Blown film characterisation
Graham Smith, Phil Coates, Mike Martyn, Mike Woodhead
University of Bradford
UK

Keywords: blown film, characterisation, analysis


Effects of process changes on polyethylene blown films were studied using profile analysis techniques. Changes in process parameters such as barrel temperature, haul off rate, extruder screw speed and cooling airflow, on film properties were studied. Profile analysis was also used to determine the effects on the bubble of running a Porpoise P3 on line rheometer concurrently with the blown film line.

The film line used consisted of a Betol 38mm single screw extruder with a spiral mandrel die. The die gap could be varied between 0.8mm and 1.2mm by changing the mandrel. The bubble was videoed using a digital video camera and profile analysis carried out using software written in house.

Two materials were studied, a film grade low density polyethylene and a metallocene polyethylene. For both materials, a stable bubble was initially formed before any changes were made to process parameters. Parameters were changed individually in order to determine their effect on bubble characteristics such as blow up ratio, height of freeze line and bubble profile. The effect of operating a Porpoise P3 online rheometer, which takes a stream of melt away from the main flow, on bubble characteristics was also studied.

Measurements were also made on extrudate after processing at points before and after changes were made to the process.