Although POY wastes without spin finishes were used in the experiments, the possible degradations effects of spin finishes and other oily impurities during extrusion stage were investigated by employing DTA and DSC analysis. As shown in Figures 1 and 2, a significant difference could not be observed between the fibers with and without oil of regular counts. In order to make full statement about the effect of oil on POY wastes, micro fibers and flat yarns wastes which have higher amount of oil should be examined. The results of experiments are shown in extrusion step. Decrease in viscosity supports the results of ACOOH end group results.
Color value b is one of the most important indicators that shows polymer degradation. When the results of color value b were examined, there is defi-nitely difference between two types of granules. The color value b of recycled granules 60% higher than that of POY wastes, which is 3.93. That amount of increase in the color value of b indicates definitely a
thermal degradation. The melting point of the polymer was also investigated. The results show that there was no significant difference between the two sample groups. Since the melting point is a secondary indication of polymer degradation, this is not an improper result and also the results are in good agreement with the industry. When the amount of DEG was looked up, there is statistically difference at 5% significance level between POY wastes and recycled granules. Increase in the amount of DEG is an indication of hydrolytic degradation of the polymer. After having carried out these experiments, it was concluded that the advises below should be taken into account in the subsequent investigation by the
researchers. It was noticed that, the conical hopper is not appropriate for feeding of fiber wastes like POY wastes. In the case of the conical hopper, the fibers block throat of the feeder or the fibers can not flow by gravity into the extruder. In sequence, the material degrades due to the mechanical friction at the entrance of the extruder. Therefore, the material runs unevenly from spinneret and that type of flow causes irregularity in the size of the granules. A force feeder
can be advised for feeding of the fiber wastes.
The venting port helps to remove impurities in
the waste material such as, humidity, spin finishes,
etc. In the tests, one venting port was employed,
however, the results indicated that, two venting port
would be more effective.
Since the application of vacuum in the venting
ports, the vaporized impurities and degradation
products will be removed more effectively. Therefore,
new negative reactions from the degradation products
and impurities will be blocked. In turn, viscosity
of the polymer will be effected positively. Vacuum
application can be employed one or two venting
ports. All combinations should be examined in terms
of vacuum application. Ethylene glycol (EG) may
release from polymer due to degradation during the
extrusion. While in the first venting port surface
humidity of the waste material is removed, in the
second venting port removal of specially released EG
will block to reverse the reaction. It is well known
that, polymerization of PET is a reversible reaction.
When excess EG is not removed, it will cause to
reverse the reaction and macromolecule chains will
start to breakdown.
Another important point is filtering in the stage
of regaining of the waste fibers. Filtering will both
catch degraded polymer parts and dust inside the
material and help mixing of the material due to increased
feed back inside the extruder.
Since a suitable dryer for the waste fiber could
not be obtained, the drying steps were not applied in
a required level. The level of drying was 300 ppm in
the experiments while the required at least 50 ppm for
staple fiber production, 30 ppm for filament fiber
production. It is believed that, it is possible to extrude
the material, which is dried up to 50 ppm level, with
the help of venting port without hydrolytic degradation.
Therefore, the material should be transported
directly to the extruder from the drier without having
contact with air.
Nitrogen feeding should be used in order to
eliminate oxidative degradation. It is thought that the
nitrogen feeding from the extruder entrance towards
the hopper side will be more beneficial. Therefore, the
oxygen entrance into the extruder will be blocked and
also some of the humidity on the material will be
removed with the pressure of nitrogen. That means,
the nitrogen feeding will both stop oxidative degradation
and decrease hydrolytic degradation.
Some additives should be used in the extrusion
of the waste material because the waste material is
subjected into more degradation than that of a virgin
material. In order to add controlled amount of
additives a special device such as a dosage unit should
be mounted to the entrance of the extruder. In
addition to decrease the degradation during reextrusion
process, the use of stabilizator is recommended.
It must also be remembered that recycled
material contains some impurities such as spin finishes
and dyes besides-COOH groups and hydroperoxides
which start, increase and catalyze degradation
reactions. Stabilizators containing phosphite and/or
phenolic antioxidants are known beneficial for recycling
process [12]. Stepek and Daoust [13] recommend
to use stabilizators containing benzene rings
and polymeric antioxidants due to decomposition of
phenolic antioxidants at 100–150C. Triphenyl
phosphate, which is a common additive used in PET
fiber production to prevent thermal degradation, was
236 Altun and Ulcay
used in pre-tests without having dosage unit. The
results from pre-tests showed that uncontrolled
addition of triphenyl phosphate decreased color value
b compared to waste material without additives.
However, the amount of DEG significantly increased
when triphenyl phosphate used. In turn, IV value of
the product was lower than that of recycled material
without additives.
The change of temperatures, even 1C, affect the
viscosity of the material. Therefore, temperature and
heat control of the extruder is so important. From the
extruder manufactured and the test made with PD
derivative control system after 50C, however, it was
concluded that the control of the heat of resistance
should be PID control system due to necessity of
sensitive heat control of polymer which is affected
with 1C temperature change. In the experiments,
type J heat element used, but the results indicated
that PT 100 would be more beneficial.
C