Ethylene dielectric loss constant

Figure 15. Dielectric loss data of poly(ethylene-co-vinyl acetate) (EVA, with 70 wt% vinyl acetate) at various combinations of temperature and pressure as indicated to demonstrate the invariance of the dispersion of the a-relaxation at constant a-loss peak frequency va or equivalently at constant a-relaxation time tx.

The term s tan <5 is called the loss factor, and is not the same as the dissipation factor. Materials with a high s tan S are suitable for high-frequency-field heating, i.e., they can be welded in a high-frequency field. These materials are not suitable, on the other hand, as insulating materials for high-frequency conductors. Nonpolar plastics such as poly(ethylene), poly(styrene), poly(iso-butylene), etc., have low dielectric constants ( 2-3) and dielectric loss factors (tan (5 = 10 " to 8 x As insulating materials they are of consi-... 

Poly (ethylene terephthalate) (PET) is one of the most common polymers provided by the polymer industry for fiber and packaging purposes [24]. As far as polymer crystallization is concerned, PET can be considered as a paradigm of a crystallisable polymer due to the fact that PET can be obtained either in the amorphous state or with a controlled amount of ciystalUnity. Therefore, PET has been used to study the influence of crystallinity in a great variety of physical properties including thermal behavior [16,25-29], structure development [30-33] and mechanical and dielectric behavior among others [13,14,34,35]. Figure 21.7 presents the dielectric loss, e", and dielectric constant, e, for amorphous PET at T > 7 as a function of frequency for different temperatures. 

UV irradiation causes changes in the electrical properties of poly(ethylene terephthalate) [1040]. Irradiation results in decreases in the relative dielectric constant and dielectric strength, whilst the dielectric loss factor is increased. 

Dielectric measurements (relative dielectric constants, dielectric strength and dielectric loss factor) have been made for photodegraded polyethylene [1284], polystyrene [840, 2227, 2228, 2248] poly(ethylene terphthalate) [1040], polyamides and polyimides [120] and polycarbonates [1738]. 

Examples of fluoroplastics include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), ethylene—chlorotrifluoroethylene (ECTFE), ethylene—tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVDF), etc (see Fluorine compounds, organic). These polymers have outstanding electrical properties, such as low power loss and dielectric constant, coupled with very good flame resistance and low smoke emission during fire. Therefore, in spite of their relatively high price, they are used extensively in telecommunication wires, especially for production of plenum cables. Plenum areas provide a convenient, economical way to run electrical wires and cables and to interconnect them throughout nonresidential buildings (14). Development of special flame-retardant low smoke compounds, some based on PVC, have provided lower cost competition to the fluoroplastics for indoors application such as plenum cable, Riser Cables, etc. 

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