201
japonica) and eucalyptus (Eucalyptus globulus) using steam-exploded methodology, and these materials were then functionalized by reaction with ECH, and catalyzed by a water-soluble phase transfer catalyst (tetramethylammonium chloride)
under alkaline conditions (30% aqueous NaOH) for ring closure using methyl ethyl
ketone as a solvent. The authors found good yields for biomass-derived epoxy resins (63.4–68.2%), and these were in line with the yield from bisphenol A (70%),
thus suggesting that biomass-based epoxy resins could be synthesized using the
same synthetic route that bisphenol A-based resins. In addition, the higher lignin
content in the cured epoxy resins reduced the T max .
Benyahya et al. (2014) reported that biobased epoxy resin cured with green tea
extract (catechin with isophorone diamine) had a T max (299 °C) much lower than
those cured low-Mw lignin epoxy resins (298–336 °C). Asada et al. (2018) also
extracted high pure lignin (99%) (Mw ≈ 5100 g/mol and hydroxyl equivalent) from
white poplar (Populus tremuloides) wastes using a steam explosion methodology
followed by water and acetone extractions for the development of epoxy resins. In
line with this, Asada et al. (2015a) determined that high Mw and the hydroxyl
equivalent lignin was extracted with acetone compared to those extracted in methanol. This means that not only low Mw lignin was extracted with acetone, but also
high Mw lignin. In addition, the tensile strength of the cured epoxy resin obtained
by Asada et al. (2015a) was (~30 MPa) similar to those obtained from epoxy resins
derived from conventional fossils (~27–80 MPa).
Yin et al. (2012) studied the preparation and properties of the lignin-epoxy resin
composite using enzymatic hydrolysis from corn straw lignin and bisphenol. The
epoxy resin could be cured together with the lignin at high temperature, but the cure
temperature for the lignin-epoxy resin mixtures could be reduced by the introduction of a polyamide curing agent. The lignin-epoxy resin composite with a lignin
content of up to 60% was prepared by mixing lignin with epoxy resin and polyamine using a hot-pressing molding process. The optimum performance of composite materials was achieved at the molding temperature of 130 °C.
Ortiz et al. (2019) studied the biobased epoxy resins from biorefinary byproducts, i.e. BCD lignin containing GDE at different mass ratios: 1:1, 1:2, and 1:4
(BCD:GDE). A direct correlation was observed between the glass transition temperature (T g ) of the resin and the lignin content of the samples manufactured under
vigorous mechanical stirring. They found that resins containing a higher BCD lignin content resulted in brittle samples. The direct use of BCD lignin for the synthesis of epoxy resin was also explored by Ortiz et al. (2019), since they are carried out
in an aqueous medium, i.e. the use of organic solvents is not considered. However,
the presence of high levels of inorganic salts with the lignin (27%) negatively
affected the mechanical properties of the resins.
Qin et al. (2013) reported that Kraft lignin (KL) was partially depolymerized by
base catalyzed depolymerization (BCD) in supercritical methanol to increase its
solubility in organic acids, and the resulting partially depolymerized lignin (PDL)
was then converted to lignin-based polycarboxylic acid (LPCA) when reacting with
succinic anhydride. These authors have indicated that LPCA could act as a curing
or cocuring agent in the preparation of epoxy resins (Qin et al. 2013). It was also
9 Lignin as a Coating and Curing Agent on Biodegradable Epoxy Resins
japonica) and eucalyptus (Eucalyptus globulus) using steam-exploded methodology, and these materials were then functionalized by reaction with ECH, and catalyzed by a water-soluble phase transfer catalyst (tetramethylammonium chloride)
under alkaline conditions (30% aqueous NaOH) for ring closure using methyl ethyl
ketone as a solvent. The authors found good yields for biomass-derived epoxy resins (63.4–68.2%), and these were in line with the yield from bisphenol A (70%),
thus suggesting that biomass-based epoxy resins could be synthesized using the
same synthetic route that bisphenol A-based resins. In addition, the higher lignin
content in the cured epoxy resins reduced the T max .
Benyahya et al. (2014) reported that biobased epoxy resin cured with green tea
extract (catechin with isophorone diamine) had a T max (299 °C) much lower than
those cured low-Mw lignin epoxy resins (298–336 °C). Asada et al. (2018) also
extracted high pure lignin (99%) (Mw ≈ 5100 g/mol and hydroxyl equivalent) from
white poplar (Populus tremuloides) wastes using a steam explosion methodology
followed by water and acetone extractions for the development of epoxy resins. In
line with this, Asada et al. (2015a) determined that high Mw and the hydroxyl
equivalent lignin was extracted with acetone compared to those extracted in methanol. This means that not only low Mw lignin was extracted with acetone, but also
high Mw lignin. In addition, the tensile strength of the cured epoxy resin obtained
by Asada et al. (2015a) was (~30 MPa) similar to those obtained from epoxy resins
derived from conventional fossils (~27–80 MPa).
Yin et al. (2012) studied the preparation and properties of the lignin-epoxy resin
composite using enzymatic hydrolysis from corn straw lignin and bisphenol. The
epoxy resin could be cured together with the lignin at high temperature, but the cure
temperature for the lignin-epoxy resin mixtures could be reduced by the introduction of a polyamide curing agent. The lignin-epoxy resin composite with a lignin
content of up to 60% was prepared by mixing lignin with epoxy resin and polyamine using a hot-pressing molding process. The optimum performance of composite materials was achieved at the molding temperature of 130 °C.
Ortiz et al. (2019) studied the biobased epoxy resins from biorefinary byproducts, i.e. BCD lignin containing GDE at different mass ratios: 1:1, 1:2, and 1:4
(BCD:GDE). A direct correlation was observed between the glass transition temperature (T g ) of the resin and the lignin content of the samples manufactured under
vigorous mechanical stirring. They found that resins containing a higher BCD lignin content resulted in brittle samples. The direct use of BCD lignin for the synthesis of epoxy resin was also explored by Ortiz et al. (2019), since they are carried out
in an aqueous medium, i.e. the use of organic solvents is not considered. However,
the presence of high levels of inorganic salts with the lignin (27%) negatively
affected the mechanical properties of the resins.
Qin et al. (2013) reported that Kraft lignin (KL) was partially depolymerized by
base catalyzed depolymerization (BCD) in supercritical methanol to increase its
solubility in organic acids, and the resulting partially depolymerized lignin (PDL)
was then converted to lignin-based polycarboxylic acid (LPCA) when reacting with
succinic anhydride. These authors have indicated that LPCA could act as a curing
or cocuring agent in the preparation of epoxy resins (Qin et al. 2013). It was also
9 Lignin as a Coating and Curing Agent on Biodegradable Epoxy Resins