Issue 06/2018

From Science & Research
PLA in the post-consumerrecycling
stream
The constant increase in global production capacities
of biobased plastics [1] results in a variety of products
made of biobased plastics that reach the established
disposal streams as post-consumer wastes after being
used. In Germany, one of these disposal streams is the collection
and disposal of lightweight packaging waste by the
yellow bin or the yellow bag system. KNOTEN WEIMAR and
TU Chemnitz have investigated the behaviour of biobased
plastic products in the sorting of lightweight packaging
wastes at operating plants and pointed out possible options
for material recycling. The research project was carried
out on behalf of the German Federal Ministry of Food and
Agriculture (BMEL) and funded by the project management
organization Fachagentur für nachwachsende Rohstoffe
(FNR) [2].
The scheme in Fig. 1 gives an overview of the various
disposal routes and the recycling and disposing processes
of various packaging waste as well as the recyclable
material fractions produced. Products made of biobased
plastics can also be integrated into this system.
Sensor-based sorting with near-infrared (NIR) devices
is a key element of modern sorting plants and enables the
sorting of different types of plastics.
Drop-in solutions such as biobased PET and PE, are
sorted out together with conventional equivalents.
However, biobased novel plastics (e.g. PLA, PLA blends or
starch based materials) can also be detected and sorted out
due to their characteristic NIR spectra.
It can be concluded that the sorting of e.g. PLA blends as
representatives of biobased novel plastics as single fraction
is technologically viable. Impurities of the sorted fractions
can thus be kept to a minimum.
In preparation for a practical field test in a conventional
sorting plant, the NIR spectra of several different PLA
blends (plastic yoghurt cups, sheets but also dishes, cups
and bottles) were scanned in the existing NIR devices.
In order to determine the current initial quantity, a sorting
test was first run for lightweight packaging sorting with
approx. 25 tonnes of lightweight packaging input material.
The result showed that the current quantity of products
made from PLA/PLA blends and starch blends in all of the
analysed material streams is predominantly below 1.1 ‰.
A further sorting test (three subtests) investigated the
detectability and sortability or material output of PLA
products/wastes at an operating plant in more detail.
The goal was to determine where PLA materials remain
under unchanged sorting conditions (without positive
sorting of PLA or without activating the PLA spectrum on
the NIR devices) and to test the detectability and sortability
of PLA materials from the post-consumer stream. Cups,
forks and dessert cups were used as PLA input material.
Subsequent to material mixing (Fig. 2) the material was
fed into the sorting process.
Three sorting tests were carried out (see above), the
Fig. 1
Disposal paths and recycling, reutilization and disposal processes of separate packaging wastes
Taking back systems for packaging waste
Deposit systems
PET -Bottles
Light weight packaging via dual systems (yellow bin/bag)
e.g. cups, bowls, bottles, films etc.
Sorting -/Pre-treatment plants (Disposal company), Sorting dry
Process steps a.o. crushing, sieving, metal separation, sensor-based sorting (NIR), air separation, manual control
Products: relevant enriched reusable materials
(incl. impurities caused by sorting performance, material-compounds / -mixtures, residues and pollutants)*
PET PS PE / PP Films MP RDF** Residues
Final recipient plant, Conditioning wet-dry-
Process steps (per material): a.o metal separation,
sensor-based sorting (NIR), crushing, washing,
sink-float separation (separation by density), drying, if any extruding
Sinking
fraction
(ρ > 1)
e.g. PET
Swimming
fraction
Sinking
fraction
e.g. PE / PP
Swimming
fraction
(ρ < 1)
Final recipient plant,
Conditioning dry
Process steps (per material):
a.o. metal separation, crushing,
sieving, air separation, sorting,
if any agglomeration
e.g. Mixed plastics (MKS)
Thermal
treatment
(MVA )
PET
a.o. residues
a.o. residues
PE / PP
z.B. PO
Recyclates,
e.g. PET, PO, PS
(material recycling)
Reductant, gases
and oils
(raw material recycling
e.g. steel plant)
Fuel
(energetic
utilisation e.g.
cement and CHP
station)
Energy
(disposal,
if possible
energetic
utilisation***)
*Specification for individual recyclable material available; **classification as final recipient plant for RDF-production; ***MVA if possible energetic utilisation
18 bioplastics MAGAZINE [06/18] Vol. 13