Enhancement of Physical and Mechanical Properties of Sugar Palm Fiber via Vacuum Resin Impregnation - Advanced Materials for Agriculture, Food and Environmental Safety - page 132

In addition to considering the quantitative results of improvement in
physical properties (Figs. 5.3 and 5.5), these photographs have been taken
as evidence that the impregnation agents are located in the cell lumen and
might also be within the cell wall. It is important to emphasize that in this
study mere lumen i lling (without dif usion of resin into the cell wall) would
not be expected to give satisfactory improvement in the dimensional sta-
bility of i bers and their composites. Polymerization of an impregnation
agent within the cell wall is still required, where it results in a lower degree
of swelling when the impregnated i ber or its composite is exposed to
moisture. If dif usion of resin did not occur in the cell wall, the water mol-
ecules would still be absorbed into the cell wall when the i ber is exposed
to water, even though the lumen is fully i lled with the resin. h is is due
to the attractive force of hydrogen bonding in the polymeric constituent
of i ber cell walls. h is causes the cell wall to swell and the swelling occurs
continuously until the cell wall is fully saturated with water molecules. h is
is called the i ber saturation point (FSP), which indicates that the cell wall
cannot increase its moisture content any further. h e water molecules that
are absorbed into the i ber beyond this point become located in the lumen,
or in other macrovoids [29], preventing further swelling of the cell wall.

5.3.2 Tensile Properties of Impregnated Fibre

Figure 5.7 shows the distinct tensile stress strain behaviors of impregnated
i bers at er impregnation with PF and UP. It shows that as the impregna-
tion pressure of sugar palm i ber increased, the tensile strength and tensile
modulus also increased and the elongation at break decreased.

UP 500 UP 60 UP 700
UP 800
UP 900
UP 1000
Control

350

PF 50 0 PF 600
PF 700
PF 800 PF 900 PF 1000

300

250

200

150

100

50

0

0 5 10 15 20 25

Strain (%)

Figure 5.7 Stress-strain behavior of PF- and UP-impregnated sugar palm i ber at various
impregnation pressures.