It was found that the ash content, alcohol–
benzene solubility, 1% NaOH solubility decreased by the
reduction of the amount of impurities such as ash, resulting in a
more stable, stronger and lighter fiber.
Lignin starts to soften
and dissolve at temperature over 70 C, and acts as a binding agent
for cellulose fibers. The pretreated (washed and boiled) fibers
have higher lignin, holocellulose and alpha-cellulose contents than
the unpretreated fibers. Thus, pretreated fibers are stiffer and
tougher. However, the percentage increase of lignin content in pretreated
fibers are lower than that of holocellulose and
alpha-cellulose due to the fact that cellulose is insoluble and more
durable than other components. In addition, cellulose is an
important factor for heat insulation and sound absorption properties
of fiber cement materials.