Chemistry Reference
In-Depth Information
COCl
2
-HCl
R-NCO
RNH
2
RNHCOCl
Scheme 6.2
Isocyanate preparation via the phosgene method.
Adapted from ref. 29.
bark liquefaction
34,35
and lignin.
36
It is known that PU foams are the most
dominant product, accounting for over 65% of the total PU demand in
2011.
19,20
PU foams are mainly employed in the construction, automotive
and furniture industries and also for footwear, packaging etc.
20
The con-
struction and automotive industries are expected to be the key growth
market for green PUs as environmental and social concerns increase. As a
lightweight and durable core material, green PU foams are used throughout
the construction and automobile industries in spray foam insulation
37
and
transportation seating systems.
38
According to PU Magazine, the drawbacks
of manufacturing PU with bio-based polyols are the need for higher levels of
additives, the installation of new mixing heads and the higher scrap rate
experienced by several foam makers.
A number of groups have conducted research into bio-based iso-
cyanates
30,31
and non-isocyanate routes for bio-based PU synthesis from
vegetable oils, and cashew nut shell liquid-based cyclocarbonate oligomers.
39
So far, 100% renewable PU foams made with both bio-degradable isocyanates
and polyols are still far off. Currently, bio-based PU products in the current
market are prepared with petroleum-based isocyanates and renewable poly-
ols. Because the OH groups of polyols are involved in a reaction with the NCO
groups of isocyanates, some hydroxyl group containing bio-masses such as
lignin, natural fibers, bark and their liquids could be used as renewable
polyols. In this chapter, we will discuss renewable PU foams and their method
of preparation using renewable polyols and/or the employment of biomass.
6.2 Bio-based PU Foams made with Bio-based Polyols
Polyols are the major component of PU products. Renewable polyols come
from plant and vegetable oils,
23,24
and bio-mass liquefaction such as
bark,
34,35
lignin
40
and nut shells.
33
Bio-based polyester polyols became
available for making PUs with higher renewable contents and equal per-
formance, following the commercialization of bio-based succinic acid.
41,42
6.2.1 Bio-based Polyols Derived from Plant or Vegetable Oils
Castor oil is commercially unique among the naturally occurring oils com-
posed of ricinoleic acid. It is known that a typical castor oil contains the
hydroxyl-functionalized unsaturated C18 triesters of rincinoleic acid and
glycerin
43
(at least 80%, see Figure 6.1). The unreacted hydroxyl groups are on
C12 and its hydroxyl value is in the range of 150-180 mg KOH g
1
(ref. 43).
Thus, castor oil can be used as a reactive monomer in PU foam preparations
