films obviously is an interesting option to streamline the development process of films. The practical use of model calculations depends on reliability and versatility of the model used. In this paper, a theological model is presented that was developed for low density polyethylene (LDPE), and relates theological properties, processing conditions and die geometry to mechanical and optical properties of the films. Validation of the model on different blown film lines has proven its reliability for LDPE. Furthermore, the model has been extended to binary LDPE/LLDPE (linear low density polyethylene) blends, demonstrating its versatility for PE in general. An oversight is given of theoretical and experimental issues encountered during the development of the model, complemented with some instructive examples of practical usage.