202
noted that LPCA could act as a curing agent to cure a commercial epoxy (DER 353)
in a temperature range similar to commercial anhydride curing agents. The LPCAcured DER 353 resin exhibited a moderate T g , i.e. 62.3 °C, and a storage modulus
comparable to curing with a commercial anhydride curing agent. The solid LPCA
could be used together with other liquid curing agents such as glycerol tris (succinate monoester) (GTA) and commercial hexahydrophthalic anhydride (HHPA) to
cure epoxies. The results found by these authors suggest that the use of a mixture of
LPCA and a liquid curing agent not only adjusted the viscosity of the resin system
but also largely regulated the dynamic mechanical properties and thermal stability
of cured resins (Qin et al. 2013). This study also demonstrated that PDL can serve
as a raw material for the preparation of the curing agent and be used for epoxy
applications.
Wang et al. (2019) reported a new use of lignin to produce graphene-based
waterborne epoxy (WEP) nanocomposites from pristine graphite in a water-only
route. The interactions between graphene particles and OH groups from lignin were
confirmed. Composite WEP coatings containing 0.5% graphene showed excellent
corrosion resistance compared to pure WEP coating. This was explained due to the
good dispersion and interactions between graphene and lignin particles, resulting in
improved thermal and mechanical properties, as well as ultra-high barrier properties. This was also attributed to the ‘labyrinth effect’ caused by the addition of lignin. The prepared nanocomposite had the potential application as an anticorrosive
coating of the metal substrate, which provided a new strategy for the use of lignin
of high added value.
Abdul Khalil et al. (2011) reported that lignin was successfully isolated from
EFB obtained from black liquor, and was used as a curing agent for epoxy resin
matrices. These authors concluded that the mechanical properties of these materials
were optimal when the composites were made from epoxy resins containing 25%
EFB (Abdul Khalil et al. 2011).
Liu et al. (2014) reported about a novel approach to harden epoxy resin with
lignin obtained from common waste materials from the pulp and paper industry.
Carboxylic acid-functionalized alkali lignin (AL-COOH) was prepared and subsequently incorporated into anhydride-cured epoxy networks via a one-pot method.
The addition of 1.0 wt.% AL-COOH produced increases of 68% and 164% in the
critical stress intensity factor and critical strain energy release rate, respectively,
compared to the pure epoxy. It is noteworthy that the tensile strength of the epoxylignin resin was almost the same as that of the pure epoxy, while Young’s modulus
of the epoxy-lignin resin increased moderately as the ALCOOH load increased. The
effectively hardened epoxy resins with low-cost biorenewable lignin have considerable potential for use as durable coating materials or matrix materials for high performance composites.
Xin et al. (2016) synthesized lignin-based epoxy resins from the reaction of ECH
and PDL. These authors found that the synthesized resins had a viscoelastic yield
greater than the DER332 epoxy resin, especially at elevated temperatures.
Nisha et al. (2019) compared different properties of epoxy composites containing lignin modified with triethylammonium hydrogen sulphate and pure epoxy
C. Asada et al.
noted that LPCA could act as a curing agent to cure a commercial epoxy (DER 353)
in a temperature range similar to commercial anhydride curing agents. The LPCAcured DER 353 resin exhibited a moderate T g , i.e. 62.3 °C, and a storage modulus
comparable to curing with a commercial anhydride curing agent. The solid LPCA
could be used together with other liquid curing agents such as glycerol tris (succinate monoester) (GTA) and commercial hexahydrophthalic anhydride (HHPA) to
cure epoxies. The results found by these authors suggest that the use of a mixture of
LPCA and a liquid curing agent not only adjusted the viscosity of the resin system
but also largely regulated the dynamic mechanical properties and thermal stability
of cured resins (Qin et al. 2013). This study also demonstrated that PDL can serve
as a raw material for the preparation of the curing agent and be used for epoxy
applications.
Wang et al. (2019) reported a new use of lignin to produce graphene-based
waterborne epoxy (WEP) nanocomposites from pristine graphite in a water-only
route. The interactions between graphene particles and OH groups from lignin were
confirmed. Composite WEP coatings containing 0.5% graphene showed excellent
corrosion resistance compared to pure WEP coating. This was explained due to the
good dispersion and interactions between graphene and lignin particles, resulting in
improved thermal and mechanical properties, as well as ultra-high barrier properties. This was also attributed to the ‘labyrinth effect’ caused by the addition of lignin. The prepared nanocomposite had the potential application as an anticorrosive
coating of the metal substrate, which provided a new strategy for the use of lignin
of high added value.
Abdul Khalil et al. (2011) reported that lignin was successfully isolated from
EFB obtained from black liquor, and was used as a curing agent for epoxy resin
matrices. These authors concluded that the mechanical properties of these materials
were optimal when the composites were made from epoxy resins containing 25%
EFB (Abdul Khalil et al. 2011).
Liu et al. (2014) reported about a novel approach to harden epoxy resin with
lignin obtained from common waste materials from the pulp and paper industry.
Carboxylic acid-functionalized alkali lignin (AL-COOH) was prepared and subsequently incorporated into anhydride-cured epoxy networks via a one-pot method.
The addition of 1.0 wt.% AL-COOH produced increases of 68% and 164% in the
critical stress intensity factor and critical strain energy release rate, respectively,
compared to the pure epoxy. It is noteworthy that the tensile strength of the epoxylignin resin was almost the same as that of the pure epoxy, while Young’s modulus
of the epoxy-lignin resin increased moderately as the ALCOOH load increased. The
effectively hardened epoxy resins with low-cost biorenewable lignin have considerable potential for use as durable coating materials or matrix materials for high performance composites.
Xin et al. (2016) synthesized lignin-based epoxy resins from the reaction of ECH
and PDL. These authors found that the synthesized resins had a viscoelastic yield
greater than the DER332 epoxy resin, especially at elevated temperatures.
Nisha et al. (2019) compared different properties of epoxy composites containing lignin modified with triethylammonium hydrogen sulphate and pure epoxy
C. Asada et al.