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and mechanical properties of PP/lignin composite were greatly improved due to its
larger interfacial area and more uniform filler dispersion compared to the pure PP
matrix. In addition, lignin improved the stability and antioxidative capabilities of
the lignocellulosic flour/PP composites, resulting in a lower loss of flexural strength
and a smoother surface than lignin-free composites after accelerated UV weathering
(Peng et al. 2015).
In addition to preventing degradation of photolabile substances and the damage
of free radicals, lignin can function as a UV blocker in composites. Avelino et al.
(2019) prepared poly(methyl methacrylate) (PMMA) films containing lignin. The
PMMA/lignin film showed high UV absorption and visible-light transparency
capacities when exposed to natural sunlight (Fig. 5.7). These properties can prolong
the service life of the film.
5.5.2 Applications in Asphalt Binders
Exposure to atmospheric oxygen causes oxidative aging of asphalt binders. This is
the main cause of its deterioration thus altering its physical properties and reducing
its service life. Many polymers, such as lead diamyl dithiocarbamate and zinc dibutyl dithiocarbamate, with anti-oxidation abilities, have been added to asphalt, but
such improved polymer asphalt demonstrates unsatisfactory in situ performance
(Ouyang et al. 2006). Lignin has been used as an asphalt additive and has shown an
ideal anti-oxidative performance. Arafat et al. (2019) reported that the addition of
6% lignin is feasible for asphalt pavements. The presence of lignin helps to inhibit
the formation of carbonyl structures during aging, thus improving the durability and
effective life of asphalt pavement. The addition of lignin at the same time also
improves the elastic recovery and reduces the irreversible deformation properties of
asphalt pavement (Xu et al. 2017). However, the oxidation of lignin itself affects its
function as an antioxidant and this should be considered. The oxidation of lignin can
be significant above 150 °C. The low Mw acid and phenolic compounds are the
main oxidation products. To achieve the best antioxidant performance in asphalt,
the temperature at which the lignin and asphalt are mixed should be controlled to
avoid the oxidation of lignin (Pan 2012).
5.5.3 Applications in Biomaterials
The damage of ROSs to cells is one of the main causes of many diseases, such as
cancer, atheroscleosis and the degenerative processes associated with aging. ROS
are produced in biological systems during metabolic processes and upon exposure
to exogenous sources, such as UV light and food ingredients. Exposure of red blood
cells (RBC) to oxygen free radical generating systems leads to lipid oxidation,
which is a type of oxidative damage. Lignin as part of dietary fiber is an efficient
5 Lignin as a Natural Antioxidant: Property-Structure Relationship and Potential…
and mechanical properties of PP/lignin composite were greatly improved due to its
larger interfacial area and more uniform filler dispersion compared to the pure PP
matrix. In addition, lignin improved the stability and antioxidative capabilities of
the lignocellulosic flour/PP composites, resulting in a lower loss of flexural strength
and a smoother surface than lignin-free composites after accelerated UV weathering
(Peng et al. 2015).
In addition to preventing degradation of photolabile substances and the damage
of free radicals, lignin can function as a UV blocker in composites. Avelino et al.
(2019) prepared poly(methyl methacrylate) (PMMA) films containing lignin. The
PMMA/lignin film showed high UV absorption and visible-light transparency
capacities when exposed to natural sunlight (Fig. 5.7). These properties can prolong
the service life of the film.
5.5.2 Applications in Asphalt Binders
Exposure to atmospheric oxygen causes oxidative aging of asphalt binders. This is
the main cause of its deterioration thus altering its physical properties and reducing
its service life. Many polymers, such as lead diamyl dithiocarbamate and zinc dibutyl dithiocarbamate, with anti-oxidation abilities, have been added to asphalt, but
such improved polymer asphalt demonstrates unsatisfactory in situ performance
(Ouyang et al. 2006). Lignin has been used as an asphalt additive and has shown an
ideal anti-oxidative performance. Arafat et al. (2019) reported that the addition of
6% lignin is feasible for asphalt pavements. The presence of lignin helps to inhibit
the formation of carbonyl structures during aging, thus improving the durability and
effective life of asphalt pavement. The addition of lignin at the same time also
improves the elastic recovery and reduces the irreversible deformation properties of
asphalt pavement (Xu et al. 2017). However, the oxidation of lignin itself affects its
function as an antioxidant and this should be considered. The oxidation of lignin can
be significant above 150 °C. The low Mw acid and phenolic compounds are the
main oxidation products. To achieve the best antioxidant performance in asphalt,
the temperature at which the lignin and asphalt are mixed should be controlled to
avoid the oxidation of lignin (Pan 2012).
5.5.3 Applications in Biomaterials
The damage of ROSs to cells is one of the main causes of many diseases, such as
cancer, atheroscleosis and the degenerative processes associated with aging. ROS
are produced in biological systems during metabolic processes and upon exposure
to exogenous sources, such as UV light and food ingredients. Exposure of red blood
cells (RBC) to oxygen free radical generating systems leads to lipid oxidation,
which is a type of oxidative damage. Lignin as part of dietary fiber is an efficient
5 Lignin as a Natural Antioxidant: Property-Structure Relationship and Potential…