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Nuclear Instruments and Methods in Physics Research B 236 (2005) 259–265
www.elsevier.com/locate/nimb
Modification of cotton-cellulose by preirradiation grafting
E. Takacs a,*, L. Wojnarovits a, J. Borsa b, J. Papp a, P. Hargittai a, L. Korecz c
a Institute of Isotopes and Surface, Chemical Research Center (CRC), Hungarian Academy of Sciences (HAS),
P.O. Box 77, H-1525 Budapest, Hungaryb Budapest University of Technology and Economics, M}uegyetem rkp. 3, H-1111 Budapest, Hungary
c Institute of Structural Chemistry, Chemical Research Center (CRC), Hungarian Academy of Sciences (HAS),
P.O. Box 17, H-1525 Budapest, Hungary
Available online 19 May 2005
Abstract
Acrylamide (AAm), acylic acid (Aac), 2-hydroxypropil acrylate (HPA), 2-hydroxypropil methacrylate (HPMA) and
N,N 0-methylene bisacrylamide (BAAm) were grafted to cotton-cellulose by the preirradiation method. The samples
were characterized by ESR, degree of polymerization (DP) and tensile strength measurements, by FTIR, gravimetry,
X-ray diffraction and iodine sorption. The grafting yield was strongly monomer dependent: the highest yield was found
for HPMA, for HPA a medium yield, whereas for the others relatively low values were measured. Grafting improved
the swelling of the samples. The highest increase in swelling was observed on samples grafted with Aac and BAAm
showing saturation at about 270% at natural pH. For AAm, HPA and HPMA at low grafting yield an increase in swell-
ing was found and then the swelling decreased with increasing grafting yield. No direct connection was found between
the grafting yield and the swelling properties.
� 2005 Elsevier B.V. All rights reserved.
PACS: 82.50; 61.80; 61.16.B
Keywords: Radiation grafting; Cotton-cellulose; Hydrogel; ESR; X-ray diffraction; Iodine sorption; SEM
1. Introduction
Hydrogels are often produced by irradiation
techniques due to the known advantages: the syn-
0168-583X/$ - see front matter � 2005 Elsevier B.V. All rights reserv
doi:10.1016/j.nimb.2005.03.248
* Corresponding author. Tel.: +36 1 392 2222x3131; fax: +36
1 392 2548.
E-mail address: takacs@iki.kfki.hu (E. Takacs).
thesis carried out in the absence of catalysts and
initiators moreover polymerization and crosslink-
ing may occur simultaneously. In many applica-
tions it is a disadvantage that the mechanical
strength of hydrogels is rather poor. In order toovercome this difficulty hydrogels are often synthe-
sized by grafting on a surface of a polymer e.g. cel-
lulose with good mechanical stability [1]. Grafting
ed.
260 E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265
may also be carried out by irradiation techniques.
In the literature there are quite a number of publi-
cations which demonstrate that monomers and
among them also hydrogel forming monomers
can be grafted onto cellulose surface by radiationinitiation. Most of the works published on this field
report on grafting of cellulose with one monomer
e.g. styrene, or N-isopropil acrylamide [2–7].
We have been studying for several years the
radiation degradation and modification of cellu-
R R1
Aac Acrylic acid H OH
HPA Hydroxypropil acrylate H OCH2CH(OH)CH3
HPMA Hydroxypropil methacrylate CH3 OCH2CH(OH)CH3
AAm Acrylamide H NH2
BAAm N,N 0-methylene bisacrylamide H NHCH2NHCOCH@CH2
lose, concentrating mostly on the chemical
changes. To observe these changes we usually ap-
plied higher doses in the range of 50–1000 kGy.
We found oxidation and at the highest doses ap-
plied also changes in the crystalline structure [8–
10]. In this work we prepare hydrogels by grafting
several monomers to cellulose by the preirradia-
tion grafting method and characterize the hydro-gels by a large variety of methods and compare
their properties. Our aim is to prepare grafted cel-
lulose with good hydrogel properties.
2. Experimental
2.1. Materials
Different types of acrylic monomers were in-
volved in the present studies which are known to
form hydrogel by radiation induced polymeriza-
tion [7,11]. We selected an acidic monomer (acrylic
acid), an acrylic acid ester (hydroxypropil acry-
late), a methacrylic acid ester (hydroxypropil
methacrylate) and two acrylamide type mono-mers, one of them was monofunctional (acrylam-
ide itself) and the other was bifunctional (N,
N 0-methylene bisacrylamide). The structures of
the monomers studied and the abbreviations ap-
plied are shown below.
Cotton fabric samples (163 g/m2, Type 405 W,
Test Fabric Inc., USA) were washed first in 1%
acetic acid solution at 50 �C for 5 min, then in dis-
tilled water and the samples were dried. The
monomers were Scientific Polymer Products. The
crystalline monomers (AAm, BAAm) were recrys-
tallized from methanol to remove the stabilizator,
the liquids (Aac, HPA, HPMA) were treatedwith the column supplied together with the mono-
mers. The reagents were of analytical grade. Puri-
fied water was obtained from an ion exchanger
equipment type ELGA Option 4.
2.2. Grafting procedure
Cotton-cellulose fabric samples were irradiatedin air, at room temperature by Co-60 gamma rays
up to 40 kGy dose (dose rate 15 kGy/h). Immedi-
ately after irradiation the samples were immersed
0 10 20 30 40
200
400
600
800
1000
1200
1400
1600
1800
0
100
200
300
400
500
600
DP
Dose, kGy
Tensile strength
DP Ten
sile
str
engt
h, N
Fig. 1. Dose dependence of the degree of polymerization (DP)
and that of the tensile strength (measured on 5 cm wide
samples).
E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265 261
in 5% monomer solutions (water/methanol = 80/
20) at 40 �C for 4 h. N2 bubbling was applied to
deoxygenate the monomer solutions. Bubbling
was started about half hour before grafting and
continued during the whole grafting procedure.Grafted samples were immersed in distilled water
and washed carefully. The remaining monomer
was then removed by extraction in boiling distilled
water for 6 h.
2.3. Characterization of samples
Radicals remaining after irradiation were de-tected by an ESR instrument type JEOL JES-
FE3X. The determination of the degree of
polymerization (DP) was based on the viscosity
measurements of the sample dissolved in cuprie-
thylenediamine (Cuen) solution [12]. The tensile
strength was measured on fabric samples of 5 cm
width using Instron type equipment.
Grafting yield (=100% · (wg � w0)/w0) wasdetermined by weighting the samples before (w0)
and after (wg) grafting. A FTIR instrument Uni-
cam Mattson Research Series 1 with diffuse reflex-
ion detection was also used to follow the grafting.
Swelling (=100% · (ws � wg)/wg) was determined
by weighting the samples after grafting and after
soaking in distilled water (ws) for 1 h.
The accessible surface was determined by iodine
sorption measurement. This method is often used
for characterizations of cellulose accessibility.
Measurements were carried out by dropping
1.2 ml iodine solution on 200 mg cotton fabric
sample. (The iodine stock solution was prepared
by dissolving 40 g KI and 5 g iodine in 50 ml dis-
tilled water.) After 3 min the sample was put into
100 ml saturated Na2SO4 solution at 22.5 �C(thermostated) for 1 h. The amount of iodine ad-
sorbed on cellulose fibre surface was calculated
after titration by Na2S2O3 solution.
The samples used for grafting yield determina-
tion, swelling and iodine sorption measurements
always were in equilibrium with the laboratory
atmosphere therefore contained absorbed water.
This water content was always determined by sep-arate measurement comparing the masses of the
equilibrated sample and heat box dried sample.
The results of these determinations were applied
in grafting, swelling and iodine sorption measure-
ments for correction of the actual mass of samples.
The X-ray diffraction patterns were taken on
samples of 20 · 30 mm using a Philips instrument
equipped with a Bragg–Brentano parafocusinggoniometer, secondary beam graphite monocho-
mator and proportional counter. The scanning
electron microscopic pictures (SEM) were taken
on single fibres coated with Pt layer using JEOL
J SM 5600LV equipment.
3. Results and discussion
3.1. Irradiation of cotton-cellulose
We characterized the irradiated samples by tak-
ing SEM micrographs, measuring the degree of
polymerization and the tensile strength; ESR and
X-ray diffraction measurements were also applied.
As Fig. 1 shows the degree of polymerization de-creases upon irradiation of the samples from an ini-
tial value of 1680 to 480 after 10 kGy irradiation
and to 230 after 40 kGy irradiation. This decrease
of the DP value reflects radiation induced fragmen-
tation of the polysaccharide chain. It is interesting
to note, however, that this fragmentation is not
accompanied by changes in the mechanical proper-
ties of the cotton. Neither the SEMpictures (Fig. 2),nor the tensile strengthmeasurements (Fig. 1) of the
Fig. 2. SEM pictures of untreated cellulose fibres, fibres
irradiated with a dose of 40 kGy and those of irradiated and
grafted.
3200 3300 3400 3500
-0.004
-0.002
0.000
0.002
ES
R s
igna
l, ar
bitr
ary
units
Magnetic field (Gauss)
40 kGy 30 kGy 20 kGy 10 kGy 5 kGy
0 5 10 15 20 25 30 35 40 450
500
1000
1500
2000
2500
Rad
ical
con
cent
ratio
n, a
rbitr
ary
units
Dose, kGy
(A)
(B)
Fig. 3. ESR signal of samples (A) and dose dependence of the
ESR (B) signal 4 h after irradiation.
262 E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265
irradiated samples indicate considerable deteriora-
tion as compared to the unirradiated samples.The samples were irradiated in plastic bags with
large excess of air. Under such conditions, accord-
ing to the literature suggestions, the radicals formed
on the polymer chain are expected to transform to
ROOH and ROOR 0 type hydroperoxides and per-
oxides. However, in our ESR measurements made
4 h after the irradiation we detected radical species
in the samples (Fig. 3(A)). The concentration of
these radials was found to increase with the increas-
ing dose as shown in Fig. 3(B). The signals are
mainly due to peroxy radicals with smaller contri-bution from other radical species. Radical signal
was well detectable even after a month�s storage
at room temperature, however, its intensity de-
creased and we noted some changes in the shape
indicating altered radical structures. The observa-
tion of radicals in the samples after irradiation in
the presence of oxygen indicates that initiation of
polymerization in the grafting experiments mayoccur both, by means of the unreacted radicals
observed in ESR measurements and also by the
thermal decomposition of labile hydroperoxides
and peroxides.
Chemical Research Centre - Laboratory of Diffraction
0
10
20
30
40
50
60
70
80
90
100
Inte
nsi
ty
[Arb
itra
ry u
nit
s]
517.674
108.845
155.906
204.440
253.562
302.979
352.564
2*theta
—— untreated—— AAm—— AAc—— HPA—— HPMA—— NNMBAAm
Fig. 4. X-ray diffraction patterns of untreated (unirradiated,
ungrafted) and grafted samples. Preirradiation dose of the
grafted samples 40 kGy.
0 10 20 30 400
25
50
75
Gra
fting
yie
ld, %
HPMA
BAAm
AAc
HPA
AAm
Gra
fting
yie
ld, %
Dose, kGy
100
200
300
Fig. 5. Grafting yield as a function of preirradiation dose.
E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265 263
Fig. 4 shows the X-ray diffractions patterns of
some of our samples (untreated means unirradi-
ated and ungrafted, the other samples were graftedafter irradiation with 40 kGy). We found no differ-
ences in the diffraction taken on unirradiated sam-
ples and on samples irradiated with the maximum
dose (40 kGy) used in the present experiments. In
another experiment [8] we noted changes in the
crystallinity after irradiation with very high doses
of about 1000 kGy. On the figure the red vertical
lines show places of diffraction maxima belongingto the crystalline phase of cotton-cellulose, and the
blue vertical line shows the center of the diffuse
peak of the amorphous region. In both the irradi-
ated and unirradiated samples the crystalline
content was about 60%.
3.2. Grafting
The grafted samples were characterized by the
grafting yield, by the accessible surface using
iodine sorption measurements, by the crystalline
content as measured by X-ray diffraction, by
SEM pictures and also by FTIR. The grafting
yields as measured by gravimetry increased nearly
linearly with the preirradiation dose (Fig. 5). By
FTIR the absorption peaks at 1740 cm�1 and as-
signed to the stretching vibrations of C@O group
were used to characterize the grafting yield. The
band at 2900 cm�1 assigned to the stretching
vibrations of aliphatic C–H was used as inner stan-
dard. As all the monomers grafted contained C@Ogroup the absorbance at 1740 cm�1 increased with
increasing grafting yield. The results were in good
agreement with those obtained by gravimetry. As
the SEM picture shows (Fig. 2) for hydroxypropil
acrylate (HPA) the grafted layer nearly homoge-
nously covers the surface of the fibres. In the cases
of acrylamide (AAm), acrylic acid (Aac) and N,N 0-
methylene bisacrylamide (BAAM) at the highestpreirradiation dose applied the percentage increase
of the sample mass due to grafting was between
25% and 35%, while for HPA this figure was
�70%. The highest grafting yield of about 270%
was measured for hydroxypropyl methacrylate
(HPMA). This result is surprising, since the meth-
acrylates generally have at least an order of magni-
tude smaller rate coefficients of propagation thanthe acrylates, but the termination rate coefficients
during their polymerizations are practically the
same as for the acrylates. Under grafting condi-
tions termination between two radicals on the
chains attached to the cellulosic fibres is hindered.
Due to the higher stability of the tertiary radicals
in methacrylates, than the secondary radicals in
acrylate polymerization termination by impuritiesis expected to be slower in methacrylates. We guess
that the initiation rate is higher for methacrylates
Fig. 6. Comparison of grafting yield, iodine sorption and
swelling of untreated and grafted samples. Preirradiation dose
30 kGy.
0 50 100
150
200
250
300
Grafting yield, %
BAAmAAc
HPA
AAm
HPMA
Sw
ellin
g, %
0 100 200 300
Grafting yield, %
Fig. 7. Swelling as a function of grafting yield.
264 E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265
than for acrylates again due to radical stability
reasons.The X-ray diffraction method we applied could
not be used for obtaining quantitative results;
however, it gives valuable qualitative information.
Due to grafting the mass of the sample increases
and the percentage of the cellulose fraction and
also the crystalline fraction decreases, at the same
time the rather ill-defined wide reflection of the
amorphous peak increases. On samples graftedby HPMA the amorphous region is very wide
and the crystalline peaks are rather weak. Since
changes in the crystalline region are not expected,
we suppose that grafting modifies not only the
amorphous regions but also the transient region
between the amorphous and crystalline phases.
In all the grafted samples we observed decrease
of the diffraction attributed to the crystalline phaseand strengthening of the amorphous reflexions.
The iodine sorption measurements in Fig. 6
indicate larger accessible surfaces for the grafted
samples than that for the untreated cotton fabric
samples. In our case iodine sorption characterizes
the accessible surface of the cotton and those of
the grafted polymer together. The change in acces-
sible surfaces is the highest for the HPMA andHPA grafted samples. For these samples we found
the largest grafting yields. It seems that iodine can
penetrate to the grafted parts too and iodine sorp-
tion measures both the cellulose accessible surface
and the accessible surface of the grafted part. In
the case of Aac and BAAm grafted samples the
iodine sorption measurements gave very low val-
ues. We think that the grafted part of these sam-
ples is more compact in the case of Aac due to
the H bonding network and in the case of BAAm
due to the crosslinks. For these reasons the huge
iodine molecules cannot penetrate into thenetwork.
3.3. Swelling
The swelling of cellulose in water is limited as a
consequence of the presence of crystalline regions
which restrict the mobility of the polymer chains
[11]. For the untreated cellulose we measured aswelling of 140% (see Fig. 7). The grafting in-
creased the swelling for all monomers used in the
experiments. In the case of Aac, and BAAm the
swelling at lower grafting yield increased with
grafting and saturated at 270%. For HPA and
AAm the swelling percentage at low grafting in-
creased to about 220% and then gradually de-
creased. With HPMA the swelling we measuredwas 180% and again a decrease was found at high-
er grafting percentages. These swelling characteris-
tic should be correlated with the structure, the
pore sizes and also the hydrophilicity of the
grafted layers. The characterization of the struc-
ture and pore size of these samples needs further
investigations.
E. Takacs et al. / Nucl. Instr. and Meth. in Phys. Res. B 236 (2005) 259–265 265
In the case of BAAm the grafted layer itself
could easily be crosslinked and the distance be-
tween the two double bonds ensures a certain min-
imum pore size resulting in good swelling
properties. In the case of Aac the partial ionizationof the COOH groups and the network formed by
H bonds increases the swelling. The hidrophylicity
of these two monomers is higher that those of the
other monomers. The swelling measured for Aac
grafted samples is in accordance with literature
value obtained at low pH values [11], at high pH
there is an increase in swelling which is attributed
to the complete ionization of the polyacrylic acidchain. The estimated pK of this dissociation is
between pH 4 and pH 5. The pH dependence also
needs further investigations.
In the case of HPMA, HPA and AAm the
decrease in the swelling after the maximum is
probably due to the gradual formation of a closed
compact structure on the surface which hinders the
penetration of water.
4. Conclusions
1. The radiation degradation of cotton-cellulose
starts at very low doses (5–10 kGy) resulting
in decrease of DP. However, the degradation
does not result in a significant change in themechanical properties: irradiation up to
40 kGy dose did not change the tensile strength,
and the SEM pictures did not indicate visually
observable damage of the samples either.
2. Long lived radicals were detected after irradiat-
ing cellulose fabric samples in air. These radi-
cals decayed on several months time scale.
The initiation of the preirradiation graftingprobably takes place by the decomposition of
peroxides and also by the long living radicals.
The grafting yield was strongly monomer
dependent. The highest grafting yield was mea-
sured for HPMA, for HPA we measured a med-
ium yield, whereas for the other monomers we
measured relatively low yields.
3. Grafting results in breakage of secondary Hbonds as indicated by an increased available
surface characterized by iodine sorption. How-
ever, a decreased available surface was mea-
sured on samples grafted by Aac due to
strong H bridges formed between the side
chains and the cellulose chains.
4. The relatively low swelling of cellulose can be
improved by grafting: water uptake increasedfor all of the grafted samples studied. The high-
est increase in swelling was observed with Aac
and BAAm showing saturation at about
270%. For all the others at low grafting yield
an increase in swelling was found and then the
swelling decreased with increasing grafting
yield. It seems that there is no direct connection
between the grafting yield and the swellingproperties.
Acknowledgments
We express our thanks to the Hungarian Sci-
ence Foundation for support (OTKA, No. T 037363, T 034 478 and T 037 294) and to I. Sajo for
the X-ray diffraction measurements.
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