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| Latest News: | |
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| During the last years the importance of PET increased tremendously and you can expect this evolution to continue. In fact, 5 million tons of PET were fabricated in 1999 and PET-bottles were used for 40% of bottled softdrinks. The advantages of the PET-bottle are unbreakableness and less weight in comparison to a glass bottle and so customers prefer more and more the PET-bottle. For this reasons recently some breweries use PET-bottles for their product. Lately, PET is used more and more as packing material for food and industrial products. |
| To use post-consumer PET to gain energy is neither economical nor ecological replaceable |
| In 1999 4.4% of the produced PET were collected for preparation. So, about 96% were burned to gain energy. PET burns nearly total to water an carbon dioxide and has a comparable calorific value like brown coal. Therefore it would be easy to say, that we should use post-consumer PET to produce energy. But you can also use post-consumer PET to produce pellets with virgin material quality and for this reason burning PET to produce energy is economically not replacable. It is a sinful waste of precious raw material, especially when think of gaining PET: PET is produced from crude oil, which is a limited raw material. Therefore more PET-recycling must be one of our goals. |
| The proceedings |
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If you want to recycle PET with a good result you have to take care
for several specialities of PET. Thermical and mechanical influences can
destroy the polymer and cause a prodauct with less quality. So you have
to adapt to proceedings for the specialities of PET. Plastmachines International
in Emmering close to Munich did it in the following way with its ZTE Combi
Unit: At the beginning of the proceedings material is fed into the Foliolux-Crystallizer
with a conveyor belt with metal detector or a feeding-screw. The metal
detector prevents metal to get into the Combi Unit system.
In the Foliolux-Crystallizer the material is predried and crystallized in one step. Drying is necessary because one of the degradation mechanism is the risk of hydrolysis. If there is too much water in the process, the polymer will be cracked and in parts because of the energy enrichment the initial reactants terephthalic acid and ethylen glycol result from PET in a chemical reaction. Crystallization and drying in one step take only 30-60 seconds, which is an important aspect for producing in an economic way. Between the Foliolux-Crystallizer and the extruder there is a Plastmachines speciality, an intermediate screw with a slide valve, which is very useful to control the material feed. |
| The intermediate screw enables you to uncouple crystallizer and extruder
and to switch over with your material without loss of time and production.
So you can change your production in a few minutes if feeding needs to
be changed. Because of the modulare system of Plastmachines Combi Unit
every part of the system also works for itself and this makes direct extruder
feeding possible with a precise operating dosing unit.
Now the extruder plasticizes the dried, crystallized and densified material. As we mentioned, mechanical influences can destroy the polymer, you have to consider this point, when you choose the screw geometry. Plastmachines uses a screw with low friction and usually with a length of 35 D. A bi-functional double vacuum devolatilisation separates the last gaseous components. A Computer controls the heating and so you get a homogenous and considerate plasticizing. After the extrusion the material goes through a continuous 2-channel screenchanger. The cylindric filter candles have a big surface and avoid angles, in which the material could be damed. Because of the 2-channel technology screenchanging is possible without production stop. After that the plasticed strands are conducted through a cooling bath and then into the strand pelletizer. The intake pressure can be varied to the optimum point with adjustable draw-in rollers. Usually wear resistant metal draw-in rollers, but according to the material also rubber draw-in rollers can be used. The rotor is equipped with 10 single blades, pitching these blades reduces the noise level and saves energy considerably. The motor of the strand pelletizer has a frequency transformer to adapt the intake speed to an optimum. |
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