On the "curiosity" of electrically conductive melt processed doped-polyaniline/polymer blends versus carbon-black/polymer compounds

Abstract

Carbon black/polymer conductive compounds have been known and commercially used for many years, and their scientific background is quite well established and documented. In contrast, polyaniline/polymer blends (PANI/polymer) processible via dry (solvent-free) melt-shaping methods are still relatively unknown, insufficiently understood, and only a single commercial PANI/polymer blend for dry melt processing is presently commercially available (PANI/PVC, Zipperling, Germany). In this communication, a mechanism of PANI structuring in dry melt-processed PANI/polymer systems is suggested. In addition, the differences between these two conductive “fillers” (carbon black and PANI) in melt blending and processing, and the rules governing their mode of dispersion in the solidified polymer matrix, which determines the blends conductivity levels, are discussed. In future papers, detailed experimental evidence, supported by molecular modeling calculations, for the PANI/polymer systems, will be presented to support the ideas expressed in the present communication further. Conducting carbon blacks (CB) often consist of elongated aggregates (low aspect ratios) composed of very small (nanometric) primary particles sintered together. Upon melt blending with a polymer and processing, the CB may undergo deagglomeration, aggregate erosion and fracturing, and reagglomeration, resulting in either a uniform or more often a nonuniform distribution of the black particles [1, 2]. The level of the particle distribution nonuniformity varies and, as a rule, higher nonuniformity levels result in higher conductivity levels owing to the formation of conducting paths [3, 4]. For example, nonuniform distributions are formed in semicrystalline polymers, where carbon black particles are selectively located within the amorphous regions, and in polymers having low affinity to the surface of the carbon black particles [5]. Thus, in semicrystalline polymers and particularly in relatively nonpolar and low surface tension polymers, represented, for example, by polyethylene and polypropylene (PP), the tiny carbon black particles tend to segregate and even percolate, by forming conducting networks at extremely low content of the CB particles, e.g. 3 wt% Ketjenblack EC in PP [6], as in Fig. 1(a). Other parameters, such as melt-blending conditions including shear level and shear history, are less important within the practical acceptable regions of blending regarding the CB structuring and conductivity levels obtained. More uniform distributions of carbon black particles are obtained in amorphous polar polymers having higher surface tensions, similar to that of CB (~50 dyne/cm). Thus, by dispersing carbon black (Ketjenblack EC) particles in a soft, amorphous and polar random co-polyamide 6/6.9 (=poly[HN– (CH2)5 – CO] – co – [HN – (CH2)6 – NH – CO – (CH2)7 – CO]) [7,8], percolation has not been realized up to the