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7.2 Biopolyols Derived From Fast Pyrolysis and PUs
Biopolyols derived from agricultural and forestry residues/by-products via fast
pyrolysis, contain some types of compounds with multiple reactive hydroxyl groups,
which can be a replacement for synthetic polyols in the PU foam preparation
(Czernik and Bridgwater 2004).
7.2.1 Biopolyols Derived From Fast Pyrolysis
The biopolyols can, for example, be obtained by means of the fast pyrolysis of oil
derived from wheat straw after the solvent extraction process (Li et al. 2017b).
Specifically, Li et al. (2017b) removed the water in the pyrolysis oil by using a
rotary evaporator at 50 °C under vacuum condition. The dehydrated pyrolysis oil
was then extracted by using an equal volume of ethyl acetate to collect the water
insoluble fractions. Finally, the extraction solvent was removed via rotary evaporation under reduced pressure. Li et al. (2017b) found an increase in the hydroxyl
values in the oil from 45.60 mg KOH/g (crude biopolyol) to 77.76 mg KOH/g (biopolyol) before/after the extraction process, while the acid value of the oil decreased
from 1.44 mg KOH/g (crude biopolyol) to 0.96 mg KOH/g (biopolyol), which suggested the enrichment of hydroxyl compounds and the rejection of acidic components to the water soluble fraction by solvent extraction.
7.2.2 Preparation of PU Foams by Using Biopolyols Derived
From Fast Pyrolysis
The viability of biopolyols derived from rapid pyrolysis has also been investigated
in terms of foam uniformity and mechanical properties for the preparation of PU
foams. For example, Li et al. (2017b) observed that an increase in catalyst concentration leads to the obtaining of more flexible materials with more uniform cell
structures. A similar trend was observed by increasing the content of the surfactant,
but this up to a point, where more addition of the surfactant led to non-uniformity of
the cells. This behavior was also observed when water was added. In contrast, more
rigid materials having smaller and non-uniform cells were obtained by increasing
the amount of biopolyol (Li et al. 2017b).
Li et al. (2017b) also observed that the mechanical properties (resilience) of the
prepared foam decreased from 37% to 26.2% as the biopolyol content increased
from 30% to 50%. Most importantly, the mechanical property of the prepared PU
foam met the mechanical requirement of Chinese standard (GB/T 10802–2006) for
flexible PU foams, indicating the high potential application for car-cushion
materials.
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes
7.2 Biopolyols Derived From Fast Pyrolysis and PUs
Biopolyols derived from agricultural and forestry residues/by-products via fast
pyrolysis, contain some types of compounds with multiple reactive hydroxyl groups,
which can be a replacement for synthetic polyols in the PU foam preparation
(Czernik and Bridgwater 2004).
7.2.1 Biopolyols Derived From Fast Pyrolysis
The biopolyols can, for example, be obtained by means of the fast pyrolysis of oil
derived from wheat straw after the solvent extraction process (Li et al. 2017b).
Specifically, Li et al. (2017b) removed the water in the pyrolysis oil by using a
rotary evaporator at 50 °C under vacuum condition. The dehydrated pyrolysis oil
was then extracted by using an equal volume of ethyl acetate to collect the water
insoluble fractions. Finally, the extraction solvent was removed via rotary evaporation under reduced pressure. Li et al. (2017b) found an increase in the hydroxyl
values in the oil from 45.60 mg KOH/g (crude biopolyol) to 77.76 mg KOH/g (biopolyol) before/after the extraction process, while the acid value of the oil decreased
from 1.44 mg KOH/g (crude biopolyol) to 0.96 mg KOH/g (biopolyol), which suggested the enrichment of hydroxyl compounds and the rejection of acidic components to the water soluble fraction by solvent extraction.
7.2.2 Preparation of PU Foams by Using Biopolyols Derived
From Fast Pyrolysis
The viability of biopolyols derived from rapid pyrolysis has also been investigated
in terms of foam uniformity and mechanical properties for the preparation of PU
foams. For example, Li et al. (2017b) observed that an increase in catalyst concentration leads to the obtaining of more flexible materials with more uniform cell
structures. A similar trend was observed by increasing the content of the surfactant,
but this up to a point, where more addition of the surfactant led to non-uniformity of
the cells. This behavior was also observed when water was added. In contrast, more
rigid materials having smaller and non-uniform cells were obtained by increasing
the amount of biopolyol (Li et al. 2017b).
Li et al. (2017b) also observed that the mechanical properties (resilience) of the
prepared foam decreased from 37% to 26.2% as the biopolyol content increased
from 30% to 50%. Most importantly, the mechanical property of the prepared PU
foam met the mechanical requirement of Chinese standard (GB/T 10802–2006) for
flexible PU foams, indicating the high potential application for car-cushion
materials.
7 Synthesis of Biobased Polyurethane Foams From Agricultural and Forestry Wastes