Equipment, compounding

In many cases, rework material is also fed to the compounding extruder. 

TABLE 14.1 Typical Form of Ingredients for Componnding Syndiotactic Polystyrene Formnlations 

Liquid ingredients are normally added with a gear pump having a proportional-differential flow meter. 

Fibrous additives are generally introduced to the compounding extruder with loss-in-weight single- or double-screw feeders that feed into the side of the compounding extruder at a point the resin is already melted. The feed system must minimize glass movement to avoid fiber attrition. Vibratory trays should not be used for fibrous additives. 

3 Pelletizers The extrudate from the compounding extruder is pelletized. These pellets are then used to feed customer polymer processing equipment to make final products. Pelletization can be accomplished through chopping strands or underwater die face cutting the extrudate [4], The technical considerations for strand-cut pelletizers are summarized in the next section. 

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and me. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

---

Alternative processes for polymer isolation have involved direct dmm drying of latex (84), extmsion isolation of coagulated cmmb (85), and precipitation/drying or spray-drying of the mbber as a powder (86). The powder can be processed directly in continuous compounding equipment (87). The manufacture and use of powdered CR has been reviewed (88). 

Basic materials such as lime or magnesium oxide increase the hardening rate of novolak-hexa compositions and are sometimes referred to as accelerators. They also function as neutralising agents for free phenols and other acidic bodies which cause sticking to, and staining of, moulds and compounding equipment. Such basic substances also act as hardeners for resol-based compositions. 

It is possible to translate the symbolism of the scissors and its basic structure into the field of molecules (cf. Fig. 11 b). Indeed, the scissor-shaped bulky binaphthyl compound equipped with two appending carboxy groups 1 (l,l -binaphthyl-2,2 -di-carboxylic acid, Fig. 11 c), as mentioned at the beginning (Sect. 1), strictly meets the general structure of an assumed coordinatoclathrate host (cf. Fig. 7). Also, the compound is in keeping with the considerations on an expectedly favorable lattice build-up (see Sect. 3.1). For checking, the crystal inclusion properties of 1 were studied in detail2). 

Todd, D. B. (ed) Plastics Compounding Equipment and Processing. (1998) Hanser Gardner Publications, Cincinnati. 

When Mark and Brill began using their X-ray equipment to investigate the lattice structure of metals, and simple organic and inorganic compounds, equipment Mark has since described as an air filled X-ray tube, a ruler, and a log table, they were early students of an infant analytical technique. 

Black, T., Single-Screw Compounding, in Plastics Compounding Equipment and Processing, Todd, D.B. (Ed.), Hanser Publishers, Munich (1998)... 

Canedo, E.L and Valsamis, E.N., Selecting Continuous Compounding Equipment Based on Process Considerations, Int. Polym. Process., 9, 225 (1994)... 

To broaden the scope of his interests, he spent another year as a postdoctoral fellow in the Physics Department of Pennsylvania State University, working on the X-ray analysis of biological compounds. Equipped with an exceptionally broad and multidisciplinary education and experience, he proceeded to The Ohio State University, Columbus, Ohio, to work with Professor M. L. Wolfrom. His initial job was to investigate the ignition of cellulose nitrate, a project left over from World War II. In Fred s hands, this project was turned into an isotopic investigation of the biosynthesis and degradation of cellulose. At this time, there was very little known about the preparation of specifically labeled sugars, let alone the biosynthesis of... 

Fig. 10.4 Hexalobal, intermeshing, counterrotating twin-screw mixing screw elements. [Reprinted by permission from W. C. Thiele, Counterrotating Intermeshing Twin Screw Extruders, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

Fig. 10.6 The single-stage FCM. (a) Size 15 FCM with chamber opened and rotated hydraulically (b) top view of staged apex twin rotors and the axial zones for carrying out the solids feed handling and the melting and mixing elementary steps (c) cross-sectional view of two rotor orientations, tip-to-tip (cx) and tip-to-flat (c2). [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Farrel Continuous Mixer Systems for Plastics Compounding, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

Fig. 10.10 (a) Top and side views of a pair of full-bore blister rings (orifice plugs), and (b) schematic of the Todd barrel valve and barrel cross sections in the fully open and closed positions there is a bypass channel in the barrel immediately above the intersection of the blister rings and the barrel valve is rotatable in this bypass channel to vary the restriction of flow. [Reprinted by permission from D. B. Todd, The APV (Baker Perkins) Systems, in Plastics Compounding— Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]... 

The effect of additives and modifiers on product properties will not be discussed here because it is beyond the scope of this textbook. We must emphasize, however, that the ultimate objective of compounding additives and modifiers in polymer matrices is to obtain specific multicomponent and multiphase structures and morphologies needed to obtain certain desired product properties. We will only discuss their effects on the compounded systems rheology and, mainly, the shear flow viscosity, and their effects on compounding equipment and processes. 

Let us now turn to the question of the consequences of the previously discussed rheological behavior to polymers compounding operations. In continuous compounding equipment we have to answer this question for each of the elementary steps involved. 

---