Section 5 Rubber Processing Equipment

In common with the thermal processes (Section 4.3), these processes and mechanical processes that use chemical agents (Section 4.4) often use supercritical fluids (e.g., supercritical CO2) as a process aid. A supercritical fluid is chosen that is compatible with the rubber that is being devulcanised so that it swells the rubber within the process equipment and so facilitates devulcanisation by ensuring a high degree of fill and, hence, shearing efficiency. It is, however, harder to maintain the fluid in a supercritical state in these types of processes, due to leakage and loss of pressure, than in sealed vessels (e.g., autoclaves), as are often used in thermal processes. 

Consequently, this book has been compiled to be used as a quick reference. It includes a glossary of terms, tables of technical data, and, for those who require more detail, there are more comprehensive text sections covering the major rubber types, compounding ingredients and the equipment used in the most common processes. 

Flame-retardant polystyrene is used primarily in expanded foam for building insulation. Rubber-modified styrenic polymers are flame retarded for use in a number of applications, such as enclosures for electronics and business equipment. By far the largest volume flame-retardant HIPS application is television enclosures (Figure 29.1) these are made primarily from flame-retardant HIPS [3]. Flame-retardant HIPS has an attractive balance of mechanical properties, processability and cost. Flame-retardant styrenic blends such as HIPS-PPO and PC-ABS also find utility in a number of electrical applications such as printers, computers and monitors. These blends have received increasing attention recently because of their ability to be flame retarded with nonhalogen flame retardants (see Section 7). 

Because of the limits of industrial equipment and cost constraints, curing is done at a constant temperature for a period of time. This can be done both to initially cure the material or to post-cure it. (The kinetic models discussed in the next section also require data collected imder isothermal conditions.) It is also how rubber samples are cross-linked, how initiated reactions are run, and how bulk polymerizations are performed. Industrially, continuous processes, as opposed to batch, often require an isothermal approach. UV light and other forms of nonthermal initiation also use isothermal studies for examining the cure at a constant temperature. 

In the case of polymer-monomer systems, it is possible to regulate the reaction by adding monomers at different stages or in different order with reactions being sufficiently rapid for commercial processes. The mastication equipment most commonly employed is standard rubber instrumentation such as roll mills, internal mixers, extruders, or related laboratory devices (see Volume 2, Section VIIA.B). 

It is silicone rubber, hot vulcanisation, liquid rubber LSR-2K ciosslinking compound, which is discussed in the following sections on LSR processing. All other silicone rubber types require different machine equipment and process conditions for LSR which are beyond the scope of this book. 

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