Process Design
The extruder is based on a normal design but it has an
adjustable support for the motor that allows the screw to be
removed in just one minute for analyzing the changes of
material inside the barrel at different process conditions [28].
To remove the screw, the gear box has two dissembling
gears than permit to separate them with a single bolt. Latter,
the motor is moved on the adjustable support for taking out
the screw in a direction opposite to the material flow. In the
spinning stage, first a slow stretching and a second stretching
are applied to the polyester fiber using three groups of five
rollers. This operation improves the molecular orientation
and crystallinity in order to increase the mechanical properties
of the polyester [19,25]. Two drying systems were used to
improve the crystalinity, dimensional uniformity and to
reduce fiber porosity [25]. One drying system used heat rolls
and the other included three heat plates operating at
o
temperatures between 10 and 100 C over the glass transition temperature of PET. The same operating conditions were used in extrusion and spinning stages and the virgin and recycled PET were processed at the values reported in Table 1.