Blend PANI/Nylon

Later, systematic study of EMI shielding behavior of highly conducting thermoplastic PANI/PVC and PANI/nylon blends (-0.1-20 S/cm) presented the theoretical as well as experimental aspects of SE in the 1 MHz to 3 GHz frequency range [18,70,113]. It was observed that both near- and far-filed SE followed the D.C. electrical conductivity and exhibited rapid initial rise followed by slow increment at higher conductivity (Figure 9.11b). 

Table 3. Percent PANIS versus log (Conductivity) for Several PANIS/Nylon Blends.

It is interesting to note that the PANI-0.5-HCSA blends at 1 % show in nylon 12 a discontinuous network, but a more fibrillar-like network when blended with nylon 6. This more aggregated morpholo in the nylon 12 is reflected in the more gradual growth versus a more continuous increase in electrical conductivity as a flmction of salt loading. (Compare 4.6-a to 4.7-a.)... 

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. 

Blends of PANIS and solutions of Celanese Nylon 6-6, Valox (Natural) and Celanex polyester PBT plastics were prepared. Ten percent (w/w) solutions were prepared. The two solutions were mixed in ratios to give mixtures which contained 5%, 25%, 50%, 75%, and 95% PANIS content. The total solids content of the solutions ranged from 2% to 9%. These mixtures were then used to cast thin films. Films prepared in this manner were uniformly poor due to the hydroscopic nature of trifluoro-acetic acid. Only those blends with greater than 75% PANIS showed any significant conductivity and these films were brittle. 

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. 

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. 

Figure 1. d.c. Electrical conductivity, ct, versus volume fraction (vol/vol) of PANI-0.5-HCSA PANI-0.5-HMSA and PANI-0.5-HDBSA salts solution blended with (a) nylon 6 and (b) nylon 12. 

The relationship between conductivity and volume fraction of PANI-0.5-HCSA in nylon 6 or nylon 12 (Figure 2-c) shows behavior similar to that of the other blends surveyed. However, the electrical conductivity in PANI-0.5-HCSA blends is seen to increase at a higher level compared to die P/ M-0.5-HMSA and the PANI-0.5-HDBSA systems. This behavior suggests that the more highly conducting salt (i.e. PANI-0.5-HCSA) is more efficiendy dispersed in the both nylons, resulting in very low onset thresholds and higher blend conductivities. 

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. 

When the three different salts are separately blended with a less polar nylon such as nylon 12, the morphology is seen to be fractal at lower salt concentrations for the case of PANI-0.5-HDBSA containing blends (Figure 7-b and c) than the PANI-0.5-HMSA and PANI-0.5-HCSA / nylon 12 blends (Figure 6-b, c, d and Figure 8-a, respectively). TTie lower onset of electrical conductivity of PANI-0.5-HDBSA / nylon 12 compared to the PANI-0.5-HMSA and PANI-0.5-HCSA containing blends reflects the presence of the fractal conducting pathways in the PANI-0.5-HDBSA blend. 

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 threshold value for electrical conductivity is shown to be sensitive to the morphological structure of the salt network. Measurable electrical conductivity of these blends shows very low values at approximately 0.5 % by volume of the salt. At this threshold value for electrical conductivity, a fi tal network is established through the nylon host. Lower onsets of electrical conduction in the PANI-0.5-HMSA / nylon 6, PANI-0.5-HDBSA / nylon 12 and PANI-0.5-HCSA / nylon 6 blends paralleled a finer, more branched network whereas the lower conductivities accompanied a coarser, more globular morphology in the PANI-0.5-HMSA/ nylon 12, PANI-0.5-HDBSA / nylon 6 blends. At concentrations less than 5 % (vol/vol) a conducting network forms throughout the nylon sample. As salt level increases above the threshold value, the network be mes dense and convoluted and the electrical conductivity becomes less sensitive to dopant anion functionality. 

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