The effects of constructional solutions of plasticizing screw configurations and extrusion conditions on polypropylene composite properties

Polypropylene (PP) composites were extruded with various mineral fillers (synthetic microsilica, surface modified chalk, talc, talc-dolomite) (Tables 1 and 2) and with compatibilizer (polypropylene grafted with maleic anhydride). Various extruders have been used: single-screw extruder (symbol I) or two types of corotating twin-screw extruders [symbol II (Figs. 1 and 2) and symbol III (Fig. 3)]. The effects of constructional features of the screws of plasticizing systems, especially of corotating twin-screw one, and rotational speed of the screws (n) on the composites properties were investigated (Tables 3-5). Namely, the effects of rotational speed of the screws on the following properties were determined: maximum tensile stress (σ M , Fig. 4), Charpy notched impact strength (a c N , Fig. 5), melt flow rate (MFR, Fig. 9), screws' drive energy consumption (Fig. 6), crystallization degree (X) and degree of filler dispergation in PP (Figs. 7 and 8). It was found that corotating twin-screw plasticizing system shows better characteristics of mixing effectiveness than single-screw one. Additionally, corotating twin-screw system makes possible the control of mixing process and this way allows obtaining the same thermo-mechanical history of the particles of the blend. It was observed the composite properties depend both on its composition and the way of introducing to the extruder.