Indian Journal of Fibre & Textile Research Vol. 24, September 1999, pp. 149-155

Graft copolymerization of vinyl monomers on nylon using the novel standing bath technique

H T Deo· , S V Mehendale, B K Desai & Arindam Chakraborty

Department of Chemical Technology, University of Mumbai , Mumbai 400019, India

Received 6 April 1998; revised received 12 August 1998; accepted 26 Octoher 1998

A novel 'Standing Bath ' techni que has been developed for grafti ng vinyl monomers (acrylonitrile and acrylic ac id ) onto polyamide fibres . The technique is based on the principle of utili zing chemi cals which form comrlexes with th e monomer molecules, thereby protecting them from the homopolymer formation reaction in successive baths. It is ohserved that the amount of utili zation of monomer in grafting can be enhanced from about 0.66% in the conventional method to about 5.56% in the new method. The use of quaternary ammonium compounds, viz. cetyltrimethyl ammonium bromide and cetyl pyridinium bromide, in graftin g has made it possible to carry out grafting three and six times from the same hath in case of acrylonitrile and acryli c acid monomers respectively. The nature of graft copolymers has also been eva lu :lted hy dyeability and moisture regain studies. The minute differences between the physical and chemical nature o/" til e grans obtained from the successive standing baths can be observed by these two techniques.

Keywords: Acrylic ac id , Acrylonitrile, Gran copolymerization , Polyamide fibres, Quaternary ammonium compounds

1 Introduction Considerable work has been carried out to improve

polyamide fibres by introd ucing different functional groups through graft copolymerization reactions using vinyl monomers . Some attempts have also been made to modify the methods of grafting with a view to utili ze higher amounts of monomers in the grafting reactions. These methods include pre-irrad iation of fibres and pretreatment of polymer with swelling agents followed by grafting reac ti ons . These attempts, however, could margina ll y increase the graft yield . Thus, in the conventional method of grafting, only about 2% of the monomer taken in the bath is converted into graft copolymer and about 98% of the monomer is wasted in the fo rm of homopolymer and other such compounds formed during the grafting reactions .

Hayashi et.al .1 observed that the presence of anionic surfactants increased the conversion of monomers into graft copolymers when methyl methacrylate was polymerized in the presence of nylon 6 and water. With the increase in pH, the conversIOn of methyl methacrylate into graft copolymer increased . The non-ionic and cationic surfactants , however, had no effect on the grafting reaction.

Skwarski and Buchenski 2 carri ed out grafti ng of

• To whom all the correspondence shou ld be addressed .

nylon 6 fibres and fabrics with acrylic acid , itaconic acid and 2-vinyl pyridine before and after their conversion into the sodium salts or quaterneri zat ion with 3-bromopropionic ac id in aqueous solution. Electrical resistance of the samples decreased and water sorpti on did not increase on treatment with sod ium carbonate or quaterni zat ion or the graft copolymer.

Severa l researchers attempted to minim ize the homopolymer fo rmation during grafting on nylon . The conversion of monomer to graft copo lymer coul d not be enhanced substantially3-'!.

In the present work , a nove l 'S tanding Bath' method has been developed for grafting vinyl monomers on polyamide fibres with a view to increase the utilization of the monomer, thereby making the grafting technique economically and industrially more viable and attract ive .

2 Materials and Methods

2.1 Materials Polyamide (nylon 6) monofil aments (Deni er , 12;

Semi-dull ) were cut into small pieces and then used for the study. Copper sulphate and potass ium persulphate, both of AnalaR grade, were used. The cationic softener Taffulon 320 A (suppli ed by Dai­ichi Karkaria, Mumbai) and cetyl trimethyl ammonium bromide (C.P. grade) and cetyl pyrid inium bromide (C. P. grade), both supplied by

150 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1999

Fluka A. G. (Switzerland), were used to pretreat the fibres. Acrylonitrile Ce. P. grade), supplied by Sisco Research Laboratories, Mumbai, was distilled to make it free from inhibitors. The fraction, boiling in the range 76°-78°C, was collected and used. Acrylic acid (e. P. grade), supplied by Fluka A. G. (Switzerland) , was vacuum distilled to make it free from inhibitors. The pure monomer was stored at low temperature. All other chemicals used were of e.P. grade.

Two cationic dyes, namely Rhodamine B (BASF)-e. 1. Basic Violet 10; and Sandocryl Blue B-3G (Sandoz)-e. I. Bas ic Blue 3, were used.

2.2 Methods

2.2. 1 Fibre Purification Nylon 6 fibres were extracted with petroleum ether

(b.p. 70-80°C) in sox hlet ex traction unit for 8 h to remove sp inning oil from fibres.

2.2.2 Grafting with Conventional Method A 50 ml of reaction soluti on consisting of water,

5-8% acrylonitrile/acrylic ac id monomer, 0.125% (w/w) potassium persulphate and 0.25 M/I copper sulphate, was prepared and then 0.5 g of polyamide fibre was added 10 it. The fl ask was kept in a thermostated water bath maintained at 80°C and the contents were stirred occasionally during the polymerization reaction . After I h, the contents were filtered on a sintered glass crucible and washed with water. In case of grafting with acrylonitrile, the polyamide fibres were kept in dimethylformamide at IOO°C to remove the homopolymer completely. Finally, the sample was taken out, washed with distilled water, dried in an oven at 105°C, cooled to room temperature and weighed . The homopolymer dissolved in pimethylformamide was re-precipitated with methanol. This re-precipitated homopolymer plus the homopolymer on the sintered glass crucible were weighed together to calculate the total homopolymer formed . In case of grafting with acrylic acid, the polyamide fibres present on sintered glass crucible were kept in boiling water for 4 h to remove the homopolymer. The fibres were then taken out, washed with cold water, dried in an oven at 105°C, cooled to room temperature and weighed. The homopolymer dissolved in water was re-precipitated with acetone. This re-precipitated homopolymer plus the homopolymer on the sintered glass crucible as well as the homopolymer re-precipitated from the filtrate were weighed together to calculate the total homopolymer formed.

2.2.3 Grafting with Standing Hath Method

2.2.3.1 Pretreatment of Polyamide Fibres About 0.5 g of polyamide fibre was trea ted with a

solution of Taffulon 320 A for 30 min at 30"e. Similarly, about 0 .5 g of polyamide fibres were treated separately with the soluti ons of cety l trimethyl ammonium bromide (CTMAB) and cety l pyridinium bromide (CPB), both of 5 g/I concentration , fo r 30 min at 30°e. The treated fib res were was hed with distilled water, dried at room temperatu re and then treated with 2% solution of potassium pe rsulph ate for 30 min at 30°e. Finally , the fibres were again was hed with distilled water and dried at room temperature.

2.2.3.2 Grafting with Acrylonitrile and Acrylit Acid Monomers

Two samples (each of O.S g) of pretreated polyam ide fibres were put into separate 100 ml­Erlenmeyer fl asks, eac h containing SO ml of the thermostated reacti on mixture. The reac ti on mixture consisted of water, different concentrations of the acrylonitrile/acry lic ac id (5-8 % w/w) and copper sulphate (0.25 mM/I). Each flask was connected to a water condenser and kept in a thermostared water bath maintained at 80°C, and the content s were stirred occasionally during polymerizati on. Afte r I h, the contents were filtered on a sintered glass crucible and the filtrate was collected. The total vo lume of the filtrate was adjusted again to 50 ml and then it was taken into another Erlenmeyer fl ask. Fresh pretreated polyamide fibre (0 .5 g) was added to thi s flask and the reaction was allowed to continue for one more hour. After this, the grafted fibres were given the above treatment. This procedure was repeated tilt no grafting of AN or AA onto polyamide fibres was observed. Recovery of the respective homopol ymers was carried out by the same method as followed in the case of conventional grafting (Section 2.2.2).

2.2.4 Determination of Graft Add-on and Homnpolymer

The amount of graft add-on was determined gravimetrically and then % graft on fibres was calculated using the following formula:

W -W Graft add-on (%) 2 I X 100

WI

where WI is the weight of original polyamide fibres taken; and W2 , the weight of graft copo lymerized polyamide fibres .

The amount of homopolymer formed was calculated by the following equation:

DEO el al.: GRAFT COPOLYMERIZATION OF VINYL MONOMERS ON NYLON lS I

H I (01) Weight of homopolymer 100 omopo ymer -10 = x Weight of monomer used

2.2.5 Dyeing Procedure The original and grafted polyamide fibres were

subjected to cationic dyeing (2% shade) in an open bath following a standard method . The cationic dyes were purified by the Balmoforth 's method ' O before use.

2.2.6 Estimation of Dye Content The dye contents in dyed samples were calculated

in terms of KIS values fo llowing a standard method, using the SP8-400 uv/vi s spectrophotometer (Pye Unicam Ltd) at the appropriate Amax .

2.2.7 Determination of Moisture Regain The grafted fibre samples were conditioned at 6S%

R.H. and 30°C and the moi sture regain was determined by the standard desorption method.

3 Results and Discussion

3.1 Conventional Method Table I shows that maXImum I.S2% of the total

monomer taken is utilized in the formation of graft copolymer and about 98% of it is wasted due to homopolymer formation in the grafting bath . These resul ts are quite consistent with the known fact that both acrylic acid (AA) and acrylonitrile (AN) undergo autoacceleration duri ng polymerization, leading to poor grafting and formation of large amount of

homopolymers. The above fact is perhaps one of the most negati ve factors, which makes the graft ing process uneconomical.

3.2 Standing Bath Method The amount of homopolymer formed was

calculated by the following equation: Tables 2 and 3 show the results of AN graft ing by

the modified method . On comparing the results of Tables I and 2, it is observed that the modified grafting method enhances the graft add-on from 7. 18% to 60.60% at 8% AN concentrati on. Th is is also reflected in the hi gher amou nt of monomer utilization in the grafting reaction, coupled with lowering of homopolymer format ion. In sp ite of the fact that the graft add-on increases to such a high level, the extent of monomer convers ion into graft copolymer in still meager (7.6] %). The high molecular weight homopolymer fo rmed accounts for 3.82% of the total monomer. Thus , the res idual bath contains 88.SS% unutili zed monomer for the main grafting reaction . To check whether the resid ual acrylonitrile remained as a monomer in the bath , especiall y after the grafted fibres and the high molecular homopolymer were removed, a fres h lot of PQlyamide fibres pretreated firs t with Ta ffulon ]20 A and then with the initi ator was put into the used bath. It was interesting to observe that the grafting reacti on was possible in the used bath , showing that some quantity of AN monomer remained in tact after the bath was used once. It may be seen that the graft add­on from the used bath steadily increases with the

Table I - Resul ts of A and AA gra ftin g on to polya mide fibres by conventional method

Mono mer cone. Gra n add-on Monomer conversion % (w /w ) % (OWF) Gran copolymer High molecul ar wei ght Low mol ccular weight

% homopol ymer. % homopolymer, %

AN AA AN AA AN AA A AA

5 6.22 2. 12 1.26 0.42 0. 11 70.71 99.47 27.03 6 9.00 2.82 1.52 0.47 0.24 77.47 99 .29 21.() I 7 7.02 3.64 1.02 0 .52 0.57 77.07 98.91 2 1.') I 8 7. 18 5.26 0 .91 0 .66 0 .87 75.88 98.45 23 ~ I

Table 2 - Resulls of AN grafting onto polyamide fibre by modified method ( tibre pretreated wi th TatTulon 320 A)

Monomcr Graft add-on , % Monomer conversion cone. Fresh bath Used bath Graft copolymer, % High molecu lar weight Remaining monomer + low

% (w/w ) homopolymer, % molecular weight homopol ymer, 0/('

Fresh bath Used bath Fresh bath Used bath Fres h bath Used bath

5 35.80 7. 26 0 .56 9~ . 1 ~ 92 . 18 6 42.48 2.32 7.18 0.39 1.2 1 0.09 91.6 1 91.13 7 54.14 14.50 7.86 2. 1 I 2. 13 0. 14 90.0 1 87.76 8 60.60 22.10 7.72 2.82 4.14 0.59 8~. 14 84.73

152 INDIAN 1. FIBRE TEXT. RES. , SEPTEMBER 1999

Table 3-Result of AA grafting onto polyamide fibre by modified method (fibre pretreated with CTMAB )

Monomer Graft add-on Monomer conversion conc. % Graft copolymer High molecular weight Remaining monomer +

% (w/w) % homopolymer low molecular weight % homopoly mer

%

Fresh bath

5 6.52 1.30 98.70 6 8.80 1.48 98.52 7 10.06 1.43 98.57 8 10.88 1.35 98.65

Once used bath

5 5.86 1.16 97.54 6 7.20 1.19 97.33 7 7.90 1.13 97.44 8 9.20 1.15 97.50

Twice used bath

5 5.20 1.04 96.50 6 6.60 1.10 96.23 7 7.26 1.03 96.41 8 8.04 1.00 96.50

Thrice used bath

5 4.64 0.92 95 .58 6 5.10 0.85 95.38 7 5.76 0.46 95.95 8 6.40 0.80 95.70

Four times used bath

5 4. 16 0.83 94.75 6 4.52 0.75 94.63 7 4.70 0.67 95.28 8 5.52 0.69 95.0 1

Five times used bath

5 3.20 0.64 6 3.26 0.61 7 4.00 0.57 8 4.60 0.57

increase in monomer concentration from 5% to 8%. As high as 22.10% graft add-on is possible utilizing additional 2.82% monomer for the graft copolymerization in case of 8% monomer concentration . The homopolymer formation also reduces substantially (0.59%). However, no grafting is possible from the twice used bath although a considerable amount of monomer remains unutilized (84.73%) which may be in the form of dimer, trimer and higher forms of homopolymer. The above experiment assumes a great significance with high importance as it gives the idea of reusing the baths for further grafting. For the first time, it has been shown that cons iderable amount of graft add-on can be possible from the used baths, which were hitherto

94. 11 94.02 94.71 94.44

considered as obsolete and hence discarded. The above results give ri se to a totally new concept of standing baths for the graft copolymerizat ion reaction , which essentially means using the baths repeatedly for many times either with or without repleni shment of grafting baths with monomers .

It was, therefore, decided to search for better compounds which could be more efficient in suppressi ng homopolymer formation during the grafting reactions. Two quaternary ammonium compounds, vaz. cetyl trimethyl ammonium bromide (CTMAB) and cetyl pyridinium bromide (CPB), were selected to verify the standing bath concept in case of acrylonitrile and acrylic acid monomers.

DEO el al.,' GRAff COPOLYMERIZATION OF VINYL MONOMERS ON NYLON 153

Fig. 1 shows that with the increase in monomer concentration from 5% to 8%, the graft add-on increases when AN is grafted on nylon in presence of CTMAB and CPB. The increase is 70.39% at 8% AN concentration and 43.53% at 5% AN concentration in case of fresh bath. The homopolymer formation reaction was, on the contrary, suppressed to a greater extent in the successive baths. These factors have contributed to 36.82% and 18.27% graft add-on from the once used and twice used baths respectively at 8% AN monomer concentration for the CTMAB treated nylon fibres.

Table 3 shows that in case of acrylic acid grafting onto CTMAB treated polyamide fibres, as many as six standing baths could be used. This clearly shows that the use of quaternary ammonium compounds for pretreatment suppresses, to a great extent, the homopolymerization reaction and alters the nature of homopolymer itself. For 8% concentration of acrylic acid in the standing bath, the graft add-on on polyamide fibres in the fresh, once used, twice used, thrice used, four times used, and five times used baths are 10.88%,9.20%, 8.04%, 6.40%, 5.52% and 4.60% respectively. The sum total monomer utilization for graft add-on is 5.56% as compared to only 0.66% in the conventional method of grafting, giving an increase of over 740%.

These findings indicate that a suitable interacting quaternary ammonium compound could be chosen to increase the graft add-on and to inhibit formation of all forms of homopolymer in the standing bath technique.

3,3 Dye Uptake Figs 2 and 3 show the cationic dye uptake of AN-g­

PA and AA-g-PA respectively using standing bath technique, It is observed from Fig. 2 that good dyeability could be imparted to the AN grafted substrate which is a function of graft add-on on the fibres. The fibres containing 70.39% graft add-on show the dye content of 2.40 g/kg of fibres as compared to 0.99g1kg for the control. This graft add­on is obtained from fresh bath containing 8% acrylonitrile monomer. The dye uptake values are lower for the substrates grafted from once and twice used baths . This is expected as the amount of graft add-on is lower for these substrates. Fig. 2 also shows that the points representing the dye content values for the PA grafted in fresh and once used baths lie on a common curve, but those for twice used bath follow entirely a different curve, exhibiting hysterisis . This indicates the existence of difference in the physical

100

--- Fresh Bath (CTMAB)

90 --Once Used Bath (CTMAB) -6-Twice Used Bath (CTMAB) -..- Fresh Bath (CPB) -;r- Once Used Bath (CPB) --Twice Used Bath (CPB)

80

70

;:,!? o~ 60 z-0

I

0 0 50 <l: I-u.. ;2 40 C>

30

20

10

O. 5 5.5 6 6.5 7 7.5 8

CONCENlRA liON OF AN MONOMER ,Of. wI w

Fig. I-Effect of AN concentration on graft add-on of pol yamide fibres treated with CTMAB and CPB

2 '~r--------------------'

w lli 20 LL lL o

'" -" "-'" ,.: z w !z 15 o u w b

o Fresh Bath • Onc e us ed 80th 6 Tw ic e used 8ath

Dye - C.I . Basic Violet 10

o ·5L-...---'-_---L_---L_---l __ '--_'----:~~ o 10 20 10 LO 50 60 70 80

AN-GRAFT ADD-DN. 'f , ~

Fig. 2-Relationship between dye content and AN-graft add-on onto CTMAB pretreated polyamide tlbre

154 INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 1999

W !k: (D

iL 1L. 0

'" 2 oX "-0>

t-" Z W t-Z 0 U

W >-0

u Z 0 ;::: « u

o Fresh Bolh

• On ce used Bath 6 Tw ice used 80 Ih

• Th ri ce used Balh o Four lim es. used 8alh

• Five l imes used Both

Dye - C. 1. Basic Blue 3

•

2 3 ~ 567 8 9

AA-GRAF T ADD -ON. 'f ,

10

Fig. 3-Relationship between dye COlllent and AA- gran add-on onto CTMAB pretreated polyamide fibre

and chemical nature of the above two types of substrates. It may be noted that in the fresh and once­used baths, the grafti ng reaction takes pl ace in the presence of comparatively larger number of monomer molecules, sati sfy ing the majority of the free rad icals on the back-bone of polyamide chain. Under these conditions, the length of a side chain of the graft may be small containing possibl y on ly one nitri le (-eN) group at its end. In such a situation, the dye si tes may be easily avai lable for dyeing to take place.

Fig. 3 shows the results of the grafting of PA using acry lic ac id (AA) by standing bath technique. It is observed that the poin ts representing dye content values for PA grafted from fresh, once used , and twice used baths lie on one curve and those for thrice, four times, and five times used baths lie on another common curve showing hysterisi s . These resul ts are simi lar te ~i,, ) ~,-" obtained in case of AN-g-PA fib res .

3.4 Moisture Regain Fig. 4 shows the moisture regain of AN-g-PA from

standi ng baths. T hree different trends are observed for moisture regain va lues of the fi bres grafted from fresh, once used and twice used baths, ind icating further minute differences in the physical and chemical nature of the above three subs trates . Water molecu les, being of much smaller s ize as compared to dye cations, bring out fi ne differences in fibre structu re more clearl y th an in case of the dyeability studies . Moisture regain va lues of the AA-g-PA obtained from six standing baths also show di fferent trends (Fig. 5). Here, of course, six di fferent curves were obtained.

z ~ W !k:

W !k: ~

o Fresh 8 0th

• Once u sed Ba th

{', Tw ice u sed 8a t h

tIi 2· 5 \ o L

2·25 L-__ ~ ____ L-__ -L ____ ~ __ ~~ __ ~~ __ ~~

o 10 20 30 ~ O 50 60 70

AN-GRAF1 ADD-ON, 'f ,

Fig. 4~Re l ati on s hi p between moisture regain and AN-gran :ldd­on onto CTM AB pretreated polyaillide fibre

~ z « '" w oc w oc ::> tii (5 ~

)·5,----------__________________________ --.

) · 4

).)

o Fresh 8alh • Once used 8ath 6 Twice used 80th

• Thrice used Bath o Four t imes used 8alh • Five t imes used 8ath

o

/

)25 _~-.J----"--'-----'---'----'---'---:'--L-.-'---->-J o G 10

AA-GRAFT ADD -ON. 'f ,

Fig. 5-Relationship between moistllre regain and J\ -grail add­on onto CTMAB pretreated po lyam ide ri brc

The above results ind icate that the nature of the grafted fib re progressive ly undergoes fine changes with the increase in the consecut ive number of the

DEO et al.: GRAFf COPOLYMERIZATION OF VINYL MONOMERS ON NYLON 155

standing bath. Depending upon the technique used for the analysis of these copolymers, it may be possible to group them into one, two or even 'n' groups . The dyeability studies may bring out only the major differences in the fibre structure and thus the six substrates in case of AA-g-PA fibres have been grouped in only two groups.

4 Conclusion The results of the present study necessitate further

refinement of this novel 'Standing Bath' technique so that the graft add-on from each of the standing bath must be the same, showing minimum variations, if any, in the physical and chemical structure. Thi s will help in mixing all these graft copolymers together and utilize as one substrate. This perhaps is possible by replenishing the used standing bath with fresh quantity of the monomer equivalent to that utilized for grafting and homopolymer formation reactions. In such a situation, the quantity of the monomer available for the grafting will be exactly equal to the one which was available in the fresh bath. Therefore, it may be expected that the resultant graft copolymer

might be identical to the one obtained in the preceding as well as in the succeeding baths .

References I Hayashi S, Yoshinaga M & . 1100 10 M. KolJ/llIshi Kagakll ,

26(4) (1969) 288 ; World Text Ahstr , I ( 1969) 4041, p. 711. 2 Skwarski T & Buchenski J, Chelll Abstr. l:!4 ( 1976) I l:!985. 3 Teichmann R & Zeiss D, Aeta Polwll. 30(3) ( 1979) 135;

Chem Abstr, 91 (1979) 92879. 4 Zheltobryukhov V F, Drllzhinina T V. Gabriclyan G A &

Rogovin Z A, Khim Volokll o. 19(5) ( 1977) 65 : Chl' lI/ Ahslr . 87 (1977) 18595 .

5 Shalaby S, Pyankova A B. Gabridyan G A. Drll zh inina T V & Rogovin Z A, Khilll Voloklla, 24(3) ( 1982) 10; World Text Abstr, 14 (1982) 5120, p.477.

6 Shalaby S E, EI-shahed M F & Hcbcish A. A C/(I Po/rill . 35(4) ( 1984) 321.

7 Buchenska J, Fibre Text £(I.I't £111' , 4(2) ( 19%) 65 : Cilelll Abstr ,126 (1997) 105366.

8 Yuriy R, Yuriy P, Sofya B & Rosa F, A('/(1 Polrtl'ch Sew/d. Chern Tee/mol Ser, 247( 1997) 106; Chl'llI Ab.l'tr, 127 (1997) 162664.

9 Yinghai L, Weihong L, Min Z & Jingong M. C{lofl'lI : i Xuebao ,5 (1997) 597; Cilelll Abstr , 128 ( 1(98) 13493.

10 Balmforlh D, Bowers C A & Guion T H . .I Soc Drers Colollr. 80 ( I I) (1964) 577.