138
7.1 Introduction
Polyurethane (PU) is one of the most important polymers with various industrial
applications, predominantly as PU foams with different flexible properties for bedding, cushion, flotation, furniture, packaging, insulation and structural materials
(Ge et al. 2000; Petrovic 2008). The process of preparing PU foams involves mixing
isocyanates and polyols (commonly polyester and polyether polyols) with other
additives (such as filler and pigment), chemical or physical blowing agent and catalysts (Xu et al. 2014). However, these commercial chemicals, including polyols,
depend mainly on petroleum and generate a great diversity of toxic substances during the production process (Araque et al. 2018; Mali 2018; Pachori et al. 2019). Due
to concerns about the depletion of fossil resources and the desires to create an ecologically friendly environment, the development of biobased polyols from renewable resources would be an irresistible trend for the PU materials industry.
Lignocellulosic biomass is commonly obtained from agriculture and forestry
residues, consisting of cellulose, hemicellulose and lignin, which have multiple
hydroxyl groups in their structure (Gutiérrez and Alvarez 2017; Herniou--Julien
et al. 2019). Therefore, many conversion technologies for lignocellulosic resources
have been developed in recent years, such as fast pyrolysis, hydrothermal liquefaction and organosolv fractionation process. The biopolyols derived from these conversion processes have been successfully used directly in the preparation of biobased
materials (Mahmood et al. 2015; Feng et al. 2016).
7.1.1 Conversion Technologies for Ligocellulosic Biomass
Fast pyrolysis is a thermochemical conversion technology, which is carried out by
transporting biomass particles to a vortex reactor with a relatively high temperature
(commonly between 400 and 600 °C) for a fairly short residence time (usually
below 5 s), followed by the cooling of superheated steam down to liquid products
(typically called biopolyols or bio-oils) (Effendi et al. 2008; Kohl et al. 2014). The
most investigated parameters of fast pyrolysis process for the development of biopolyols are reactor temperatures, heating rates and biomass particle sizes. Taking
into account the yield and properties of biopolyol, the reactor temperature is generally around 480–590 °C (Chum et al. 1993; Amen-Chen et al. 2002) with a heating
rate of 30–150 °C/min depending on the biomass particle size (commonly less than
4 mm) (Strezov et al. 2008; Lee et al. 2010; Gao et al. 2018; Suntivarakorn
et al. 2018).
The biopolyol obtained from such conditions typically represents two distinct
phases: an aqueous phase and an organic phase. Whereas, the specific composition
of biopolyols depends significantly on the composition and source of the biomass
(Guo et al. 2011; Mythili et al. 2013). Table 7.1 lists the typical biopolyol composition obtained from various raw materials through the fast pyrolysis process. The
H. Li et al.
7.1 Introduction
Polyurethane (PU) is one of the most important polymers with various industrial
applications, predominantly as PU foams with different flexible properties for bedding, cushion, flotation, furniture, packaging, insulation and structural materials
(Ge et al. 2000; Petrovic 2008). The process of preparing PU foams involves mixing
isocyanates and polyols (commonly polyester and polyether polyols) with other
additives (such as filler and pigment), chemical or physical blowing agent and catalysts (Xu et al. 2014). However, these commercial chemicals, including polyols,
depend mainly on petroleum and generate a great diversity of toxic substances during the production process (Araque et al. 2018; Mali 2018; Pachori et al. 2019). Due
to concerns about the depletion of fossil resources and the desires to create an ecologically friendly environment, the development of biobased polyols from renewable resources would be an irresistible trend for the PU materials industry.
Lignocellulosic biomass is commonly obtained from agriculture and forestry
residues, consisting of cellulose, hemicellulose and lignin, which have multiple
hydroxyl groups in their structure (Gutiérrez and Alvarez 2017; Herniou--Julien
et al. 2019). Therefore, many conversion technologies for lignocellulosic resources
have been developed in recent years, such as fast pyrolysis, hydrothermal liquefaction and organosolv fractionation process. The biopolyols derived from these conversion processes have been successfully used directly in the preparation of biobased
materials (Mahmood et al. 2015; Feng et al. 2016).
7.1.1 Conversion Technologies for Ligocellulosic Biomass
Fast pyrolysis is a thermochemical conversion technology, which is carried out by
transporting biomass particles to a vortex reactor with a relatively high temperature
(commonly between 400 and 600 °C) for a fairly short residence time (usually
below 5 s), followed by the cooling of superheated steam down to liquid products
(typically called biopolyols or bio-oils) (Effendi et al. 2008; Kohl et al. 2014). The
most investigated parameters of fast pyrolysis process for the development of biopolyols are reactor temperatures, heating rates and biomass particle sizes. Taking
into account the yield and properties of biopolyol, the reactor temperature is generally around 480–590 °C (Chum et al. 1993; Amen-Chen et al. 2002) with a heating
rate of 30–150 °C/min depending on the biomass particle size (commonly less than
4 mm) (Strezov et al. 2008; Lee et al. 2010; Gao et al. 2018; Suntivarakorn
et al. 2018).
The biopolyol obtained from such conditions typically represents two distinct
phases: an aqueous phase and an organic phase. Whereas, the specific composition
of biopolyols depends significantly on the composition and source of the biomass
(Guo et al. 2011; Mythili et al. 2013). Table 7.1 lists the typical biopolyol composition obtained from various raw materials through the fast pyrolysis process. The
H. Li et al.