Highly Conductive Compounds

Plastics have many advantages over other materials. In certain application fields, however, these are cancelled out by lack of conductivity. Especially in potentially explosive atmospheres, in the packaging and handling of electronic components or in the transmission of radio signals, lack of conductivity can lead to failure or significant functional impairment. There is a risk of electrostatic charge.

If nonconductive plastics discharge by sparking, they can ignite explosive atmospheres such as solvent-air or dust-air mixtures. So, for such applications, nonconductive plastics must be made conductive.

Typical applications

The advantages of plastics in such cases can still be used by adding specific materials that significantly increase their conductivity by reducing their electrical resistance. For example, lowering the electrical resistance of PE from 1016 ohms to < 104 ohms makes it electrically conductive. Electrostatic charging can thus be safely prevented by grounding. Highly conductive compounds are used as the material for the bipolar plates in fuel cells.

Compounding requirements

These specific property profiles are achieved by compounding in precise compliance with very demanding requirements. Conductivity must be guaranteed both at room temperatures and under hot operating conditions. The added soot or carbon black, graphite, carbon nanotubes and carbon fibres must retain their complex structures and be distributed extremely homogeneously to form a dependable conductive network. The polymers used must be broken down as little as possible. Crosslinkability of the compounds can also be a requirement.

These sometimes-conflicting requirements are well controlled by sophisticated techniques. The BUSS Kneader has proven itself time and time again in compounding these particularly demanding materials. Its moderate and uniform shear rates, specifically adaptable for precise temperature control, play the central role thereby. In the melting zone, as much energy as necessary is dissipated without overstraining the polymeric components. The conductivity agents are distributed optimally within the shortest process length thanks to high folding rates. Downstream, the appropriate conductivity fibres are added, singulated and enveloped to preserve the maximum lengths required for their role in the conductive network. Optimal property profiles can thus be achieved even in the narrowest process windows at highest viscosities.

With the two-stage BUSS Kneader system, the compounding and pressure build-up steps are consistently decoupled from each other. They can therefore be optimized independently. Furthermore, the hinged housing of the BUSS Kneader ensures fast access and high system availability. Together with the broadly based Buss process expertise, the modular and thus adaptable design of the entire system make the BUSS Kneader an excellent investment choice for compounding these demanding high-conductivity compounds.

Nanotube carbon structure of highly conductive compounds

Typical plant layout for highly conductive compounds

BUSS compounding systems offer the following specific benefits

  • Compounding and pressure build-up optimized in two different steps
    Mixing on the Buss Kneader and pressure build-up in the discharge unit are separated to enable the efficient optimization of both steps. This allows mixing at low pressure and temperature as well as optimized pelletizing, while maintaining temperature control at all times.

  • Intensive distributive mixing
    The Buss Kneader achieves intensive distributive mixing because the combined rotation and axial motion of the Kneader screw generates extensional flow, a large number of shear interfaces, and cross channel mixing.

  • Large number of mixing cycles
    A larger number of mixing cycles is achieved with the latest Buss multiple-flight Kneaders. The unique new screw designs enable maximized splitting and recombining of the compound mass, with numerous striations and excellent mixing over a very short process length.

  • Limited damage to polymer and high-structured fillers such as carbon black
    The Buss Kneader’s uniform and moderate shear rates result in controlled shear and low temperature profiles. This guarantees better mechanical and electrical properties, improved flow characteristics, and lower consumption of expensive formulation components.

  • Wide range of formulation and throughput with one screw configuration
    While processing a wide formulation range with one screw profile is challenging, the Buss reciprocating single screw technology is well known for this capability, thanks to a process length typically half that of most other systems and great flexibility in screw configuration design.

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