Thermoplastic injection molding and

The diversity of release products and the wide range of release problems make classification difficult. One approach is by product form, with subdivisions such as emulsions, films, powders, reactive or inert sprays, reactive coatings, and so on. Another approach is by application, eg, metal casting, mbber processing, thermoplastic injection molding, and food preparation and packaging. 

Other processes deal with thermoplastics that are melted to a liquid state and then pushed throngh channels into a closed mold. Thermoplastic injection molding and all of its derivative processes use this approach to produce parts. Melted thermoplastics are normally thicker or have a higher viscosity or resistance to flow than the hquid components found in the RIM or LIM processes and require higher pressures to process. Therefore, it is difficult if not impossible to push the materials fast enough to achieve turbulent flow conditions. 

Recycling of HDPE. Polyolefins, including HDPE, are the second most widely recycled thermoplastic materials after PET (110). A significant fraction of articles made from HDPE (mostly bottles, containers, and film) are collected from consumers, sorted, cleaned, and reprocessed (110—113). Processing of post-consumer HDPE includes the same operations as those used for virgin resins blow mol ding, injection molding, and extmsion. 

Fig. 19. Typical injection molding and reaction injection molding (RIM) machines (a) injection molding machine for thermoplastics (b) reaction injection molding machine, showing A, the closed position, where reagents circulate, and B, the open position, where reagents are mixed and dispensed to mold.

One type of block polymer is known as thermoplastic elastomers. They consist of a number of rubber blocks tied together by hard crystalline or glassy blocks. These materials can be processed in injection molding and extrusion equipment since the crystalline blocks melt or the glassy ones soften at high temperatures. However, at lower temperatures, such as at room temperature, the hard blocks behave very much as cross-links to reduce creep and stress relaxation. Thermoplastic elastomers have creep behavior between that of very lightly cross-linked rubbers and highly cross-... 

The primary crystalline polymer based on CHDM is the terephthalate, poly(1,4-cyclohexylenedimethylene terephthalate) (PCT). This polyester was originally developed for fiber applications but has since found wider utility as a reinforced polymer for injection molding and (when copolymerized with a small amount of isophthalic acid) as a material for crystallized food packaging trays. The key property of PCT which sets it apart from other thermoplastic polyesters in these latter applications is its melting point. 

Fig. 6.8. Fracture toughness, K, of short glass fiber-thermoplastics injection molded composites as a function of weight fraction of fiber, fVr. (O) and (A) polyethylene terephthalate (PET) matrix ( ) and (A) polycarbonate (PC) matrix. Notches made transverse (O, ) and parallel (A, A) to the mold fill direction,...

These moldable thermoplastic polyesters are marketed under the trade names Celanex, Tenite, and Valox. These highly crystalline thermoplastics may be extruded or injection molded and may also be reinforced by fiberglass. 

The processing and applications of FIFE as described in the first edition of this book are essentially unchanged All the fluoroplastics described, with the exception of FIFE and PVF, can be processed by conventional thermoplastic techniques such as injection molding and extrusion [7, 30]... 

The organic cellulose ester plastics are versatile materials and can be processed by almost any hot-processing technique used for thermoplastics. The principal techniques for all three plastics are injection molding and extrusion. Blow molding is also possible. Butyrate and propionate powder are used in tluidized-bed and electrostatic coating processes, as well as in the rotational molding process. 

The poly(vinylidene chloride-cu-vinylchloride) may be injection molded and extruded. Extruded pipe and molded fittings which were produced in large quantity in the 1940s have been replaced to some extent by less expensive thermoplastics. A llal extruded filament is used for scouring pads and continuous extruded circular filament is used for the production of insect screening, filter clothes, fishing nets and automotive seat covers. 

TABLE 13.2 Comparison between Typical RIM and Thermoplastic Injection Molding (TIM) ... 

Thermoplastic polyurethane elastomers are processed by injection molding and other processes used for thermoplastics. Small gears, seals, and even automotive fender extensions can be produced by this means. 

THV fluoroplastics can be processed by virtually any method used generally for thermoplastics, including extrusion, coextrusion, tandem extrusion, blown film extrusion, blow molding, injection molding, and vacuum forming, and as skived film and solvent casting (only THV 220). 

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