Extrusion application

This review is concerned with the engineering thermoplastic uses of polyamide materials in injection moulding and extrusion applications. Types of polyamides are described, and their key properties are considered. Commercial applications in the automotive, electrical/ electronic, engineering and construction, and packaging industries are discussed. Polyamide processing is... 

Molecular weights (number average) in the range of 20 000 to 35 000 [88] are achieved in the melt phase and are used for fibre and engineering plastics applications. For some injection moulding and extrusion applications, molecular weights above 40 000 [88] are required. Such high valves are best achieved by SSP. 

Thomas, N. W Berardinelli, F. M. and Edelman, R., Polycarbodiimide modification of polyesters for extrusion applications, US Patent 4 071 503 (to Celanese Corporation, New York), 1978. 

Depending on the application, different demands are placed on the melt viscosity of the polymer. For injection molding applications, lower melt viscosities are required than for extrusion applications. For a given comonomer composition and processing temperature, the melt viscosity of the cycloolefin copolymers increases with the mean molecular weight. 

At times, low- or high-intensity blending alone can produce a suitable product for use by the fabricator. An example of this would be a polyvinyl chloride (PVC) blend used for several large-volume extrusion applications. More frequently, however, a compounding process is required to obtain the desired physical property. The five primary compounding processes used in the industry for controlling the above parameters are single-screw extrusion (SSE), twin-screw extrusion (TSE), continuous mixers, batch mixers, and kneaders. Table 18.1 summarizes key aspects of each process. 

The use of the Brabender Plasticorder is widespread in the development and quality control of formulations destined to be used in uPVC foam extrusion applications. The morphology transformations associated with the process have been widely studied but the particularities of the application have not often been taken into account - low K-value and high concentration of high molecular weight process aid. This work uses a commercially viable formulation to examine the fusion aspect of the transformation process. Differential scanning calorimetry is used to observe the degree of fusion. 9 refs. 

Products A wide range of LLDPE and HDPE products can be produced. LLDPE is used in film, injection molding, rotational molding and extrusion applications and can be made using either butene or hexene as the comonomer. 

Narrow molecular-weight HDPE provides superior injection molding grades. Broad molecular-weight HDPE is used for blow molding, pipe, film and other extrusion applications. 

Products Polymer density is easily controlled from 0.915 to 0.970 g/cm. Depending on catalyst type, molecular weight distribution is either narrow or broad. Melt index maybe varied from less than 0.1 to greater than 200. Grades suitable for film, blow-molding, pipe, roto-molding and extrusion applications are produced. 

The nucleophilic curing system is most common and is used in about 80% of all applications. It is based on the cross-linker (bisphenol AF) and accelerator (phase transfer catalyst, such as phosphonium or amino-phosphonium salt). Both diaminic and bisphenol type cure systems are permitted by U.S. Food and Drug Administration (FDA) regulations governing rubber articles in contact with food. The diaminic curing system is also used in some coating and extrusion applications [42]. 

Driscoll S B, Nanavaty P, Stockbower D W, Polymer Additives for Injection Moulding and Extrusion Applications. Retec proceedings. White Haven, Pa., 18th-19th Oct.1995, p.161-85. 

Only one other cellulose ether has been marketed for moulding and extrusion applications, benzyl cellulose. This material provides a rare example of a polymer which although available in the past is no longer commercially marketed. The material had a low softening point and was unstable to both heat and light and has thus been unable to compete with the many alternative materials now available. 

Materials. High density polyethylene (HDPE) having different molecular weights, and specific gravity of 0.951 (Marlex 5202, HXM 50100, made by Phillips 66 Co), were used for extrusion applications. Polyamides used were a semicrystalline copolyamide of adipic acid, hexamethylene diamine and caprolactam, and a copolyamide containing isophthalic acid as well. An anhydride modified polyethylene (3-5) as an interlaminar adhesive/compatibilizer was also used. The combinations are generally included in "Selar" barrier materials supplied by E. I. du Pont de Nemours Co. 

Extrusion-Applied Insulations. The polymers used in extrusion applications can be divided into two classes low-temperature applications and high-temperature applications. Polymers in the first category are poly(vinyl chloride), polyethylene, polypropylene, and their copolymers along with other elastomers. Polymers in the second category are mainly halocarbons such as Teflon polytetrafluoroethylene (which requires special extrusion or application conditions), fluoroethylene-propylene copolymer (FEP), perf luoroalkoxy-modified polytetrafluoroethylene (PFA), poly(ethylene-tetrafluoroethylene) (ETFE), poly(vinylidene fluoride) (PVF2) (borderline temperature of 135 °C), and poly(ethylene-chlorotrifluoroethylene). Extrusion conditions for wire and cable insulations have to be tailored to resin composition, conductor size, and need for cross-linking of the insulating layer. 

Nearly all of the dynamically vulcanized EPDM/PP blend s (Santoprene ) growth has been at the expense of thermosetting rubbers due to the blend s easy melt processability and recyclability. Much of this growth has been in automotive applications such as rack and pinion steering boots, seat belt sleeves, and air ducts. EPDM/PP blend has also been used in window and door glazing seals, weather stripping and extrusion applications in the electricaE electronic industry. 

While most of the subjects discussed up to this point involve injection molding or extrusion applications, there are a considerable number of other applications where polymer blend technology is and will be employed including adhesives, sealants, coatings, and thermosetting systems, polymeric membranes, and water-based polymers. 

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