close

Вход

Забыли?

вход по аккаунту

?

Graft copolymerization of wool using acrylate monomers. I. Optimum conditions of grafting and molecular weight of grafts

код для вставкиСкачать
Die Anqrwandte Makromolekulare Chemie 35 (1974) 203-21 1 ( N r . 510)
From the Fibre Science Laboratories, Indian Institute of Technology, Delhi Hauz Khas,
New Delhi-29, India
Graft Copolymerization of Wool Using Acrylate
Monomers
I. Optimum Conditions of Grafting and Molecular Weight of Grafts
By D. S. VARMAand R. K. SARKAR*
(Received 29 June 1973)
SUMMARY:
Wool fibres were grafted with methyl acrylate, ethyl acrylate, n-butyl acrylate and
methylmethacrylate to various percentages of grafting in nitrogen atmosphere using
ceric ammonium nitrate in nitric acid as initiator. The effects of concentration of the
initiator, acid, monomer, temperature and time on the grafting were investigated. A
comparison of such results indicated the following reactivity order of monomers: methyl
acrylate > ethyl acrylate > methylmethacrylate > n-butyl acrylate. The molecular
weights of the grafts were investigated by isolating the grafts from the fibres.
ZUSAMMENFASSUNG:
Wollfasern wurden mit Methylacrylat, Athylacrylat, n-Butylacrylat und Methylmethacrylat zu verschiedenen Pfropfungsgraden unter Stickstoffatmosphare gepfropft, wobei
Cer-ammoniumnitrat in Salpetersiiure als Initiator diente. Der EinfluI3 von Initiator-,
Saure-, Monomerkonzentration, Temperatur und Pfropfungsdauer wurde untersucht.
Es ergab sich die folgende Reaktivitatsreihe der Monomeren: Methylacrylat > Athylacrylat > Methylmethacrylat > n-Butylacrylat. Die Molekulargewichte der Pfropflinge wurden bestimmt.
Introduction
Several research workers have investigated the grafting on wool fibres
first used
by using different initiator systems. Thus LIPSONand SPEAKMAN’
the ferrous ion-hydrogen peroxide redox system of initiation for depositing
several polymers onto wool, and VALENTINE” has studied the reaction
kinetics of deposition of acrylonitrile onto wool by this method. To render
*
Present address: Shri Ram Institute for Industrial Research, 19, University Road,
Delhi-7. India.
203
D. S. VARMAand R. K. SARKAR
the processing simpler, persulphates were used successfully4~ for initiating
grafting of several monomers on natural and reduced wool. Lithium bromide
~
of vinyl monomers
persulphate system has also been u ~ e d ~for- grafting
on wool. BURKEand coworkers9 have adopted high energy radiation technique
for depositing polyacrylonitrile onto wool. Newer methods of grafting on
lo*
wool in the absence of initiators have recently been reported by TANAKA
Recently, ceric ion system has been used to initiate grafting of methylmethacrylate on wool fibres. It appears of interest to study the suitability of
grafting other acrylate monomers on wool using ceric salts which have many
advantages over other initiators because of the simplicity of application
and less homopolymer formation. The present paper reports the results of
graft copolymerization of methyl acrylate, ethyl acrylate, n-butyl acrylate
and methylmethacrylate on wool fibres using ceric salt as an initiator. The
optimum conditions of grafting and molecular weight results are discussed.
Experimental
Materials
Indian Chokla wool fibres were purified by Soxhlet extraction with petroleum ether
for about 24 hrs. followed by repeated washing with cold distilled water and then drying
in air.
Monomers of Analar grade were washed with 5 % sodium hydroxide solution to
remove the inhibitor and then distilled.
Fresh solution of required strength of ceric ammonium nitrate (Baker analyzed reagent
grade) in nitric acid was used for each experiment. Other chemicals used were also
of chemically pure grade.
Method of Graft Copolymerization
Graft copolymerization was carried out in a three-necked flask in nitrogen atmosphere.
Dried and purified wool fibres were immersed in a solution of ceric ammonium nitrate
(0.005 N to 0.05 N) in nitric acid (0.1 N to 1 N) at temp. from 20 "C to 50 "C. The required
concentration of monomer was added to the reaction mixture and the contents of
the flask were constantly stirred. The reaction time was varied from 30 min. to 6 hrs.,
and the material to liquor ratio was 1 :50. After the desired reaction time, wool fibres
were taken out, washed thoroughly with water and acetone. Finally the fibres were
Soxhlet extracted with benzene or acetone until the homopolymer was completely
removed. They were then dried in an oven, cooled to room temp. and weighed. The
graft-on was calculated as the per cent increase in weight over the original weight
of the sample.
204
Graft Copolymerization of Wool Using Acryiate Monomers
Molecular Weight
For the determination of the molecular weights of the grafts, the method proposed
et al. was used. The wool component of the grafted samples was removed
by NEGISHI
by decomposing the samples with 72% sulphuric acid for 2hrs. at 40°C at a liquor
ratio of 40: 1, then diluting with eight times as much water and then heating in a
boiling water bath until complete decomposition occurred. The insoluble residues were
filtered off, washed well until the filtrate was neutral. The polymer was then dissolved
in acetone and reprecipitated by adding water as non-solvent. The molecular weights
were determined by viscosity measurements using the K and a values given in l i t e r a t ~ r e ' ~ .
A dilute solution of polymer (0.1-0.5g/dl) in desired solvent was used and the measurements were carried out in an Ubbelohde viscometer at desired temperature.
R esu Its and Discussion
1. Optimization of the Conditions for the Grafting with Methyl Acrylate
a) Effect of Acid C o n c e n t r a t i o n
By varying the concentration of nitric acid in the reaction bath, the effect
of pH on the grafting of methyl acrylate on wool was studied. A range
of acid concentrations (from 0.1 N to 1 N) was taken, and the results are
6o
t
1
0.2
0.3
I
0.4
I
I
0.6 0.7
Normality of acid
0.5
1
I
0.8
0.9
1
.O
Fig. 1. Effect of acid concentration in the bath on grafting of methyl acrylate on
wool. Initiator conc. 0.01 N ; 5 % monomer; temp. 30°C; reaction time 4 hrs.
205
D. S. VARMA
and R. K. SARKAR
shown in Fig. 1. It is found that the percentage graft-on increases with
the increase of acid concentration up to OSN, and with further decrease
of pH the per cent graft-on begins to decrease progressively. Similar behaviour
has been observed in case of grafting of cellulose by acrylate monomers
by V A R M A and NARASIMHAN15 where a decrease in grafting was obtained
after an acid concentration of 0.25 N. A mechanism similar to the one proposed
therein can perhaps explain these findings in case of wool.
b) Effect of I n i t i a t o r C o n c e n t r a t i o n
Different concentrations of ceric ammonium nitrate (from 0.005 N to 0.05 N)
were employed in several grafting experiments keeping the concentrations
of other reagents and temperature of the reaction constant. Fig. 2 shows
the results of graft-on at different initiator concentrations. It may be seen
that the percentage grafting increases with increasing initiator concentration
up to 0.01N, after which the grafting decreases with further increase of the
concentration of initiator. This behaviour can be accounted for by a kinetic
scheme similar to the one proposed earlier 1 5 .
701
60
I
"0
0.005 0.010
0.020
0.030
Concentration o f i n i t i a t o r
0.040
0.050
(N)
Fig. 2. Effect of initiator concentration on grafting of methyl acrylate on wool. Acid
conc. 1 N ; 5 % monomer; temp. 30°C; reaction time 4 hrs.
206
Graft Copolymerization of Wool Using Acrylate Monomers
c) Effect of T e m p e r a t u r e
Grafting reactions were carried out at four different temperatures between
20°C and 50°C, keeping the concentrations of all the reagents as well as
that of the monomer the same. The results indicate (Fig. 3) that the per
cent graft-on is maximum at 30°C, after which it decreases with the increase
of temperature. In a redox system, polymerization can be initiated at relatively
low temperature due to formation of radicals. At higher temperatures although
the rate of formation of radicals is higher there is a possibility of higher
combination rates which results in a decrease in rate of grafting. Similar
and MEHTA
l 6 when grafting acrylonitrile
results were reported by HEBEISH
on cellulose by ceric ammonium nitrate initiator. A probable explanation
as given by them was the increased rate of termination of growing polymer
chains at higher temperatures.
'O
O
t
7
20
30
40
50
60
Temperature ( " C )
Fig. 3. Effect of temperature on grafting of methyl acrylate on wool. Initiator conc.
0.01 N ; acid conc. 0.5 N; 5 YOmonomer; reaction time 4 hrs.
d) Effect of M o n o m e r C o n c e n t r a t i o n
The effect of monomer concentration on grafting was also studied by varying
the monomer concentration from 2 to 10 v01.-% keeping the concentrations
207
D. S. VARMA
and R. K. SARKAR
I
1
1
I
4
5
6
7
8
Monomer concentration ('lo)
J
I
I
9
1
0
Fig. 4. Effect of monomer concentration on grafting of methyl acrylate on wool. Initiator
conc. 0.01 N ; acid conc. 0.5 N; temp. 30°C; reaction time 4hrs.
of other reagents constant. The percentage graft-on increases steadily up
to 5 % monomer concentration (Fig. 4) after which there was a levelling
off with further increase in monomer concentration. It was observed that
the homopolymer formation was higher at higher monomer concentration.
As the monomer concentration is increased, the available sites for grafting
on fibre are activated and therefore an increase in percentage graft-on is
seen with increasing monomer concentration. After all such sites are occupied
further increase in grafting with increase in monomer concentration may
not take place and hence a levelling off is observed.
2. Grafting of Different Monomers on Wool
It can be seen from the results of the previous section that the optimum
conditions of grafting are obtained at an initiator concentration of 0.01 N,
an acid concentration of 0.5N taking 5 % monomer at a temperature of
30°C. Under this optimum set of conditions, grafting of four acrylate monomers
(viz. methyl, ethyl, n-butyl acrylates and methylmethacrylate) was studied.
The results of graft-on obtained at different reaction time are plotted in
208
Graji Copolymerization of Wool Using Acrylate Monomers
Fig. 5. It is observed from the figure that the number of molecules grafted
onto wool in the cases of four different monomers are in order: methyl
acrylate > ethyl acrylate > methylmethacrylate > n-butyl acrylate. Thus
as the size of the monomer is increased, the diffusion of monomer to all
available sites on the fibre is not possible and therefore, in the monomers
which are bulky the percentage grafting is less. The levelling off in the percentage
graft-on after certain time periods in most of these monomers can be explained
due to non-availability of reactive sites on the fibre.
0
' '. O
8I
Reaction t i m e (hrs)
Fig. 5. Effect of time of grafting of different monomers on wool: ( I ) methyl acrylate;
(2) ethyl acrylate; (3) methylmethacrylate; (4)n-butyl acrylate.
3. Molecular Weight
Table 1 summarises the values of the molecular weight of the different
polymers grafted onto wool fibres to different degrees. It is seen that in
the case of polymethyl acrylate and polybutyl acrylate the molecular weight
as well as the number of monomer units per mole of polymer increased
with the increase of percentage graft-on up to a certain extent after which
it decreased with further grafting. However, in the case of polyethyl acrylate,
it behaves in a different way where a slight decrease is found with increase
ofgraft-on after which it again increased. In the case of polymethyl methacrylate
the molecular weight decreased continuously with the increase of graft-on.
209
D. S. VARMA
and R. K. SARKAR
Table 1. Molecular weights of different polymers at different percentage graft-on. Experimental conditions: wool/liquor ratio 1 :50; monomer concentration 5 %; initiator concentration 0.01 N; acid concentration 0.5 N; temperature 30°C; reaction
time 4 hrs.
Polymer grafted
Graft-on
("/.I
Mol.-wt.
(M x 10- ')
No. of monomer
units per mole
of polymer
Polymethy lacrylate
27.2
35.1
57.5
5.22
9.62
1.15
6 070
11 186
1337
Polyethy lacrylate
19.6
27.9
32.2
5.30
4.02
5.12
5 300
4020
5 120
Poly-n-but y lacrylate
3.3
6.9
11.2
1.87
3.14
2.94
1461
2453
2 297
3.1
7.9
9.7
0.54
0.36
0.19
540
360
190
Polymethylmethacrylate
The variation in the molecular weights can be explained by the type of
branching formed by the grafts along the wool molecule. In the initial stages
the grafting takes place in the amorphous regions of the fibre and since
the space available is larger so the grafts attain an optimum size. However,
as the percentage graft-on increases, grafting in the semicrystalline regions
of the fibres also takes place and here the size of the grafts may not be
as big as in the amorphous regions. The overall distribution of the polymer
molecular weight is thus increased and the amount of low molecular weight
material perhaps is higher. Thus a decrease in the average molecular weight
is observed. A more detailed study of the type of branching formed by the
grafts and the distribution of molecular weights is necessary to get a clear
picture of this phenomenon.
Conclusion
The optimum conditions of grafting methylacrylate onto wool were obtained
at an initiator concentration of 0.01 N, acid concentration of 0.5N nitric
210
Graft Copolymerization of Wool Using Acrylate Monomers
acid taking 5 % monomer concentration at a temperature of 30°C for 4
hrs. The grafting of other monomers under these optimum conditions showed
the following reactivity order: methyl acrylate > ethyl acrylate > methylmethacrylate > n-butyl acrylate. The molecular weight results of different polymers
separated from the graft copolymers generally showed that with the increase
of graft-on the molecular weight initially increases, but it decreases on further
graft-on. An exception was, however, found in the case of polyethyl acrylate.
'
lo
'I
l3
l4
Is
l6
M. LIPSONand J. B. SPEAKMAN,
J. SOC.Dyers Colour. 65 (1949)390
L.VALENTINE,
J. Textile Inst. 46 (1955)T270
L.VALENTINE,
J. Textile Inst. 47 (1956)T 1
G. W.MADARAS
and J. B. SPEAKMAN,
J. SOC.Dyers Colour. 70 (1954)112
A. SCHOBERL
and D. WAGNER,Melliand Textilber. 41 (1960)984
M.NAGANOand Y. KURODA,Sen-i Gakkaishi 22 (1966)479
M. NEGISHI,K. ARAIand S. OKADA,Sen-i Gakkaishi 23 (1967)379
M. NEGISHI,K.ARAI, and K. TABEI,
Sen4 Gakkaishi 25 (1969)31 1
M. BURKE,R. KENNY,and C. H. NICHOLLS,
J. Textile Inst. 53 (1962)T370
Z.TANAKA,
Sen4 Gakkaishi 28 (1972)492
Z.TANAKA,
Sen-i Gakkaishi 28 (1972)498
A. KANTOUCH,
A. HEBEISH,
and A. BENDAK,
Eur. Polym. J. 7 (1971)153
M. NEGISHI,K. ARAI,and S. OKADA,J. Appl. Polym. Sci. 11 (1967)115
Polymer Handbook, J. BRANDRUP
and E. H. IMMERGUT
(Eds.), Interscience Publishers,
New York, 1965.
D. S. VARMAand V. NARASIMHAN,
J. Appl. Polym. Sci. 16 (1972)3325
A. HEBEISHand P. C. MEHTA,J. Appl. Polym. Sci. 12 (1968)1625
21 1
Документ
Категория
Без категории
Просмотров
1
Размер файла
353 Кб
Теги
monomerl, using, woolf, molecular, graf, optimum, acrylates, weight, copolymerization, conditions, grafting, grafts
1/--страниц
Пожаловаться на содержимое документа