318
14 Cellulose
residual material. It is important to maintain the structural integrity of the cellulose
during the process of extraction as this eventually affects the quality and applicability
of the cellulose obtained. Properties such as crystallinity, degree of polymerization,
microfibril structure, wettability and mechanical properties are used to measure the
quality of cellulose extracted. Here, we consider extraction methods that have been
reported for the main cellulose sources in the aquatic ecosystem.
14.5.1 Extraction of Cellulose from Aquatic Plants
High moisture content of water hyacinth means the process of drying may require
more time and energy input compared to other plants. Water hyacinth has a moisture
content of around 93–96%. Following the drying, the water hyacinth fibers are heated
at 115 °C in toluene solvent for a duration of 3 h. The next step is the removal of color
by bleaching in sodium hypochlorite NaClO (3%) under heating for 2 h at 80 °C.
The hemicellulose within the cell wall is removed using the process of hydrolysis
with sodium hydroxide (1%) at a temperature of 60 °C for 2 h. Further treatment is
carried out with sodium hypochlorite at 1% at 75 °C while stirring for a duration of
3 h, to remove the residual lignin (Istirokhatun et al. 2015).
To extract cellulose from Azolla plant, in the method by Miranda et al. (2016), the
Azolla plants harvested were washed and dried in hot air oven at 70 °C overnight. This
was followed by grinding to reduce particle size. Lignin was removed by autoclaving
in sodium acetate at 121 °C for 20 min. The remaining mass contains a mixture
of polysaccharide starch and cellulose. The starch can be removed by chemical
treatment with sodium hydroxide and heat or enzymatic treatment with amylase and
amyloglucosidase which reduces the starch to glucose. Where the goal is to obtain
cellulose, the glucose can then be washed off as it is water soluble leaving behind
cellulose fibers. This process is summarized in Fig. 14.1.
14.5.2 Extraction of Cellulose from Algae
One key advantage of cellulose extraction from algae over aquatic plants such as
Azolla is the very little to no lignin content in algae. This eliminates the high energy
and chemically demanding delignification process. Although cellulose is not a main
structural polymer in brown algae, some have been reported to have no cellulose
content, for example, brown algae is made up of 32% alginate, 15% laminarin which
is the glucose polymer in brown algae, 18% mannitol and the rest ash or salts This
composition was based on average values from three harvests of S. latissima, a strain
of brown algae commonly used in the industry (Konda et al. 2015). Red algae on
the other hand contain cellulose, glucans and galactan (Wi et al. 2009; Yoon et al.
2010). Nanocellulose extraction from red algae (Gelidium elegans) involved alkaline
treatment, bleaching and acid hydrolysis. The nanocellulose extracted had diameter
14 Cellulose
residual material. It is important to maintain the structural integrity of the cellulose
during the process of extraction as this eventually affects the quality and applicability
of the cellulose obtained. Properties such as crystallinity, degree of polymerization,
microfibril structure, wettability and mechanical properties are used to measure the
quality of cellulose extracted. Here, we consider extraction methods that have been
reported for the main cellulose sources in the aquatic ecosystem.
14.5.1 Extraction of Cellulose from Aquatic Plants
High moisture content of water hyacinth means the process of drying may require
more time and energy input compared to other plants. Water hyacinth has a moisture
content of around 93–96%. Following the drying, the water hyacinth fibers are heated
at 115 °C in toluene solvent for a duration of 3 h. The next step is the removal of color
by bleaching in sodium hypochlorite NaClO (3%) under heating for 2 h at 80 °C.
The hemicellulose within the cell wall is removed using the process of hydrolysis
with sodium hydroxide (1%) at a temperature of 60 °C for 2 h. Further treatment is
carried out with sodium hypochlorite at 1% at 75 °C while stirring for a duration of
3 h, to remove the residual lignin (Istirokhatun et al. 2015).
To extract cellulose from Azolla plant, in the method by Miranda et al. (2016), the
Azolla plants harvested were washed and dried in hot air oven at 70 °C overnight. This
was followed by grinding to reduce particle size. Lignin was removed by autoclaving
in sodium acetate at 121 °C for 20 min. The remaining mass contains a mixture
of polysaccharide starch and cellulose. The starch can be removed by chemical
treatment with sodium hydroxide and heat or enzymatic treatment with amylase and
amyloglucosidase which reduces the starch to glucose. Where the goal is to obtain
cellulose, the glucose can then be washed off as it is water soluble leaving behind
cellulose fibers. This process is summarized in Fig. 14.1.
14.5.2 Extraction of Cellulose from Algae
One key advantage of cellulose extraction from algae over aquatic plants such as
Azolla is the very little to no lignin content in algae. This eliminates the high energy
and chemically demanding delignification process. Although cellulose is not a main
structural polymer in brown algae, some have been reported to have no cellulose
content, for example, brown algae is made up of 32% alginate, 15% laminarin which
is the glucose polymer in brown algae, 18% mannitol and the rest ash or salts This
composition was based on average values from three harvests of S. latissima, a strain
of brown algae commonly used in the industry (Konda et al. 2015). Red algae on
the other hand contain cellulose, glucans and galactan (Wi et al. 2009; Yoon et al.
2010). Nanocellulose extraction from red algae (Gelidium elegans) involved alkaline
treatment, bleaching and acid hydrolysis. The nanocellulose extracted had diameter