Issue 04/2018

Basics
PEF and PET bottle recycling
Last year Synvina, the joint venture of Avantium and BASF,
received interim approval from the European PET bottle
platform (EPBP) for the market introduction of PEF up to
2 % of the total European PET consumption. The actual recyclability
of a PEF end-product, as any product, will however depend
on how it is designed and where it is launched, influencing
what type of collection and sorting infrastructure is present and
if this can divert the products components to recycled material
streams. Why then, did the EPBP already grant an interim approval?
One of the reasons was that Synvina already at an early
stage gathered and shared a significant amount of data that
demonstrated that PEF is not only sortable, but that low levels of
PEF are compatible with PET. Although not unique, this is a rare
feature for plastics while the more common incompatibility has
caused issues for some bioplastics in the past. In this article we
take a deeper look into the nature of this compatibility and how
it can put PEF in a unique position for a circular bottle economy.
Why introduce a new bottle material?
PET bottles are amongst the most successful examples
of plastics recycling. However, in smaller size bottles, PET by
itself is not always able to reach a logistically relevant shelf life.
For example the mechanical criteria of a 8 oz (237ml) bottle
can be met with 9-13 grams of PET while yielding a CO 2
shelf
life of only 4-6 weeks (4.2→3.5 Vol). To increase this, a bottle
is often complemented by a coating or barrier layer. Coating
equipment is not always economically attractive, for example
if (seasonal) demand changes require flexible output. Using
multilayer preforms for bottle production on the other hand may
impose recyclability limitations for the bottles; infrared sorting
equipment may still recognize them as PET while the barrier
layer, if not removed, may disrupt rPET quality.
PEF has been previously shown to enable logistically
attractive shelf lives in small bottles and this is continuously
being improved, as exemplified by the recent achievement of 16
and 20 weeks shelf life in 10g and 14g PEF bottles respectively.
Simultaneously PEF more and more exceeds mechanical
performance over PET, while PET remains economically
unattractive to produce from 100 % renewable sources. As such,
PEF is becoming increasingly attractive as a bioplastic that
brings material reductions beyond any other solution for small
size plastic bottles. And because PEF is chemically different
than any other plastic, near-infrared sorting equipment can
automatically sort them from the PET stream.
Controlling after-use material streams
As most new (non-drop-in) bioplastics, PEF is chemically
different from known materials and therefore has a unique
infrared spectrum. This allows PEF bottles to be sorted out
using automated near-infrared (NIR) sorting technology.
Recent ambitions for higher recycling targets drive increased
use of such technology to create separate streams beyond
the most common streams of PET and HDPE, for example
PP, PS and opaque PET. These infrastructure changes may
also accommodate the creation of streams for bioplastics with
interesting end-of-life options such as composting or recycling
into new high value products. In the case of PEF, the similar
chemistry to PET may even allow the use of existing PET
Vol. CO2
Vol. CO2
4,30
4,20
4,10
4,00
3,90
3,80
3,70
3,60
3,50
3,40
3,30
0 5 10 15 20 25
4,30
4,20
4,10
4,00
3,90
3,80
3,70
3,60
3,50
3,40
Weeks
3,30
0 5 10 15 20 25
Weeks
237 mL Bole
-17.5% CO 2
237 mL Bole
-17.5% CO 2
recycling technology and assets. Nevertheless, automated
sorting is not fail-safe and many recovery systems rely to a
large extent on human sorting, either by the consumer or by
professional sorters, for whom a PEF bottle is not always easy
to distinguish from PET.
PEF and PET compatibility
Synvina has done multiple recycling tests using PEF and
PET resins and bottle flakes, and consistently found that low
levels of PEF did not affect the thermal profile of PET in a DSC
experiment, while increasing levels started to induce melt point
depression particularly at longer extrusion times. Furthermore,
extrudates remained transparent. Further analysis by 13C NMR
showed increased splitting of the furan ring ipso carbon with
increased residence time, which an earlier study on PET copolyesters
attributed to a transition from a blocky long-segment
to a random co-polyester [1]. These observations confirm that
PEF and PET undergo trans-esterification during processing,
yielding a random co-polyester as the end-product. Extruded
pellets remained transparent and had a lower tendency to form
crystalline haze than neat reprocessed PET.
50 bioplastics MAGAZINE [04/18] Vol. 13