Chemistry Reference
In-Depth Information
Petroleum-based PU takes hundreds of years to break down in nature due to
its insucient carbon and nitrogen sources for microbial growth, even when
exposed to extreme conditions.
22
The growing demand for bio-based PUs has
manufacturers around the world increasing their commitment to using re-
newable and eco-friendly bio-materials in their products. Thus, a dynamic
development is foreseen for bio-based PUs, which are chemically identical to
their petrochemical counterparts, derived from bio-mass with increasing
regulatory pressure for sustainable solutions. Bio-based PUs are spearheaded
by bio-based polyols which are derived from feedstocks.
23,24
The use of bio-
based polyols decreases the petrochemical content of PU formulations and
increases their economic allocation (defined as economic partitioning the
input or output flows of a process or a product system, i.e. between the
product system under study and other product systems).
25
According to in-
dustrial estimates, natural-oil-derived polyols produce 36% less greenhouse
gas (GHG) emissions, use 61% less non-renewable energy, and have 23% less
total energy demand.
25,26
Bio-based PUs have significantly improved bio-
degradability compared to PU products made from petrochemicals.
27,28
Traditionally, the isocyanates and their derivatives used for PU manu-
facture were prepared by well-known methods via nitrene intermediates, as
described in Scheme 6.1.
29
Currently, there are no 100% sustainable PU
products through non-isocyanate reactions. However, some laboratory-scale
methods have reported bio-based diisocyanates from fatty acids via the
phosgene and azide methods.
30
Hojabri and co-workers have prepared fatty-
acid-derived diisocyanate, using a Curtius rearrangement, which was similar
to traditional aliphatic diisocyanate.
31
So far, commercial technology for bio-
based isocyanates is still under evaluation.
It is known that a few plant oils, such as cashew nut oil, are rich in
phenolic compounds.
32
However, triglycerides are the main constituents of
most vegetable or plant oils. According to a report by Twitchett,
29
aliphatic
and aromatic isocyanates can be obtained by phosgenation of the corres-
ponding primary amines, indicated in Scheme 6.2.
Though isocyanates are non-bio-degradable, green PU products are mostly
manufactured from green polyols derived from plant and vegetable oils,
23,24
O
O
O
NaN
3
-N
2
R
R
R-NCO
Curtius
R
N
-
N
3
Cl
NaOH/Br
2
O
O
O
-HBr
R
R
R-NCO
Hofmann
R
N
-
NHBr
NH
2
O
O
-H
2
O
O
NH
2
OH
+
R'OH
Lossen
R
R-NCO
R
R
N
-
OR'
NHOH
Scheme 6.1
Isocyanate syntheses on a laboratory scale.
Reproduced from ref. 29.
