bioplasticsMAGAZINE_1205

Polyurethanes / Elastomers
Polyurethanes from
orange peel and CO 2
by
Rolf Mülhaupt and Moritz Bähr
Freiburg Materials Research Center (FMF)
and Institute for Macromolecular Chemistry
University of Freiburg
Freiburg, Germany
The Freiburg Materials Research Center (FMF) of the
University of Freiburg, jointly with Volkswagen, has
developed novel families of 100% renewable resource
based polyurethanes derived from natural terpene oils and
the greenhouse gas carbon dioxide (CO 2
). In contrast to the
conventional polyurethanes, neither hazardous isocyanate
resins nor fossil resources are required. Produced by a great
variety of plants as essential oils, terpenes are exclusively
recovered from bio-wastes and do not compete with food
production. Prominent terpene raw material for the production
of non-isocyanate polyurethanes is the citrus oil limonene,
obtained from orange peel as a waste product in
the manufacturing of orange juice. Based upon limonene and
the chemical fixation of carbon dioxide recovered from the
exhausts of power plants and as a by-product of liquid air
production, a very versatile and cost-effective molecular toolbox
has been developed at FMF for tailoring rigid and flexible
polyurethanes with diverse applications ranging from automotive
parts to textiles, rubbers, foams, coatings, sealants,
and adhesives.
Stimulated by the expected skyrocketing costs of crude
oil and growing public awareness of global warming, the
lean and clean production of renewable resource based
plastics with a low carbon footprint has gained high priority
[1]. Going well beyond the traditional scope of renewable
polymers, bio-based intermediates supplied by biorefineries
and the chemical fixation of carbon dioxide offer
attractive opportunities for tailoring environmentally benign
polyurethanes (PU). Conventional PU technology requires
very strict health and safety precautions, owing to the severe
health hazards upon exposure to toxic isocyanate monomers.
In contrast, non-isocyanate polyurethanes (NIPU) are formed
without using hazardous isocyanate resins at any point in the
production process. Key NIPU intermediates are non-toxic
polyfunctional cyclic carbonate monomers, which are readily
produced by chemical conversion of epoxy resins with carbon
dioxide [2, 3]. When cured with amines the cyclic carbonates
undergo ring opening, thus forming poly(N-hydroxyethylurethanes).
In contrast to the highly moisture-sensitive
isocyanates, cyclic carbonate resins tolerate humidity and
can be cured on wet substrates without foaming. Tedious
drying of fillers is not required. NIPUs (Green Polyurethane TM )
based upon fossil resources and conventional epoxy resins
are commercially available as zero VOC coatings with
improved adhesion and better resistance to chemical
degradation, corrosion, organic solvents, and wear [4, 5].
Most attempts towards the development of 100 % renewable
resource based NIPU make use of epoxidized soybean and
linseed oils, which are converted with carbon dioxide into
the corresponding bio-based cyclic carbonate resins [6, 7,
8]. However, the ester groups of plant oil carbonates are
partially cleaved during amine cure. These side reactions
can cause undesirable emission problems and impair NIPU
properties due to plasticization of the NIPU matrix. Therefore,
at FMF an innovative generation of 100% renewable resource
based NIPU has been produced from novel ester-fee cyclic
carbonate resins derived from terpenes [9]. The limonenebased
NIPU process is illustrated on the next page.
Terpenes represent highly unsaturated, ester-free, natural
hydrocarbons. Typical members of the terpene family include
limonene, camphene, vitamin A, steroids, carotenoids and
natural rubber. More than 300 plants produce limonene. For
example, orange peel contains up to 90 wt.-% of limonene,
which is readily recovered on a commercial scale using the
waste products from orange juice production. The colorless
viscous oil limonene dioxide, produced by oxidation of
40 bioplastics MAGAZINE [05/12] Vol. 7