Nylon-polyaniline blends

The Effect of Dopant Counter Ion on the Conductivity and Morphology of Polyaniline-Nylon Blends... 

Film preparation All filtered, doped polyaniline salt and blend solutions were solution cast onto a Teflon coated glass substrate. They were covered with a glass dish to allow for slow evaporation (over a period of 24 hours) of the solvent at room temperature. HFIP, with a boiling point of 60 "C, allows gentle stripping at room temperature. All films were peeled off the Teflon tape substrate and (Med in a dynamic vacuum oven at 75 C for approximately 24 hours. From fluorine elemental analysis, percent residual HFIP solvent in films was less than 0.5% (wt/wt). This casting process from HFIP produced robust, free standing and solvent f e polyaniline / nylon blend films. 

In summary, the polyaniline blends studied exhibit a conductivity which rises smoothly and rapidly from the insulating state with increasing polyaniline concentration. However, ihc onset of conduction seems to be dependent on the nature of the conductive pathways that are present at low loading fictions. Polyaniline salts with the more polar counter-anions (e.g. MSA-) blended with the more polar polyamide (e.g. nylon 6) show signs of a continuous, multi-cormected network whereas herical salt domains are characteristic of a more nonpolar PANI-0.5-HDBSA blended with nylon 6. Hie threshold for electrical conductivity is sensitive to the morphologic structure of the polyaniline / nylon blends. 

Transport in conducting polyaniline / nylon blends is observed to be independent on the composition, dopant anion, host matrix and structure of the conducting phase. The microscopic transport in all salt networks remains unchanged by the dilution of the salt in the nylon matrix. The conductivity follows a temperature dependence characteristic of generalized variable r e hopping mechanism with % = -1/4. The slope of the temperature dependence increases with dilution, indicating increased disorder in the polyaniline salt. 

We have prepared a series of nylon / poly aniline blends using the solvent hexafluoroisdpropanol (HFIP), which is an excellent solvent for polyaniline emeraldine base (PANI-EB), polyaniline doped with various sulfonic acids (PANI-ES) and for hi molecular weight nylon 6 and nylon 12. It was observed that conductivity and morphology of the blends varied with the compatibility of the sulfonic acid anion with the nylon. Methanesulfonic acid, butane sulfonic acid dodecylbenzene sulfonic acid and camphor sulfonic acid were used as PANI dopants and the PANI-ES / nylon blends were characterized by electrical conductivity (room and low temperature) and transmission electron microscopy. The results of these various measurements and the conclusions which can be drawn regarding morphology and conductivity of Ihe blends, will be reported. 

Mirmohseni, A., Salari, D., 2006. Preparation of conducting polyaniline/nylon 6 blend fiber by wet sppinning technique. Iran. Pol5m. J. 15 (3), 259-264. http //works.bepress.com/cgi/ viewcontent.cgi article=1016 context=reza nabavi (accessible on 08.06.2014.). 

Doping Doped polyaniline solutions were prepared in HFIP by a solution doping method (22). Solutions turned from blue / brown to forest green, characteristic of doped polyaniline. Molar doping of undoped polyaniline is calculated for polyaniline emeraldine salt from the mole ratio y = (moles of dopant) / (moles of phenyl-NH), determined by elemental analysis. Optimally doped polyaniline has the value of y = 0.5. Dopants used were camphor sulfonic acid (HSCA), (Aldrich) methane sulfonic acid (HMSA), Aldrich and dodecyl benzene sulfonic acid (HDBSA), TCI America. Nylon 6 and 12 (Aldrich) were vacuum dried before solution blending. All PANI-ES solutions were filtered with a 0.50 pm filter. 

Since low concentrations are technologically more important, we restricted work to these blend concentrations. At these lower levels, the electrical conductivity of the polyaniline blends is quite sensitive to salt levels. Figure 2 shows the effect on conductivity when the host nylon is changed from nylon 6 to nylon 12. As seen in Figure 2- 0.5 % concentration of P/5 I-0.5-HMSA salt in nylon 6 shows a conductivity of 10-4 S/cm, whereas a similar concentration value of the same salt in nylon 12 has a conductivity of 10-5 S/cm. TTie level of conductivity above the... 

The low onset value of electrical conductivity in all the blends suggests a branch-like structure of the polyaniline phases in the nylon. The biphasic nature of these materials was established by a series of experiments using transmission electron microscopy (TEM)... 

Figure 3. (a) Onset of electrical conductivity for x % (vol/vol) of PANI-0.5-HMSA / nylon 6 blend system, (b), (c) and (d) TEM micrographs of 0.5 %, 1.5 % and 5 % salt blends, respectively. Dark areas in micrographs represent stained polyaniline salt imbedded in polyamide. 

In blends containing polyaniline doped with HDBSA, no significant variation in the temperature dependence behavior between PANI-0.5-HDBSA / nylon 6 and PANI-0.5-HDBSA / nylon 12 is observed, although a weaker temperature dependence is expected for tiie latter blend. In this case, a larger fraction of the doping acid is expected to remain in the nylon 12 matrix rather than in nylon 6. This would result in lower carrier concentration for the PANI-0.5-HDBSA in the nylon 12 host and a stronger than expected temperature dependence of conductivity. 

The major difficulties involved in making electrically conductive thermoplastic blends using polyaniline, polypyrrole, or their composites, are two-fold. The first is the thermal instability of doped polyaniline and polypyrrole at melt processing temperatures (1-3), The second is the chemical incompatibility of acidic conductive polyaniline with acid sensitive polymers such as the nylons. Conductive polyaniline is quite acidic and the adjustment of its acidity to neutral pH values eliminates its high conductivity (4,5). The authors present here thermal aging studies of conductivity and thermal gravimetric analysis - mass spectroscopy (TGA-MS) of Eeonomers which show pH independence of conductivity in acidic to neutral environments. The tunable surface properties of Eeonomer composites allows one to optimize the processibility as well as the electrical and mechanical properties of their blends with various thermoplastics. 

DMTA together with other techniques such as DSC have been used in morphological studies on a variety of polymers including epoxy-polyaniline resin [53], ethylene-propylene 5-ethylidene-2-norbornene terpolymer-polyaniline blends [54], Nylon 6-ethylene vinyl alcohol blends [55], polyoxymethylene [56], ethylene-propylene-... 

Raman spectroscopy has been used in structural studies of a wide range of homopolymers and copolymers [109-122] including crystalline PE [123], polyaniline [124], polystyrene-co-p-(hexafluoro-2 hydroxyisopropyl)-alpha methyl styrene/polypropylene carbonate blends [125], PE [126], PP [126], polylactide [127], polyacrylonitrile [128], Nylon-6 - polyvinyl alcohol blends [129], poly(4-vinyl pyridine cupric salt complexes [130] and regenerated cellulose [131]. 

SEM has been used extensively in morphological studies on polymers. Polymers studied include epoxy resin-polyaniline composites [3], polyoxyethylene [15], polypropylene-polycaprolactone blends [16], polydimethylsiloxane-co-ethylene oxide [17], PET fibres [18], polyurethane/polybutylmethacrylate polymer networks [19], methylacrylate-co-cellulose [20], styrene-butadiene copoylmer [21], Nylon 6-ethylene vinyl alcohol [22] and propylene-calcium carbonate or talc composites [23]. 

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