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FIGURE 6.13 Thermoset polymer showing cross-links. (From McMurry, J., Organic Chemistry, 3rd ed., 1992.
Reproduced with kind permission of Brooks/Cole, a division of Thomson Learning: www.thomsonrights.com.)

FIGURE 6.14 Plastics extruder.

opening or die with the desired shape for the finished product (Figure 6.14). As the working piece
is removed from the die it is fed onto a conveyor belt where it is cooled, typically by blowers or by
immersion in water. In the production of wide film or sheeting, the plastic is extruded in the form
of a tube. This tube may be split as it comes from the die and then stretched and thinned to the
dimensions desired in the finished film (SPI, 1999). Extruded products include plastic pipe and
plastic lumber (Rhyner et al., 1995).

6.11.3 BLOW MOLDING
Blow molding is a method of forming hollow molten tubes out of thermoplastic materials, then with
the use of compressed air, blowing up the tube to conform to the interior of a chilled blow mold
(SPI, 1999).