Hydrocarbon Processing - April 2022 - 69

Green Petrochemicals
The procedure to measure corrosion
is shown in FIG. 3. Two soft iron plates
are put separately into an aluminum plate
filled with a PP compound and placed in
a ventilated oven at 230°C for 4 hr. After
taking the soft iron plates out of the oven
and removing the molten PP compound
from their surfaces, the soft iron plates are
hung in a tightly-closed glass bottle saturated
with water vapor at room temperature
for 7 d. Weights and photographs of
the soft iron plates before and after testing
are recorded.
FIG. 4. shows the appearance of metal
plates that are non-treated, treated with
recycled PP from the market, and the
same recycled PP compounded with 500
ppm proprietary acid scavenger and stabilizerb
.
It becomes obvious that an acid
scavenger is needed to neutralize acidic
residues from recycled PP; 500 ppm of
the proprietary acid scavenger and stabilizerb
reduces
corrosion significantly, but it
does not eliminate it fully. Depending on
the quality of the mold and the intensity
of exposure during injection molding, it
remains to be clarified whether 500 ppm
of the proprietary acid scavenger and stabilizerb
is
sufficient in such a case to neutralize
the acidic content.
The weight increase of the iron plates
varies from 0.0002 without polymer exposure
to polymer melt, to 0.0016 with
recycled PP, to 0.0004 with recycled PP
and 500 ppm of the proprietary acid
scavenger and stabilizerb
. This reflects an
improvement of 75% by using this highperformance
acid scavenger. Therefore,
it is recommended to include additional
additivation with acid scavengers at the
stage of recyclate extrusion at the recycler
to increase the quality of the recyclates
and reduce the negative impacts on
processing efficiency.
Collaboration is a key enabler to
identifying circular solutions. Understanding
the root causes for polymer quality
loss along the lifecycle of the product
calls for an understanding of the requirements
and opportunities within several
technological steps in the lifecycle. Working
in and analyzing the conditions within
value chain collaborations is one way forward
to achieve this understanding.
Industry consortia-e.g., the EUfounded
Circular Plastics Alliance (CPA),
with more than 290 signatories from public
and private sectors along the plastics
FIG. 4. Appearance of soft iron plates after exposure to saturated water vapor conditions
at room temperature for 7 d.
value chain-are well placed to combine
expertise and propose new ideas and solutions
to overcome the obstacles to implementation.
For example, the CPA recently
announced a design work plan supporting
the development of a guideline on design
for plastics recycling.
Companies around the globe are also
launching activities to foster value chain
collaboration. Within the chemical industry,
for example, the authors' company
launched its circular plastics program EcoCircle
in 2019. This program facilitates
discussions with customers and players
across the value chain, focusing expertise
and combining product solutions with established
system competences. By developing
products collaboratively with customers
and proving the solutions against
circularity criteria along the value chain,
real product solutions can be created that
support the circularity of the plastics value
chain. Similar programs have since been
set up by other chemical companies.
Whereas this article concentrates on
the impact that the implementation of correct
additivation within the mechanical recycling
step can have on polymer quality, it
is well acknowledged that there are industry
developments covering other recycling
technologies such as, for example, chemical
recycling. While immediate solutions
are needed to make these technologies viable,
the need for joint development, collaboration
and an understanding of value
chains remains the same, independent of
the recycling technologies approached.
Product design, product composition
and additivation, processing parameters
and recycling technologies all must be
aligned. This can be best achieved when
collaborating across the value chain.
Takeaway. This article demonstrates
how additivation in the recycling process
can play a crucial part in providing the
required recyclate quality for achieving a
circular economy. It also emphasizes that
industry collaboration is a key enabler to
developing new solutions and transitioning
towards a circular economy.
It should be noted that from a statistical
point of view, a long polymer chain is
attacked with a higher probability than a
short polymer chain and that it is almost
impossible to reconnect polyolefin chains
in a linear way once they are broken-
long chain polyolefins are connected to
high processability and melt stability and
have good ESCR. Accordingly, the avoidance
of any chain breakage while using
antioxidants should be a priority within
polyolefin recycling to help bring circular
plastic to fruition.
NOTE
a Clariant's Hostanox® P-EPQ® powder
b
Clariant's Hycite® 713
LITERATURE CITED
Complete literature cited available online at
www.HydrocarbonProcessing.com.
Hydrocarbon Processing | APRIL 2022 69
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