Chapter 7
Rubber Reinforcement with Lignin
Abstract Lignin has been one of the biomass to be utilized more effectively from
the viewpoint of sustainable development. In spite of the increasing interest in lignin
wastes, a few industrialization of the lignin has been successful. Here, lignin as a
rubber reinforcing filler is evaluated, and a soft processing method of lignin-loaded
rubber vulcanizates is proposed. The traditional rubber processing, which is a highly
mechanical method, has not worked well for the powdered lignin as a rubber compounding ingredient. Some ideas on the soft processing method of rubber–lignin
mixtures are suggested for further developmental research. If in success, unique bionanocomposites are to be prepared, when natural rubber is employed as a matrix
rubber.
Keywords Lignin as a filler · Biomass · Sustainable development · Soft
processing · Natural rubber
7.1 Lignin: Old, Still a Promising Filler
Lignin is an amorphous natural polymer, and its worldwide abundance is next to cellulose among many biomasses [1–5]. Lignin is amorphous and the main constituent
of natural trees, in a sense natural biocomposites, together with crystalline cellulose.
In woody plants, high levels of lignin are synthesized in wood and account for 15–
36% of dry weight of wood materials [6]. Hence, the worldwide presence of lignin is
an immense amount. Consequently, the lignin wastes which have naturally rotten in
forest as well as those having been discharged from paper manufacturing industries
are tremendous, too. Under this circumstance, it is more or less of its own accord
that utilization of lignin waste in rubber as a filler has been focused and researched
for many years among rubber engineers [7–14].
Waste lignin from the pulp industries is a main by-product of the papermaking
process, and it is estimated to be a mixture of chemicals produced by complex chemical reactions. In order to mass-produce paper, cellulose, rayon, and so on, pulp
industries need only cellulose, and they have established a process to exclude the
other components of woods. The chemical structure of one of the possible main components in the so-called lignin is schematically shown in Fig. 7.1, which represents
© Springer Nature Singapore Pte Ltd. 2020
S. Kohjiya et al., Reinforcement of Rubber, Springer Series on Polymer
and Composite Materials, https://doi.org/10.1007/978-981-15-3789-9_7
123
Rubber Reinforcement with Lignin
Abstract Lignin has been one of the biomass to be utilized more effectively from
the viewpoint of sustainable development. In spite of the increasing interest in lignin
wastes, a few industrialization of the lignin has been successful. Here, lignin as a
rubber reinforcing filler is evaluated, and a soft processing method of lignin-loaded
rubber vulcanizates is proposed. The traditional rubber processing, which is a highly
mechanical method, has not worked well for the powdered lignin as a rubber compounding ingredient. Some ideas on the soft processing method of rubber–lignin
mixtures are suggested for further developmental research. If in success, unique bionanocomposites are to be prepared, when natural rubber is employed as a matrix
rubber.
Keywords Lignin as a filler · Biomass · Sustainable development · Soft
processing · Natural rubber
7.1 Lignin: Old, Still a Promising Filler
Lignin is an amorphous natural polymer, and its worldwide abundance is next to cellulose among many biomasses [1–5]. Lignin is amorphous and the main constituent
of natural trees, in a sense natural biocomposites, together with crystalline cellulose.
In woody plants, high levels of lignin are synthesized in wood and account for 15–
36% of dry weight of wood materials [6]. Hence, the worldwide presence of lignin is
an immense amount. Consequently, the lignin wastes which have naturally rotten in
forest as well as those having been discharged from paper manufacturing industries
are tremendous, too. Under this circumstance, it is more or less of its own accord
that utilization of lignin waste in rubber as a filler has been focused and researched
for many years among rubber engineers [7–14].
Waste lignin from the pulp industries is a main by-product of the papermaking
process, and it is estimated to be a mixture of chemicals produced by complex chemical reactions. In order to mass-produce paper, cellulose, rayon, and so on, pulp
industries need only cellulose, and they have established a process to exclude the
other components of woods. The chemical structure of one of the possible main components in the so-called lignin is schematically shown in Fig. 7.1, which represents
© Springer Nature Singapore Pte Ltd. 2020
S. Kohjiya et al., Reinforcement of Rubber, Springer Series on Polymer
and Composite Materials, https://doi.org/10.1007/978-981-15-3789-9_7
123