Filled polymers, electrical properties

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

The results of the above section show that the significant nonuniformity of the distribution of the filler particles in the thickness of sample is observed during injection moulding of the filled polymers. This nonuniformity must affect the electrical properties of CCM owing to the strong dependence of the CCM conductivity on the filler concentration. Although there are no direct comparisons of the concentration profiles and conductivity in the publications, there is data on the distribution of conductivity over the cross-section of the moulded samples. 

The Emerman model described in the previous section is hardly applicable to the carbon black-filled CCM as the black particles have sizes of hundreds angstrom and such a composite, compared with the molding channel size, may be considered as a homogeneous viscous fluid. Therefore, the polymer structure, crystallinity and orientation play an important role for such small particles. The above-given example of manufacture of the CCM demonstrates the importance of these factors being considered during processing of a composite material to and article with the desired electrical properties. 

For specialised applications where electrical conductivity is required, such as antistatic flooring or shielding of electromagnetic induction, specific carbon black pigment/filler is used. Copper and nickel metal powders have also been studied (112). A review is available of the electrical properties of polymers filled with different types of conducting particles (416). 

A review is presented of the electrical properties of polymers filled with different types of conducting particles. Following a theoretical description of a general effective media equation, experimental conductivity-volume fraction data for thermoplastic filled with vanadium oxide particles as well as thermosetting polymer composites, were fitted to the equation. The calculated property-related parameters in the equation are discussed. Data are given for PVC, HDPE, LLDPE, LDPE, and epoxy resin. 12 refs. 

Domkin, V. S. Electrical properties of gas-filled polymers. All-Union Seminar on Plastic Foams, Leningrad USSR, 1975 (in Russian)... 

The use of high temperature thennoplastics for electronic applications is of considerable and growing interest because of the enhanced thermal and electrical properties of these materials. One such material is GE s Ultem polyetherimide which can be injection molded as well as extruded. This latter property is important for utilizations such as flexible circuits where a pliable film is required. The inherent physical properties of the polymer can be enhanced through the addition of fillers. A potential disadvantage, however, is that the nascent translucence of the polyetherimide is eliminated. Visual clarity may be desirable in certain applications such as automatic climate control systems wherein an LED must be read through a patterned circuit board. In addition, neat polymer material may be desirable because of its improved flow properties relative to filled polyetherimide. 

For many applications of filled polymers, knowledge of properties such as permeability, thermal and electrical conductivities, coefficients of thermal expansion, and density is important. In comparison with the effects of fillers on mechanical behavior, much less attention has been given to such properties of polymeric composites. Fortunately, the laws of transport phenomena for electrical and thermal conductivity, magnetic permeability, and dielectric constants often are similar in form, so that with appropriate changes in nomenclature and allowance for intrinsic differences in detail, a general solution can often be used as a basis for characterizing several types of transport behavior. Useful treatments also exist for density and thermal expansion. 

Electrical properties such as conductivity, resistivity, I (current)-V (voltage) characteristics of vegetable oil-based polyurethane nanocomposites are sometimes influenced by nanocomposite formation with a suitable nanomaterial. BaTiOs superfine fibre-filled castor oil-modified polyure-thane/poly(methyl methacrylate) interpenetrating polymer network nanocomposites exhibit an increase in conductivity between insulator and semiconductor with an increase in nanofibre loading. ... 

The thermal characteristics of NR-metal composites are close to the properties of metals, whereas the mechanical properties and the processing methods are typical of polymers.Thermally conducting, but electrically insulating, polymer-matrix composites are increasingly important for electronic packaging because the heat dissipation ability limits the reliability, performance and miniaturization of electronics.Thermal properties such as thermal conductivity, thermal dilfusivity and specific heat of metal (copper, zinc, Fe and bronze) powder-filled polymer composites are investigated experimentally in the range of filler content 0-24% by volume. ... 

Mao et al. had tuned the morphology to improve the electrical properties of graphene filled immiscible polymer blends. PS and PMMA blends filled with octadecylamine-functionalized graphene (GE-ODA) were fabricated to obtain conductive composites with a lower electrical percolation threshold. The dependence of the electrical properties of the composites on the morphology was examined by changing the proportion of PS and PMMA. The electrical conductivity of the composites was optimal when PS and PMMA phases formed a co-continuous structure. For the PS/PMMA blend (50 wt/50 wt), the composites exhibited an extremely low electrical percolation threshold (0.5 wt%) because of the formation of a perfect double percolated structure (Mao et al. 2012). 

Dalmas F, Cavaille JY, Gauthier C et al (2007) Viscoelastic behavior and electrical properties of flexible nanoflbre filled polymer nanocomposites. Influence of processing conditions. Compos Sci Technol 67 829-839... 

Paul A et al (1997) Electrical properties of natural fiber reinforced low-density polyethylene composites a comparison with carbon black and glass fiber filled low-density polyethylene composites. J Appl Polym Sci 63 247-266... 

Feng, J. and Chan, C.M. (1998) Carbon black-filled immiscible blends of poly (vinylidene fluoride) and high density polyethylene electrical properties and morphology. Polym. Eng. Set., 38, 1649. 

Gubbels, F., Blacher, S., Vanlathem, E., Jerome, R., Deltour, R., Brouers, F., and Teyssie, Ph. (1995) Design of electrical conductive composites key role of the morphology on the electrical properties of carbon black filled polymer blends. Macromolecules, 28, 1559-1566. 

Bigg, D.M. (1986) Electrical properties of metal-filled polymer composites. Chapter 3, in MeUd-FiBed Polymers Properties and Applications (ed. S.K. Bhattacharya), Marcel Dekker, Inc., New York. 

Addition of small amount of nanofillers may improve the properties of mbber and thermoplastics. In the polymer industry, polymer-filler nanocomposites are a promising class of material that offers the possibility of developing new hybrid materials with desired set of properties. Properties of mbbers and thermoplastics which have shown substantial improvements due to the incorporation of nanoparticles, are mechanical properties, decreased permeability to gases, water and hydrocarbons, thermal stability and heat distortion temperature, flame retardancy and reduced smoke emissions, chemical resistance, surface appearance, electrical and thermal conductivity, optical clarity in comparison to conventionally filled polymers [107]. 

Besides mechanical properties, fillers change the optical and electrical properties, chemical and weathering resistance, flammability and density of polymers. In particular, most fillers destroy optical translucency, unless their refractive index (see Table 4.4) is the same as that of the polymer. Close agreement between the fibre and the polymer refractive index is required for translucency. Feldspar has a refractive index very similar to that of several polymers and so filled, translucent products can be obtained, but it is abrasive to processing equipment. 

Calcium carbonate can be mixed with 0.5 to 1% by weight of stearic acid and subjected to high shear mixing at high temperatures. The stearic acid is converted to calcium stearate in the process. The treatment improves the processability, reduces moisture absorption, and improves the mechanical and electrical properties of the filled polymer. 

Pourabas and Peyghambardoost [53] showed that copper filled epoxy resin composite had electrical conductivity properties. Afzal and co-workers [104] studied the electrical properties of PANI/silver nanocomposites. The silver nanoparticles in PANI reduced the charge trapping centres and increased the conducting channels of the polymer. 

The band structure of fully protonated emeraldine salt was studied previously by semiempirical molecular orbital (MO) calculations and more recently by ab initio calculation [41,42]. A half-filled polaron band formed via the interaction between separate polarons (there are two polarons per tetrameric repeating unit) was proposed to explain the observed optical and electrical properties of fully protonated PANI-ES. The PANI-HCSA films used in these studies were, however, cast from NMP solutions in the form of EB and then doped into the form of ES. The polymer chains in these polymer films, therefore, have the same conformational structure. 

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