 |
|
Pet
Recycle:- |
|
|
|
Challenges to PET
Recycling
|
-
During the life cycle of a PET
bottle, material characteristics change due to thermal
influences, resulting in a reduction of viscosity (from IV
0,82 to IV < 0,76 dl/g), which in turn leads to a
deterioration of the stability and pressure-resistance of the
bottle.
-
The diffusion of filled product
(i. e. components of the filled liquid) into the PET material
also presents a challenge, especially where the consumer has
made alternative use of the bottle (e.g. for aggressive
substances like acids, fertilizers, household detergents etc).
|
|
Aim of PET Recycling |
-
The material characteristics
return to those required for bottle production (IV= or > 0,82
dl/g).
-
Aromatic substances and
chemicals are effectively removed.
-
No chemical additives should be
used.
-
Gas chromatography analyses show
that the sensory characteristics of recyclate are even better
than those of virgin product. The acetaldehyde and ethylene
glycol contents for example are far lower than the required
values as a result of solid stating under vacuum.
|
|
Procedure of PET
Recycling |
-
the PET bottle flakes are
continuously fed into a modified two shaft extruder without
preliminary drying. Utilizing a specific worm configuration as
well as a certain arrangement of differentiated degassing
zones, the ground material is carefully dried and the melt
efficiently degassed. Comparison of different extrusion
systems during production showed that the modified two shaft
extruder guarantees the most unique treatment of all the
different post-consumer flakes on the market. Additionally, a
down-stream melt filter ensures that non-melt able solids are
separated from the melt to avoid unnecessary losses in
quality. A slight increase of yellowing with minimal
degradation is however unavoidable.
-
After palletizing the resulting
amorphous PET chips are fed into a discontinuous solid state
process (SSP) and are set at the parameters necessary for
conformity with foodstuffs. In a vacuum-tight Stehning tumble
dryer the reaction runs in two main phases - crystallization
and condensation/decontamination. The process parameters
necessary for the reaction, i.e. pressure, temperature and
holding time, are stored and varied fully automatically
according to the process phase.
|
|
