320
14 Cellulose
Compared to the extraction from aquatic plants, the extraction of nanocellulose
from terrestrial wood is more intensive. The pulp used for this process contained
lignin of 0.7% and hemicellulose 13.8%. The pulp had been pretreated to reduce
lignin content. The pulping process requires the use of either the kraft process (Lahnalammi et al. 2018) or the acid sulfite process (Hanhikoski et al. 2019). The kraft
process involves treatment of wood with high concentrations of sodium hydroxide
and sodium sulfide at elevated temperatures while the acid sulphite process makes
use of high concentration of sulfuric acid at high temperatures. The process to convert
pulp to nanocellulose involved suspension of wood pulp in water at a ratio of 1:100
(grams wood pulp to water). This is then followed by oxidation with 10 mmol of
sodium hypochlorite per every gram of cellulose mediated by a mixture of 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) and sodium bromide. Sodium hydroxide is
then added to increase the pH to 10 and the reaction allowed to take place for 5 h to
form cellulose nanoparticles, which was then washed with water and the cellulose
nanoparticles separated by centrifugation at 14,000 rpm (Olatunji and Olsson 2015).
The extraction of cellulose from wood requires a more rigorous process to remove
the lignin and hemicellulose which are present at a higher content.
14.6 Environmental Implications
Here, some environmental issues arising from the extraction of cellulose from aquatic
plants and algae are discussed. In this section, more focus is directed at the process of
extraction as discussed in the previous section. Further environmental issues arise in
additional processes such as transportation of the raw materials to the factory and the
packaging process. These issues have been discussed in other sections of the book
and will not be discussed here to avoid repetition.
14.6.1 Energy for Drying
Most of the aquatic plants contain a considerable amount of water. Water hyacinth
contains the most amount of water ranging between 93 and 96% (Penfound and Earle
1948). Drying could be done prior to transportation to factories where the biopolymers are extracted or the biomass could be transported before drying. Spoilage could
be prevented by initial drying, and the reduced moisture content cold also reduces
transportation cost. To dry a sample of duckweed, for example, required drying at
60 °C for 2 days (Chen et al. 2012) while Azolla required drying at 70 °C for several hours overnight (Miranda et al. 2016). Drying of biomass is usually done using
electric-powered hot air ovens. This could be from hydroelectricity, nuclear or renewable energy-powered source. Drying could also be achieved using open air drying in
hotter climates, where high level of purity is not required at this stage.
14 Cellulose
Compared to the extraction from aquatic plants, the extraction of nanocellulose
from terrestrial wood is more intensive. The pulp used for this process contained
lignin of 0.7% and hemicellulose 13.8%. The pulp had been pretreated to reduce
lignin content. The pulping process requires the use of either the kraft process (Lahnalammi et al. 2018) or the acid sulfite process (Hanhikoski et al. 2019). The kraft
process involves treatment of wood with high concentrations of sodium hydroxide
and sodium sulfide at elevated temperatures while the acid sulphite process makes
use of high concentration of sulfuric acid at high temperatures. The process to convert
pulp to nanocellulose involved suspension of wood pulp in water at a ratio of 1:100
(grams wood pulp to water). This is then followed by oxidation with 10 mmol of
sodium hypochlorite per every gram of cellulose mediated by a mixture of 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO) and sodium bromide. Sodium hydroxide is
then added to increase the pH to 10 and the reaction allowed to take place for 5 h to
form cellulose nanoparticles, which was then washed with water and the cellulose
nanoparticles separated by centrifugation at 14,000 rpm (Olatunji and Olsson 2015).
The extraction of cellulose from wood requires a more rigorous process to remove
the lignin and hemicellulose which are present at a higher content.
14.6 Environmental Implications
Here, some environmental issues arising from the extraction of cellulose from aquatic
plants and algae are discussed. In this section, more focus is directed at the process of
extraction as discussed in the previous section. Further environmental issues arise in
additional processes such as transportation of the raw materials to the factory and the
packaging process. These issues have been discussed in other sections of the book
and will not be discussed here to avoid repetition.
14.6.1 Energy for Drying
Most of the aquatic plants contain a considerable amount of water. Water hyacinth
contains the most amount of water ranging between 93 and 96% (Penfound and Earle
1948). Drying could be done prior to transportation to factories where the biopolymers are extracted or the biomass could be transported before drying. Spoilage could
be prevented by initial drying, and the reduced moisture content cold also reduces
transportation cost. To dry a sample of duckweed, for example, required drying at
60 °C for 2 days (Chen et al. 2012) while Azolla required drying at 70 °C for several hours overnight (Miranda et al. 2016). Drying of biomass is usually done using
electric-powered hot air ovens. This could be from hydroelectricity, nuclear or renewable energy-powered source. Drying could also be achieved using open air drying in
hotter climates, where high level of purity is not required at this stage.