bioplasticsMAGAZINE_1205

Basics
Sustainable Plastic
from CO 2
Waste
Fig. 1: Vacuum cleaner cover
By
Robert Greiner
Corporate Research and Technologies
Siemens AG
Erlangen, Germany
Fig. 2: Door-holder for refrigerators
As part of the project ‘CO 2
as a polymer building
block’, funded by the German Federal Ministry of
Education and Research, scientists from Siemens
Corporate Technology, together with their project partners
from BASF, the Technical University of Munich and
the University of Hamburg, have been seeking an alternative
for the standard plastics ABS (acrylonitrile butadiene
styrene) and PS (polystyrene). Both plastics are frequently
used in consumer products. Compounds based on PHB
(polyhydroxybutyrate) could be a competitive alternative
to ABS. PHB is a polymer produced by micro-organisms
as a form of energy storage molecule based on sugar
(mostly cornstarch) or plant oils as renewable feedstock.
But PHB is a very brittle plastic and, unless modified,
is unsuitable as a material for example for housings. A
transparent alternative to PS could be compounds based
on PLA.
For these two materials polypropylene carbonate (PPC)
can be used as an impact modifier. PPC is an amorphous
thermoplastic material and shows a glass transition
temperature of around 30 °C. Thus it is very flexible at
room temperature, and moreover it shows at least a
partial miscibility with both bioplastics and therefore it is
suitable for adjusting the ductility of PHB and PLA. PPC
consists of around 43% by wt. of carbon dioxide obtained
by removing CO 2
from waste gases, e.g. from power
plants. The copolymerization occurs with PO (propylene
oxide) in the presence of appropriate catalysts. These
catalysts are the key to a new CO 2
-chemistry which uses
carbon dioxide as a valuable resource for base chemicals.
H 3
C
O
CO 2
catalyst
CH 3
O
O
C
O
n
propylene oxide
polypropylene carbonate
48 bioplastics MAGAZINE [05/12] Vol. 7