Filled and Reinforced Thermoplastics (FRTP)

There are basically two reasons for working fillers into a plastic matrix: to optimize the compound material properties, such as for breathable foils or sound-absorbing pipes, or to save costs.

Three variables play key roles in the interaction between fillers and polymer matrix:

  • Particle shape: a small aspect ratio such as of glass beads, CaCO3 or BaSO4 usually improves the modulus of elasticity, while particles with a large aspect ratio, such as talcum or wollastonite, tend to improve tensile and tear strength as well as the modulus of elasticity.
  • Particle size distribution affects how well the fillers are worked in. Important here are the Van-der-Waals cohesion forces between particles more than 1 μm in size, and the dispersive shear forces exerted by the BUSS Co-Kneader within the FRTP compounding system on particles less than 10 μm diameter.
  • Surface area of the fillers: the number of potential cohesion points between fillers and polymer chains depends on the specific surface area (m²/g) of the fillers. The larger the fillers surface area, the more cohesion points and the stronger the material (rigidity, tensile strength, tear and impact strength). The surface gloss is also better.

Surface coatings are another important aspect. They can for example influence agglomerate formation, material flowability for easier handling, and adequate wetting during compounding.

Compounding requirements for reinforced compounds

BUSS process expertise is key for highly filled compounds. Apart from optimal distribution of the material flows, particular attention must also be paid to air and moisture entrained during the feeding of fillers. The process geometry must therefore be optimally configured accordingly. With the right configuration, the BUSS Kneader’s large capacities and associated torques enable efficient production of reinforced compounds.

With its outstanding allrounder qualities and enormously wide operating window, the BUSS Kneader can handle the widest range of processes with fillers such as talcum, titanium dioxide or barium sulphate, as well as aluminium (aluminum) or magnesium hydroxides. A welcome side effect of the BUSS Kneader’s moderate shear rate is much less wear and tear than with other screw kneaders. The modular design and resultant adaptability of the entire BUSS Co-Kneader line makes it an excellent choice for compounding filled and reinforced thermoplastics.

Red car of reinforced compounds showing the importance of frtp compounding for the car industry.

Typical plant layout for FRTP compounding systems

Typical plant layout for FRTP compounding systems

BUSS FRTP compounding systems offer the following specific benefits

  • High filler loadings
    Filler loadings of up to 90% are possible with BUSS compounder 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.

  • Uniform, moderate shear rates
    Uniformly moderate shear rates allow controlled mixing in the compounder at lower temperatures while imparting only the required shear for the task at hand. The narrow shear rate distribution compared to alternative systems ensures uniform shear histories for every individual particle. This results in high quality compounding with reduced energy input.

  • Limited damage to polymer, fibre and high-structured fillers
    The BUSS Kneader’s uniform and moderate shear rates result in controlled shear and low temperature profiles, stressing the structure of fibres and highly-structured fillers such as carbon black much less than with other systems. This leads to better mechanical and electrical properties, improved flow characteristics, and lower consumption of expensive formulation components.

  • 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.

  • Precise temperature control
    The BUSS Kneader permits precise temperature control owing to controlled energy input and uniform, moderate shear rates, along with precise temperature monitoring by thermocouples mounted at relevant positions along the barrel in hollow-bored kneading pins surrounded by polymer.

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