Indian Journal of Fibre & Textile ResearchVol. 17, September 1992,pp.130-135

Graft copolymerization of nylon-6 with glycidylmethacrylate usingpotassium persulphate-cupric ion system

S H EI-Hamouly, A M EI-Torgoman, U S Yousef & M F EI-Shahed"Faculty of Science, Menoufeia University, Egypt

Received 8 August 1991; accepted 24 September 1991

The kinetics of grafting of glycidylmethacrylate onto nylon-6 fibre induced by potassium persulphate-cupric ion system was investigated. The rate of grafting was determined by varying the concentrations ofthe monomer, potassium persulphate and cupric ion. The reaction order was calculated. Raising thereaction temperature from 60°C to 80°C enhanced the rate of grafting significantly, and the apparent ac-tivation energy was 68.94 kllmol.

Keywords: Glycidylmethacrylate, Graft copolymerization, Nylon-6 fibre

1 IntroductionGraft copolymerization onto textile fibres offers

intriguing possibilities since grafting is usually con-sidered to leave the backbone of the polymer cssen-tially intact and provides additional propertiesthrough the added polymer'. In recent years, muchinterest has been focussed on vinyl graft copolymer-ization of nylon. This is indeed a potentially power-ful method for producing substantial modificationof fibre properties.

Several methods have been used for grafting vinylmonomers onto nylon. The most important meth-ods which have attracted attention in recent yearsare radiation initiation" - h and chemical initiationusing eerie salt", dimethylaniline/Cu(lI) ions x, man-gancse (III)Y,manganese (IV)!Oand dimethylanilinecoupled with benzyl chloride!'. However, most ofthcse methods have limited usefulness due to mon-omer wastage through undesired homopolymeriza-tion. Shalaby et alY·13 developed a method basedon complexation of potassium persulphate with nyl-on molecules containing a surface active substancein presence of cupric ion. It was found that the graftpolymerization of acrylonitrile with nylon-6 pro-ceeds without homopolymer formation.

In this paper, a kinetic study of the grafting of gly-cidylmethacrylate onto nylon-6 induced by pota-ssium persulphate-cupric ion system is reported.

"Present address: Faculty of Petroleum and Mining Eng., SuezCanal University, Suez, Egypt.

2 Materials and MethodsNylon-6 (PA) staple fibres supplied by Artificial

Silk Company, Alexandria were used. These fibreswere treated at 60-70°C with a mixture containingsurface active substances (SAS) which were techni-cal-grade chemicals marketed by Badische Anilin-and Soda-Fabric AG (West Germany) under thecommercial names Soramin and Basosoft. After thistreatment the PA fibres contained 0.3% SAS. Unlessotherwise indicated, the SAS-treated PA was usedas a starting material for the grafting reaction.

Glycidylmethacrylate (GMA) of pure grade wasfreshly distilled at 75°C and 10 mm Hg before using.

Potassium pcrsulphate and copper sulphate usedwere of analytical grade.2.1 Polymerization IJ

0.5 g Nylon-6 fibre (PA) was immersed in 2% aq.K2S20X solution for 30 min at room temperature,thoroughly washed with distilled water andsqueezed till almost dry. The PA sample was thenintroduced into a 100 ml stoppered Erlenmeyerflask containing 50 ml of the thermo stated reactionsolution. The latter consisted of water, GMA mon-omer, copper sulphate, and univadine PA as softner.The flask was stoppered, placed in a thermostat andstirred occasionally in air during the polymerization.After the desired reaction time, the contents were fil-tered in a sintered glass crucible, washed with water,dried in an oven at 105°C for 5 h, cooled to roomtemperature and weighed. The dried sample wasthen repeatedly Soxhlet extracted with methyl ethylketone for 48 h till constant weight was obtained.

EL-HAMOULY et al.: GRAFT COPOLYMERIZATION OF NYLON-6 131

The percentage of graft yield was calculated asfollows:% Graft yield

Grafted sample dry wt - Original sample dry wt= - . x 100Original sample dry wt

Determination of K2S20g in the potassium per-sulphate-treated PA was carried out iodimetricallyaccording to the method described in literature 14.

2.2 Determination of Epoxy Content!'The method is based on the addition reaction of

hydrogen halide to epoxy groups (1 mol of hydrog-en halide being equivalent to 1 mol of epoxy group)and was carried out as follows:

0.125 g of sample (nylon-6 fibre grafted withPGMA) was refluxed for different time intervals(15,30,45 and 60 min)with 20 ml ofpyridinium hy-drochloride solution (16 rnl of pure cone. HCl dilut-ed to 1 litre with pure pyridine). After cooling, themixture was titrated with 0.1 N NaOH against phen-olphthalein. The control experiment was also carri-ed out for nylon-6 fibre. The epoxy number repre-sents the gram equivalents of epoxide oxygen/IOO gof nylon-S fibre.

(a-b)Nx 100The epoxy number = ,--~_...c....:.s» 1000

where a = Quantity of 0.1 N NaOH consumed bythe pyridine hydrochloride solution.

b= Quantity of 0.1 N NaOH consumed bythe sample.

N = Normality of the NaOH solution.g= Weight of the sample in gram.

The equivalent weight is that amount of the sam-ple that contains 1 epoxide equivalent, it is then100/epoxy number.

3 Results and DiscussionIt has been established'j'? that the graft polym-

erization reaction of acrylonitrile with PA, using po-tassium persulphate as initiator, proceeds withouthomopolymer formation if the PA fibres contain asmall amount of quaternary ammonium salt. It hasalso been suggested that the reaction mechanism in-volves complexation of K2S20X with the quaternaryarnmoruum groups.

Since the aim of this work was to study the kinet-ics of grafting of GMA onto nylon-S fibres, the graftpolymerization was carried out under differentreaction conditions. It was observed that no graftingoccurs when untreated PNGMAlH20 or untreatedPNGMNK2S20gIH20 system is used. Withthe latter system, a tremendous amount of homo po-

lymer formation was observed. On the other hand,grafting was found to proceed successfully when PAwas treated with surface active substance (SAS) pri-or to the polymerization reaction. This signifies therole of SAS. It was found that K2S20g reacts with ca-tionic SAS to form an insoluble compound. Appar-ently, this compound is formed on the surface ofSAS-treated PA and dissociates to produce PA mac-roradicals. The mechanism is represented as fol-lows:

PATCONH~ PA+K2S20a-PATcONH; PA 0

+ - " II(SAS) (SAS) O-S-O-O-S-OKII IIo 0

(I)

... (1)

(I )-- PA ~ C~NH----------PA + so;:I + _ 1\ •

(SAS) o-s-oIIo (II)

. _. (2)

PATCONH~PA+sO;;-PATCON~PA+HS64- --(3)

(III )(SAS) (SAS)

~H3(lI)+nCH2= ~ -----_ •.

c=oI0-CH2-CH-CH2

'0/

PAi.CONH

(SASt o-~-OJCH2J~:~-0-CH2-CH,-}~ 1.o L 0 o]ln7H3

(111)+ nCH2=~

c=oIo -CH2-CH - CH2

'0/

... (4)

•

3.] Effect of Cupric Ion ConcentrationThe effect of CuS04·5H20 cone, on graft yield is

shown in Fig. 1. It is observed that the graft yield in-creases with increase in CuS04• 5H20 concentra-tion up to 3 mmolJl. Further increase in cupric ionconcentration causes no more increase in graftyield.

The accelerated effect of the Cu2 + ions may be at-tributed to the association of the metal cations withthe amide groups in the polymer backbone as sug-gested in the following mechanism.

, _ '+ k- PA-CO-NH - + S20-. + Cu· ....•complex

k.t • +

complex ....•- PA-CO-N - + Cu + HSO. . .. (I)

132 INDIAN J. FIBRE TEXT. RES., SEP'IEMBER 1992

As a result, Cu2 + is converted to Cu + ion as shownin Eq. (1). The cuprous ion would be oxidized backto the cupric state by S04 - which is formed in thereaction medium.Cu+ + so·; - cu2+ +SO-4- ... (2)

This reaction must suppress homopolymerization byrendering S04 - ineffective. This was confirmed bysoxhlet extraction of the grafted samples with me-thyl ethyl ketone at different time intervals of thegrafting process, which showed no homopolymerformation. Fig. 1 also shows that the grafting ofGMA onto PA fibres occurs even in the absence ofCu2+. Nevertheless, the rate of reaction is slow(7.5% grafted after 20 min) and the formation of"" 5% homopolymer is observed.

To account for the dependencegrafting on Cu2 + concentration,scheme could be suggested'<"In itiation:

- PA-CON - + M ~ - Pa-CO-N-M

of the rate ofthe following

... (3)macroradical growing chain

M = GMA monomerPropagation:

-N-M+M~ -N-M;

-M'-l +M kp M'n -+ n •.. (4)

Termination:

N. . k,

- -M, + - N-Mn-+ grafted nylon-o

-N-M~ +CU1+~ -N-Mn+Cu' +H' ... (5)

Oxidation: •

-N+Cu1+ - oxidation producr+Cu ' +H' ... (6)

The overall rate of polymerization could be ob-tained by assuming that the steady state assumptionis valid and consequently we get the following ex-pression:

d[NJ- dt = k [PACONH][complexj- kJN][Mj = 0 ... (7)

[N] = macro radical on backbone of nylon-6 fibre

[NJ k[PACONH][complexJk;[MJ

... (8)

d[N-M'J- ~ = k;[N][MJ - k,[N-M~J2= 0

[N-M~J= (k'[~],[MJ) III

... (9)

... (10)

then putting the value of [N] in the above equation

[N-M] = [k[PA-CO-N;J [COmPlexJr2

(k) IIIRp=kp k. (PA-CO-NH)'/l (complex)!" [MJ ... (11)

It has been found experimentally that the rate ofgrafting is proportional to the [CuSO ·5H 0]°.4(Fig. 2) which can justify the proposed ;che~e asgiven above.

3.2 ElTectofinitiator ConcentrationThe effect of K2S20g concentration on the graft

yield was investigated over a range of 2.53 x 10-3-

10.18 X 10-3 mol/I, The results are shown in Table 1.It is observed that the graft yield increases as the

JOr----===::::==;;=====::;::====::::;;;::======~~o '0

250'.;20c

10

5~O--~OD<OO~laO~O~02100~O~OJIQ.O·F,OOU4~O~OOn.5~O~On,O~6eO~O~O7~O~OO~8~O~OO~9~0~OIConc. ot CuSO,·SH20,mOI/I-1

•Fig. I-Effect of CuS04' SH20 concentration on graft yieldllGMAj, 1.48 x]() I mol/I; [K,S,OH]' 10.18 x 10- 3 molll; Tem-perature, I)OOC; Reaction time, 30 min; and Material-to-liquor

ratio, I: 100 f

+

.:

M 2

0.a:-J:

O·~O----~----~2----~3~--~4~--~5----~In [eu S04·5H20]+12

Fig. 2-Dependence of the rate of grafting (R) onCuS04' SH20 concentration llGMAj, 1.48 x 10- I Pmol/I;

[K2S20KJ. 10.18 x 10 - 3 mol/l; Temperature. 80°C; andMaterial-to-liquor ratio. 1: 100 I

ElrHAMOULYetaL: GRAFfCOPOLYMERlZATIONOFNYLON-6 133

Table I-Effect ofK2S20s cone, on grafting([GMA), 1.48 x 10 -I mol/l; [CuS04.5HzO], 0.008 mol/I; Temperature, 80·C; and Material-to-liquor ratio, 1:1001

K2S20S cone. Grafting (%) aftermol/I

15 min 30min 45 min 60min 90min 120 min

2.53xlO-3 10.8 29 44 60 70.3 71.924.26 x 10-3 16 34.08 55.3 73.42 77.52 79.026.06 x 10-3 18 41.08 62 76.48 81.32 81.32

10.18 x 10-3 26 46 65.4 86.26 90.26 91.08

2-2Rp - [Kz5zOsJ 0'4 260

2·1 220

2·0180

M1·9

;!60

+ g'140Q.

a:: E'C 1-8o 100

17

60

1-6

1-5y~-'--_...I....-_--'--_--L_---''--_-'--_...I....-_-Io 1{) 1-2 1-4 1-6 18 2-0 2-2 24

In [K2 52°6]+ 7

Fig. 3-Dependence of the rate of grafting (~) on K2S20S con-centration {fGMA). 1.48 x 10 - J mol/I; [CuS04• 5H201. 0.008

mo1!l; Temperature, 80·C; Reaction time, 120 min; andMaterial-to-liquor ratio, 1:100\

K2S20g concentration increases. The dependenceof the initial rates (~) on the concentration ofK2S20g included in PA fibres is represented by In-Inplot in Fig. 3. The slope of this yieldss, -IKzszOs],,4

The initiator exponent for GMA graft copolymer-ization is 0.4 which is due to the termination by pri-mary radicals. Similar observation was made byShalaby et al:18 in the case of grafting of dimethylam-inoethyl methacrylate onto PA in presence ofK2S20g as initiator.

3.3 Effect of Monomer ConcentrationThe effect of monomer concentration on grafting

was investigated by changing the monomer concen-tration and keeping the concentrations of other rea-gents constant. The results (Fig. 4) show that in-crease in monomer concentration causes significantincrease in the graft yield. This increase in graft yieldcould be associated with the favourable effect of themonomer concentration on producing a larger num-

(0)GMA Cone.

-1(0) 2 -96 X10 molll

-1(b)2-22XIO molll

- -1(e)148 Xl0 molll

(d)0-74 X10-1 molll ( b)__------o---~--~/0o

o

(e)

(d)--------o---~--~105 12045 60 75

Time- ,min90

Fig. 4-Effect of GMA concentration on the rate of grafting([KZSzOK]' 10.18 x 10-3 mol/I; lCuSO •. 5HzO]. O.OOS mol/I;

Temperature. 80·C; and Material-to-liquor ratio, 1: 1001

ber of growing polymer chain. Fig. 4 also shows thatincrease in reaction time also causes a significant in-crease in the graft yield. The grafting reaction ischaracterized by an initial fast rate followed by aslower one and then levels off.

The leveling off of grafting is in accordance withprevious report", which ascribed this to depletion inmonomer concentration and reduction in activesites (free radicals) on the PA backbone as the reac-tion proceeds. Also, it is very likely that the higheramount of graft formation occurred during the in-itial stages of the reaction acts as a diffusion barrierfor the monomer in the latter stages of the reaction.

Fig. 5 shows the effect of GMA concentration onthe rate of grafting (~). The slope of this yieldss, -[GMAjI"'

The higher exponent of the monomer concen-tration than predicted in Eq. (11) in the abovesuggested mechanism may be explained by theconsumption of GMA in steps 3 and 5 in thefirst suggested mechanism, i.e. its reaction both withthe complex site and the macroradical respectively.

134 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1992

~r-----------__-------,Rp ~[GM A] 183

3

/

/~+--0.2 0

a:

.=

/o~ ~ ~o 1

In[GMA] +3

Fig. 5-Dependence of the rate of grafting (~) on GMA con-centration UKZSZOH)'10.18 x 10- 3 mol/I; [CUSO.· 5HzO), 0.008mol/I; Temperature, 80°C; and Material-to-liquorratio, 1:100l

3r----------------------------,M

- 2+Co

a:

O~2.~8~2--~2·~8&~~2~·9~O--~2.~94~--~29~8~~J~·O~2~lOJ/T,K

Fig. 6-Arrhenius plot for graft copolymerization of GMA inpresence of PA UGMA], 1.48 x 10 - 1 mol/I; [K2SzOH),

10.18 x 10-3 mol/l; [CuS04' 5HzO), 0.008 mol/I; andMaterial-to-liquor ratio, 1:100}

3.4 Effect of Reaction TemperatureThe graft polymerization was carried out at four

temperatures in the range 60-80°C, keeping theconcentrations of all other reagents constant. Table 2indicates that the percentage of graft yield in-creases with the increase in temperature. This is inaccordance with previous studies" which attributedthis to the favourable effect of temperature on: (a)the monomer diffusion from the solution phase tothe fibre phase, (b) adsorption of the monomer onthe fibre and its complexation with nylon moleculesto enhance availability and reactivity of monomer,and (c) initiation and termination of free-radical

Table 2-Effect of temperature on grafting.UGMA], 1.48 x 10-1 mol/I; [KZS20H), 10.18 x 10-3 mol/l;

[CuS04' 5HzO), 0.008 mol/I; and Material-to-liquorratio, 1:100}

Temp. Grafting (%) afterK

15 min 30min 45 min 60min 90min333 4.22 9.66 14.18 22.8 29.66338 12.04 22.5 35.2 44 55348 20 42.14 57 68.94 73.8353 26 46 65.4 86.26 90.26

Table 3-Stability of epoxy ring in nylon-6 fibres polymerizedwithGMA

Grafting%

Epoxy content, g

Calculated Estimated Stability"0/0

Pure nylon-6fibres48.48

52.757.1462.54

0.2290.2430.2560.270

0.2240.2320.240

0.248

97.8295.4793.75

91.85

Estimated epoxy content 00'Stability (%) = x 1

Calculated epoxy content

sites on the nylon backbone. The net effect of allthese factors leads to higher grafting with increase intemperature.

A plot of the logarithmic rate of polymerization(~) against the reciprocal of the absolute tempera-ture (Fig. 6) in the range 60-80°C gave 68.94 kJ/mol for the overall activation energy.

3.5 Stability of Epoxy GroupsTable 3 shows the calculated amount of epoxy

groups (based on the increase in weight) and the ex-perimentally determined amount (using back titra-tion method). The data indicate that about 2-8% ofthe epoxy groups in the grafted polymer are subject-ed to hydrolysis, probably by the action of H20.

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ELrHAMOULY et ai: GRAFT COPOLYMERIZATION OF NYLON-6 135

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