PLASTIC PRODUCTS - Plastics and Environmental Sustainability - page 130

remelts to mix them, and pelletizes the mix prior to processing the mix into
a product. The mixing is typically carried out in a compounding extruder or
in an internal mixer. The scope of this work does not permit any substantial
treatment of these steps or even an adequate technical discussion on the
topic. Only basic information that allows the reader to appreciate the
contentinthefollowingchaptersisincludedinthefollowingsection.Several
excellent topics on the topic are available (Manas-Zloczower, 2009; Todd,
1998).
4.2.1.3 Processing into Product
Plastics industry uses several different processing techniques to convert
plastic resin into different products. These are summarized in Table 4.2
(with those for thermoset plastics summarized in Table 4.3 ) . The most
used of these by far are injection molding and extrusion, each accounting
for about 1/3 of the global thermoplastic processing capacity. Other less
common techniques are blow molding of bottles, film blowing, and coating
of paper goods. Each of these techniques requires dedicated machinery
that automates the process. In general, all processing techniques heat the
plastic pellets (which are precompounded) and either force it through a
specially designed die (extrusion) or inject it into a cavity mold (as with
injection molding and blow molding). Naturally, these are energy-intensive
processes as the polymer needs to be softened and the viscous melt worked
mechanically to plasticize it. The mechanical forcing of the melt is usually
via a rotating screw system, and during passage an enormous amount of
frictional heat is generated that further heats up the melt. Thermal
stabilizers are generally used as additives to minimize the heat-induced
degradation of resin during processing. Either air or water is used to cool
the equipment and to solidify the plastic shape created.