Single-screw extruder, blending performances

The results reported in this paper are characteristic not only of grafting of lA onto PP/PE blends carried out in the Brabender plastograph equipped with a dynamic mixer, but also of lA grafting performed in reactors of other types, particularly in a single-screw extruder. 

In a single-screw extruder, a screw is rotated inside a cylindrical barrel. The feed may be in the form of a pre-blend or dry blend, pellets or in the form of viscous melt in melt extrusion. The extruder acts as a pumping and mixing device. The extruder performs the additional functions of conveying and melting and also performs compounding and devolatilisation functions. 

In the first studies on MFCs, the composites were prepared on a laboratory scale performing every one of the three aforementioned processing stages separately, one after another. Blending was done in a laboratory mixer or a single-screw extruder to obtain non-oriented strands that were cold-drawn afterward in a machine for tensile testing, followed by annealing of the oriented strands with fixed ends [14,15,58-60]. 

All extrusion runs were performed with a laboratory single screw extruder (D=19 mm, L/D = 25) fitted with a venting port. The blends were mixed by hand and fed to the extruder. Most of the extrusion runs were done with a temperature profile of200-230-240-260°C and a screw speed of 80 rpm. Other runs were carried at a screw speed of 20 rpm. 

As mentioned in Section 14.1, blends without compatibilisation may have poor mechanical properties. Consequently, in comparing twin and single screw extruders for compounding mixed polymer waste streams with real situations in mind, their relative performances should ideally include compatibilisation. This approach has been taken by both Kallel and co-workers [39], and Bertin and Robin [40], the latter using actual waste polymers. 

In judging polymer blending performance in single screw extruders, the important role played by screw speed should also be considered. Joshi and co-workers [41] found an optimum screw speed was dictated by shear rates and residence time. 

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