Compounding Systems for Polycarbonate Compounds

Polycarbonate (PC) based compounds belong to the technical plastics sector, often known as Engineering Plastics due to their main strengths and respective applications: technical components with excellent impact strength over a wide range of continuous operating temperatures whose excellent transparency enables widespread optical and data medium applications. PC based compounds are also a preferred construction material due to their good flame retardant properties.

Typical applications

Polycarbonate was first mentioned at the end of the nineteenth century, but not produced on a large scale until the 1950s, by Bayer (now Covestro) and General Electric (now Sabic), followed later by other manufacturers. Apart from the aforementioned advantages, great significance is now attached to the following properties as well: excellent electrical insulation, sterilisability and combinability with other plastics such as ABS, ASA and PBT into customized blends accordingly.Polycarbonate (PC) based compounds have therefore become very important for electronics and electrical applications as well as in medical technology, the automotive and aircraft industries.

Compounding requirements

The compounding system is critically important for all Polycarbonate (PC) based materials. PC ingredients, mostly in powder or chip form, are compounded together with additive components into pellets such as for transparent moulding compounds in the compounding system. In many cases reinforcement agents, flame retardants, dyes or the aforementioned blend partners are also added. Compounding these materials is therefore very demanding and requires customized solutions such as some of the following. Polymer components must be melted as gently as possible, flame retardants have to be perfectly distributed, and reinforcement fibers must be added and processed in such a way as to optimize mechanical properties.

All these requirements are well mastered by sophisticated compounding process technology accordingly. The BUSS Kneader can make much better use of its strengths here than other compounding systems. Thanks to extremely uniform and moderate shear rates, yellowing is minimized because no hotspots occur. This is critically important for transparent formulations. Moreover the BUSS Kneader’s characteristically perfect handling of wide viscosity ranges enables very wide and dependable operating windows. PC blends, reinforced, flame retardant or high-viscosity formulations and other combinations can usually be compounded without any change in screw geometry.

The BUSS Kneader’s two-stage system clearly separates the compounding and pressure build-up stages so that each stage can be independently optimized. Pressure build-up for pelletizing PC compounds is usually by gear pump.

Details of a car headlamps made of Polycarbonate (PC)

The hinged housing of the BUSS Kneader ensures fast and easy access for high system availability. Together with broadly based BUSS process expertise, the modular design and therefore adaptable arrangement of the entire compounding line make the BUSS compounding systems and the the BUSS Kneader first choice for complex polycarbonate production, which has provided maximum investment security for decades.

Typical compounding plant layout for Polycarbonate (PC)

Typical plant layout for Polycarbonate (PC) compounding systems

BUSS compounding systems offer the following specific benefits

  • High filler loadings
    Filler loadings of up to 90% are possible with BUSS compounding technology owing to partitioning into two or three feeder openings, the use of feed-in vessels such as side-feed screws, separate gravimetric feeding of filler, removal of trapped air by back venting, and excellent conveying efficiency. The moderate shear rates allow perfect handling of the highest viscosities at such high loadings.
  • Intensive mixing at low specific energy input
    BUSS multiple-flight compounders of the latest generation achieve better mixing at 15-40% lower overall specific energy input. This is because of an increased number of mixing cycles according to the needs of each individual process section. The energy for melting and mixing is provided almost entirely mechanically and optimally dissipated according to the imparted shear rates.
  • Narrow temperature range
    A narrow and defined temperature range can be maintained with a BUSS Kneader due to consistent and moderate shear rates throughout the entire screw length. Therefore, the typically excessive temperature peaks of alternative compounding systems are eliminated. This enables precise temperature control along the entire processing length.
  • Degassing of volatiles
    Volatiles are typically removed by a vacuum degassing opening at the end of the barrel or additionally in the discharge unit. Continual high level compound surface renewal is achieved with the large number of mixing cycles, striations and foldings created by the BUSS Kneader technology, thus enabling entrapped air or volatiles to be minimised in a highly efficient manner.
  • Temperature monitoring at any position
    Thermocouple pins, which can be mounted anywhere along the process section, enable optimal temperature control by precisely monitoring the temperature limits of the respective compound. A high degree of accuracy is assured since the thermocouple pins are constantly surrounded by molten compound and the influence of the barrel temperature control can be ignored. This feature enables online quality control.

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