Despite the high competition within the paper production industry, fibre crops are developing an increasing presence, and Arundo donax (the giant reed) is a good source of fibrous raw material for making quality paper and also appears to be suitable for generic grades of tissues for both facial tissues and toilet paper. Finding non-wood paper alternatives is crucial, since over 30 million acres of forest are cut down every year. Destroying forests for products such as pulp and paper creates long-term environmental disturbances in forest habitats.
Arundo donax versus Eucalyptus globolus as non-wood paper alternative
A perennial rhizomatous grass, Arundo donax is widely distributed in all the warm temperate areas of Europe (mainly in the Mediterranean region) and can be easily adapted to different ecological conditions (Perdue, 1958).
Huaiyu et al. (2006) prepared and pulped harvested material of Arundo donax to confirm the paper making qualities of the plant. Tests on the fibre and pulp quality of samples of giant reed stems confirmed it is a valuable non-wood paper alternative as a pulp feedstock for paper making.
It was observed that Arundo donax cooks more rapidly than wood and its cellulose yields are rather high, varying from 33% to 53%. Another great advantage of using giant reed for paper production is that its bleach response is good, which means it requires less chemicals. The strength properties of Arundo donax were proven superior to hardwood. The comparison of giant reed with hardwoods in particular is driven by the similarity in fibre length and length to diameter ratio of the fibres. Estimates indicate that giant reed has the potential to produce 500% more air dry pulp per hectare per year compared to blue gum (Eucalyptus globulus) hardwood trees.
In general, the kraft pulping of giant reed is characterised by a lower cellulose yield (43.8 vs. 52.4%) and a higher content of residual lignin, compared to kraft pulping of Eucalyptus globulus wood performed under identical cooking conditions (Valente et al., 1991). Bulk of Arundo donax kraft pulps is higher compared to wood (2.05 cm3/gramm for Arundo vs. 1.63 cm3/gramm for Eucalyptus globulus), suggesting lower wet fiber compactability. However, viscosity and, especially, tearing strength of pulps from Arundo donax are higher than those from Eucalyptus globulus.
Huaiyu’s study (carried out in Australia) concluded that Arundo donax can be grown at yields of up to 40 dry tonnes of stems per hectare per year and the stem material can be processed into a valuable alternative to hardwood for pulp and paper manufacturing. In the future giant reed is considered to replace part of the Eucalyptus hardwood feedstock used in paper making.
Which part of Arundo donax is the most suitable for pulp production?
The stem of Arundo donax consists of two botanically distinct parts: nodes and internodes. The nodes are composed of a nodal diaphragm, embedded inside the hollow cylinder of the stem, and the adjacent transition regions. Similar to such industrial crops as bamboo or wheat straw, the stem of the giant reed is hollow in internodes, but solid in nodes.
These botanically distinct parts of the stem of giant reed (nodes and internodes) showed some differences in chemical and anatomical composition and a different access to pulping.Under equal cooking conditions of a conventional kraft process, pulps with higher yield and lower content of residual lignin were produced from internodes. The strength properties as well as brightness and viscosity were also higher for pulps from internodes, compared to nodes.
Kraft pulps from giant reed showed much faster response on beating than wood pulps, and the strength properties were easily improved with minimal energy requirements on beating. Pulp beating improved much more actively the strength properties of kraft pulps from internodes, creating however noteworthy dewatering problems. Increase in drainage resistance was more evident for beaten pulps from nodes, which was connected with the higher content of hemicelluloses and of short non-fibrous cells.The nodes of the plant stem can be reckoned as an undesirable component for pulp manufacturing which have an adverse effect on yield and properties of pulps from Arundo as a whole.However, this negative impact can be minimised using suitable screening techniques to eliminate nodes from the crushed stems before pulping.
To conclude, the internodes of the stems of Arundo donax are more suitable for pulping and the presence of nodes could have an opposing effect on pulp yield. This is indisputably connected with their anatomical structure, namely, with a pre-dominance of the non-fibrous short-cell tissues in the nodal diaphragm.
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