147
7.3.2 PU Foams Preparation by Using Biopolyols Derived
From Liquefaction
BPU foams have also been prepared by using biopolyols derived from the liquefaction process. Li et al. (2018) prepared BPU foams with various biopolyol substitutions. These authors observed that the cream and the free rise time for the preparation
of all the BPU foams were dramatically shorter than the values for the reference PU
foam, since a base catalyst could facilitate the isocyanate-water and isocyanatepolyol reactions (Dworakowska et al. 2014). BPU foams compared to the reference
foam (with a density of 79.2 kg/m
3
) have much lower densities in the range of 20.2
to 23.9 kg/m
3
(Li et al. 2018). In this sense, Luo et al. (2013) suggested the great
potential for applications of BPU foams as lightweight packaging/insulation materials
(Bernardini et al. 2015).
There are several factors that influence the properties of PU foams prepared from
biopolyol derived from biomass liquefaction, including the use of a catalyst. The
catalyst plays an important role in adjusting foaming/rising and gelatinizing/creaming rate. Guo et al. (2011) reported that the formulation of a PU foam reached its
maximum compression strength of the PU foam with a catalyst content below 1%.
Excessive use of catalysts in the foam formula may thus hinder the foam expansion,
resulting in a higher density with poorer foam properties (Zhao et al. 2014). Lim
et al. (2010) also demonstrated that addition of a small amount of water is necessary,
due to its high blowing efficiency. However, excessive addition of water in the PU
foam formula could cause a negative pressure gradient because of the rapid diffusion of carbon dioxide through the foam cell wall, which results in cell deformation/
collapse and low compression strength of the overturned foams (Oertel and Abele
1994; Goods et al. 1999). Some literature studies have shown that an adequate value
of NCO/OH ratio improves the elastomeric properties of the prepared BPU foam,
while an excessively high NCO/OH ratio could produce fragile/brittle foam materials (Saleh 1990; Huang and Zhang 2002; Mohammed et al. 2008).
Li et al. (2018) prepared a BPU foam with biopolyols derived from liquefaction
of wheat straw with a foam formulation of 12.11% glycerol, 0.76% catalyst, 1.31%
water and an NCO/OH ratio of 1.24. They found a compression strength of
178.9 ± 1.7 kPa for the BPU foam, which was comparable to that of a PU or clay
nanocomposites foam (200 kPa) prepared by Cao et al. (2005).
7.4 Biopolyols Derived From Organosolv
Fractionation and PUs
Biopolyol, derived from organosolv fractionation of biomass, is usually a mixture
of degraded hemicellulose and lignin. However, there is rare report on the substitution of petroleum polyol with biopolyol derived from organosolv fractionation in
the preparation of PU foams.
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes
7.3.2 PU Foams Preparation by Using Biopolyols Derived
From Liquefaction
BPU foams have also been prepared by using biopolyols derived from the liquefaction process. Li et al. (2018) prepared BPU foams with various biopolyol substitutions. These authors observed that the cream and the free rise time for the preparation
of all the BPU foams were dramatically shorter than the values for the reference PU
foam, since a base catalyst could facilitate the isocyanate-water and isocyanatepolyol reactions (Dworakowska et al. 2014). BPU foams compared to the reference
foam (with a density of 79.2 kg/m
3
) have much lower densities in the range of 20.2
to 23.9 kg/m
3
(Li et al. 2018). In this sense, Luo et al. (2013) suggested the great
potential for applications of BPU foams as lightweight packaging/insulation materials
(Bernardini et al. 2015).
There are several factors that influence the properties of PU foams prepared from
biopolyol derived from biomass liquefaction, including the use of a catalyst. The
catalyst plays an important role in adjusting foaming/rising and gelatinizing/creaming rate. Guo et al. (2011) reported that the formulation of a PU foam reached its
maximum compression strength of the PU foam with a catalyst content below 1%.
Excessive use of catalysts in the foam formula may thus hinder the foam expansion,
resulting in a higher density with poorer foam properties (Zhao et al. 2014). Lim
et al. (2010) also demonstrated that addition of a small amount of water is necessary,
due to its high blowing efficiency. However, excessive addition of water in the PU
foam formula could cause a negative pressure gradient because of the rapid diffusion of carbon dioxide through the foam cell wall, which results in cell deformation/
collapse and low compression strength of the overturned foams (Oertel and Abele
1994; Goods et al. 1999). Some literature studies have shown that an adequate value
of NCO/OH ratio improves the elastomeric properties of the prepared BPU foam,
while an excessively high NCO/OH ratio could produce fragile/brittle foam materials (Saleh 1990; Huang and Zhang 2002; Mohammed et al. 2008).
Li et al. (2018) prepared a BPU foam with biopolyols derived from liquefaction
of wheat straw with a foam formulation of 12.11% glycerol, 0.76% catalyst, 1.31%
water and an NCO/OH ratio of 1.24. They found a compression strength of
178.9 ± 1.7 kPa for the BPU foam, which was comparable to that of a PU or clay
nanocomposites foam (200 kPa) prepared by Cao et al. (2005).
7.4 Biopolyols Derived From Organosolv
Fractionation and PUs
Biopolyol, derived from organosolv fractionation of biomass, is usually a mixture
of degraded hemicellulose and lignin. However, there is rare report on the substitution of petroleum polyol with biopolyol derived from organosolv fractionation in
the preparation of PU foams.
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes