141
liquefaction in alcohols (ethanol and methanol), water, or their mixture can be
recovered by rotary evaporation under reduced pressure, while the biopolyols from
the liquefaction of lignocellulosic biomass in polyhydric alcohols (ethylene glycol,
glycerol, glycol and/or polypropylene glycol 400 - PPG400) are usually presented
as a mixture without separation due to the high boiling points of polyhydric alcohols. The liquefaction process is generally carried out in the presence of an acid
catalyst by using polyhydric alcohols, while the liquefaction process is commonly
performed in the presence of an alkaline catalyst by using alcohols and/or water as
a liquefaction solvent. The main components in biopolyols are alcohols, phenols
and their derivatives which are rich in hydroxyl groups. It has been expected that
biopolyols produced in an alkaline medium have a better potential in the preparation
of biobased PU (BPU) foams due to their unique alkaline environment which could
accelerate the foaming process (Li et al. 2017a; Li et al. 2018).
Organosolv fractionation is typically performed at a relatively mild temperature
(140–220 °C) by mixing a lignocellulosic raw material with a solvent which contains a catalyst. This in order to produce a cellulose pulp, or a degraded hemicellulose and/or lignin product (biopolyol) (Villaverde et al. 2015; Li et al. 2016; Shui
et al. 2016). The solid/solvent (S/L) ratios tested in literature have been mostly
evaluated in the range of 1:10–1:20 (g/mL), due to the relatively lower biomass
density.
The organic solvents used for fractioning lignocellulosic biomass are commonly
acetone, alcohols, dioxane, and formic/acetic acid, which are often mixed with
water varying the concentration of the organic solvent from 40% to 90% (Sarkanen,
1980; Pan et al. 2007). Organic acids, especially acetic/formic acid, have been popularly applied for the fractionation of lignocellulosic biomass due to their close
Hildebrand’s solubility (δ) to lignin (δ acetic acid = 10.1 and δ formic acid = 12.1) (Zhao et al.
2009). Table 7.3 presents some organosolv fractionation processes of different raw
materials using acetic/formic acid solvents. The process of fractionation in acetic
acid, formic acid and water solvents, is usually carried out at a very low temperature
(90–180 °C) with a residence time of 90–240 min, thus producing a yield of
~40–50% crude cellulose, while degraded lignin and hemicellulose can generally be
used for lignin recovery (Snelders et al. 2014; Shui et al. 2016).
7.1.2 Polyurethanes
Polyurethanes (PUs) are polymers containing urethane bonds (-NHCOO-) produced
by polyaddition reactions between isocyanates and polyols (e.g. polyphenylmethane polyisocyanate - PMDI or toluene diisocyanate - TDI, Fig. 7.1). PU has many
industrial applications, predominantly as foam for furniture (Zammarano et al.
2014), mattresses (Scarfato et al. 2017), insulating materials (Li et al. 2018), as well
as adhesives for wood lamination (Juhaida et al. 2010; Somani et al. 2003), among
others. During the PU foam production process, other ingredients, such as blowing
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes
liquefaction in alcohols (ethanol and methanol), water, or their mixture can be
recovered by rotary evaporation under reduced pressure, while the biopolyols from
the liquefaction of lignocellulosic biomass in polyhydric alcohols (ethylene glycol,
glycerol, glycol and/or polypropylene glycol 400 - PPG400) are usually presented
as a mixture without separation due to the high boiling points of polyhydric alcohols. The liquefaction process is generally carried out in the presence of an acid
catalyst by using polyhydric alcohols, while the liquefaction process is commonly
performed in the presence of an alkaline catalyst by using alcohols and/or water as
a liquefaction solvent. The main components in biopolyols are alcohols, phenols
and their derivatives which are rich in hydroxyl groups. It has been expected that
biopolyols produced in an alkaline medium have a better potential in the preparation
of biobased PU (BPU) foams due to their unique alkaline environment which could
accelerate the foaming process (Li et al. 2017a; Li et al. 2018).
Organosolv fractionation is typically performed at a relatively mild temperature
(140–220 °C) by mixing a lignocellulosic raw material with a solvent which contains a catalyst. This in order to produce a cellulose pulp, or a degraded hemicellulose and/or lignin product (biopolyol) (Villaverde et al. 2015; Li et al. 2016; Shui
et al. 2016). The solid/solvent (S/L) ratios tested in literature have been mostly
evaluated in the range of 1:10–1:20 (g/mL), due to the relatively lower biomass
density.
The organic solvents used for fractioning lignocellulosic biomass are commonly
acetone, alcohols, dioxane, and formic/acetic acid, which are often mixed with
water varying the concentration of the organic solvent from 40% to 90% (Sarkanen,
1980; Pan et al. 2007). Organic acids, especially acetic/formic acid, have been popularly applied for the fractionation of lignocellulosic biomass due to their close
Hildebrand’s solubility (δ) to lignin (δ acetic acid = 10.1 and δ formic acid = 12.1) (Zhao et al.
2009). Table 7.3 presents some organosolv fractionation processes of different raw
materials using acetic/formic acid solvents. The process of fractionation in acetic
acid, formic acid and water solvents, is usually carried out at a very low temperature
(90–180 °C) with a residence time of 90–240 min, thus producing a yield of
~40–50% crude cellulose, while degraded lignin and hemicellulose can generally be
used for lignin recovery (Snelders et al. 2014; Shui et al. 2016).
7.1.2 Polyurethanes
Polyurethanes (PUs) are polymers containing urethane bonds (-NHCOO-) produced
by polyaddition reactions between isocyanates and polyols (e.g. polyphenylmethane polyisocyanate - PMDI or toluene diisocyanate - TDI, Fig. 7.1). PU has many
industrial applications, predominantly as foam for furniture (Zammarano et al.
2014), mattresses (Scarfato et al. 2017), insulating materials (Li et al. 2018), as well
as adhesives for wood lamination (Juhaida et al. 2010; Somani et al. 2003), among
others. During the PU foam production process, other ingredients, such as blowing
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes