Combined infrared spectroscopy and ultrasound studies of changing melt composition during single screw extrusion

In-Line ultrasound velocity measurements hake been made simultaneously with on-line mid-and near- infrared spectroscopy during single screw extrusion of a range of blends of an HDPE and a PP, to assess the sensitivity of these techniques to blend composition. Ultrasound velocity was sampled at 1Hz, using in-house process monitoring technology; mid-infrared data was obtained at 1 'sample' per minute (16 scans at 2 cm(-1) resolution). Under these conditions, it was found that the ultrasound technique could successfully resolve a change of 1 wt% PP in HDPE, whereas the infrared spectroscopy (using specific peak height change) could not resolve better than similar to 2wt%. The techniques showed very close agreement in monitoring the dynamics of change from one blend composition to another. The original blends were made by mixing pellets; twin-screw compounded blends of the PE, PP are being investigated, to assess any effects of blending process history.