Insulation Materials Made with Vegetable Fibres - Nearly Zero Energy Building Refurbishment - page 413

Table 2 Chemical composition of some vegetable fibres (percentage of total)

Cellulose Hemicellulose Lignin Pentin

Flax 71 19 2.2 2.0

Hemp 75 18 3.7 0.9

Jute 72 13 13 0.2

Ramie 76 15 0.7 2.1

Abaca 70 22 5.7 0.6

Sisal 73 13 11 0.9

Cotton 93 2.6 0 2.6

Kapok 64 23 13 -

lignin (Reddy and Yang 2005 ). Other components, such as pectin, ash and waxes,
can be found in much lower quantities generally. Table 2 illustrates an example of
the chemical analysis of the major components of some vegetable fibres (Roberts
2007 ). As can be seen, a substantial variation is observed for the constituents
which can be attributed to nature.
A more detailed description of the chemical composition of vegetable fibres can
be found in (Mishra 2000 ; Saheb and Jog 1999 ; Bismarck et al. 2005 ). Most of
them, such as, flax, hemp, jute, ramie, sisal and palm, are composed of cellulose,
hemicelluloses and lignin with varied proportions, except for cotton that has
principally cellulose.
Cellulose is generally the main component of the cell walls in vegetables and
makes the fibres strong and flexible. Cellulose is a long-chain polymer made by the
linking of smaller molecules. Its long-chain polysaccharides consist of glucose
units as links. Figure 6 presents the basic chemical structure of cellulose. Each
monomer bears hydroxyl groups which form hydrogen bonds. The hydrogen bonds
play a major role in directing the structure and governing the physical properties of
the cellulose, for example its moisture-absorbable property.
Specifically, cellulose acts as the basic building block for the fibrous materials
for providing strength and stability to the walls and the fibre (Paster et al. 2003 ).
The existence of cellulose as in plant and vegetable cell walls was first discovered
by Anselm Payen in 1838. The Young's modulus of the basic cellulose crystalline
nanocrystal is roughly 130 GPa, and its tensile strength is close to 1 Gpa which is
potentially stronger than steel and similar to Kevlar (Gibson 2012 ; Dufresne 2008 ).
Gibson reviewed the composition and microstructure of the cell wall and the

Fig. 6 Basic chemical
structure of cellulose