Conductive Nonwoven Mats

The physical characteristics of electrospun nanofibres, such as fibre diameter, depend on various parameters which are divided into three main categories (a) solution properties (solution viscosity, solution concentration, polymer molecular weight, and surface tension) (b) processing conditions (applied voltage, volume flow rate, spinning distance, and needle diameter) and (c) ambient conditions (temperature. 

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Pure PPy was used to prepare conductive nonwoven mats. PPy was synthesized using ammonium persulfate (APS) as the oxidant and dodecylbenzene sulfonic acid (DBSA) as the dopant. Chloroform and excessive amount of DBSA were used to obtain solubility. The intermolecular interaction between PPy chains were reduced by doping with high amount of D BSA but the reduction of intermolecular interaction between PPy chains decreased the interchain conduction of charge carriers and led to the decrease in bulk conductivity. 

S. Nair, E. Hsiao, and S. H. Kim Fabrication of electrically-conducting nonwoven porous mats of polystyrene-polypyrrole core-shell nanofibers via electrospinning and vapor phase polymerization, J. Mater. Chem., 18, 5155-5161 (2008). 

A nonwoven mat of smooth flexible aluminum coated oriented glass fibers, Metafil, has been developed by Tracor Aerospace and BGF Industries, USA, for electrically or thermally conductive applications, such as parabolic dish antennae. It is compatible with most resin systems and processing is said to be similar to uncoated glass mat, but cost is lower than other conductive materials. 

The workhorse of the RTS industry is TS polyester (also called polyester-TS) with glass fiber. The fiber reinforcement may be in the form of chopped fibers, porous nonwoven mats, woven fabrics, or continuous fibers. The combination of plastics and reinforcements results in versatile materials with unusual characteristics. The reinforcement adds strength and toughness to inherent weather resistance, moldability, and colorability. Thus RTSs are used because of their increased tensile, flexural, torsional, and impact strengths increased modulus of elasticity increased creep resistance reduced coefficient of thermal expansion increased thermal conductivity and, in many cases, lower costs. 

To improve PANI processability, the first approach to obtain polyaniline doped with camphorsulfonic acid (PANI-CSA) and doped nanofibers blended with common pol5miers by electrospinning was done by MacDiarmid s group. In another study a nonwoven mat was obtained by using a PANI/poly(ethylene oxide) (PEO) solution dissolved in chloroform. By controlling the ratio of PANI to PEO in the blend, fibers with conductivity values comparable to that of PANI-CSA/PEO cast films were produced. 

Conducting PANl/PLA nanofibers by electrospinning were reported and conductivities between bulk and nanofiber films were compared. It was found that nanoflber mats had lower crystallinity due to the fact that rapid evaporation of the solvent prevents chains to organize into a suitable crystal structure. The high porosity of the nonwoven mats and lower crystallinity resulted in a decrease in the electrical conductivity. 

In the present work, we used polyaniline (PANI)/polyacrylonitrile (PAN) blend to form a nonwoven mat. The PANI exists in a large number of intrinsic redox states. The half oxidized emeraldine base is the most stable and widely investigated state in the PANI family that can be dissolved in N-methyl-2 pyrohdon (NMP). The polyaniline emeraldine base (PANIEB)/polyacrilonitrile blend solution in NMP was prepared and then it was electrospun with different blending ratio. The fibers diameter, fibers morphology, and electrical conductivity of the mats were analyzed and discussed. 

Figure 4.3 shows the image of a nonwoven mat of electrospun N6 fibers on a foil of aluminum. The SEM micrographs in Figs 4.4 and 4.5 show some beads in electrospun N6 fibers. The results showed that with increasing applied voltage formation of beads decreased. The beads can be removed by controlling solution viscosities and electrical conductivities of the polymer solution. ... 

The thermal resistance and the thermal conductivity of nonwoven fabrics, slabs, and mats can be measured with a guarded hot plate apparatus according to BS 4745 1990, ISO 5085-1 1989, and ISO 5085-2 1990. For testing the thermal resistance of quilt and building materials, the testing standard is defined in BS 5335 Part 1 1991 and BS EN 12667 2001, respectively. The heat transfer in the measurement of thermal resistance and thermal conductivity in the current standard method is the overall heat transfer by conduction, radiation, and by convection, where applicable. 

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