Resins, properties volume resistivity

The ionic chemical species resulting ffom the manufacturing process affects the antistatic properties of PVC. Tlius, emulsion polymers have better antistatic properties in comparison with relatively clean suspension and more clean mass process resins. The volume resistivity of pure PVC is about lO" -lO ohm-cm, whereas depending upon the application, lower values are desirable, therefore, antistatic properties are improved by compounding. Typical examples of some antistats used in PVC conqxiunds areas follows ... 

Electrical, electronic, and technical appHcations use polycarbonates for a variety of purposes. The woddwide market is about 156,000 t aimuaHy. Because of exceHent electrical properties (dielectric strength, volume resistivity), and resistance to heat and humidity, polycarbonate is used for electrical connectors (qv), telephone network devices, oudet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin has been largely supplanted by blends of polycarbonate with ABS. OveraH, however, the total use of polycarbonate continues to increase. 

The volume resistivity of polytetrafluoroethylene remains unchanged even after a prolonged soaking in water, because it does not absorb water. The surface arc-resistance of PTFE resins is high and is not affected by heat aging. They do not track or form a carbonized path when subjected to a surface arc in air [39]. The electrical properties of PTFE are summarized in Table 3.6. 

The DC properties of anti-static epoxy GFR pipes The use of glass-fibre reinforced (GFR) epoxy resin pipes is, especially in tankers, hampered by the bad electrostatic properties of these pipes. The possibility to decrease the volume resistivity to an acceptable level using only a small amount of carbon black (see 5.3.2) resulted in the development of the WAVIMAR anti-static GFR pipe system by Wavin BV. This pipe system is based on a liquid DGEBA/MDA (100/27) and cured for two hours at 120°C, containing about 1.5 %wt. (on the resin phase) of Ketjen black EC-2000 carbon black. The specific volume resistivity of a sample of such a pipe was measured as a function of the direction, the field strength and the pipe wall thickness. 

Retaining a high electrical volume resistivity in the presence of moisture is one of the most important properties of moulding powder resin systems which are used for the encapsulation of electronic components. 

Kaolin or clay, its more common name, is a naturally occurring mineral with the chemical formula Al Si, 0, (OH)5. It has a plate-like structure, and is refined and treated for specific uses, the largest of which is the paper industry. Metakaolin, produced by the dehydroxylation of kaolin, is often used to improve the electrical properties of PVC wire and cable compounds. At loadings of about 30 weight percent of the resin in a wire and cable PVC formulation, a doubling of the volume resistivity can be achieved. 

BS 4618, Recommendations for the Presentation of Plastics Design Data. Part 2. Electrical Properties, Section 2. 3 Volume Resistivity Section 2.4 Surface Resistivity (London, 1975) BS 5102, Phenolic Resin Bonded Paper Laminated Sheets for Electrical Applications (London, 1974) BS 5762, Methods for Crack Opening Displacement Testing (British Standards Institution, London, 1979)... 

Allylic monomers are sometimes used with alkyds to produce polyesters, with the orthophthalate resin being the most widely used because of its lower cost and very low water vapor pressures. Alkyd-diallylphthalate copolymers have significantly lower exotherm than an alkyd-styrene copolymer. The electrical properties of allylic resins are excellent and the variations of dissipation factor, dielectric constant, and dielectric strength with temperature and frequency are given in Figs. 2.12 and 2.13. The surface and volume resistivities remain... 

Table 10.8 shows electric strengths. Table 10.9 shows volume resistivities, Table 10.10 shows dielectric constants, and Table 10.11 shows dissipation factors for coatings using most of the available resins. Magnet wire insulation is an important use for organic coatings. National Electrical Manufacturer s Association (NEMA) standards and manufacturers trade names for various wire enamels are shown in Table 10.12. This information can be used to guide the selection of coatings. However, it is important to remember the aforementioned warnings about blends of various resins and the effects on performance properties.

It can be seen in Table 4.3 that electrical properties cover a wide range and thus the volume resistivity of various polymers is between 2 ohm.cm for epoxy resins to 10 ohm.cm for fluorinated ethylene-propylene copolymer. Similarly, dielectric strength is in the range from 12 mV/m for urea-formaldehyde resins to 55 mV/m for fluorinated ethylene-propylene copolymer and 60 mV/m for PA 12. 

The fact that plastics are good insulators does not mean that plastics are inert in an electrical field. They can in fact, be made to conduct electricity by the addition of fillers such as carbon black and metallic flake. The type and degree of interaction depends on the polarity of the basic resin material and the ability of an electrical field to produce ions that will cause current flows. In most applications for plastics, the intrinsic properties of the polymer are related to the performance under specific test conditions. The properties of interest are the dielectric strength, the dielectric constant at a range of frequencies, the dielectric loss factor at a range of frequencies, the volume resistivity, the surface resistivity, and the arc resistance. The last three are sensitive to moisture content in many materials. These properties are determined by the use of standardized tests described by ASTM (Table 16-1). These properties of the plastics are temperature dependent as are many of their other properties. Temperature dependence must be recognized to avoid problems in electrical products made of plastics. 

Uses. Furfuryl alcohol is widely used as a monomer in manufacturing furfuryl alcohol resins, and as a reactive solvent in a variety of synthetic resins and appHcations. Resins derived from furfuryl alcohol are the most important appHcation for furfuryl alcohol in both utihty and volume. The final cross-linked products display outstanding chemical, thermal, and mechanical properties. They are also heat-stable and remarkably resistant to acids, alkaUes, and solvents. Many commercial resins of various compositions and properties have been prepared by polymerization of furfuryl alcohol and other co-reactants such as furfural, formaldehyde, glyoxal, resorcinol, phenoHc compounds and urea. In 1992, domestic furfuryl alcohol consumption was estimated at 47 million pounds (38). 

Although these resins have been on the market for a number of years, volumes and appHcations remain low in spite of favorable properties including high temperature resistance, excellent wear and friction properties, good electrical properties, chemical inertness, and inherent nonflammability. ProcessibiHty and price may be the limiting factors. 

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

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