EDITOR’S CHOICE
IMPROVED SUSTAINABILITY
SULZER
PLA advances are changing the plastics industry
Independence from petroleum-based
plastics is becoming more achievable,
as it develops into an issue of national
importance…
The recent development of new
polymerization methods that allow the
economical production of poly lactic acid
(PLA) with a higher molecular weight have
effectively removed many of the limiting
factors on its use, opening-up a greatly
expanded application base for the plantbased
bioplastic. This is happening just at
a time when pressures on extended supply
lines for crude oil derived products have
increased in many highly industrialized
countries due to stay-at-home policies for
workers and tighter border controls.
Sulzer technology is included in almost all
PLA plants worldwide, and while not an
instant fix - the timing for Sulzer Chemtech
to develop a flexible and robust technology
to enable the production of various new
PLA grades, could not be more prescient.
The company has developed a turnkey
process with partners to produce PLA
from sugars via lactic acid followed by a
downstream dimerization and ring opening
polymerization process that has already
been installed and is operating in six distinct
production facilities worldwide.
Improved sustainability and lower energy
usage have proved to be a strong
driver for the use of PLA in plastic food
containers, films, and wraps, whereas
high biocompatibility has led to numerous
biomedical applications. In the past however,
the usage of PLA, or plant-based bioplastic
was limited by its mechanical properties
in production (technically its viscosity in
the melt), and by the thermo-mechanical
properties of the finished product. The new
processes solve both these issues and
as a result extend its economic use to a
much wider spread of consumer goods and
packaging applications.
Benefits such as its low toxicity, along with
better sustainability as a result of using
renewable resources as raw materials
make the new grades of PLA an ideal
material for the food packaging and
consumer product industries. Due to a high
level of robustness, biocompatibility and
sterilization options they are also suitable
for a number of medical applications such
as implant devices, tissue scaffolds and
internal sutures, plus a wide variety of other
pharmaceutical devices and packaging
applications.
Torsten Wintergerste, Division President
from Sulzer Chemtech comments, “It’s
evident that going forward nation states
can’t operate on a business-as-usual
basis. We need a domestic supply chain
solution that is more reliant on national
resources, with production facilities
that are strategically located. When the
in-feed materials are based on corn, or
other domestically farmed sugars, for
example local plants, can be built to
produce sustainable plastics for making
both essential medical supplies and food
packaging by injection molding, 3D printing,
film forming and extrusion. The latest grades
of PLA are highly flexible and have a much
wider scope of useable properties, making
them ideal for all these plastics production
methods.”
In the last few years great strides have
been made with commercializing bio-based
plastics produced from renewable sugars
and starches. More efforts are needed to
increase the use of biopolymers such as
PLA in substitution of conventional fossilbased
and non-biodegradable commodity
polyolefins such as polyethylene (PE). PLA
is biodegradable under certain conditions
and many PLA-based film applications
are proven to be industrially compostable
according to the recognized standard EN
13432.
The ideal biodegradable polymer for use in
medicine and pharmacy should also have
certain key properties: it must not promote
inflammation or cause toxic reactions; it
has to be easy to sterilize and after serving
its purpose, it needs to be possible to
enzymatically biodegrade it using an
appropriate metabolic pathway. PLA fulfils
all these requirements and therefore
is a natural choice for the applications
described.
HOW THE NEW GRADES OF PLA
ARE PRODUCED
PLA can be produced starting with
hydrolyzed starch or sucrose transformed
to lactic acid (2-hydroxy propionic acid)
building blocks, which exist in optically
active D- or L-enantiomers. Depending on
the proportion of the enantiomers, PLA
with different properties can be produced.
This enables the development of multiple
processing methods to produce a wide
range of PLA grades with properties
suitable to differing applications. The
differences are based on molecular weight
and content of D-lactic acid units. The
molecular weight affects the rheological
properties (viscosity in the melt), whereas
the content of D-lactic acid units affects
thermo-mechanical properties.
PLA with a high molecular weight is one
of the main drivers for the economical
production and consequent expanded use
of this polymer. There are two methods to
prepare PLA: the condensation of lactic
acid and the ring opening polymerization
of lactide, however the latter is the one
preferred by Sulzer engineers as it provides
improved control over quality and more
flexibility in terms of the material properties
of the end product.
Sulzer can design and execute whole
projects, from the first concept to an
industrial scale plant using in house
engineering, equipment, assembly,
commissioning, and start-up capabilities.
This allows PLA producers to enter into
the biopolymer market with the capacity
to produce the new formulations at a
customizable scale.
For further information, please visit www.sulzer.com
16 PECM Issue 45