148
7.4.1 Biopolyols Derived From Organosolv Fractionation
The biopolyols derived from organosolv fractionation have typically been from
degraded lignin and hemicellulose (Li and Zhao 2007). The most common fractionation process is usually carried out at mild temperatures of 80–110 °C in a wateracetic/formic acid solvent mixture (Vanderghem et al. 2011; Snelders et al. 2014;
Shui et al. 2016). Temperature is the most influential parameter for a fractionation
process. In general, increasing the reaction temperature in an appropriate range promotes biomass fragmentations, resulting in a high yield of biopolyol products
(Muurinen 2000; Zhao et al. 2009), i.e. the increase in reaction temperature, hydrolysis of lignin and hemicellulose in Miscanthus giganteus fiber material could be
promoted (Wang et al. 2008). However, when the fractionation temperature rises to
110 °C, the percentage of α-cellulose decreases slightly, indicating that a too high
temperature could be detrimental by depolymerizing cellulose into glucose (Onda
et al. 2008).
Residence time is also an important factor in a fractionation process and the
increase in residence time produces more biopolyol (Sannigrahi et al. 2011).
However, the biopolyol yield decreases as the residence time is even longer, which
is probably due to the promoted re-polymerization of the fractionated products in a
too long residence time (Sannigrahi et al. 2011). Penín et al. (2019) also observed
that the biopolyol yield decreased as the residence time in the wood fractionation of
Eucalyptus nitens was further increased. It was generally believed that that repolymerization reactions of degraded products would result in a low biopolyol
yield. Thus, generally a longer fractionation residence time is detrimental, which
leads to degradation of cellulose and re-polymerization of the degraded products
(Onda et al. 2008; Sannigrahi et al. 2011; Li et al. 2016). The biopolyols (degraded
lignin and hemicellulose) obtained in our research group has a hydroxyl number of
157 mgKOH/g, an average Mw of 1936 g/mol with a relatively low viscosity (Li
et al. 2016). These properties of biopolyol indicate that it has the potential as a
petroleum-polyol substitute for the preparation of BPU materials.
7.4.2 PU Foams Preparation By Using Biopolyols Derived
From Organosolv Fractionation
The application of biopolyol derived from organosolv fractionation for the preparation of BPU foams has rarely been reported. In our research group, hydroponic BPU
foams with biopolyols have prepared by using one-shot foaming method (Li et al.
2018). The foam had a uniform layer structure (Fig. 7.2a), though there were some
large holes due to the appearance of foam sample (Fig. 7.2b). In addition, the foams
have a high content of open cells and a high-water absorption capacity. The compression strength (at 10% deformation) and modulus of the prepared foams were
lower than those of hydroponic BPU foams prepared by Hatakeyama et al. (2012)
H. Li et al.
7.4.1 Biopolyols Derived From Organosolv Fractionation
The biopolyols derived from organosolv fractionation have typically been from
degraded lignin and hemicellulose (Li and Zhao 2007). The most common fractionation process is usually carried out at mild temperatures of 80–110 °C in a wateracetic/formic acid solvent mixture (Vanderghem et al. 2011; Snelders et al. 2014;
Shui et al. 2016). Temperature is the most influential parameter for a fractionation
process. In general, increasing the reaction temperature in an appropriate range promotes biomass fragmentations, resulting in a high yield of biopolyol products
(Muurinen 2000; Zhao et al. 2009), i.e. the increase in reaction temperature, hydrolysis of lignin and hemicellulose in Miscanthus giganteus fiber material could be
promoted (Wang et al. 2008). However, when the fractionation temperature rises to
110 °C, the percentage of α-cellulose decreases slightly, indicating that a too high
temperature could be detrimental by depolymerizing cellulose into glucose (Onda
et al. 2008).
Residence time is also an important factor in a fractionation process and the
increase in residence time produces more biopolyol (Sannigrahi et al. 2011).
However, the biopolyol yield decreases as the residence time is even longer, which
is probably due to the promoted re-polymerization of the fractionated products in a
too long residence time (Sannigrahi et al. 2011). Penín et al. (2019) also observed
that the biopolyol yield decreased as the residence time in the wood fractionation of
Eucalyptus nitens was further increased. It was generally believed that that repolymerization reactions of degraded products would result in a low biopolyol
yield. Thus, generally a longer fractionation residence time is detrimental, which
leads to degradation of cellulose and re-polymerization of the degraded products
(Onda et al. 2008; Sannigrahi et al. 2011; Li et al. 2016). The biopolyols (degraded
lignin and hemicellulose) obtained in our research group has a hydroxyl number of
157 mgKOH/g, an average Mw of 1936 g/mol with a relatively low viscosity (Li
et al. 2016). These properties of biopolyol indicate that it has the potential as a
petroleum-polyol substitute for the preparation of BPU materials.
7.4.2 PU Foams Preparation By Using Biopolyols Derived
From Organosolv Fractionation
The application of biopolyol derived from organosolv fractionation for the preparation of BPU foams has rarely been reported. In our research group, hydroponic BPU
foams with biopolyols have prepared by using one-shot foaming method (Li et al.
2018). The foam had a uniform layer structure (Fig. 7.2a), though there were some
large holes due to the appearance of foam sample (Fig. 7.2b). In addition, the foams
have a high content of open cells and a high-water absorption capacity. The compression strength (at 10% deformation) and modulus of the prepared foams were
lower than those of hydroponic BPU foams prepared by Hatakeyama et al. (2012)
H. Li et al.