Silicone Elastomers compounding technology

Due to their typically inorganic basic structure on the one hand and their organic radicals on the other, silicones hold a structurally intermediate position between inorganic and organic compounds. They are hybrids and have a unique range of properties unmatched by any other plastic.

Early in the 20th century, the English chemist Frederic Stanley Kipping succeeded in synthesizing the first organic silicon compounds, the basis of polyorganosiloxanes. With the search for alternatives to natural rubber, Kipping’s work and other earlier work on the chemistry of silicon became interesting for industrial research. In 1940, the U.S. chemist Eugene G. Rochow and the German chemist Richard Müller almost simultaneously found a way to produce chloromethylsilanes, the most important precursors for the production of silicones, on an industrial scale. The process is now known as the Müller-Rochow synthesis.

Silicone polymers are prepared either with linear oligomers in a polycondensation process or with cyclic siloxanes in a ring-opening polymerization process.

As components of silicone compounds, the type and quantity of reinforcing substances and fillers influence the mechanical and chemical behaviour of the silicone elastomers produced by crosslinking. They can also be easily coloured with suitable pigments and dyes.

Typical applications

Due to their special and broadly adaptable characteristics profile, silicone elastomers can be used to advantage in many applications. Their good electrical insulation properties and physical properties that remain constant over a wide temperature range, for example, make them an excellent choice for applications in the electrical and electronics industry. Thanks to their water-repellence, resistance to ageing and weathering, and absorption of expansion and vibration movements, complex challenges in structural and civil engineering can be solved. Wide-ranging applications are known in the automotive and aircraft industries, the chemical industry, plastics technology and many other areas.

Compounding requirements

Leading market players in the silicone industry have used the Buss Kneader very successfully for decades, on the one hand as a high-capacity continuous reactor in polymer production by polycondensation or polymerization. Important reasons for this include the Buss Kneader’s excellent handling of very wide viscosity spectra, precise feed of reactants through hollow-drilled kneading pins, perfect temperature control, and trouble-free operation at very low absolute pressure.

Another application area is the compounding of silicone elastomers (HTV) and silicone sealants (RTV). Reinforcing materials such as highly dispersed silicic acid or classic fillers and other formulation components are fed in during compounding, and undesirable accompanying materials are removed. In combination with extremely high fold numbers, the moderate shear rates enable excellent mixing results and very high viscosity compounding without local overheating.

Thanks to the modular and thus adaptable design of entire systems, and the broad-based Buss process expertise, the Buss Kneader is an excellent choice for silicone polymer production and silicone compounding in all classes.

Silicon hose bands

Typical plant layout for silicone elastomers

BUSS compounding systems offer the following specific benefits

  • Continuous process
    The BUSS Kneader offers a continuous process with all the advantages of a system for continuous, uninterrupted production. Highly accurate metering systems ensure exact recipe specifications, and are realized in low to high throughputs. High product homogeneity and more efficient production are the advantages of continuous production processes such as the BUSS Kneader.

  • Liquid injection at any position
    Injection pins that can be mounted at any pin position along the process section allow liquid additives injection directly into the molten polymer. These are encapsulated and mixed in instantly.

  • Precise temperature control
    The Buss Kneader technology has been widely recognized for precise temperature control since more than 6 decades. This is achieved via controlled energy input due to uniform, moderate shear rates and precise temperature monitoring by thermocouples mounted in pins at any position along the process section.

  • Uniform, moderate shear rates
    Uniformly moderate shear rates allow controlled mixing at low-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.

  • 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.

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