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Redox-initiated vinyl graft copolymerisation onto wool with thiourea as the reductant. II. Fe3+-thiourea co-catalyst induced graft copolymerisation of methyl methacrylate on wool and modified wool fibres

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Die Angewandte Makromolekulare Chemie37 ( 1 9 7 4 ) 1 1 -25 ( N r . 5 2 2 )
From theTextile Research Laboratories, National Research Centre, Dokki,Cairo, Egypt
Redox-Initiated Vinyl Graft Copolymerisation onto Wool
with Thiourea as the Reductant
11. Fe3+-’IhioureaCo-CatalystInduced Graft Copolymerisationof
Methyl Methacrylateon Wool and Modified Wool Fibres*
By Ali Hebeish, Saleh H. Abdel-Fattah,and Ahmed Bendak
(Received 31 July 1973)
SUMMARY:
The capability of Fe3 * -thiourea redox system to induce graft polymerisation of methyl
methacrylate onto wool fibres was investigated under various conditions. Variables
studied include sequence of addition of reagents, acidity of the reaction medium, temperature, monomer concentration and nature of the substrate. In addition, alkali solubility
of wool before and after grafting was examined.
Allowing the ferric ion to be absorbed first on wool before addition of the thiourea
and monomer leads not only to higher grafting but to greater grafting efficiency and
total conversion than when all the reagents were present together. The graft yield increases
significantly by increasing reaction time in the initial stages of the reaction but it does
slow down on prolonging the duration of grafting. The effect of increasing monomer
concentration is to bring about a significant enhancement in the graft yield. The same
holds true for acidity of the reaction medium and temperature. The graft yields are
considerably influenced by chemical modification prior to grafting. For instance, wool
reduced via treatment with thioglycolic acid is more amenable to grafting than untreated
wool. The opposite holds true for csterified and dinitrophenylated wools. The alkali
solubility of wool decreases significantly by increasing the graft yield; a graft yield
of ca. 95 % makes wool practically unimpaired with aqueous sodium hydroxide.
ZUSAMMENFASSUNG:
Die Pfropfcopolymerisation von Methylmethacrylat auf Wolle mit dem Redoxsystem
Fe3’ /Thioharnstoff wurde unter verschiedenen Bedingungen untersucht. Dazu wurden
die Reihenfolge der Reagenzzugabe, die Aciditat des Reaktionsmediums, die Temperatur,
die Monomerkonzcntration und die Art des Substrates variiert. AuRerdem wurde die
Alkaliloslichkeit der Wolle vor und nach der Pfropfung gepriift.
.- -.
* Part I: Ref. ”.
11
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
LaDt man die Fe3'-Ionen von der Wolle absorbieren, ehe man den Thioharnstoff
und das Monomere zusetzt, so werden hohere Pfropfausbeuten erzielt, als wenn alle
Reagenzien gleichzeitig zugegeben werden. Die Pfropfausbeute steigt zunachst steil an,
nimmt aber mit zunehmender Pfropfdauer langsamer zu. Bei hoherer Monomerkonzentration erhoht sich die Pfropfausbeutc deutlich, ebenso bei hoherer Aciditat und Temperatur.
Ferner werden die Ausbeuten betrachtlich durch eine chemische Vorbehandlung der
Wolle beeinfluDt. Zuvor mit Thioglycolsaure reduzierte W o k 1aDt sich leichter pfropfen
als unbehandelte. Das Gegenteil gilt fur veresterte und fur dinitrophenylierte Wolle.
Die Alkaliloslichkeit von Wolle nimmt dcutlich mit wachsender Pfropfausbeute ab;
bei einem Pfropfungsgrad von 95 % wird die Wolle praktisch nicht mehr von Natronlauge
angegriffcn.
Introduction
In recent years, graft copolymerisation of vinyl monomers onto wool has
gained considerable importance since preformed polymers are incapable of
diffusing into the internal structure of wool. Initiation must be controlled
so that the radicals are formed on the fibres which will initiate polymerisation
of monomer diffusing into the interior of the wool. It should be emphasized,
however, that the total polymer add-on on the wool fibres corresponds not
only to the grafted polymer but also to ungrafted polymer. The latter is
entangled within wool matrix and may not be removed by the solvent extraction
technique which is usually used for this purpose'.
Vinyl graft copolymerisation of wool is initiated by several free radical
or radical-ion techniques including high energy radiation2- ', low energy
radiation in presence and absence of sensitizer5- ' or chemical initiation8- 18.
Chemical initiations include peroxidisulphate anion8, Fez +/H,O,', Ceric
Manganese (IV)16, periodate ion", azobisisobutyronitrile18 and
ion
copper-(11)-complexes 2 - 15.Very recently, the use of thiourea-hydrogen peroxide redox system in initiating grafting of wool with methyl methacrylate
has been studied 19.
In this work, the feasibility of Fe3+-thiourea redox system to induce graft
copolymerisation of methyl methacrylate on wool was investigated. It is shown
that the grafting efficiency can easily be increased by making use of the
ion binding capacity of wool.
''*'',
Experimental
Materials
Merino wool fibres were purified by extraction with acetone in a Soxhlet apparatus
for 24 hrs., followed by washing with distilled water and air drying.
12
Graji Copolymerisation of M M A on Wool
Esterified wool was prepared by treatment of purified wool with anhydrous methanol
in presence of HCI (0.1N) at 65°C for 6 hrs. using a material to liquor ratio 1 :50".
Reduced wool was prepared by treating purified wool with 0.2N thioglycolic acid
solution for 24hrs. at 30°C using a material to liquor ratio 1 : 100.
Dinitrophenykated wool was prepared by treatment of purified wool with l-fluoro-2.4dinitrobenzene (FDNB) in ethanolic solution for several days at room temperature
according to the Middlebrook methodz1.
Methyl methacrylate (MMA) was washed with 5 % sodium hydroxide solution and
water, it was then dried with anhydrous sodium sulphate and distilled under reduced
pressure in nitrogen before use.
Ferric chloride used was of pure grade chemicals, thiourea of pure grade chemicals
was employed.
Treatment of Wool With Ferric Chloride
Wool fibres were treated with 1 M ferric chloride solution using a material to liquor
ratio 1 : S O at 60°C for 30 min. The wool samples were then washed with water and
dried. The amount of iron bound with wool was estimated iodometricillyzz.
Copolymerisation Reaction
Two methods were employed for graft copolymerisation of MMA onto wool fibres.
The experimental technique adopted for each method is given below:
Method I
A 12.5ml portion of 1 M F&13 solution acidified with nitric acid (4N, 10ml) was
taken in a 100-ml glass stoppered Erlenmeyer flask. The latter was kept at a specified
temperature (50°C). Freshly distilled MMA (552 mmole.1- '), wool ( O S g ) , thiourea (1 M,
20ml) were successively added. The content of the flask was shaken well and the reaction
was allowed to proceed for different lengths of time (15-120 min). After the desired
grafting time the sample was removed and washed well with water and repeatedly
Soxhlet extracted with acetone till constant weight.
Method I1
A 20ml portion of thiourea solution (1 M)acidified with nitric acid (4N, 10ml) together
with methyl methacrylate (552 mmole.1- I ) was taken in a 1Wml glass stoppered Erlenmeyer flask. To this wool (0.5 g) pretreated with ferric chloride was added. The grafting
reaction was then allowed to proceed for different times (15 120min) at specified
temp. (50 'C). Removal of homopolymer was performed as described in method I.
The percent grafting was calculated as follows:
% Graft
Dry weight of grafted wool - Dry weight of orig.
wool
~.
- xtoo
Dry weight of original wool
= __---
13
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
The homopolymer formed during grafting was estimated gravimetrically. The percent
conversion of monomer to homopolymer was calculated as follows:
Dry weight of homopolymer
x 100
Weight of monomer used
% Homopolymer = --
To make the percent grafting comparable to the percent homopolymer formed, these
quantities were calculated on the weight of monomer present at the start of the reaction.
The graft efficiency was calculated as follows:
Graft efficiency % =
Weight of grafted polymer
x 100
Weight of grafted polymer + weight of homopolymer
The percent total conversion was calculated according to the following formula:
% Total conversion =
Weight of grafted polymer + Weight of homopolymer
x loo
Weight of monomer used
~
Alkali Solubility
The alkali solubility was performed in aqueous sodium hydroxide solution (0.1 N )
at 65'C for one hr., using a wool: liquor ratio 1 :
Results and Discussion
The cation binding capacity of wool particularly in acidic medium is usually
high. This is due to the fact that besides the carboxyl groups at the end
of the polypeptide chains of wool, free carboxyl groups are created as a
result of breakage of salt linkages:
I
I
I
.'H~N-C-
R -c -COOT .
R
Acid
R -C
I -COOH
I
I
I
H2N -C -R
( 1 )
Polypeptide chains
In order to make use of the cation binding capacity of wool in enhancing
grafting, Fe3+-thiourea redox system in acidic medium was studied. Graft
polymerisation of a vinyl monomer by this couple would be expected to
proceed by the formation of isothiocarbamido radicals:
14
GraJ Copolymerisation of M M A on Wool
The isothiocarbamido radicals abstract hydrogen from thio, amino or
hydroxyl groups in wool (WH) to yield wool radicals (W')
-
WH + 'S-C
W'
+
HS-c
'\NH
This is followed by addition of vinyl monomer to wool radicals in a chain
process.
Evidently, ferric ion can be bound to the carboxyl groups in wool and
these become sites at which polymerisation occurs. Since homopolymerisation
takes place mainly in the reaction medium, while graft polymerisation can
only occur on or within the solid wool, the probability of grafting would
be enhanced when the initiator-binding sites are present in high concentration
in the fibres.
In Table 1 the results of polymerisation of methyl methacrylate in presence
of wool fibres are shown using the redox initiation of thiourea and Fe3'
in dilute nitric acid. Here all the components are present together, whereas
the results of Table 2 were obtained under similar conditions except that
the oxidant (Fe3') was attached to the wool fibres by ion-exchange, and
the reducing agent (thiourea) was subsequently applied with the monomer.
Thedata ofTable 1 indicate that the graft yield and homopolymer formation
increase by increasing reaction time. However, the amount of monomer converted to grafted polymer is significantly lower than that convertcd to homopolymer. This could be interpreted in terms of the following possibilities:
I. Some of the wool radicals were trapped and, therefore, were less available
for the monomer. However, this is rather improbable since more or less
cqual quantities of grafting and homopolymerisation occurred by modifying
the technique of the copolymerisation reaction (see Table 2).
2. Addition of methyl methacrylate onto the isothiocarbamido radicals
proceeds much easier than the abstraction of hydrogen from the wool molecule
under these conditions. i.e. method I.
15
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
--
.~
r
Reaction
time
(min)
__
~-
15
Graft
yield**
(YO)
~
12.96
(2.25)
16.00
(2.78)
17.08
(2.96)
20.26
(3.52)
23.34
(4.05)
30
45
60
90
~.
~
Homopolymer
based on
monomer
weight (YO)
_ _ _ _ ~
- . ..
Graft
efliciency
Total
conversion
W)
(70)
-
____.
4.36
4.44
38.5
7.22
6.60
44.95
9.56
7.88
30.85
11.40
10.30
28.22
14.35
_____
-..
* FeCI3 1 M; thiourea 0.4M; nitric acid 0.8N; methyl methacrylate 552mmole 1-
**
I;
temperature 50 C; material :liquor ratio 1 : 100.
Values in parentheses are graft yields based on monomer weight.
3. The free wool radicals may be terminated by other means rather than
initiating polymer chains on the wool backbone.
4. The capability of wool to bind Fe3+ may be impeded by the presence
of monomer under the conditions studied, i. e. method I.
Table 2 shows that the graft yields obtained with method 11, in which
Fe3+ was bound with wool before addition of thiourea and monomer, are
significantly higher than those of method I. Furthermore, the amount of
grafted polymer is equal to the amount of homopolymer formed during
the copolymerisation reaction, unlike method I.
Under theconditions of method 11, the concentration of the initiator-binding
sitcs in the fibres would be high. Furthermore, the gencrated isothiocarbamido
radicals would be in intimate contact with wool molecules. Grafting would,
thus, be promoted over homopolymerisation under the conditions of method
I1 as compared with those used in method I.
An interesting feature (cf. Tables 1 and 2) is that with both methods despite
the use of cxcess monomer, fairly high efficiency of grafting could be obtained.
Nevertheless, the efficiency of grafting for method I1 is substantially greater
than that of method I. The efficiency of grafting is also found to decrease
16
GruB Copolymerisation of M M A
011 Wool
Table 2. Polymerisation of MMA in presence of wool under the catalytic influence
of Fe3'-thiourea redox system using method ]I*.
-
Reaction
time
(min)
-.
15
30
45
60
90
-
Graft
yield**
(YO)
~
.
~
1 11.6
( 19.38)
123.8
(21.5)
148.4
(25.76)
185.0
(32.12)
188.0
(32.64)
Homopolymer
based on
monomer
weight (%)
-.
__
Graft
efficiency
Total
conversion
(O h )
(O/O)
__
-
19.38
50
38.75
2 1.49
50
42.98
25.67
50
5 1.52
32.00
50
64.23
32.65
50
65.27
-
~
* Wool pretreated with 1 M F&l3 for 1 h at 60 C; squeezed, washed. dried. This
**
was then treated with 0.4M thiourea and 552 mmole I - ' MMA in 0.8N nitric
acid at 50 C using a material : liquor ratio of 1 : 100.
Values in parentheses are graft yields based on monomer weight.
with increasing percent grafting only in case of method I while it remains
constant with respect to method 11. This reflects the importance of binding
the cation, i.e. Fe3', in controlling the number and directing the location
of grafting sites on the wool backbone.
Another point of interest (Table 1 and 2) is that within the range studied
the maximum total conversion of monomer to polymer obtained under the
conditions of method I is about one fourth of the corresponding conversion
achieved with method 11. This could be associated with the following:
1. Wool pretreated with Fe3' (used in method 11) may acquire higher
affinity to the monomer (MMA). Consequently, complexation of wool with
monomer will be easier in case of method I1 than in method I. Such complexation was reportedz4 to increase monomer reactivity due to formation of
a donor-acceptor complex in which the uncomplexed monomer, though normally an electron acceptor, behaves as a donor relative to the complexed
monomer which has been converted to a stronger acceptor.
2. Presenceofexcess Fe3' in the treatingsolution ofmethod I may participate
in termination of the growing chains thereby lowering their molecular weights.
17
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
3. The efficiency of Fe3+-thiourea redox system in producing isothiocarbamido radicals seems to be decreased by the presence of excess Fe3+.
Evidently, method I1 is much more efficient than method I. Hence, unless
otherwise stated, method I1 was employed for studying variables affecting
grafting such as temperature, monomer concentration, etc. to discover the
optimal conditions for grafting.
Monomer Concentration
Fig. 1 shows the rates of grafting of methyl methacrylate on wool fibres
at differentmonomer concentrations. It is clear that regardless of the concentra200
180
160
140
."
-
L
m
120
100
L
a
80
60
40
20
Time ( m i n )
Fig. I .
18
Graft yield as a function of reaction time at various monomer concentrations:
-0
92 mmole I - . 1 ; -8- 184 mmole I - ' ;
-0-368 mmole I - ' ; - 0552 mmole I - ' MMA. Wool pretrcated with 1 M FeC13 at 6O'C for 30min
using a material : liquor ratio of 1 : 50, washed, dried, and then grafted at 50 'C
using 0 . 4 M thiourea at a material : liquor ratio of 1 : 100.
Graft Copolymerisation of M M A
011
Wool
tion used, the grafting occurs immediately without any induction period.
The graft yield also increases very significantly by increasing reaction time
in the initial stages of the copolymerisation reaction but it does slow down
on prolonging the duration of grafting. However, within the range studied,
both the initial increment in the graft yield and the maximum graft yield
are much greater at higher than at lower monomer concentrations.
Since the copolymerisation reaction was carried out at the same temperature
and at fixed concentrations of Fe”, thiourea and acidity, it is possible to
assume that the concentration, nature and efficiency of the free radical and
other species generated during the reaction would be the same. Hence, the
higher rates of grafting observed upon using increased amounts of monomer
could be attributed to a variety of reasons. First, complexation of wool
with monomer which is required for enhancing monomer activity would
be favoured at higher monomer concentration. Secondly, gel effect, i. e. increase
in medium due to the solubility of polymethyl methacrylate in its own
monomer, would be more pronounced at high monomer concentration. This
causes hinderance in termination particularly by coupling of the growing
polymer chains. Besides this the gel effect also causes swelling of wool, thus
facilitates diffusion of monomer to growing chains and active sites on the
wool backbone, thereby enhances grafting. Third, some species, which are
either present or generated during the copolymerisation reaction, are acting
as an efficient radical scavenger. Competition between this and the monomer
in capturing the free wool radical would play the key role in the amount
of graft formation. It is likely that capturing of wool radicals by monomer
predominates at higher monomer concentration.
Temperature
The effect of increasing the copolymerisation temperature is to bring about
a significant acceleration in the rate of grafting. This may be realized from
Fig. 2. As is evident, the rate of grafting follows the order 60’ > 5 0 > 30°C.
The dependence of the rate of grafting on temperature could be ascribed
to the greater activation energy induced in the copolymerisation system at
higher temperature. This results in an increase in the extent of dissociation
oftheFe3’ boundswith wool, thusassists the reaction of Fe3’ with isothiourea
leading to higher concentration of isothiocarbamido radicals. This and the
point that swellability of wool, solubility of monomer and its diffusion are
19
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
200
180
160
140
0"
c
Y-
120
100
m
5
80
60
40
20
,
'0
15
30
45
I
~~
60
Time (min)
90
120
Fig. 2. Effect of temperature on grafting of methyl methacrylate to wool fibres using
Fe3+-thiourea redox system (--O- 30°C; -6- 50°C; --060°C). Wool
pretreated with 1 M FeCL at 60°C for 30min using a materia1:liquor ratio
of 1 :50, washed, dried, and then grafted by using 552 mmole 1 * MMA, 0.4M
thiourea at a materia1:liquor ratio of I : 100.
enhanced by rising the reaction temperature would account for the higher
grafting rates observed when temperature is increased from 30" to 60°C.
Acid Concentration
The effect of nitric acid concentration on the rates of grafting of methyl
methacrylate on wool fibres is shown in Fig. 3. It is apparent that increasing
the acid concentration in the wool-Fe3+-thiourea-monomer-HzO
system from
0.05N to 0.2N is accompanied by a significant enhancement in the rate
20
120
1
Graft Copolymerization of M M A on Wool
Fig. 3. Variation of the graft yield with nitric acid concentration: . .O.- 0.05 N HNO3;
-0-0.2N
HN03;--0--. 0.4N HN03;--6-0.8N HNO3. Wool pretreated
with 1 M FeC13 at 6 0 T for 30min using a materia1:liquor ratio of 1:50,
washed, dried, and then grafted by using 368 mmole I - ' MMA and 0.4M
thioureaat 50°C in presence of different concentrations of nitric acid; material: liquor ratio 1 : 100.
of grafting. Further increment in acid concentration up to 0.8 N causes also
enhancement in the grafting rates but to a lower degree.
The increased initiating eficiency of the system at higher acid concentration
suggests that besides initiation by isothiocarbamido radicals (eq. 3), initiation
by the radical formed according to equation 6 may take place2'.
H
I
=
H'
HS-(f
,NH2
s=f
'N-H
(5)
NH2
NH2
H
H
I
HS-c
/FH \
+ Fe3'
NH2
I
'5-C
TH
\
H'
i
i
Fe2'
(6)
NH2
However, the increase in the reducing property of thiourea at higher acid
concentration and its effect on wool giving rise to reduced wool with greater
susceptibility to grafting cannot be ruled out.
21
A. Hcbeish, S. H. Abdel-Fattah, and A. Bendak
Nature of the Substrate
The effect of the changes in the physical and/or chemical structure of
wool brought about by reduction, esterification or dinitrophenylation on
its behaviour towards grafting may be realized from Table 3. It is apparent
that thegraft yield of reduced wool is significantly higher than that of untreated,
esterified, and dinitrophenylated wool; it follows the order: reduced wool
> unmodified wool > esterified wool > dinitrophenylated wool.
The higher graft yield obtained with reduced wool is unequivocally due
to the presence of thiol groups (-SH) in the wool molecule. The thiol groups
are formed as a result of treatment of wool with thioglycolic acid. Abstraction
of the hydrogen from thiol groups by the initiator radicals seems to proceed
much more easier than abstraction of hydrogen from amino and hydroxyl
groups in the wool molecule. It is well known that the thiol group has
the ability of participating in radical formation from the initiator radical
and in chain transfer from the growing homopolymer radicals'. This and
the fact that treatment of wool with thioglycolic acid increases its accessibility
would account for the higher graft yields obtained with reduced wool.
It should be noted, however, that some of the thiol groups in wool molecule
may be oxidized to disulphide bonds under the catalytic influence of Fe3'
during the pretreatment of wool with FeC13. This would lead to a decrease
in the thiol as well as in the Fe3+ content of wool. The graft yields obtained
under the conditions studied indicate that the thiol and Fe3' contents
of reduccd wool are sufficient enough to bring about higher grafting than
untreated wool.
The esterified wool showed graft yields which are substantially lower than
those of unmodified wool (Table 3). This could be associated with the effect
of introduction of methyl groups in the wool molecules during the esterification
reaction. Such groups would be expected to cause blocking some of the
carboxyl groups (sites for binding Fe3+)as well as decreasing the swellability
of wool thereby impeding monomer diffusion. Both functions lead to lower
grafting.
In Table 3 it can also be seen that the dinitrophenylated wool shows
graft yields which are significantly lower than those of the unmodified. Besides
blocking of the free amino and hydroxyl groups which are the main sites
for initiation of grafting on wool l o * 1 2 , dinitrophenylation seems to reduce
significantly the swellability of wool. Hence the bulkiness of the dinitrophenyl
groups and the decreased swellability of wool would render the binding
22
Gruff Copoljmcrisution of MMA on Wool
Table 3. Graft polymerisation of methyl methacrylate on wool and modified wool
fibres using Fe3'-thiourea cocatalyst*.
___.
Reaction
time
(min)
~-
K ed wed
wool
Graft yield percentage
-
tsterilied
.~
15
30
45
60
90
120
124.8
200.2
2 16.6
247.6
266.8
268.4
~~
Dinitrophenylated
wool
7
~
_
-
Unmodified
wool
~
54.x
7X.2
88.2
117.4
135.6
140.0
1.4
2.2
3.6
3.6
3.6
3.6
1 1 1.6
122.4
158.4
185.0
188.0
194.4
* Wool and modified wools were pretreated with 1 M FeCI, solution for 1 h at 6O'C,
squeezed, washed, dried. This was then treated with 0 . 4 M thiourea solution and
552 mmolc
methyl methacrylate, in 0.8 N HNO, at 50°C using a matcria1:liquor
ratio of 1 : 100.
of Fe3+ with the wool carboxyl a very difficult task during pretreatment
of wool with the ferric salt. The same effects would also operate during
the grafting reaction since diffusion of methyl methacrylate would be hindered
owing to lower swellability of wool and its absorption would be less because
of the negative charge on the nitro group which would repel the similarly
charged molecule of M M A thereby decreasing the graft yield.
Ferric Ion Content
The Fe3+ contents of wool and modified wool fibres are shown in Table
4. Obviously, the untreated wool shows the highest Fe3+ content whereas
the dinitrophenylated wool shows the lowest and follows the order unmodified
> reduced > esterified > dinitrophenylated wool.
The lower Fe3' content observed with reduced wool compared with unmodified wool suggests that some of the Fe3' is reduced to Fe" under the
influence of reduced wool. It has been reported that ferric cysteinate is formed
upon addition of ferric ion to either acid or alkaline cysteiflate solutions,
the complex being reduced to ferrous complex with formation of cystine26.
With respect to esterified wool, the lower Fe3' content is undoubtedly
due to blocking most of the carboxyl groups during thc esterification reaction.
However, the adverse effect brought about by introducing methyl groups
23
A. Hebeish, S. H. Abdel-Fattah, and A. Bendak
Table 4. Fe3+ Content of wool and modified wool fibres treated with 1 M FeC13
for 30min at 60'C, material : liquor ratio 1 :50.
_____
Substrate
Fe3' (g/lOOg wool)
Untreated
Esterified
Reduced with thioglycolic acid 0.2 N
Dinitrophenylated
1.56
0.46
0.95
0.23
in wool on its swellability cannot be ruled out. On the other hand, the
lowest Fe3+ content observed with dinitrophenylated wool substantiates the
assumption that presence of bulky groups in the wool molecule such as
dinitrophenyl groups reduces the swellability as well as the cation binding
capacity of wool.
Alkali Solubility
In Table 5 the alkali solubility for grafted wool and wool treated with
Fe3+-thiourea cocatalyst under the same conditions of grafting in absence
of monomer is shown. It is apparent that the solubility of wool significantly
decreases as the graft yield increases. A graft yield of ca. 95% makes wool
practically unimpaired with alkali. The outstanding reduction in alkali solubility suggests that the polypeptide chains, salt linkages and disulphide linkages
in wool are protected by the presence of the grafted polymer. The latter
Table 5. Alkali solubility ofwool graft copolymers and wool oxidized under the influence
of Fe3'-thiourea system.
Reaction time (min)
Graft yield (YO)
Alkali solubility (YO)
Grafted
Untreated
-
15
32.8
30
45
60
90
120
49.4
68.9
93.4
95.4
95.6
24
Oxidized
15.00
3.0
2.0
27.5
28.0
1.3
29.0
0.7
0.5
0.5
30.0
32.0
34.0
Grafi Copolymerisation of M M A on Wool
seems to produce a diffusion barrier for the alkali to penetrate into the
interior of wool. It is rather possible that some stable crosslinks are formed
in wool via termination of two radicals and/or growing chain radicals by
coupling. The resistance conferred on wool via grafting during the reaction
makes wool less amenable to the initiator attack.
Treatment of wool with Fe3+-thiourea redox system, on the other hand,
causes a substantial enhancement in alkali solubility. This is expected since
this redox system generates free radicals (eq. 3 and 6) which subsequently
attack the wool molecule to give rise to oxidation products of wool. In
contrast to the grafted material, the oxidized wool formed in the early stages
of the treatment seems to acquire greater susceptibility to alkali.
1
7
3
4
5
6
H. L. Needles, L. J. Sarfeld, and D. M. Dowhamiuk, Text. Res. J. 42 (1972) 558
I. C. Watt, J. Macromol. Chem. C 5 (1970) 175
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woolf, induced, reductant, fibre, methacrylate, thioureas, copolymerisation, fe3, onto, methyl, graf, redox, vinyl, modified, catalyst, initiate
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