Environmental Engineering Reference
In-Depth Information
Water molecules
Dry
microibrils
Figure 5.9 Illustration of wet and dry microi brils of natural i bers.
intermolecular and intramolecular bonding in the i ber. On the other
hand, if the water molecules were removed, the microi brils would shrink
and decrease in size, causing the cellulose chains to become closer and
form stronger intermolecular bonding among the microi brils as well as
intramolecular bonding within the microi brils. Fibers are stronger as the
cellulose chains form strong bonding among themselves. h is is illustrated
in Figure 5.9 where there are portions of wet microi brils (at both ends of
the microi brils) due to the presence of moisture, while the dry portion of
the microi brils shrink (the middle portion). h e decrease in the strength
of natural i ber due to the presence of moisture has also been reported
by several researchers [48-60, 18] found an interesting result in that the
strength of pineapple leaf i ber (PALF) decreased by 50% when tested
under wet conditions.
Figure 5.10 indicates that the strength of the natural i ber increased expo-
nentially with the reduction of MC. It also shows the changes in strength
and shrinkage that took place at a MC below the FSP value. h is explains the
point at which water molecules are present in the cell wall and that no free
water molecules (whether liquid or vapor) are present in the cell lumen. As
the number of water molecules in the cell wall (referred to as bound water)
is reduced, the i ber shrinks linearly and swells when moisture is absorbed
until the moisture content reaches the FSP. As a consequence, when the MC
is higher than the FSP, water molecules (vapor or liquid) are present in the
cell lumen and i ber swelling stops despite further increase in i ber moisture
content. h us, if the strength and swelling are determined as a function of
i ber MC, it exhibits a constant value above the FSP [25, 26].
h e resin that was locked in the i ber caused the i ber to become more
rigid and stif where it approached the behavior of brittle PF and UP res-
ins. It can be observed in Figure 5.11 that there is an increase in tensile
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