76
Lignin also can improve the photostability of UV sensitive substances (e.g. quercetin). Quercetin is an excellent antioxidant and has some benefits for human health
when taken, such as anti-cancer, anti-inflammatory, and anti-diabetic activities.
However, it shows a photodegradation behavior when exposed to UV radiation.
Therefore, maintaining its stability in the UV environment is important to maintain
its antioxidant activity and other functions in cosmetics and other topical pharmaceuticals. Liu et al. (2017) formed conjugate structures from the quercetin and lignin mixture. Due to the antioxidant protection of lignin, a synergistic influence
between lignin and quercetin was obtained, thus improving antioxidant performance
(Liu et al. 2017).
Pyrethrins are currently widely used natural pesticides, which are derived from
plants, however, their photodegradability limits their use in agriculture. FernándezPérez et al. (2014) successfully prepared the pyrethrin formulation in which the
pyrethrin was encapsulated with LS and KL to protect them from volatilization and
photodegradation.
Plastics can degrade after irradiation with UV light, due to the formation of free
radicals. Lignin because of its free radical scavenging properties can be used as a
low-cost UV stabilizer in plastics. However, lignin has a large number of polar
groups in its molecule structure, such as carboxyl and hydroxyl groups, while plastics such as polypropylene (PP) are non-polar. This dissimilarity causes a poor compatibility, which in turn causes a poor dispersion of lignin into the plastic matrix. A
good dispersion of lignin in non-polar polymers is key to using lignin as an excellent barrier and UV stabilizer in plastics. Chen et al. (2016) successfully prepared
sheet-like AL particles via freeze-drying. The reduced size and the increased aspect
ratio of the lignin particle increased the dispersion of lignin into PP. The PP/lignin
composite was obtained by melting the lignin particles with PP. The UV-resistant
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
Nu
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
R
RH
hv
second radical abstraction by SH
combination with R
in the presence of
nucleophiles(NuH)
potential for further reaction
R
Fig. 5.7 Proposed major radical termination reaction of lignin-PEGMA copolymers with
UV-induced radicals
Z. Qin et al.
Lignin also can improve the photostability of UV sensitive substances (e.g. quercetin). Quercetin is an excellent antioxidant and has some benefits for human health
when taken, such as anti-cancer, anti-inflammatory, and anti-diabetic activities.
However, it shows a photodegradation behavior when exposed to UV radiation.
Therefore, maintaining its stability in the UV environment is important to maintain
its antioxidant activity and other functions in cosmetics and other topical pharmaceuticals. Liu et al. (2017) formed conjugate structures from the quercetin and lignin mixture. Due to the antioxidant protection of lignin, a synergistic influence
between lignin and quercetin was obtained, thus improving antioxidant performance
(Liu et al. 2017).
Pyrethrins are currently widely used natural pesticides, which are derived from
plants, however, their photodegradability limits their use in agriculture. FernándezPérez et al. (2014) successfully prepared the pyrethrin formulation in which the
pyrethrin was encapsulated with LS and KL to protect them from volatilization and
photodegradation.
Plastics can degrade after irradiation with UV light, due to the formation of free
radicals. Lignin because of its free radical scavenging properties can be used as a
low-cost UV stabilizer in plastics. However, lignin has a large number of polar
groups in its molecule structure, such as carboxyl and hydroxyl groups, while plastics such as polypropylene (PP) are non-polar. This dissimilarity causes a poor compatibility, which in turn causes a poor dispersion of lignin into the plastic matrix. A
good dispersion of lignin in non-polar polymers is key to using lignin as an excellent barrier and UV stabilizer in plastics. Chen et al. (2016) successfully prepared
sheet-like AL particles via freeze-drying. The reduced size and the increased aspect
ratio of the lignin particle increased the dispersion of lignin into PP. The PP/lignin
composite was obtained by melting the lignin particles with PP. The UV-resistant
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
O
H 3 CO
SH
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
OH
H 3 CO
Nu
lignin
CH 3
H 3 C
H 3 C
H 3 C
PEG
R
RH
hv
second radical abstraction by SH
combination with R
in the presence of
nucleophiles(NuH)
potential for further reaction
R
Fig. 5.7 Proposed major radical termination reaction of lignin-PEGMA copolymers with
UV-induced radicals
Z. Qin et al.