Plastics News Europe - September 2019 - 13

injection moulding

lower emissions through
process optimisation
It is common knowledge that plastic parts emit
volatile organic substances. If these substances
could be measured during production instead of
afterwards, when the part has been moulded,
manufacturers could avoid emission-related
problems from ever arising
Why an emission tool?
While volatile organic substances are
known to be emitted by plastic parts,
the influence of individual process
parameters and the degradation reactions that occur during processing
are often unknown. Now, researchers at Kunststoff-Institut Lüdenscheid have developed an emission
tool that "brings light into the darkness and enables process optimisation towards the production of
low-emission components".
Plastics are already subject to
heated public debate due to topics
such as marine littering and microplastics. It is a discussion with little
to no regard for any distinction between high-quality technical products
and simple packaging. For the plastics
industry, it is vital that plastics do not
add to this negative image with finished components that produce emissions, whether harmful or otherwise.
To that end, plastic products are
subject to various tests - depending
on their area of application - following production in order to determine
their emission behaviour. Limit values
are determined and unauthorised
substances identified in order to ensure accptablee air quality. This applies, for example, to all components
used in automotive interiors. If components fail such emission tests, entire batches must be discarded, wasting significant resources.
Hitherto, the causes of excessively
high emissions have in most cases
been unknown, making countermeasures and avoidance strategies
impossible.
Neither the degradation reactions
themselves nor the specific reaction
products have been investigated or
are known. Considering the huge
range of different types of plastics in
combination with various additives,
even a non-empirical approximation
using a theoretical approach is hardly
feasible, as formulations of plastic
materials and details of ingredients
are almost never disclosed to the

september 2019

plastic processor or his customers for
competitive reasons.
Uncontrolled degradation processes during manufacturing not only
lead to high emissions of the moulded part, but also to a shorter tool life
due to mould corrosion, coating formation and the resulting problems
with demoulding and venting. At
best, this results in reduced part quality and high processing costs. In the
worst case, these degradation reactions can lead to the complete destruction of the mould. Bio-based
plastics in particular, are known for
potentially causing problems of this
kind, with the risk of tool damage.
This not only leads to unnecessary
downtime, but also higher personnel
costs, start-up costs and a high number of rejects.
However, until now, no research
had been conducted into this issue,
which meant there was also no possibility available for taking long-term
action.

Emission analysis can lead
to process optimisation
The Kunststoff-Institut Lüdenscheid
has now, therefore, built a prototype
tool for the direct recording of emissions during processing. It has already
registered a utility model. This specially developed emission tool is designed in such a way that the air exhausted from the cavity by the
injected plastic melt can only escape
through a ventilation passage. This
air is enriched with volatile components escaping from the plasticised
plastic. A thermodesorption tube is
attached to the venting duct, which
is filled with adsorber material that
traps the substances present in the
exhaust air.
The collected substances are then
released in a controlled gas stream,
separated chromatographically and
analysed with a mass spectrometer.
An examination of the injected components - a procedure for which the
laboratories of the Kunststoff-Institut

Emission tool developed by Kunststoff-Institut Lüdenscheid

Lüdenscheid are accredited - provides additional information about
the resulting component emission.
This makes it possible for the first
time to demonstrate that there is a
causal relationship between process
parameters in injection moulding and
emissions from the finished component and that component emissions
can be specifically influenced. Furthermore, based on the results of the
experiments carried out, targeted
tool coatings can be recommended
which protect the tool surface from
aggressive cracking products and, if
necessary, minimise deposits. The
emission tool thus joins the range of
process test benches at the Kunststoff-Institut Lüdenscheid.

The information potential
of emissions
The emission mould makes it possible
to directly measure and compare the
emission spectra of a resin, the resulting component and the emissions
during injection moulding. Not only
are the component emissions measured; further degradation products
can be recorded and identified.
Particular attention is paid to the
corrosive substances that attack both
the tool and the component, reducing their quality and increasing component emissions. Furthermore, tiny
amounts of volatile synthesis precursors can be found, which are only

➡ Continued on page 14

Plastics News Europe - September 2019

Table of Contents for the Digital Edition of Plastics News Europe - September 2019