Experimental investigation of the morphology development of polyblends in corotating twin-screw extruders

Abstract

Compounding extruders are still designed based on experience and timeconsuming experimental examinations. This work investigates the morphology development of incompatible polyblends along a mixing zone at the end of a corotating twin-screw extruder. During the process, the samples are taken from the running extruder using special barrel plates. These samples are subsequently examined by means of scanning electron microscopy (SEM). This method allows sampling in less than 1 min and thus extremely fast and almost unaffected. The experimental investigation of the morphology development improves the knowledge about the factors essentially influencing the blending process. It also allows the verification as well as improvement of theoretical models. Polyblends of polypropylene (PP) and polyamide (PA) with 7.5, 15, and 30 wt % PA were examined. As well as the relevance of the mass percentage of the dispersed phase, the influence of the screw geometry, the screw speed, the melt temperature, the melt throughput, and the pressure profile was investigated. Apart from the melt throughput, all varied factors show an influence on the resulting blend morphology that may not be neglected. However, the changes of the mean particle sizes in the observed mixing zones are only gradual (mean particle size Ϸ 1-4 m), which can be attributed to the extremely fine blend morphology already existing during or after the melting. That means that the application of "classic melting zones" generally already produces finely dispersed blend morphologies, thus proving the essential importance of the melting zones regarding the development of the blend morphology. Consequently, the mean particle sizes, calculated by means of quantitative image analyses of SEM micrographs in the mixing zones following the homogenizing section only slightly depend on the compounding conditions (screw speed, melt throughput, screw geometry, melt temperature, and pressure profile). However, the direct visual analysis of the SEM images, especially in the first parts of the mixing zones, shows the simultaneous existence of large PA6 particles in the PP matrix. In addition, a downstream unification of the particle size distribution can be observed. Especially the number and size of the coarser particles decreases in the mixing zones.

Tailoring the mechanical, thermal, and flammability properties of high-performance PEI/PBT blends exhibiting dual-phase continuity

“…However, it is difficult to work with these polymers due to their poor melt processability and high costs. Despite the expected benefits of combining HPP in a single material, most efforts in blending technology are focused on the production of commodity polymer blends [7][8][9][10][11][12].…”