RECYCLING POLYOLEFINS
Bernd Esmarch-Krones AG, Flensburg Plant
By : VGS BABU - HEAD SALES-KRONES INDIA PVT LTD
N
umerous inquiries from customers, and the steadily rising
requirements posed for the recycling of re-usable materials
from the waste flow, have impelled Krones to develop a washing
technology for polyolefins, too. This was recently launched on the
market under the name of MetaPure W-PO.
The MetaPure W from Krones has already acquired an
enviable reputation for its excellent washing performance in
the recycling process of PET containers. This is because the
sturdy and compact-size washing module has been developed
and built for continuous operation in plastics recycling lines.
The washing process is fundamentally the process step that
crucially determines the recyclate’s quality: poor washing
performance cannot be compensated for during downstream
processing of the washed flakes.
Polypropylene (PP) and polyethylene (PE)
Polyolefins are semi-crystalline thermoplastics. Their
most important representatives are divided up into two
subgroups:
1) Polypropylene (PP)
2) Polyethylene (PE) with its most frequently encountered
variants of LDPE (low-density polyethylene) and
HDPE (high-density polyethylene)
These polyolefins are used mainly for packaging, and
account for around 50 per cent of the total plastics market.
By way of comparison: PET’s share comes to roughly
2.5 per cent.
The polyolefins’ relatively low density, and their concomitant
ability to float, are very helpful in the washing process for
PET when it comes to separating the cap material from the
PET itself. In the washing process for polyolefins, this material
characteristic required some procedural adjustment. But the
overall concept continues to be based on the comprehensive
fund of experience gathered in the field of PET washing
technology.
Individual tried-and-tested units were here adapted to suit
the PO-specific idiosyncrasies, but the process-engineering
features of Krones’ washing technology remained unchanged.
– Trials in the in-house pilot plant produced a very good
washing quality.
– Finally, these washing results were confirmed in external
laboratories, and validated in the production of test
specimens
Odour-neutrality achieved
One problem encountered with polyolefins is material
collection, and the resultant side-effects. The packages we’re
talking about here are collected in the household garbage, or
in separate bins or sacks for plastics. Since the material thus
obtained is usually not cleaned before recycling, it is invariably
in contact with organic residues like ketchup, mayonnaise,
oil, yoghurt, shampoo, soap, household cleaning agents and
many other substances. This creates an enormous biological
and chemical loading, going hand in hand with an unpleasant
smell. And that in turn renders it relatively difficult to make
sure the end-product is odour-neutral. However, with the
standard washing module used in the in-house pilot plant,
optimum results in regard to cleanliness and odour-neutrality
could indeed be achieved.
Complete systems from Krones as well
In the meantime, demands have also been voiced on the
market to recycle polypropylene and polyethylene as well, so
as to render them suitable for high-grade re-use. Following
extensive trials in its plant’s own washing system, Krones was
able to demonstrate that it is possible to treat these polyolefins
so as to create top-quality recyclates – in a process that is both
ecologically and economically viable.
Besides individual modules, Krones plans and supplies
complete systems for polyolefin recycling. ln these projects,
Krones handles factory planning, the relevant engineering,
and all the service work required for creating a complete
recycling line. The washing module for PET will in future be
available on the market under the name of MetaPure W-PET,
and that for polyolefins under MetaPure W-PO.
Very good washing quality for polyolefins
One of the polyolefins’ salient characteristics is their density
of lower than one, which is why they float on the water’s
surface, whereas PET is significantly heavier than water, so
that it sinks to the bottom.
Density (in g/cm³)
Polyolefins: < 1
o PP: 0.90 to 0.915
o LDPE: 0.915 to 0.935
o HDPE: 0.94 to 0.97
PET: 1.38 to 1.40
It recycles polypropylene and
polyethylene, and renders
them amenable to re-use:
the MetaPure W-PO washing
module.
Drink Asia
39
September-October 2019