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8/12/2019 Mechanisms of Degradation of Cotton and Effects of Merceri
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Die Angewandte Makromolekulare Chemie 111 1983) 69- 84 Nr.
1707)
National Research Centre, Dokki, Cairo, Egypt,
Textile Research Division, * Physics Division
Mechanisms of Degradation of Cotton and Effects
of Mercerization-Stretching upon the Course
of these Mechanisms,
VI
Structural Differences between Scoured Cotton and Slack
Mercerized-Stretched Cottons**
A. Hebeish, M. H. El-Rafie, N. Y. Abou-Zeid, M. M. Kamel, A. Waly,
A. T. El-Aref, and I. S. Fraag*
(Received 14 December 1981)
SUMMARY:
Scoured ply cotton yarn (substrate I) was slack mercerized (substrate 11) and slack
mercerized followed by stretching to 94% (substrate 111) and 103%
of
original length
(substrate IV). These substrates were given an acid pretreatment (0.5 N HC1, 6OoC,
15 min). The four substrates and their corresponding HC1-treated substrates
(substrates I-H, II-H, III-H and IV-H) were reacted under similar conditions with
N,N-diethylaziridinium chloride to yield diethylaminoethyl (DEAE)-cottons. In
addition, DEAE-cottons of substrates I, I-H, I1 and II-H were hydrolyzed with 0.5
N
HCl at 80C for 0.5, 1, 2, 3, 5 and 7 h and the ratio of substituents in the D-gluco-
pyranosyl units of these DEAE-cottons as well as in those of DEAE-hydrocelluloses
were determined. It was found that there is a considerable difference between the
reactivitiy
of
scoured cotton and slack mercerized-restretched cottons. This was inter-
preted in terms of differences in the microstructure between the substrates ik
question, which in turn, are reflected on availability, accessibility and state of order
of the cellulose hydroxyls in the scoured and mercerized cottons. Nitrogen-, chemical,
microscopical and X-ray analyses were used to assess the structural differences among
the substrates.
ZUSAMMENFASSUNG:
Gebeiztes Baumwollgarn (Substrat I) wurde spannungslos mercerisiert (Substrat 11)
und spannungslos mercerisiert, dann verstreckt um 94% (Substrat 111) und 103% der
** This research has been financed in part by a grant made by the U. S. Department
of Agriculture, Agricultural Research Service, authorized by Public Law 480.
1983 Hiithig Wepf Verlag, Basel 0003-3146/83/11 0069-16/$03.00/0 69
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A. Hebeish et al.
urspriinglichen Lange (Substrat IV). Diese Substrate wurden einer Saurevorbehand-
lung unterworfen
(0,5
N HCl, 6OoC, 15 min). Die vier Substrate und ihre ent-
sprechenden HC1-behandelten Substrate (I-H, 11-H, 111-H und IV-H) wurden unter
ahnlichen Bedingungen mit N,N-Diethylaziridinchlorid umgesetzt, um D iethylamino-
ethyl (DEB)-Baumwolle zu erhalten. Zusatzlich wurden DEAE-Baumwollproben
der Sub strate I, I-H , I1 und 11-H mit
0,5 N
HCl bei 80C
0,5, 1 , 2 , 3 , 5
und
7
hydro-
lysiert und das Verhaltnis der Substituenten in den D-Glucopyranosyl-Einheiten die-
ser DEAE-Baumwollproben sowie in denen der DEAE-Hydrocellulosen wurde be-
stimm t. Es wurde gefunden, d& ein beachtlicher Unterschied zwischen der Reaktivi-
tat gebeizter und spannungslos mercerisierter nachverstreckter Baumwolle besteht.
Dies wurde im Sinne von Unterschieden in der Mikrostruktur der verschiedenen Sub-
strate interpretiert, die umgekehrt Verfugbarkeit, Zuganglichkeit und Ordnungs-
zustand der Cellulose-Hydroxylgruppenin gebeizter und mercerisierter Baumwolle
widerspiegeln. Stickstoff-, chemische, mikroskopische und Rontgenanalysen wurden
benutzt, um die strukturellen Unterschiede zwischen den Substraten festzustellen.
Introduction
Crystallinity, orientation of crystallites as well as tensile and mechanical
properties of cotton fibres can be considerably modified by subjecting the
fibres to swelling and stretching treatments with caustic soda of mercerizing
strength
5 .
Furthermore previous reports from this division6- o have
disclosed that mercerization alters the molecular structure of cotton in such a
way that mercerized cottons undergo higher degradation yet retain higher
strength than the corresponding unmercerized cottons when degraded under
identical conditions. The susceptibility to chemical degradation decreases by
increasing the tension applied for stretching the slack mercerized yarns
beyond their original length.
The reaction of N,N-diethylaziridinium chloride (DAC) with cellulose has
been served as a chemical microscope to clarify the availability of 0(2)H,
O(3)H
and
O(6)H
for the reaction. Rowland et al.
l 2
have shown that certain
hydroxyl groups (i.e. those of C-2 in cotton cellulose) are more readily
available for reactions than others (at
C-6
and C-3). This was interpreted to
be a reflection of an ordered presentation of hydroxyl groups on the surfaces
of crystalline microstructural units. In further investigations 13-23, reactions
of DAC with cotton fibre to introduce diethylaminoethyl (DEAE) sub-
stituents have been proved to be valuable
for
assessing the degree of order
which characterizes reactive crystalline surfaces of the elementary fibril.
The present work was undertaken with a view to clarify structural differ-
ences among scoured and slack mercerized-restretched cottons. To achieve
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Degradation of Cotton
this, chemical, microscopical as well as X-ray analyses
of
scoured cotton,
slack mercerized cotton, and slack mercerized-restretched cottons were
carried out.
Experimental
Co tton Fibres
Egyptian cotton fibres, Giza 75,were combed and spun over conventional ring
spinning t o produ ce singles yarn count Ne
60
(twist factor 4). These singles yarn were
plied t o produce N e 60/2.Th e twist (twist factor
2.4)
in plying the yarns was made
opposite t o th e twist in the singles yarn. The physicomechan ical properties
of
the fibres
an d yarns were reported elsewhere6.
Scouring
Scouring
of
the ply yarn was carried out under pressure (4
5
kg/cm2) and
at
a
temp. of 120C or 2 in
a
solution containing caustic soda
6
/l), sodium carbonate
1
g/l) and a wetting agent (0.5 g/l) using a material to liquor rat io of
1 :
s described
in details in a previous publication6.
Mercerization
Skeins of the scoured yarns were slack mercerized in an aq ueous solution of caustic
soda (298 /l) at21 C nd slack mercerized followed by restretching to various lengths
viz. 94% and 103% of original length, w hile the yarn was still wet w ith the m ercerizing
solution. D etailed conditions were reported earlier
6.
For convenience, the yarn before
and afte r mercerization will be referred t o as:
Substrate I: scoured yarn,
Substrate 11: slack m ercerized yarn,
Substrate
111:
mercerization
as
nearly slack as possible on the machine (ca.
15%
shrinkage), followed by partial restretching to 94% of the original
length while the yarn was still wet with the m ercerizing solution ,
Substrate IV: mercerization as nearly slack as possible on the machine (ca. 15%
shrinkage), followed by partial restretching to
103%
of the original
length while the yarn was still wet with the mercerizing solution.
Preparation of Hydrocellulose
Heterogeneous acid hydrolyses of th e scoured yarn (substrate
I),
slack mercerized
yarn (substrate 11 an d the two slack mercerized-restretched yarns (substrates 111and
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A. Hebeish et al.
IV were carried out in steeping the samples in 0.5 N HC1 at 60 C for 15 min, keeping a
material to liquor ratio of 1 10. After acid hydrolysis the samples were washed
repeatedly with distilled water until they were free from acid, dried in air at room temp.
and designated as I-H, 11-H, 111-H, and IV-H.
Preparation of DEAE-Cotton
Reaction of N,N-diethylaziridinium Chloride (DAC) with Substrates I-IV
and I-H V-H
The N,N-diethylaziridinium chloride was prepared by neutralizing an aqueous
solution of crystallized 2-chloroethyldiethylamine hydrochloride, separating the
2-chloroethyldiethylamine and shaking it with water as described by Roberts et al.
24.
Air dried samples (10 g) were impregnated in 0.55 M N,N-diethylaziridinium
chloride for 45 min and subsequently filtered on a sintered glass funnel
G3)
o remove
the excess solution till a wet pick up of ca. 200%. The wet sample was impregnated in
0.5
N aqueous NaOH solution, M/L ratio of 1
:
0, and the reaction was allowed to
proceed for 45 min. The detailed procedure has been described elsewherei3.
Preparation of DEAE-Hydrocellulose yarn from DEAE-Cotton (Substrates
I-V and I-H V-H)
Approximately 7 g of DEAE-Cotton skeins were treated with 0.5 N HCl solution
(using an M/L ratio of 1 10) at 80C for 0.5, 1 2, 3, 5 and 7 h. At the end of each
treatment, the insoluble fraction was removed by filtration on a sintered glass filter
and was washed with 50 ml
0.5
N HCl. The filtrate was collected and the solid was
washed on the filter with distilled water till it was acid-free. The water was discarded
and the solid fraction (DEAE-hydrocellulose) was air dried at 25 C.
Hydrolysis of DEAE-Hydrocellulose
1 g
of
each
of
the chemically modified celluloses (the DEAE-cotton
of
substrates
I-IV and I-H V-H as well as the insoluble portion derived thereof after HCl treat-
ment) was dissolved in 72% sulphuric acid and hydrolyzed during stepwise dilution of
the acid. The method is described in detail by Rowland et al. j 3 . The mixtures
of
glucose
and substituted glucoses was isolated as anhydrous freeze-dried solids or directly
subjected to fermentation to remove unsubstituted glucose23.
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Degradation of
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Analysis f o r 2-0-, 3 0 and 6 0 DEAE)-SubstitutedD-glucopyranoses
The distribution of DEAE groups among the 2-0-, 3-0- and 6-0- positions
of
D-glucopy ranoses in each of the freeze-dried products f or each sample was determined
by gas-liquid chromatography (GLC) on
an
instrument Varian 1440 with flame
ionization detector. The column was a 1/8 in. nickel tube 10 f t long. It was packed with
3% OV-1 on Chrom osorb W (80 100 mesh). The column was operated isothermally
at 195 C. All samples to be analyzed were trimethylsilylated by the method of Sweeley
et a1.z5.
Nitrogen Content
DEAE-cellulosic materials were analyzed for nitrogen content. The latter was
monitored according to t he Kjeldahl method.
X-R ay Analysis
X-Ray diffractograms were obtained with a D-500 X-ray diffractometer (Siemens
corporation) having a measuring range (29) fro m 100 to 168 . Th e reproducibility
of 29 is 0.001 an d the diameter of the measuring circle is 401 mm . Th e detector is
a
scintillation coun ter, w ith a dead time of less than s. Th e operation of the X-ray
unit and the preparation of the pellet samples were similar t o those of Segal et a1.26.
Th e samples were ground t o 20 m esh in a Wiley mill and pressed into pellets weighing
100 mg. A pressure of 25000 psi was applied.
Th e sample was mo unted in the reflection position of the goniometer, an d a pattern
made over the range for 2 8 from 6 to 30 . Native cot ton has the reflection of the
l i
plane at 16.3 an d of the 002 plane at 22.5 . F or mercerized cotton cellulose, the l i
plane occurs a t a value for 29 of 20.5 and th e 002 plane is at 22.5 . Th e crystallinity
index (Cr
I)
for native co tton z6 s computed by measuring the intensity of diffraction
fro m the 002 plane minus the intensity at 18 . The angle tha t represents amorphous
cellulose, divided by the intensity f ro m th e 002 plane, is
I092 18- 100
C r I =
1092
Results and Discussion
Reaction
of
N,N-DiethylaziridiniumChloride With Scoured and Mercerized
Cottons
Four cotton substrates (yarns), viz., scoured (I), slack mercerized (11),
slack mercerized-restretched to 94%
(111)
and slack mercerized-restretched to
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A. Hebeish et al.
103
(IV) were subjected to acid treatment
(0.5
N HC1
at
60C
for
15
min).
The original four substrates and their corresponding HC1-treated substrates
(substrates I-H, II-H, III-H and IV-H) were treated under similar conditions
with N,N-diethylaziridinium chloride (DAC). The eight chemically modified
celluloses were analyzed for nitrogen and the results obtained are shown in
Tab. 1
Tab. 1. Nitrogen contents resulting from the reaction of different substrates with
DAC.
Substrate N (Yo)
Scoured cotton (substrate I) 0.107
0.076
Slack mercerized cotton (substrate 11)
0.151
0.110
0.112
0.092
0.097
0.085
* Scoured cotton treated with HCl (substrate I-H)
* Slack mercerized cotton treated with HC1 (substrate II-H)
Slack mercerized cotton restretched to 94 (substrate 111)
*
Slack mercerized cotton restretched to 94
and treated with HCl (substrate III-H)
Slack mercerized cotton restretched to 103 (substrate IV)
and treated with HCl (substrate IV-H)
*
Slack mercerized cotton restretched to 103
* 0.5 N HCl at 6OoC for 15 min.
It is seen (Tab. 1) that slack mercerization of scoured cotton prior to
reaction with DAC enhances considerably the susceptibility
of
cotton to the
reaction since the nitrogen content obtained with slack mercerized cotton
(substrate 11) is higher than that of scoured cotton (substrate I). The same
holds good for slack mercerization followed by stretching to 94 of original
length, but stretching reduces the enhanced reactivity brought about by slack
mercerization. Increasing the magnitude
of
stretching to
103
produces a
substrate (substrate IV) the reactivity of which is even lower than that of
scoured cotton.
When cotton fibres are subjected to swelling treatment with caustic soda
solution of mercerizing strength, decrystallization of cotton takes place4.
Slight improvement of crystallites in cotton may occur when the fibres are
allowed to shrink freely in the swelling solutions. On the other hand, substan-
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Degradation of
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tial improvements occur when stretch is applied to cotton fibres after slack
swelling27.Furthermore, X-ray analysis of the substrates in question showed
that although the samples (except scoured cotton) were slack mercerized
under the same conditions, the samples with the most restretching had a
higher cellulose I content 28. This suggests that the stretching has an effect on
the crystal structure. With this in mind, the availability and accessibility of
cellulose hydroxyls (sites for reaction with DAC) would be much greater in
slack mercerized cotton (substrate 11) than in scoured cotton (substrate I).
The relative accessibilities of the three different hydroxyls
of
cellulose in slack
mercerized cotton (substrate
11
would be much greater than scoured cotton
(substrate I). Stated in other words, involvement of the three hydroxyl groups
at C-2, C-3 and C16
of
the D-glucopyranosyl units of slack mercerized cotton
cellulose in hydrogen bonding is less than that of scoured cotton. The same
holds, to some extent, good for mercerized cotton restretched to 94 of
original length (substrate 111). As
a
result there is a relatively good
opportunity for the hydroxyl groups to react. That is why substrates I1and
I11
showed higher nitrogen content than substrate I .
Intreasing the magnitude of stretching is accompanied by increasing
~ r i e n t a t i o n ~ ~nd crystallinity28.Consequently, the hydroxyl groups become
relatively highly ordered, selective and difficult to react. This would account
for the lower nitrogen content observed with slack mercerized cotton re-
stretched to
103
of original length (substrate
IV).
Treatment of the four substrates in question with hydrochloric acid (0.5
N
at 60C for
15
min) prior to reaction with DAC decreases considerably the
response of these substrates to the reaction. As is evident from Tab.
1 ,
the
nitrogen content is lower with the previously acid treated samples than with
the original substrates.
A previous report6 showed that acid hydrolysis, under the conditions used,
causes degradation of scoured cotton (substrate
I)
via creation of aldehydic
groups along the cellulose chain molecules, as evidenced by the increase in
copper number, as well as chain scission, as evidenced by the fall in the degree
of polymerization. However, this degradation does not seem to affect the
removal of the accessible surfaces of the cellulose elementary fibrils nor does
it alter the susceptibility of these surfaces to iodine sorption. Mercerization of
the scoured cotton increases not only the accessible surfaces but it seems also
to create in the cellulose structure very accessible surfaces which have very
little or no resistance to the acid attack and are removed almost completely
during washing. Recrystallization is also very likely to occur during the acid
treatment. Hence the most onset of acid degradation together with recrys-
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A. Hebeish et
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tallization are responsible for the decreased susceptibility of the acid treated
samples (substrates I-H V-H) to react with DAC (Tab. 1).
Four of the above chemically modified substrates, namely scoured cotton
(substrate I), HC1-treated scoured cotton (substrate I-H), slack mercerized
cotton (substrate 11) and HC1-treated slack mercerized cotton (11-H) were
hydrolyzed with HCl(O.5
N)
at 80C for varying lengths of time (0.5, 1,2,3,
5 and 7 h) and the nitrogen contents (expressed as Yo N) of the DEAE-hydro-
cellulose (insoluble fractions)
so
obtained are given in Tab.
2.
Tab. 2. Effect of duration of acid hydrolysis (0.5N HCl, 8OoC) on the nitrogen
content of DEAE-cellulose.
Substrate Acid treatment (h) Loss in
N
in DEAE-
0
0.5
1
2 3
5
7
cotton
hydrolyzed
for 5 h
Nitrogen content Olo) (VO)
I
0.107
0.101 0.108 0.105 0.102
0.099 0.089
8.08
I-H
0.076 0.074 0.074 0.063 0.073 0.073 0.073 4.10
I1 0.151 0.146 0.146
0.145
0.121
24.80
11-H 0.110
0.110
0.110 0.108
0.099 0.106 0.109 3.80
It is clear (Tab.
2)
that there is
a
decrease in the nitrogen content of DEAE-
cellulose after HC1 treatment. This is observed irrespective of the substrate
used. However, this decrease is neither striking nor significantly affected by
the duration of the acid treatment. The only exception is found with slack
mercerized cotton (substrate 11) where the decrement in nitrogen content is
quite substantial particularly after 5 h. The data of Tab. 2 further signify (a)
that with the exception of slack mercerized cotton (substrate 11) the accessible
surfaces of the elementary fibril of the modified cotton is slightly affected
(removed) under the acid conditions examined, (b) that the acid conditions
used are too mild to have a strong action on these accessible surfaces, (c) that
the accessible surface of the elementary fibrils of previously acid treated
cottons (substrates I-H and 11-H) are more resistant to acid hydrolysis than
the corresponding original samples and (d) that the elementary fibrils in slack
mercerized cotton (substrate 11) seem to acquire the most and the relatively
high accessible surfaces which are susceptible to acid attack.
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Degradation of Cotton
Distribution of Substituents
n
0- 2-Diethylaminoethyl)-D-Glucose
The DEAE-cottons derived from substrates I, I-H, I1 and 11-H before and
after being subjected to hydrolysis with HC1 at 80 C for 0.5 ,1,2,3 ,5 and 7 h
were dissolved in
72
sulphuric acid and hydrolyzed during stepwise dilution
of the acid. This was followed by neutralization with barium hydroxide and
concentration of the filtrates under vacuum to yield residues. The latter were
extracted with distilled water and filtered to get rid of any traces of barium
sulphate. The filtrates containing glucose and substituted glucoses were
subjected to fermentation followed by filtration. The filtrates were freeze
dried, silylated and analyzed by gas-liquid chromatography. At the end, the
distribution of 2-(diethylamino)ethyl substituents in the 2-0- and 3-0-posi-
tions relative to the 6-0- position of the D-glucopyranosyl units of the
insoluble fraction (i. e. DEAE-hydrocelluloses) of substrates I, 11, I-H and
11-H were calculated and set out in Tab. 3.
Tab. 3 shows that with scoured cotton (substrate I) the 2-046-0- ratio
remains almost constant during the first hour of hydrolysis and then slightly
decreases. On the other hand, the 3-046-0- ratio remains practically un-
altered during the entire course of hydrolysis. The insignificant and indistin-
guishable differences between the ratios of substituents before and after
hydrolysis for different durations are rather a consequence of the relatively
mild acid conditions used. As already indicated cellulose surfaces in scoured
cotton of even low order have not been substantially removed during the for-
mation of DEAE-hydrocelluloses. Moreover, data of X-ray analyses to be
presented later substantiate this (Tab.
5).
Tab. 3 shows the ratios of substituents resulting from the reaction of slack
mercerized cotton (substrate 11) with DAC before and after hydrolysis in
0.5
N
HCl at 80C for varying lengths of time. Apparently, there is no
change in neither the 2-046-0-ratio nor in the 3-046-0-ratio with increasing
duration of hydrolysis. These ratios remain almost constant during the entire
course of hydrolysis. This suggests that the DEAE substituents in this sub-
strate are present in D-glucopyranosylunits in relatively ordered arrangement
in surfaces of cotton elementary fibrils which are resistant to acid hydrolysis
under the conditions used. This state of affairs arises perhaps during the acid
treatment via recrystallization. The fact that the cellulose I content of DEAE-
slack mercerized cotton increases by increasing the duration of acid treatment
as will be shown later (Tab. 6) supports this.
It is as well to emphasize that the 2-046-0-ratio of DEAE substituents in
the D-glucopyranosyl units of slack mercerized cotton (substrate 11) are
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T
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Degradation
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comparable with their corresponding ratios in the D-glucopyranosyl units of
scoured cotton (substrate I) before and after hydrolysis of these two sub-
strates for different times (Tab. 3). Since slack mercerized cotton is expected
to exhibit much greater susceptibility to acid hydrolysis than scoured cotton,
data of current work would suggest that slack mercerized cotton is more
amenable to recrystallization during acid treatment than scoured cotton.
Tab. 3 shows also the changes in the 2-046-0- and 3-046-0-ratios before
and during hydrolysis of previously hydrochloric acid treated scoured cotton
bearing DEAE groups (substrate I-H). Obviously, acid hydrolysis for up to
1 h has practically no effect on these ratios. Prolonging further the duration
of hydrolysis up to
7
h is accompanied by a noticeable decrement in the
2-046-0-ratio and a marginal decrement in the 3-046-0-ratio.
That no significant changes in the 2-046-0- and 3-0-/6-0-ratios occur
during the first hour of hydrolysis is an indicative of the fact that D-gluco-
pyranosyl units in relatively ordered arrangement on surfaces of highly crys-
talline regions are involved in the reaction with DAC, whereas the decrease in
these ratios upon increasing the duration
of
hydrolysis reflects the changes in
the microstructure of substrate I-H during the later stages of hydrolysis. It
seems that the accessibility of this substrate increases as a result
of
disruption
of perfect crystalline order, which in turn, is caused by
a
bending strain under
the influence of progressive acid attack as the duration increases. Indeed,
X-ray analysis has shown that this substrate (substrate I-H) exhibits lower
cellulose I content and lower crystallinity particularly in the very late stages of
hydrolysis (Tab.
7 .
Tab. 3 contains the 2-046-0- and 3-0-/6-0-ratios obtained with the reaction
product of previously hydrochloric acid treated slack mercerized cotton (sub-
strate 11-H) and
DAC
before and after hydrolysis in
0.5
N
HC1 at
8 0 C
for
different periods of time. It is evident that there is no significant change in the
2-046-0-ratio even after hydrolysis for 7 h. The same holds true for the
3-046-0- ratio. This is rather in contrast with the corresponding ratios found
with previously hydrochloric acid treated scoured cotton, a point which again
reflects the greater ability of slack mercerized cotton bearing DEAE groups
to undergo recrystallization during the course of acid hydrolysis. As it will be
shown later, X-ray analysis indicated that the cellulose I content of substrate
11-H increases after acid hydrolysis.
It may be further noted that the 2-046-0-ratio before and after hydrolysis
of previously acid treated slack mercerized cotton (substrate 11-H) is substan-
tially lower than its mate in previously acid treated scoured cotton (substrate
I-H). This again suggests that the tendency of slack mercerized cotton to
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undergo recrystallization during the acid pretreatment is greater than that of
scoured cotton.
X Ray Analysis
When cotton cellulose is treated with sodium hydroxide solution of
mercerizing strength, cellulose I is converted t o cellulose 11. The 1Oi plane
increases in intensity as the cellulose I is converted to cellulose 11, and the 002
plane decreases in intensity29. It has been determined that the ratio of 101
plane intensity to 002 plane intensity givesa measure of the penetration of the
swelling agent into the crystalline regions
of
the cellulose30. In other words,
the indication of the amount of conversion from cellulose I to cellulose I1 can
I (101)
be obtained by computing the ratio
(oo2) *
The changes in the microstructure of scoured cotton yarn (substrate I)
brought about by slack mercerization (substrate 11) and slack mercerization
followed by restretching to
94
and 103 of original length of the yarn
(substrate I11 and substrate IV) were assessed by X-ray analysis. The latter
was also used to determine further changes in the microstructure
of
scoured
and mercerized cotton after being reacted with DAC as well as after acid
hydrolysis of DEAE-cottons. The results obtained are given in Tab. 4 7.
The results of Tab.
4
show that, although all samples (except scoured
cotton) have been slack mercerized under the same conditions, the sample
with the most restretching (substrate IV) has a higher cellulose
I
content.
Stated in other words, the largest changes in the microstructure of these
cottons (substrates I V) observed has been the increase in cellulose I
content with increased restretching of the yarns. This suggests that the
stretching has an effect on the crystal structure of the yarns, in accordance
with the previous studiesz8. An analogue has also been proposed for
Pachyman triacetate
Tab.
4
shows ratios of peak intensities I (101)/1(002) for scoured and
mercerized cottons after treatment with DAC. It is seen that the latter treat-
ment decreases slightly the cellulose I content irrespective of the substrate
used. However, the differences in cellulose I content between scoured and
mercerized cottons still persists. That is, the samples with the most restretch-
ing have a higher cellulose I content even after DAC treatment.
Tab.
5
shows the ratio of peak intensities I (lOi)/I
(002)
for scoured and
mercerized cottons (substrates I V) treated with
0.5 N
HC1 at 60C for 15
min followed by treatment with DAC. Obviously, treatment of these sub-
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Tab. 4. Ratio of peak intensities I(IOi)/I(002) for scoured and mercerized cotton
before and after reaction with DAC.
Substrate
I(Ioi)/1(002)
before DAC
after DAC
treatment treatment
~~ ~~
I
(scoured cotton)
0.22
0.238
I1
(slack m ercerized cotton ) 0.67 0.710
I11 (94 restretched) 0.49 0.554
IV (103
restretched)
0.41 0.452
Tab.
5.
Ratio of peak intensities
I(IOi)/I(002)
for scoured and mercerized cotton
treated with
0.5 N
HC1
at
60C for
15
min followed by treatment with
DAC.
Substrate 1(10i)/1(002)
I-H (scoured cotton) 0.238
11-H (slack m ercerized cotton) 0.663
111-H (94 restretched) 0.543
IV-H (103
restretched)
0.428
strates with HC1 under these conditions prior to treatment with DAC has
practically no effect on the cellulose
I
content.
Tab.
6
shows the crystallinity index as well as ratio of peak intensities
I (IOi)/I (002) for scoured cotton bearing DEAE groups after being subjected
to 0.5
N
HC1 at
80
C for varying lengths of time. The results indicate that the
changes in the crystallinity index of this modified cotton are within the experi-
mental errorz6during the course of hydrolysis. There is also no change in the
cellulose
I
content. The implication of this is that the conditions of the acid
hydrolyses used are too mild to have
a
significant effect on the microstructure
of scoured cotton bearing
DEAE
groups.
Tab.
6
shows also changes in peak intensities I (IOi)/I (002) and crystallin-
ity index for previously HCl treated scoured cotton bearing DEAE groups
(substrate I-H treated with DAC) with duration of hydrolysis with
0.5
N
HC1
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Tab.
6 .
Effect
of duration
of
acid hydrolysis (0.5
N HCl at 80C) on the ratio of the
peak
intensities I(lOi)/1(002)
and crystallinity
index (Cr. I.)
of DAC treated
substrate
I
and DAC treated substrate
I-H.
Hydrolysis
Substrate I treated with DAC Substrate I-H
treated with DAC
(h)
1(10i)/1(002) Cr. I. 1(10i)/1(002) Cr.
I.
0.0 0.238 0.238
0.5 0.211 89.5 0.29 80
1
.o
0.211 88.0 0.28 81
2.0 0.189 90.0 0.30 82
3.0 0.204 89.4 0.30 80
5.0 0.227 88.8
7.0 0.195 89.8 0.25
at 80C. It is seen that the cellulose I content decreases by increasing the
duration of hydrolysis. The same holds good for the crystallinity index. This
suggests that pretreatment of scoured cotton with HCl and reacting the HCl
treated cotton with DAC brings about a modified cotton cellulose (substrate
I-H bearing DEAE groups) the crystalline elementary fibrils
of
which are
more susceptible to disruption by the acid attack than its mate derived from
scoured cotton (substrate I bearing DEAE groups). The microstructure of the
latter substrate, as pointed out above, remained apparently intact during the
course of HCl hydrolysis.
Tab. 7 shows changes in the peak intensities I(lOi)/I(002) for slack
mercerized cotton containing
DEAE
substituents before and after treatment
with
0.5 N
HC1 at 80C for varying lengths of time. The results indicate that
there is an increase, though very little, in the cellulose I content by increasing
the duration of acid hydrolysis. Increasing the cellulose I content in slack
mercerized cotton (substrate I1 treated with DAC) by prolonging the duration
of acid treatment indicates that mercerized cotton is more amenable to recrys-
tallization than scoured cotton since the latter, as shown above, does not
reveal any significant change in its microstructure after being subjected to
similar acid treatment.
Tab.
7
shows also the ratio of peak intensities I (lOC)/I (002) for previously
HC1 treated slack mercerized cotton bearing DEAE groups (substrate 11-H
treated with DAC) before and after subjecting it to
0.5 N
HCl at 80C for
different periods of time. It is apparent that there is
a
substantial increment in
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Tab.
7.
Effect
of
duration
of
acid hydrolysis (0.5 N HCl, 80C) on the ratio of peak
intensities
1(101)/1(002)
of DAC-treated substrate I1 and DAC treated
substrate 11-H.
Hydrolysis (h) 1(1oi)/r(oo2)
Substrate I1 Substrate 11-H
treated with DAC
treated with DAC
0
0.670 0.663
0.5
0.704
0.800
1
o 0.686 0.820
2.0 0.721 0.750
3.0 0.650 0.750
5.0 0.636 0.740
7.0 0.810
the conversion ratio of cellulose I to cellulose I1 after acid hydrolysis, though
no clear cut between duration of acid hydrolysis and this increment is
observed. That is, acid treatment brings about
a
decrement in cellulose
I
content irrespective of the time of acid hydrolysis within the range studied.
A
similar observation was found with the corresponding substrate derived from
scoured cotton (substrate I-H treated with DAC) as indicated above.
It should be emphasized that the acid conditions used in this investigation
(0.5
N
HC1, 8 0 T , 0.5 7 h) are too mild to be adequate for characterizing
structural differences among scoured and slack mercerized stretched cottons.
Severe acid hydrolyses (2.5 N HC1 under reflux for different periods of time)
are now being performed. This will be published in a forthcoming paper.
The authors wish to express their sincere thank appreciation and gratitude
to
Dr.
S . P. Rowland, Research Leader, Natural Polymer Structure Research,
Natural Polymer Laboratory, SRRC, New Orleans, Louisiana,
U.S.A,
for his
invaluable guidance and critical evaluation of this work.
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