Deposition of Cationic Polystyrene Latex on Fibers 1 HISASHI TAMAI, A K I N O R I H A M A D A , AND T O S H I R O S U Z A W A Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Senda-machi, Naka-ku, Hiroshima, 730, Japan R e c e i v e d M a r c h 10, 1981; a c c e p t e d D e c e m b e r 16, 1981
The deposition of cationic polystyrene latex prepared by using N,N-dimethylaminoethyl methacrylate as comonomer and 2,2'-azobis (2-amidinopropane) hydrochloride as initiator on polyacrylonitrile, polyamide, and polyester fibers was investigated as a function of pH. The rates of deposition of cationic latex on three kinds of fibers increased with increasing pH and had maximum values. From ~"potentials of latex and fibers, it was indicated that these maximum rates of deposition were present not in the region of opposite sign of ~"potentials, but in the vicinity of the isoelectric point of cationic latex. The application of heterocoagulation theory suggested that the deposition was highly influenced by the stability of cationic latex in addition to the total interaction energy between fiber and latex particles. It was shown by the observation with a scanning electron microscope that cationic latex particles deposited in a block layer in the vicinity of the isoelectric point of latex.
It has been reported that stable emulsifierfree cationic latices can be obtained by using cationic initiator ( 1), by copolymerizing cationic monomers (1, 2), or by using simultaneously both substances. Homola and James (3) have prepared stable amphoteric polystyrene latices by using N,N-diethylaminoethyl methacrylate (DE) and methacrylic acid as comonomers, and using potassium persulfate (KPS) as initiator. Alince et al. (4-6) have studied the deposition of cationic styrene-butadiene latex prepared by using hydrogen peroxide and ferric nitrate as initiator and DE as comonomer on negatively charged pulp fiber, because the use of latex is the most convenient way of introducing the polymer into paper. The authors have studied the deposition of anionic polystyrene and polymethyl methacrylate latices prepared by using KPS
as initiator on synthetic fibers and cotton fiber (7-9). Since synthetic fibers are generally negatively charged, it is important that the deposition of positively charged latex particles, namely, cationic latex, on those fibers be studied. This paper reports the deposition of cationic polystyrene latex prepared by using N,N-dimethylaminoethyl methacrylate (DM) as comonomer and 2,2'-azobis (2amidinopropane) hydrochloride (AAP) as initiator on polyamide, polyester, and polyacrylonitrile fibers. The effect of pH has been considered from the rate of deposition, the interaction energy between latex particles and fibers determined by the application of heterocoagulation theory (10), and the state of latex particles deposited on each fiber observed by a scanning electron microscope. EXPERIMENTAL
1 This p a p e r is P a r t V in a series on " I n t e r r a c i a l electrical studies on the deposition of p o l y m e r l a t e x e s onto
fabrics and the removalof these depositedlatexes";Part IV: H. Tamai and T. Suzawa, J. Colloid Interface Sci. 88, 372 (1982).
Styrene and DM (Wako Pure Chemical Comp., Ltd.) were purified three times and 378
0021-9797/82/080378-0752.00/0 Copyright © 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.
Journal of Colloid and InterfaceScience,Vol. 88, No. 2, August 1982
D E P O S I T I O N OF C A T I O N I C L A T E X
TABLE I Polymerization Conditions Sample
Stylene (mole/liter) DM (mole/liter) AAP (mole/liter) Temperature (°C) Speed of stirring (rpm) Polymerization time (hr) Diam. of particle (nm)
0.60 5 X 10-3 1.0 X 10-2 70 350 24.0 572
0.60 1.0 X 10-2 1.0 X 10-2 70 350 24.0 699
twice, respectively, by distillation under reduced pressure. AAP (Wako Pure Chemical Comp., Ltd.) and KPS were recrystallized from water and then dried under vacuum. Sodium chloride, sodium hydroxide, and hydrochloric acid were all analytical grade materials and were used without futher purification. Distilled and deionized water was used throughout the experiments. Cationic polystyrene latices were prepared in the absence of emulsifier (1). The polymerization condition of latices are shown in Table I. The latices obtained were first dialyzed with Visking tube for 4 weeks and then electrodialyzed to remove residual monomer and free ions from the initiator. The particle sizes of these latices were determined by electron microscopy. The electron microscope used was a JEOL JEM 100U. The average diameters of latices are shown in Table I, and these latices were monodisperse. Fabrics of polyamide Nylon 6 (Toray Comp., Ltd.) polyester Tetoron (Toray Comp., Ltd.), and polyacrylonitrile Vonnel (Mitsubishi Rayon Comp., Ltd.) were used as fibers. These fabrics were purified by the methods described previously (7).
Methods Rate of deposition. Five-grams weighed fabric (1 X 2 cm) was immersed in a 200ml latex dispersion (4.0 X 10 -2 g/liter solid content) adjusted to the required pH. The pH was varied with hydrochloric acid and
sodium hydroxide. The ionic strength was adjusted with sodium chloride and was kept constant at 1 X 10-3. The amount of latex deposited on the fabric was determined as a function of time by turbidity measurements of latex dispersions. Turbidity measurements were performed at wavelength of 540 nm by using a Hitachi 100-10 type spectrophotometer. Interaction energy. The interaction energy between fiber and latex particles was estimated by application of heterocoagulation theory for spheres and plates (10). The details of this application were described in previous papers (7, 8). In order to calculate the interaction energy of electrical double layers, ~"potentials were used as surface potentials of latex particles and fibers. ~" potentials of fibers and latex particles were measured by the methods of streaming potential and microelectrophoresis, respectively (8). The interaction energy of van der Waals forces was calculated by the equation described in the previous paper (7, 8). For values of the Hamaker constant in water, 5 X l0 -14, 4.1 X 10 -13, 6.1 X 10 -13, and 3.6 X 10 -13 ergs were used for latex, Nylon, Vonnel, and Tetoron, respectively (7). State of latex particles deposited. Fivegrams weighed fabric (about 1 X 2 cm cloths) was immersed in a 200-ml latex dispersion (1.0 g/liter solid content). These cloths were withdrawn from a latex dispersion after 12 hr, and were rinsed instantly with a solution of the same composition (pH and electrolyte concentration) without latex particles for 1 rain to remove undeposited free particles. The sample was dried in air and coated with gold and was observed by a scanning electron microscope (JEOL JSM T-20). RESULTS AND DISCUSSION
Potential Figure 1 shows ~"potentials of latices as a function of pH. ~"potentials of cationic latJournal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
TAMAI, HAMADA,AND SUZAWA
-20[ -60 i
FIG. I. ~" potential of latices as a function of pH at l0 -3 ionic strength. O: latex A; Q: latex B.
ices are positive in an acidic solution and negative in an alkaline one, and the isoelectric points of latex A and latex B are pH 7.4 and pH 6.6, respectively. The decrease of positive g'potentials of latices with increasing pH may be attributed to the degree of dissociation of DM amino groups. However, in spite of the use of cationic initiator and cationic comonomer, these latices are negatively charged at high pH. According to Goodwin et al. (1 I), the amidine group of AAP used as the initiator may hydrolyse to amide at high temperature and high pH. Fitch et al. (12) reported that the ester group of DM used as comonomer may also hydrolyse. Negative ~"potentials of latices A and B at high pH may be attributed to anionic groups resulting from hydrolysis of surface amidine group of AAP or the ester group of DM. However, on hydrolysis of the amine surface group of amphoteric polystyrene latex, Homola et al. (3) described that the isoelectric point of amphoteric latex did not shift when latex was adjusted to the desired pH and allowed to equilibrate by shaking in a water bath (25°C) for about 72 hr. For the cationic latices used in this study, g" potentials measured after about 1 year agreed with those shown in Fig. 1. Consequently, the hydrolysis of surface groups of the cationic latex may probably occur upon the polymerization. Journal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
With respect to the stability of the cationic latices, Fig. 1 indicates that two kinds of cationic latices are colloidally stable to homocoagulation at more acidic pH or alkaline pH than the isoelectric points of the latices because of the repulsive energy of electrical double layers of latex particles. In practice, in analogy with anionic polystyrene latex prepared by usingKPS as initiator (7), these cationic latices did not change for long period at those pH. However, these cationic latex particles may coagulate in the vicinity of the isoelectric points of the latices, because the large repulsive energy of electrical double layers is not present between latex particles. Figure 2 shows ~"potentials of fabrics as a function of pH. ~"potentials of three kinds of fabrics, viz., Nylon, Tetoron, and Vonnel, are all negative in all pH sOlutions. The negative values of ~" potentials of Nylon and Tetoron fabrics increase with increasing pH. Those of Vonnel fabric approximate the constant value with increasing pH. Deposition
In order to determine the rate of deposition of latex on fiber, the amount of latex deposited on fiber was measured as a function of time. In this experiment, since the
-lOC -8C v
-6c "6 ~ -4C i
FIG. 2. ~"potential of fabrics as a functionof pH at 10.3 ionicstrength. 13: Vonnelfabric;O: Nylonfabric; A: Tetoron fabric.
DEPOSITION OF CATIONIC LATEX
60 Time ( m i n . )
F I G . 3. D e p o s i t i o n o f l a t e x A o n V o n n e l f a b r i c a s a
function of pH and time at 10-3 ionic strength. O: pH 3.2; A: pH 5.9; n: pH 7.0; ~: pH 7.4; A: pH 7.9; ill: pH 8.3; O: pH 9.3; i: pH 9.7; I: pH 10.7.
mixtures of latex and fabric were not stirred, the deposition of latex probably occurred by Brownian motion of latex particles. The resuits of deposition of cationic latex A on Vonnel and Nylon fabrics are shown in Figs. 3 and 4, respectively. It is assumed that the deposition depends on the first order of latex concentration, and according to the procedure described previously (13) the rate constants of deposition on fabrics are determined from the results of deposition measurements shown in Figs. 3 and 4. Figure 5 shows the rate constants of deposition of latices on Vonnel fabric as a function of pH. The rates of deposition of latices A and B increase with increasing pH and have maximum values at about pH 7.4 and p H 6.6, respectively. From the results of ~" potentials shown in Fig. 1, these maximum
rates of deposition are present in the vicinity of the isoelectric points of latices A and B. The maximum rates of deposition may be related to the stability of latex, because cationic latices are colloidally stable for homocoagulation at more acidic pH or alkaline pH than the isoelectric points of the latices and may coagulate in the vicinity of the isoelectric points of the latices as already described with respect to the stability of cationic latices. The rates of deposition decrease sharply with increasing pH at more alkaline pH than the isoelectric points of the latices, because ~" potentials of cationic latices and Vonnel fabric are the same in sign and those values increase with increasing pH. Figure 6 shows the rates of deposition of latex A on Tetoron and Nylon fabrics as a function of pH. The rates of deposition of cationic latex on Tetoron and Nylon fabrics exhibit the same tendency as that on Vonnel fabric with respect to the change of pH. However, the maximum rate of deposition on Nylon fabric is smaller than that on Vonnel and Tetoron fabrics.
Relation between Rate of Deposition and Interaction Energy Since the deposition of latex particles on fabric is supposed to be a heterocoagulation between fiber and latex particles, the total interaction energy, VT, between fiber and latex particles is determined by the sum-
~2 eLI 03
t.) 0J 0
60 Time (min.)
FIG. 4. Deposition of latex A on Nylon fabric as a function of pH and time at 10-3 ionic strength. O: pH 3.2; A: pH 4.1; n: pH 5.8; 0t: pH 6.7; A: pH 7.6; rl: pH 7.7; I): pH 7.9; O: pH 8.3; i: pH 9.7; I: pH 10.8.
FIG. 5. Rate constant of deposition of latices on Vonnel fabric as a function of pH at 10 -3 ionic strength. ©: latex A; 01: latex B. Journal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
TAMAI, HAMADA, AND SUZAWA
mation of electrostatic potential energy and van der Waals force energy, which are calculated by the heterocoagulation theory (10). The value of VT between latex A particles and Vonnel fabric is shown in Fig. 7 as a function of p H and the distance between both substances. The value of VT is attractive at more acidic p H than the isoelectric point of latex and repulsive at more alkaline pH than that, and the repulsive energy increases sharply with increasing pH. The value of VT between Tetoron fabric and latex A particles and Va- between Nylon fabric and latex A particles exhibited the sam e tendency as that between Vonnel fabric and latex particles with respect to the change of pH. From these results, it is expected that cationic latex particles deposit rapidly on the three kinds of fabrics used at pH more acidic than the isoelectric point of latex, and the rate of deposition decreases with increasing pH at pH more alkaline than the isoelectric point of latex. However, as shown in Figs. 5 and 6, the rates of deposition of cationic latex on the three kinds of fabrics are maximum in the vicinity of the isoelectric point of latex. Accordingly, it is suggested that the deposition of cationic latex on fabrics is highly influenced by the stability of latex in addition to VT between latex particles and fiber. If VT is repulsive, the rates of deposition are significantly affected by the maximum value of total interaction energy, tit . . . . as
200 F 0
200 H (A)
FIG. 7. Total interaction energy between latex A particles and Vonnel fabric as a function of pH and distance at 10 -3 ionic strength. A: pH 3.2; B: pH 5.9; C: pH 7.0; D: pH 7.4; E: pH 8.3; F: pH 9.3; G: pH 10.7.
a function of distance. The relation between the rate constants of deposition and VT m a x is shown in Fig. 8. The rate constants of deposition on the three kinds of fabrics used decrease with increasing Vr .... However, latex deposits on those fabrics even though the values of Vr max are very large as shown
v "~ r•
pH FIG. 6. Rate constant of deposition of latex A on Nylon and Tetoron fabrics as a function of pH at 10 -3 ionic strength. O: Nylon fabric; A: Tetoron fabric. Journal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
500 V-r,,,,,~ (
l ooo kT)
FIG. 8. Rate constant of deposition of latices on fabrics as a function of Vrmax-O: latex A on Vonnel fabric; O: latex B on Vonnelfabric; A: latex A on Nylon fabric; 0: latex A on Tetoron fabric.
DEPOSITION OF CATIONIC LATEX
FIG. 9. Scanning electron micrographs of fabrics deposited with latex A particles at 12 hr of deposition time. A: Vonnel fabric at pH 3.2; B: Vonnel fabric at pH 7.4; C: Nylon fabric at pH 3.2; D: Nylon fabric at pH 7.4; E: Tetoron fabric at pH 4.2; F: Tetoron fabric at pH 7.4.
in Fig. 8. O n the deposition of anionic polym e t h y l m e t h a c r y l a t e latex on fabrics (9), it was reported that, in addition to the interaction energy, the deposition m a y be influ-
enced by the characteristics of fiber, e.g., surface roughness described by M a r s h a l l et al. (14) on the deposition of c a r b o n black particles onto solids, heterogeneity of elecJournal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
TAMAI, HAMADA, AND SUZAWA
trostatic potential by Hull et al. (15) on the deposition of polystyrene latex particles onto plastic films, and absorption of water by Boughey et al. (16) on the deposition of polystyrene latex particles onto dispersed Nylon. Similarly these fiber characteristics probably cause the deposition of cationic latices in" spite of the presence of large VTm a x - But it is not clear why the rates of deposition of cationic latex on Vonnel fabric are slow, compared with those of anionic polymethyl methacrylate latex (9) when repulsive energy is present between latex particles and fiber. State o f Latex Particles Deposited on Fiber
Figure 9 :shows photographs of cationic latex A particles deposited on fibers at various pH. If ~"potentials of latex particles and fibers are opposite in sign and the latex is stable, latex particles deposit on the three kinds of fabrics in a single particle layer (A, C, and E in Fig. 9). On the other hand, latex particles deposit in a block layer in the vicinity of the isoelectric point (B, D, and F in Fig. 9). From these results, it is suggested that the state of cationic latex particles deposited on fibers is mainly influenced by the stability of the latex, because cationic latices are coll o i d a l l y s t a b l e to h o m o c o a g u l a t i o n a t m o r e acidic p H t h a n t h e i s o e l e c t r i c p o i n t s o f t h e
latices and may coagulate in the vicinity of the isoelectric points of the latices. However, it is n o t c l e a r w h e t h e r t h e flocculants o f l a t e x
Journal of Colloid and Interface Science, Vol. 88, No. 2, August 1982
particles deposit on fiber, or latex particles coagulate on ~the surface of fiber. ACKNOWLEDGMENTS The authorswish to thankToyobo Comp., Ltd., Toray Comp., Ltd. and Mitsubishi Rayon Comp., Ltd. for providing the fabrics. REFERENCES
1. Sakota, K., and Okaya, T., J. Appl. Polym. Sci. 20, 1725 (1976). 2. Alince, B., Inoue, M., and Robertson, A. A., J. AppL Polym. Sci. 20, 2209 (1976). 3. Homola, A., and James, R. O., J. Colloid Interface Sci. 59, 123 (1977). 4; Aiince, B., Robertson, A. A., and Inoue, M., J. Colloid Interface ScL 65, 98 (1978). 5. Alince, B., Inoue, M., and Robertson, A. A., J. AppL Polym. ScL 23, 539 (1979). 6. Alince, B., J. Colloid Interface Sci. 69, 367 (1979). 7. Suzawa, T., Tamai, H., Shirahama, H., and Yamamoto, K., Nippon Kagaku Kaishi 1979, 16 (1979). i: 8. Tamai, H., Hakozaki, T., and Suzawa, T., Colloid Polym. Sci. 258, 870 (1980). 9. Tamai, H., and Suzawa, T., Colloid Polym. Sci. 259, 1100 (1981). 10. Hogg, R., Healy, T. W., and Fuerstenau, D. W., Trans. Faraday Soc. 62, 1638 (1966). 11. Goodwin, J. W., Ottewill, R. H., Pelton, R., Vianello, G., and Yetes, D. E., Brit. Polym. J. 10, 173 (1978). 12. Fitch, R. M., Gajria, C., and Tarcha, P. J., J. Col..... loid Interface Sci. 71, 107 (1979). 13. Tamai, H., and Suzawa, T., to be published. 14. Marshall, J. K., and Kitehener, J. A., J. Colloid Interface Sci. 22, 342 (1966). i15. Hull, M:, and Kitehener, J:A., Trans. Faraday Soc. 65, 3093 (1969). 16. Boughey~ M. T., Duckworth, R. M., Lips, A., and Smith, A. L., J. Chem. Soc. Faraday Trans. 1, 74, 2200 (1978).