Conservation Science

62 Chapter 4

crystallinity, lacking long-range ordering, and amorphous regions, in which
the ordering of the polymer breaks down completely; among these, additional
matrix components such as hemicelluloses, pectins and lignin are also found.
At the molecular level, the cellulose chains are organised into parallel – and
hence crystalline – bundles of 100 or so chains. These then group to form
micelles or elementary fibrils, typically 5–6 nm in diameter. Aggregates of 15 or so
micelles, within the amorphous intermicellar space, form microfibrils, which are
roughly 75–90 nm in diameter. Bundles of microfibrils, again embedded within
amorphous material, the interfibrillar space, form fibrils or macrofibrils, typ-
ically 0.5 m in diameter. Macrofibrils are found as lamellae in the cell walls.
The intermicellar and interfibrillar matrices, as well as the intercellular middle
lamella, are composed of the non-crystalline components mentioned above –
amorphous cellulose, hemicellulose, pectin and lignin; within these regions
there are extensive networks of capillaries (Figure 5).
The cell walls are organised in layers, of which the secondary wall is the
thickest (several microns), possessing the greatest degree of crystallinity and
making the dominant contribution to the physical properties of the fibre. Within
these walls the macrofibrils are wound around the fibre axis, with a sense and
angle characteristic of the fibre species – for flax, the secondary cell wall is S
(i.e.anticlockwise) wound at about 6.5°.
Hemicelluloses (polysaccharides composed primarily of xylose and man-
nose) are much shorter in length than cellulose and are extensively branched;
these species may act to cross-link cellulose and other polymers, and also
form the amorphous matrix of the interfibrillar space, in which cellulose
microfibrils are embedded. Pectins are jelly-like, acidic polymers composed

+ +

+ +

β=

84 ̊

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+ +

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c= 7.9

Å

a= 8. 35 Å

++ ++

++ ++

• 
  

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β = 84 ̊O

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b= 10.

3 Å

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a= 8. 35

c= 7.9 Å Å

Figure 4bThe unit cell of crystalline cellulose I