Processing, thermoplastics extrusion

VAE, a copolymer of vinyl acetate with minor amounts of ethylene is used as an adhesive for paper, plastics and leather and as a binder for different paints. Shoes, tubes, toys and other articles of daily use also contain VAE polymers. The hydrolysis product of VAE polymers, EVOH, is a thermoplast and can therefore be processed by extrusion and injection moulding and is used as barrier polymer for O2 and CO2 (e.g. in packaging applications). 

Thermoplastic extrusion technology has been used to texturize many defatted vegetable protein ingredients, and produce many fibrous structures and meat-like textures. Such processes have been used extensively to prepare meat analogs (1, which have found their widest application in formulation of foods for institutional markets (3). A primary disclosure of extrusion texturization of vegetable proteins was made by Atkinson ( ). General descriptions of various extrusion processes have also been reported (1, 5-14). ... 

Polycarbonates. Polycarbonates (qv) are pardy crystalline thermoplastics with some disorder in the crystalline part and considerable order in the amorphous part. This disorder conveys high impact strength which, combined with its good transparency and outdoor exposure resistance, makes polycarbonates useful for vandal-resistant glazing and outdoor lighting. It is easily processed by extrusion and injection molding. Various uv and flame-retardant agents are often added. 

Ethyl cellulose (EC) is a water-insoluble cellulose ether. It is produced by reaction of alkali cellulose with ethylene chloride. It has film-forming and thermoplastic properties. As a plastic, it can be processed by extrusion and injections. It is hard, stiff and with good resistance to impact. It is soluble in the molten state with other thermoplastics. As for its film-forming properties, it is used in the formulation of varnishes, inks and glues. It forms removable coatings. 

Thermo set as well as thermoplastic and elastomer binders are used in compression, injection and calendaring process respectively. Extrusion moulding uses elastomers as well as thermoplastic materials such as PVC. Compression and injection moulding processes make only rigid magnets, calendaring makes flexible magnets and extrusion can lead to both states. 

Normal stress differences also have practical relevance for extrusion They assist in centering the shaft in the extruder when processing thermoplastics as the rotation of the screw generates radial forces (from the shaft to the wall). 

Thus, prepolymer processing contrasts sharply with thermoplastic processing. Thermoplastics are polymerized to completion during the plastics manufacture. The fabricator apphes heat and pressure by means of extrusion, injection molding, or calendering to produce the finished article. 

PHB can be processed like a conventional thermoplastic in most industrial transformation processes, including extrusion, injection molding, and thermo-pressing [26, 27]. 

These demonstrations of melt processability for PAn provide an avenue for the convenient preparation of films and fibers of CEPs. The absence of solvent makes the melt-processing route more attractive and environment-friendly than alternative solvent processing. In addition, the melt-processable CEPs are then easily incorporated into polymer blends using the well-developed processing techniques (extrusion and so on) widely used for thermoplastic polymers. 

Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity. 

Although the concept of the molecular composite was demonstrated by the work on PBT/ABPBI, the resulted composite was not melt-processible since the melting points (if there is one) of the two component polymers are well above 800 °C. Efforts were then put on systems with a thermoplastic polymer as the matrix. One such system was PBT/nylon 66 (Chuah et al, 1987). Thus, the PBT/nylon 66 in different ratio was dissolved in methane sulphonic acid to make 2 wt-%-3 wt-% (rapid coagulation into thin films. The films were optically clear and did not show gross phase separation in... 

Polyolefin - Polyolefins are a large class of carbon-chain elastomeric and thermoplastic polymers usually prepared by addition (co)polymerization of olefins or alkenes such as ethylene. The most important representatives of this class are polyethylene and polypropylene. There are branched and linear polyolefins and some contain polar pendant groups or are halogenated. Unmodified polyolefins are characterized by relatively low thermal stability and a nonporous, nonpolar surface with poor adhesive properties. Processed by extrusion, injection molding, blow molding, and rotational molding. Other thermoplastic processes are used less frequently. This class of plastics is used more and has more applications than any other. Also called olefinic resin, olefinic plastic. 

Typical thermoplastic binders which are found in literature for injection molding of ceramic bodies are, styrene-butadiene, polyethylene, polypropylene, polybutene, ethylene vinyl acetate, polymethylmethacrylate and polyoxymethylene. When selecting one of these binders for thermoplastic extrusion of ceramic bodies, it should be noted that the shrinkage of par-tially-crystalline polymers is higher than for amorphous polymers, and hence warping during cooling is more critical in the former case. This is, however, not the only criterion for selection price and processability at adequate temperatures are also important factors to consider. 

Generally for the thermoplastic extrusion of ceramic bodies, a binder which melts or softens at higher temperature is used. Figure 3 shows the processing steps for the extrusion of ceramic bodies when using thermo-... 

Fig. 3 Process schematic for thermoplastic extrusion of ceramic bodies at EMPA. Depending on the process requirements in other applications of thermoplastic extrusion, the high shear mixer and single-screw extruder shown here can be replaced with pieces of equipment which have other operating principles, but perform the same function.

Acrylate Styrene Acrylonitrile Polymer Acrylic rubber-modified thermoplastic with high weatherability. Acrylate Styrene Acrylonitrile Polymer has good heat and chemical resistance, toughness, rigidity, and antistatic properties. Processed by extrusion, thermoforming, and molding. Used in construction, leisure, and automotive applications such as siding, exterior auto trim, and in outdoor furniture. 

Acrylonitrile Copolymer A thermoplastic prepared by copolymerization of acrylonitrile with small amounts of other unsaturated monomers. Has good gas barrier properties and chemical resistance. Processed by extrusion, inj ection molding, and thermo forming. Used in food packaging. 

Low Density Polyethylene A branched-chain thermoplastic with density 0.91-0.94 g/cm. Has good impact strength, flexibility, transparency, chemical resistance, dielectric properties, and low water permeability and brittleness temperature, but poor heat, stress cracking, fire resistance, and weatherability properties. Processed by extrusion coating, injection and blow-molding, and film extrusion. Can be cross-linked. Used in packaging and shrink films, toys, bottle caps, cable insulation, and coatings. Also called LDPE. 

Olefinic Thermoplastic Elastomers Blends of EPDM or EP rubbers with polypropylene or polyethylene, optionally eross-linked. Has low density, good dielectric and mechanical properties, and processibility but low oil resistance and high flammability. Processed by extrusion, injection and blow-molding, thermoforming, and calendering. Used in auto parts, construction, wire jackets, and sporting goods. Also called TPO. 

Polyamides Thermoplastic aromatic or aliphatic polymer of dicarboxylic acids and diamines, of amino acids, or of lactams. Has good mechanical properties, chemical resistance, and antifriction properties. Processed by extrusion and molding. Used in fibers and molded parts. Also called PA. 

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