Nylon dielectric properties

Moisture has, in itself, usually not much effect on polymer properties, though the amount of moisture which can be absorbed by polymers varies within wide limits (between zero and a few %). Logically, the electric properties such as resistivity and dielectric losses are the most sensitive to water. As to mechanical properties, nylons show the strongest dependence on water absorption. PA-6 is able to take up a... 

Brassylic acid, a 13-caihon saturated dibasic acid, can be derived from the oxidative cleavage of erucic acid and used as a feedstock for the production of nylon (Scheme 1). Brassylic acid is made by ozonolytic cleavage of erucic acid in acetic acid followed by oxidation of the resultant aldehyde by oxygen at elevated temperatures (100°C) to give the diacid. Crystallization from toluene gives a polymer-grade brassylic acid (6). Pilot-scale production of nylon-1313 (7) as well as nylon-613 was found to have exceptionally low sensitivity to moisture, excellent dimensional stability. and dielectric properties. Long-chain nylons of this type have found niche markets in automotive parts. 

It is interesting to mention that the first truly synthetic (not based on natural products) polymer material was bakelite obtained in 1907 via polycondensation of phenol and formaldehyde. This material had good dielectric properties and was used mainly as an electrical insulator. The most famous polycondensation polymer is probably nylon belonging to the class of polyamides. Other common classes of polycondensation polymers are polyesters (like polyethylene terephthalate), polysiloxanes, polycarbonates, polysulfides, polyethers and polyimides. 

Bose, S., Raghu, H., and Mahanwar, P.A. (2006) Mica reinforced Nylon-6 - effect of coupling agent on mechanical, thermal and dielectric properties. J. Appl. Polym. Sci., 100, 4074-4081. 

Nuriel H, Kozlovich N, Feldman Y and Marom G (2000) The dielectric properties of nylon 6,6/ aramid fiber microcomposites in the presence of transcrystallinity. Compos Part A 31 69-78. 

Noda, N. Lee, Y.-S. Bur, A.J. Prabhu, V.M. Snyder, C.R. Roth, S.C. McBrearty, M. Dielectric properties of nylon 6/clay nanocomposites from on-line process monitoring and off-line measurements. Polymer 2005, 46, 7201-7217. 

Numerous account of the dielectric properties of partially crystalline polymers are available [3,12,14,17,44,45]. Two classes partially crystalline polymers are important, those (rf hi crystallinity, such as polyethylmre, i-polypropylene and polyoxymethylene, and those having only a medium degree of crystallinity, such as the nylons and polyethylene terephthalate (up to 50% crystallinity). Multiple relaxations are observed, e.g. lightly oxidized and lightly chlorinated polyethylenes have, in descending order of temperature, and relaxations. 

They exhibit excellent dielectric properties over a wide range of frequencies and temperatures. PPE/ PS alloys are supplied in flame-retardant, filled and reinforced, and structural foam molding grades. PPE can also be alloyed with polyamide (nylon) plastics to provide increased resistance to organic chemicals and better high-temperature performance. 

In terms of environmental exposure, water and humidity must be carefully evaluated in electrical applications. In general, if a plastic absorbs a significant amount of water, the electrical resistivity drops. As examples this is the case for nylons and phenolic. Care must be used in selecting a dielectric to insure that the electrical properties such as the insulation resistance and dielectric strength, as well as other electrical properties are adequate under the conditions of field use, particularly if this involves exposure to high humidity conditions. Temperature also causes changes in most electrical products. 

Electrooptical properties will be covered only briefly. Fluorocarbons find widespread utility in altering electrooptical properties of coatings. These properties are to be considered as derived from bulk properties of the fluorocarbon. In that regard, fluoropolymers are the most often selected. It is known from Eq. (2) that the electrooptical properties of fluorocarbons can be linked directly to the nature of the C—F bond (a oc n and e <=< n ). It is instructive to consider some relevant values. The dielectric constants e of PTFE, PE, and nylon-6,6 have been determined to be 2.1 (60 Hz-2 GHz), 2.2-2.3 (1 kHz), and 3.6-3.0 (100 Hz-1 GHz), respectively. The dielectric constants for PE and PTFE are comparable. The explanation can be found by comparing segmental polarizabilities a for groups with C—F bonds versus those with C—H bonds, as shown in Table 4.1. They are nearly identical. As e is related to a, it is not surprising that PE and PTFE have similar dielectric constants. The value of e for nylon-6,6 is included above for comparison. 

Nearly every polymeric system absorbs some moisture under normal atmospheric conditions from the air. This can be a difficult to detect, very small amount as for polyethylene or a few percent as measured for nylons. The sensitivity for moisture increases if a polymer is used in a composite system i.e. as a polymeric matrix with filler particles or fibres dispersed in it. Hater absorption can occur then into the interfacial regions of filler/fibre and matrix [19]. Certain polymeric systems, like coatings and cable insulation, are for longer or shorter periods immersed in water during application. After water absorption, the dielectric constant of polymers will increase due to the relative high dielectric constant of water (80). The dielectric losses will also increase while the volume resistivity decreases due to absorbed moisture. Thus, the water sensitivity of a polymer is an important product parameter in connection with the polymer s electrical properties. The mechanical properties of polymers are like the electrical properties influenced by absorption of moisture. The water sensitivity of a polymer is therefore in Chapter 7 indicated as one of the key-parameters of a polymeric system. 

The maximum use temperature is a term coined by the US organization. The Underwriters Laboratory, and it is the maximum temperature at which a polymer can be used continuously, under low stress conditions, with the loss of no more than 50% of the original useful properties (tensile and impact strength, for example, or dielectric strength in the case of cable insulation). For the engineer unfamiliar with plastics, the low values of typical maximum use temperatures can come as a shock. For example, glass-filled nylon 6,6 has a heat distortion temperature of 252°C, but the resin can embrittle as a result of thermal oxidation within 2 h at 250°C. Even at 70°C, embrittlement will still occur within two years [1]. 

---