POLYCOND was a transnational project which lasted from 2005 to 2009, and was financed by the European Commission under the Sixth Framework Programme (FP6). The project aimed to achieve new advances for obtaining Intrinsically Conducting Polymers (ICP), and enhancing the conductivity and processing window of existing melt-processable ICPs. Moreover, another objective consisted in improving the compatibility and dispersion of Carbon NanoTubes (CNTs), which are conductive nanofillers, in complex matrices.
The primary material for modifying polymers consisted of polyaniline (PANi), an intrinsically conductive polymer. It was doped with organic acids in order to increase its conductivity and make this polymer compatible with non-conductive injection matrices. Then, PANi was compounded with different polymers (e.g. polypropylene) by extrusion, leading to doped polymers.The modified PANi was characterised after injection moulding, showing a big influence of nano, micro and macroscopic morphology on conductivity. Additionally, a converse strategy for increasing polymer conductivity was studied. This alternative approach consisted in blending polyaniline with CNTs, creating a complex through in-situ synthesis. This method allowed the production of hybrid materials with surface resistances lower than 50 Ω. CNTs could also be incorporated in thermoset polyurethanes, thermoplastic polyesters, and acrylic resins for coating after their modification.
It has been found that Controlling processing conditions and tailoring rheological properties was critical for ensuring hybrid materials properties. Therefore, several compounding devices were studied, and finally a specific machine was designed and built within the project. The so-developed device was based on the chaotic mixing principle, and was intended to induce conductive networks in hybrid materials. This machine was composed of two independent rotors, and produced an elongating flow that mixed more efficiently polymers, keeping their connectivity/conductivity.
Hybrid conductive compounds were applied in several case studies; compounds based upon PP with polyanyline and CNTs were used to produce automotive housings, revealing a high level of shielding to the electronic devices. Moreover, PC/ABS containing Carbon Nano-tubes (CNTs) showed good recyclability, easy manufacturing and good shielding properties when applied to a medical device for blood pressure monitoring. Other suitable applications were high shielding moulded materials (60 dB) for substitution of metal casings in military radios, and polyurethane-based housings for shielding casings and covers.
The project showed a good way to increase the shielding levels (higher than 70dB with some materials) and conductive properties (lower than 10 kOhms) of conventional polymers. Furthermore, these conductive properties could be tuneable by selecting proper PANi complexes/polymer proportions. Consequently, most of the generated knowledge, concerning both products and processes, has been applied in the RECYTUBE project for recovering CNT scraps and obtaining conductive polymers.
John A Colbert, Richard Venables and Hartmut Fischer. Conductive Compounds-An Update on the Polycond Project.