A Study of Polycarbonate / Poly (butylene terephthalate) Compounding in a Twin Screw Extruder

Abstract

In this work, the compounding of polycarbonate (PC) / poly-butylene terephthalate (PBT) blends was studied for the purpose of improving quality of products with reduced wastage and finally to satisfaction of end users. The effect of material rheological characteristics and processing conditions on compounding of PC /PBT was investigated through statistical experiments carried out on a 58 mm twin-screw extruder at SABIC Innovative Plastics Limited (formerly GE Plastics Limited) in Cobourg, Ontario.

Melt Volume-Flow Rate (MVR) is the most commonly used property to monitor the quality of products of PC/PBT blends. The MVR was studied with different sampling times and correlations between product properties (melt flow) and processing conditions (screw speed, flow rates) were discussed.

The rheological behavior of PC/PBT blends was investigated by dynamic and capillary rheometers. The effects of processing conditions (screw speed, feed rate) on viscosity were measured and it was found that the Cox-Merz rule is not valid for PC/PBT blends.

The change of morphology of PC/PBT blends was observed under a scanning electron microscope (SEM) by using different types of samples. Those samples were (i) PC/PBT blends pellets, (ii) PC/PBT blend samples, but collected after completing the rheological tests in the parallel plate rheometer, and (iii) PC/PBT blend samples, but collected after completing the rheological tests in the capillary rheometer. There was evidence that the samples collected after completing the tests in the parallel and capillary rheometer might be degraded due to temperature and time.