Issue 04/2016

Basics
Bioadditives?
By:
Rodion Kopitzky
Fraunhofer UMSICHT
Oberhausen Germany
Last but not least, there are product depending
requirements which are independent of the selected
material-type like toughness, strength, elasticity,
color, flame retardance, electrostatic behavior and
so on. Nevertheless, cost is also an important factor.
Fillers and reinforcing agents, plasticisers and impact
modifiers, antifogging additives and whitening agents,
pigments and dyes, antistatic and antimicrobial
additives and so on can be used for tailoring the
overall properties to get a serviceable plastic.
To make the right choice of additives, which can a)
influence each other and b) may have opposite effects
on properties is often a difficult task for a developer.
To focus on biobased plastics, there are in principle,
no particularities concerning additives. If the biobased
polymer is a drop-in material like biobased PE,
formulations with additives can be transferred directly.
In the case of starch, appropriate plasticisers must
be chosen to get thermoplastic starch. Figuratively it
is the same as choosing the right plasticiser for PVC
depending on the overall requirements. PLA is known
to be susceptible to water to some degree. Therefore
scavengers or chain extenders which react with water
or with the polyester degradation product can be
used. The molecular chemical basis of these additives
is the same for fossil and biobased polyesters and
sometimes the commercialised products only have
different names. Concerning reactive additives like
chain extenders, there may be differences between
fossil and biobased plastics. But this is due to the
processing conditions which alter the kinetics of
the reactive process. A branching chain extender
like glycidyl based polyepoxides (Joncryl) reacts
very quickly at 280 °C, the processing temperature
of PET, but much slower at 190 °C, the processing
temperature of most polyesters in biobased
formulations. Therefore, not all additive types are
transferable to other formulations when changing
the polymer and polymer-type specific additives have
to be used or developed. This is evident in the field
of reactive compatibilisers for fiber filled plastics
or in blends. These additives must be designed
according to the molecular basis of the components
and the polymer-type depending on mechanisms of
compatibilisation.
Do bioplastics need additives? Yes they do! Do
they need Bio-Additives? Summing up the previous
paragraphs the reason for an additive should not be
the material basis but rather the achievable overall
properties of the final plastic material formulation.
Additives based on vegetable oils or fatty acids,
for example, have been used as plasticisers and
lubricants for fossil based polymers for several
decades. The coplasticiser and acid scavenger
epoxidised fatty acid ester is, on a volume basis, one
of the biggest additives, used predominately with PVC.
From a sustainable point of view biobased additives often have an
advantage in short use application like packaging, due to low carbon
footprint (if the footprint is not destroyed by inefficient energy use during
production, due to lower production amounts). Biobased additives can
also raise the biobased carbon content in blends with biobased and
fossil based polymeric components. In respect to regulations (using the
term bio or biobased or biodegradable) they may be a must. However, the
terms biodegradation and biobased should not be confused. Additives
disregarding their material basis should not have an effect on the
degradation process. An acid scavenger like the above mentioned epoxy
would be contraproductive for use with PLA in short use applications
because it will decelerate the first step of biodegradation.
Nowadays, due to the discussion of the raw material basis beyond
fossil resources and the industrial availability of new building blocks like
succinic acid, new additives are under development or are in the market
entrance phase. Long term development of the biorefinery concept to
provide new biobased chemicals might even initiate the synthesis of
special additives like the UV-absorbers on a biobased basis in sufficient
amount and at acceptable costs. Nevertheless, until then, competitive
cost will be a critical factor in many cases.
www.umsicht.fraunhofer.de
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bioplastics MAGAZINE [04/16] Vol. 11 43
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