TABLE OF CONTENTS In discussing processing techniques it is important to distinguish the type of waste we wish to process. A homogeneous waste stream can be reprocessed on the same machinery that virgin materials are processed on. A heterogeneous mixed plastic waste stream may also be processed, in some cases, on these machines, but a number of specialised reprocessing techniques may be applicable. A brief introduction to each of these processes will be provided along with examples of their use.
Extrusion is a continuous process for the production of components such as pipes or sheets. It can also be used to produce compounds, which are mixtures of polymers or plastics and further additives. The most important features of an extrusion system are shown in Figure 6.1. These are:
Extruders can be of two types, i.e., single-screw or twin-screw machines. These two types of equipment perform slightly different tasks although the basic principles apply to both.
This fits onto the end of an extruder and shapes the extrudate as it exits.
This is required to cool the molten material and in its simplest form may be a bath either filled with or spraying water. Rollers are used to help feed the material to the cutting device.
This is required to cut the extrudate to an appropriate size.
Whatever the end use destination is for a material, the chances are that at some point in...
