Single-screw extruder, blending

In preliminary tests, melt mixed blends of PP and LCP were processed at six different temperatures (Tcyi 230, 240, 250, 260, 270, and 280°C) with a Brabender Plasti-Corder PLE 651 laboratory single-screw extruder. The measured melt temperatures were about 10°C higher than the cylinder temperatures (Tcyi). The objective was to study the influence of temperature on the size and shape of the dispersed LCP phase. Two different polypropylenes were used to ascertain the effect of the viscosity of the matrix on the final morphology. Different draw ratios were obtained by varying the speed of the take-up machine. 

The blends prepared by twin-screw extruder with two different draw ratios were extruded with the Brabender single-screw extruder at temperatures ranging from 180 280°C, The sample designation and specific processing conditions are given in Table 1. 

Figure 2 Optical micrographs of melt mixed PP-LCP blends single-screw extruded at melt temperatures of (a) 250°C, and (b) 260°C.

Extruded Model System. For this investigation, 100 parts zein, 40 parts corn amylopectin and 5 parts corn oil were blended thoroughly, and water was added at 307. of the total dry weight. Volatiles collected from extruded samples of this model system were compared to volatiles from the same system heated in an oven for 30 minutes at 120°C or 180°C and to volatiles from extruded samples of zein with 30% added water. The extruded samples were prepared on a C. W. Brabender single-screw extruder, type 2003, with a barrel diameter of 1.9 cm and an L/D ratio of 20 1. The first heating zone of the barrel was held at 60°C, and the second was set at either 120°C or 165°C. The die diameter was 6.5 cm. 

Bastioli et al.172 claimed expanded articles from extruded compositions of starch, mixtures of EAA and EVOH copolymers, and an inorganic carbonate. Typically, the synthetic copolymers comprised 20-40% of the composition. Preferred extrusion temperatures were in the range 180°C to 210°C. Extrusion of a typical blend in a single-screw extruder at a temperature of 180°C produced a closed cell foam with a density of approximately 1.2 lb/ft3 (19kg/m3). 

Several liquid cryatalline polymers were melt blended with an amorphous (Ultem) and two semicrystalline (PEEK and PPS) engineering thermoplastics in a single screw extruder. Flat film was processed with different degrees of stretch imparted while the film was being cooled. In the case of Vectra, which was thought to be ideally suited to be blended with PPS based on thermal and rheological... 

PP/EVAl blends with lamellar morphology were produced either in a single screw extruder with a specially designed die [Lohfink and Kamal,... 

The single-screw extruders are being used for the preparation of blends that either do not require... 

In the LDPEIPIB blend (Lupolen 250H), a LDPE with relatively low branching density (higher crystallinity) is used. Thus both LDPE and PIB have similar densities. The extruded parts are less transparent and glossy than those made of neat LDPE. All-purpose 3-zone screws with L/D = 18 to 22 was found suitable for processing. Standard practice favors single screw extruders with barrels of 25 to 200 mm. 

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. 

Shujum et al. described compatible TPS/LLDPE blends, produced by one-step reactive extrusion in a single-screw extruder. Maleic anhydride (MAH), and dicumyl peroxide (DCP) were used to graft MA onto the LLDPE chain [88]. 

Single-screw extruders have been widely used for blend preparation however, they do not offer sufficiently high stress levels to improve mixing thus, special designs of screws have been developed such as those with mixing heads or barrier zones that increase residence time and enhance blend mixing. 

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