ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 9, pp. 1542!1545. + Pleiades Publishing, Inc., 2006.
Original Russian Text + M.V. Shishonok, V.I. Shadrina, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 9, pp. 1558!1561.
AND POLYMERIC MATERIALS
Recovery of Wool from Flax Fibers Using Nitric Acid
M. V. Shishonok and V. I. Shadrina
Belarussian State University, Minsk, Belarus
Received June 4, 2006
Abstract-The principal possibility of preparing wool from cottonized flax fibers using nitric acid both in the
course of cooking and in the bleaching step was studied. The influence of the nitric acid concentration and
cooking time on the extent of flax delignification was examined.
About 12% of cellulose is produced in the world
from annual plants, including flax ; according to
estimates , by 2010 this share can reach 19.8%.
For Belarus and Russia, flax is a domestic raw materi-
al capable to replace imported cotton. National and
international programs concerning integrated process-
ing of flax are being realized in Germany, Finland,
Denmark, Sweden, and the United States .
Flax contains from 60 to 90% cellulose; the lignin
content varies from 2 to 5%, reaching 37% in flax
boon [3, 4]. Only long flax fibers, accounting for only
1/5 of the total, are suitable for production of high-
quality textiles; the remaining flax fibers are short and
are either processed to obtain heat-insulating materials
or burnt . At the same time, short fibers are a valu-
able source of cellulose. Thus, recovery of cellulose
from substandard flax fibers with the aim to produce
useful materials (in particular, wool) is an urgent
problem. Flax wool is characterized by high sorption
activity, hygroscopicity, antiseptic and hemostatic
properties, and good air permeability ; it is even
more hygroscopic than cotton wool .
Only 1/3 of wool consumed in Russia is produced
at domestic plants; the raw material is expensive
cotton . The demand of Belarus for wool is about
2000 t annually. The use of local resources, primarily
flax, would allow partial replacement of imported
Flax fiber is produced in industry by alkaline cook-
ing followed by hypochlorite bleaching . From the
economical and environmental viewpoints, Ryzhkov
 considers it appropriate to replace chlorine-con-
taining agents by peracetic acid. Methods for produc-
tion of flax wool by oxidative bleaching with com-
plexones  and by reductive cooking of flax fol-
lowed by peroxide bleaching in an alkaline medium
 have been patented.
It is known  that nitric acid is an excellent
delignifying agent for nonwood fibrous raw materials,
such as straw of cereals, cane, or manioc. Reaction of
nitric acid with lignin involves electrophilic substitu-
tion in the aromatic ring (nitrosation, nitration), elec-
trophilic displacement, aliphatic substitution, addition,
and oxidation . The thus modified lignin is ex-
tracted with a dilute alkali solution. According to
Nikitin , 335% HNO
is the most suitable for
cooking of nonwood plant materials. It was shown
previously  that the optimal HNO
for nitric acid cooking of rye straw is 2.0%. As for
flax fibers, we found no systematic data on the recov-
ery of flax cellulose with nitric acid; only superficial
information about delignification of flax with nitric
acid was available .
This study deals with optimization of the condi-
tions of nitric acid cooking of flax fibers with the aim
to obtain wool.
As starting material we used cottonized flax fibers
(Groniteks State Unitary Enterprise, Grodno, Belarus).
The weight fraction of boon and foreign impurities
in the cottonized fiber was 1.0%, and the mean fiber
length, 30.0 mm. The lignin content was 6.2%; Kapp
number, 18.1; content of pentosans, 3.7%; and ash
residue, 1.4%. Nitric acid delignification of fibers
involved impregnation of the flax fiber with an aque-
solution (for 30 min at liquid : solid ratio
of 20 ml g
and room temperature), cooking of the
swollen fibers in the same HNO
solution at 60oC,