Extrusion direct

Recently, it has been proposed that direct extrusion processing may be a far better alternative for the blend preparation. It has various advantages, such as a one-step fabrication process, a reduction of the production... 

Direct extrusion of methyl nitrene has been discounted as an explanation of these deamination reactions, which are apparently induced by attack of the acetylenic ester and thus more likely take place via an intermediate analogous to 176. On the other hand, the products from pyrolysis of 107 at 325° include 1,2,3,4-tetrafiuoronaphthalene (132) and hydrogen cyanide, and it was suggested that methyl nitrene was the precursor of the latter compound (see Section III,D). The adduct (180) of tetrafiuorobenzyne and thiophen extrudes sulfur so readily... 

Figure 7.12 Schematic illustration of direct extrusion of a metallic biUet. From Z. Jastrzebski, The Nature and Properties of Engineering Materials, 2nd ed. Copyright 1976 by John WUey Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Side vents are often used with polymers for optical applications (PC, PMMA, PET), direct extrusion of high quality films (PET), or for fiber spinning (PA) they ensure that condensate or degraded polymer cannot re-enter the product flow of the ZSK (see Fig. 10.12). 

Figure 10.19 System diagram for direct extrusion of non-pre-dried PET to produce a cast film...

The analogous large-volume series ZSK MEGAvolume with 8.7 Nm/cm3, a diameter ratio of 1.8, and screw speeds of up to 1800 rpm is used for compounds with a high solid matter content, such as those often found in the chemical/food/pharmaceutical industries. The maximum speeds of up to 1800 rpm are used mainly for low-viscosity products, such as pressure-sensitive adhesives and silicon sealants because they provide better elastomer and filler dispersion. Other processes often require large volume only and operate at very moderate speeds of 100 to 600 rpm to protect the product or for direct extrusion into films, sheets, or profiles. 

Typical applications for products and processes with high and low torque requirement are shown in Fig. 14.9. Typical uses of high torques are reinforcing and alloying of engineering plastics and compounding and pelletizing of polyolefin powders into polyolefin pellets, or direct extrusion of films. Low torques are used for products that are shear-sensitive or difficult to feed, such as those often found in the chemical/food/pharmaceutical industries. 

The relationships shown in Fig. 14.11 were experimentally determined for direct extrusion of non-dried PET with two vacuum zones at 5 mbar absolute pressure the 20% torque increase in the ZSK Me PLUS may be used to halve hydrolytic degradation at the same throughput or to increase throughput by 75% by additional speed increases while maintaining the same quality. The same process was successfully transferred to non-dried PLA. 

Figure 14.11 Use of a 20% torque increase to increase quality or throughput in direct extrusion of non-dried PET...

Figure 14.25 Example of a line for direct extrusion of cast film made from non-dried PLA...

Extrusion can fall into one of two categories direct extrusion and indirect extrusion (Figure 7.17). In direct extrusion a metal billet is placed into a container and driven though a die by a ram, usually attached to a hydraulic press. In indirect extrusion the billet is again placed in a container, but the container end is closed. A hollow ram, carrying a die of the desired shape, is forced into the billet, with the extrusion exiting through the ram Indirect extrusion may occur as a result of die movement or container movement. Because there is no movement between the container wall and billet surface, frictional forces are lower in this method, which reduces the force needed to extrade. There are, however, some limitations on the load that can be applied by the hollow ram. 

Figure 7.17 (a) Direct extrusion process where billet moves against a stationary die by a moving ram (b) indirect extrusion, where the billet is fixed in a container and the die is at the end of a hollow, moving ram. 

Monofilament polypropylene fibres were prepared by direct extrusion having a rectangular cross section of 0.5 x 1.3 mm, a length of 40 mm, a specific gravity of 0.91, a tensile strength of 120 MPa, and an elongation at break of 14%. The fibers were placed under 18% humidity at ambient temperature air and then treated with 20% F2 and 80% N2 at apressure of 45 kPa at 38°C for 2.5 hours. Thereafter the reaction vessel was evacuated, and the product was isolated. 

Downstream equipment generally involves a vacuum pump, for devolatilization, and pelletizing hardware. Strand pelletizers are located at the end of a water trough, while hot-face pelletizers cut the extrudate immediately upon die exit. When direct extrusion... 

Photolytic decomposition of a diethyl ether solution of 3-methyl-3-phenyldiazirine (7) in the presence of A -methylmaleimide afforded cyclopropanated products 9 and 10 via an alkylcar-bene intermediate 8 by direct extrusion of nitrogen." Phenyldiazomethane was involved as an intermediate when the photolytic decomposition of 3-methyl-3-phenyldiazirine was carried out in the absence of solvent as shown by the formation of dihydropyrazoles as side products, in addition to cyclopropanated products. 

Tiling, G. Direct extrusion of nylon products from lactams. Modern Plastics 1969, 46 (18), 73 76. 

Weinrich, C. Direct extrusion of wood flour/ plastics composites on conical counterrotating twin screw extruders. In Wood-Plastic Conference, Conference Proceedings, Baltimore, MD, December 5-6, 2000 207-215. 

Paper may also be solvent or aqueous coated, e.g. PVdC, emulsions, varnishes, lacquers, or laminated to plastics by adhesion or direct extrusion or to foils by adhesion, all to form laminates. These laminates containing paper are dealt with in Chapter 9. 

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