Melting of Polymer Blends in Co-rotating Twin Screw Extruders

Abstract

Abstract Experimental studies of the melting process in extruders generally involve a high outlay and can only be performed with certain restrictions, both in respect of the method employed and with regard to the evaluation of the results. This part of the work describes one possible way of studying the melting of binary incompatible polymer combinations. The method described makes it possible to estimate the degree of melting of the two components over the length of the screws of the twin screw extruder. Experimental studies were performed of polypropylene/polyamide 6 (PP/PA6) blends containing low weight contents of the disperse PA 6 phase. In order to verify the theoretical models set out in Part I, page 124 of this issue, not only were the process conditions of screw speed and throughput varied but also the viscosity ratio. This was achieved by using two different PP grades. In addition, comparable tests were performed on two different sizes of extruders. The tests show that the melting of polymer blends, and particularly the melting of the second component, which melts at a higher temperature, is determined to a significant extent by the screw rotational speed, the throughput, the ratio of the extruder channel depth to granule diameter and also the material combination (viscosity ratio). Comparisons of calculations and experiments show that the melting profiles calculated for different material combinations and process conditions tally well with the experimental studies in overall terms.