Intercalation of methacrylamide into sodium, calcium and alkylammonium exchanged montmorillonites

ELSEVIER

Applied Clay Science 9 (1994) 199-210

Intercalation of methacrylamide into sodium, calcium and alkylammonium exchanged montmorillonites Vladimfr Hlavat~ a'*, Asao

Oya b

aFaculty of Nature Sciences, Comenius University, Brafislava, Slovak Republic bFaculty of Engineering, Gunma University, Kiryu, Gunma 376, Japan Received 15 March 1993; accepted after revision 30 March 1994

Abstract

Methacrylamide was intercalated into hydrophilic and organophilic exchanged forms of montmorillonite from various solvents. The increase of the basal spacing depends on the interlayer cation and the polarity of used solvent. The largest basal spacing (doo~= 3.35 nm) was observed for the longchain alkylammonium montmorillonite and polar organic solvents. The alkyl chain length of the alkylammonium cation is a limiting factor for the interlayer expansion. An attempt was made to polymerize intercalated monomer by gamma-ray initiation. Subsequently, an additional swelling of the silicate structure was observed. Decomposition products of intercalated material and long-chain alkylamides were identified in the acetone extract. The additional swelling seems to be related to the gamma-ray initiated reaction products in the interlayer space.

1. Introduction The dispersion of an inorganic phase in an organic polymer in a certain ratio, for example via extrusion process, can provide a radical change in the mechanical properties of the resulting composite (Okada, 1991). Clay minerals, in particular smectites, are potential fillers for organic resins. What makes them even more interesting for this purpose is the possibility to modify the silicate surface by ion exchange with various cationic surfactants and to form intercalation complexes. However, smectite minerals have the disadvantage that they form rather large aggregates in organic resins. Thus, the main purpose of this study is to reduce the attractive forces *Corresponding author. 0169-1317/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved

SSDIO169-1317(94)OOO12-F

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between the silicate layers to make easier their separation and fine dispersion in the bulk polymer matrix. One way to reduce the interaction forces between the silicate layers is to increase their distance by intercalation of suitable organic compounds (Theng, 1974; Fukushima and Inagaki, 1987). Fukushima et al. (1988) reported the unlimited swelling of montmorillonite structure during the polymerization of organic monomers in the interlayer space. Ogawa et al., (1989) found that methacrylamide forms monolayers in the interlayer space of sodium montmorillonite during solid-solid reaction.

2. Experimental 2.1. Materials Sodium montmoriUonite (Kunipia F) was used as a starting material (CEC = 119 meq/ 100 g clay). Exchanged forms were prepared by repeated saturation of the clay with solutions of chlorides and subsequent washing with water and a water-methanol ( 1:1 ) until the supernatant was free of chloride anions (AgNO3-test). The following derivatives were prepared: sodium montmorillonite calciummontmorillonite hexylammoniummontmorillonite dodecylammoniummontmorillonite octadecylammoniummontmorillonite cetyltrimethylammoniummontmorillonite cetylpyridiniummontmorillonite

(Na-M)

(Ca-M) (HA-M) (DD-M) (OD-M) (CT-M) (CP-M)

Saturated methacrylamide (MA) solutions in toluene, chloroform, water, acetone and methanol were allowed to interact with these montmorillonites.

2.2. Sample preparation Thin films of montmorillonites on glass slides, prepared by drying of 4% clay suspension (Na-M and Ca-M in water, organophilic montmorillonites in methanol) under ambient conditions (T = 25°C) for 24 hours, were immersed in saturated solutions of methacrylamide and kept in contact for 24 hours at room temperature. Samples were then dried under ambient conditions, irradiated by gamma-rays ( 104 Gy and 2 X I05 Gy) to polymerize the monomer and subjected to XRD-measurements. The effect of solvent on the silicate structure expansion was also tested. The clay films on glass slides were immersed in pure solvents and treated in the same manner as the intercalated samples mentioned above. The powder sample OD-M/MA(m) was prepared by interaction of MA with OD-M (3:1 weight ratio) in methanol at T = 60°C for 24 hours under stirring. The suspension was

V. H lavat):, A. Oya / Applied Clay Science 9 (1994) 199-210

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then cooled to room temperature, filtered, freeze-dried and exposed to gamma-rays (2 × 105 Gy). The irradiated sample was extracted with acetone (ultrasonic dispersion) and the reaction products were analysed by GC/MS. 2.3. Methods Diffraction patterns were recorded on a Rigaku RAD-B diffractometer (Cu-Ka, 20-20 ° 2 0 ) . Thermoanalytical data were obtained from a Rigaku TG 8110 thermoanalyser with a-Al203 as reference material. The IR spectra of selected samples (KBr-discs) were measured by a Hitachi 270-50 infrared spectrophotometer. The acetone extract of the irradiated sample was analysed with a Shimadzu GCMS-QP1000 gas chromatograph coupled with a mass spectrometer.

3. Results and discussion

3.1. XRD investigation The dool values of starting materials were unchanged after pure solvent treatment and air drying for 24 hours. Hence, the effect of pure solvents on the montmorillonite structure expansion under conditions described in Section 2.2 can be neglected. The basal spacings of MA-intercalated Na-M and Ca-M oriented samples (see Section 2.2) are between 1.50 nm and 1.95 nm and are slightly higher than for the original materials [dool(Na-M) = 1.41 nm and dool(Ca-M) = 1.54 nm] (Table 1). The basal spacings of MA-intercalated organophilic species OD-M, CT-M and CP-M, are between 2.41 nm and 3.36 nm. The basal spacings of starting montmorillonites are 1.97 nm (OD-M), 1.97 nm (CT-M) and 2.07 nm (CP-M). The maximum dool values of MAintercalated samples with short-chain alkylammonium cations are 1.88 nm (HA-M) and 2.83 nm (DD-M). Table 1 Interlayer distances of exchanged montmorillonites before (original) and after MA intercalation. (All samples are air dried at T= 25°C for 24 hours.) Sorbent

doo~ (nm) Original

After intercalation of MA methanol

Na-M Ca-M HA-M DD-M OD-M CT-M CP-M

1.41 1.54 1.35 1.79 1.97 1.97 2.07

1.89 1.89 1.87 2.83 3.22 3.35 3.34

acetone

water

chloroform

toluene

1.91 1.95 3.23 3.36 2.99

1.84 1.72 1.88 2.18 3.03 2.82 2.68

1.5 1.58 !.86 2.39 2.69 2.74 2.84

1.5 1.54 1.86 2.19 2.67 2.48 2.41

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Fig. 1. The basal spacings of oriented samples of sodium and calcium montmorillonites and the organic derivatives after intercalation of MA from various solvents.

The basal spacings of the MA-intercalated long-chain alkylammonium montmorillonites are about 1 nm higher than those of the sodium and calcium montmorillonites (Fig. 1 ). The interlayer separation/1 (A = doo~-0.96 nm) of MA-intercalated Na-M and Ca-M roughly corresponds to one or maximum two layers of methacrylamide. The diameter of the MA molecule is about 0.55 nm. The large basal spacing of MA-intercalated organophilic species results from the reorientation of the alkyl chains of the alkylammonium cations from the parallel two-layer arrangement into structures with tilted chains. It is difficult to evaluate the exact structure in the interlayer space. Probably, conformers with gauche bonds or kinks are more likely to occur than all-trans chains of varying tilting angles (Lagaly and Weiss, 1973). The detailed study of hydrocarbon chains arrangements in the interlayers under some aromatic liquids was reported by Lagaly et al., (1973). The simplyfied scheme of possible arrangements of MA molecules in the interlayer space is shown in Fig. 2. The relation of basal spacing and the hydrocarbon chain length of the alkylammonium cation is shown in Fig. 3. The maximum basal spacing is determined by the length of the alkyl chain in all trans conformation oriented perpendicularly to the silicate layer and is not exceeded by any sample. The calculated alkyl chain lengths are 1.30 nm (HA), 2.06 nm (DD) and 2.81 nm (OD) (C-C bond: 0.154 nm, C-N bond: 0.147 nm, C-H bond: 0.111 nm, van der Waals radius of terminal hydrogen atom: 0.12 nm). The maximum basal spacings of alkylammonium montmorillonites are 2.26 nm (HA-M), 3.02 nm (DD-M) and 3,77 nm (OD-M).

V. Hlavat~,A. Oya /Applied Clay Science 9 (1994) 199--210

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c) Fig. 2. The possiblearrangementsof MA moleculesin the interlayerspace : (a) monolayers,(b) bilayers (sodium and calciummontmorillonites),and (c) multilayers(organo-montmorillonites). The effect of solvent is more pronounced in the organophilic montmorillonites. The spacing increases with increasing dipole moment of the solvent molecules. Methacrylamide molecules do not enter the interlayer space of Ca-M from the low polarity solvents due to high hydration energy of Ca 2+ cations. The effect of other substituents on the nitrogen atoms of the alkylammonium cations (methyl groups of quaternary CT cation, aromatic unit of CP cation) on the basal spacing after MA intercalation appears to be of minor importance.

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The XRD-patterns of intercalated samples are changed after gamma-irradiation. The (001) reflections are broadened and shifted in most cases dependent on irradiation dose and probably other factors such as the amount and local arrangement of interlayer sorbate (Fig. 4). The changes of shape and position of dool reflections of the MA-intercalated OD-M after gamma-irradiation indicate a rearrangement of the interlayer structure. The gradual disappearance of the reflection of free methacrylamide (at about 11° 2 0 ) is caused by disintegration of the regular crystal structure of the monomer in excess. The basal spacing of the powder sample OD-M/MA(m), prepared in methanol (see Section 2.2) is somewhat smaller (door = 2.49 nm) than for the oriented samples as a nonsaturated methacrylamide solution was used during the intercalation. Nevertheless, irradiated by a dose of 104 Gy, the basal spacing increased to 2.92 nm and after another dose of 2)< l0 s Gy to 3.31 nm (Hlavat2~ and Oya, 1992). The dool value of OD-M/MA(m) after extraction with acetone decreased to 2.3 nm while the basal spacing of the irradiated ODM / M A ( m ) was unchanged. This suggests the presence of some unsoluble, volumous substances in the interlayer space, including polymerization products, which were not removed with acetone.

3.2. Thermal analysis Alkylammonium montmoriUonites are stable up to about 150°C (Chou and McAtee, 1969) though some authors showed that measurable changes of organic cation (decomposition to corresponding free amines and halogenated alkanes) occur from 100°C (Eibeman and Lara, 1991; Lara and Eiceman, 1991 ). OD-M does not show a desorption of water below 200°C (Fig. 5). A significant weight loss, accompanied by series of exothermic peaks, occurs from about 200°C to 400°C due to successive decomposition of the organic cation and oxidation of products (Kuchta et al., 1991 ). The following gradual weight loss

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3.3. GC/MS analysis The following three compounds were identified in an acetone extract of the irradiated sample OD-M / MA (m) : (1) (2) (3)

methacrylamide monomer long aliphatic chain fragments with seventeen carbon atoms long chain aliphatic compounds of the composition C19H39CONH 2.

The occurence of residual methacrylamide monomer is the result of the low conversion rate of methacrylamide polymerization in the solid state, as initiated by gamma-rays (Restanio et al., 1956; J~iger and Waight, 1963). Polymer fractions were not detected in the acetone extract; however, this does not exclude the presence of polymer in the interlayers. The presence of long-chain amide indicates that a reaction of MA with the alkyl chains is also taking place.

V. Hlavat:, A. Oya / Applied Clay Science 9 (1994) 199-210

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3.4. Infrared spectroscopy The infrared spectra of examined species are shown in Fig. 6. The IR spectrum of Na-M shows absorption bands of O-H stretching vibrations at 3630 c m - i and around 3450 c m - 1, a broad 81-I20 absorption band at 1640 cm- 1 and absorption of structural groups of montmorillonite in the range from 1040 c m - 1 to 470 cm- 1. OD-M has also absorption bands at 3430 c m - , and 3250 c m - ' which can be ascribed to N-H stretching as well as C-H stretching absorption bands at 2920 c m - ' and 2850 c m - ' . Absorption bands in the region from 1700 cm-~ to 1200 cm-~ are deformation vibrations of-NH2, --CH3 and -CH2- groups. The MA monomer can be detected by the N-H stretching vibrations (3390 c m - , and 3190 cm-1). Strong absorption bands are observed at 1668 cm -1 and 1606 cm -1 corresponding to C=O, C=C stretching and NH2 bending vibrations. The series of peaks between 1470 c m - , and 1370 c m - ' is ascribed to --CH3, --CH2- and CH2= deformations including

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C - N stretching vibrations, and those from 1240 cm-~ to 800 cm -~ belong to the CH2=CCH 3 - group with distinct out of plane deformations of the CH2= group at 934 c m - l (Bellamy, 1975). Irradiation of the O D - M / M A ( m ) sample brings about the following principal changes in the IR spectra: The intensity of peaks at 3390 cm-1 and 3190 c m - l decreases significantly as well as the intensity of peaks at 1606 c m - 1, 1234 c m - 1,934 c m - 1 and the series of peaks around 1390 c m - 1 A new, weak peak appears at 1206 c m - l, ascribable to the skeletal vibrations of a branched chain. The absence of the peak at 934 c m - 1 and the decreased intensity of the peak at 1606 c m - 1 indicate partial decomposition of methacrylamide. The appearance of the new peak at 1206 c m - 1 indicates the creation of new bonds in the irradiated sample.

V. Hlavat~, A. Oya / Applied Clay Science 9 (1994) 199-210

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4. Conclusions Methacrylamide can be intercalated into the interlayer space of montmorillonite. This results in increased basal spacing with one and two layers of M A in the interlayer space of sodium and calcium montmorillonites, while a multilayer arrangement of methacrylamide, proportionally to the alkylammonium chain length, is formed in alkylammonium montmorillonites. These intercalation complexes have a low thermal stability. Gamma-irradiation of the methacrylamide intercalated octadecylammonium montmorillonite results in a thermally more stable intercalation complex with additional structure expansion. This is probably due to the rearrangement of the interlayer structure caused by gamma-ray initiated reactions. As indicated by the results of G C / M S measurements, reactions between octadecylammonium cations and methacrylamide occur. Thus a certain degree of cross-linking can be expected in the interlayer space which may have a negative influence on separation of the silicate layers.

Acknowledgements The authors would like to thank the C A L P Corporation for supplying with methacrylamide monomer as well as valuable discussions, and Ms. Hagiwara from Gunma University for carrying out the G C / M S measurements.

References Bellamy, L.J., 1975. The Infra-Red Spectra of Complex Molecules.Chapman and Hail, London, 433 pp. Chou, C.C. and McAtee, J.L., 1969. Thermal decomposition of organoammonium compounds exchanged onto montmorilloniteand hectorite. Clays Clay Miner., 17: 339-346. Eiceman, G.A. and l.ara, A.S., 1991. Gas chromatographic properties of organoammonium exchanged onto montmorillonitesI. J. Chromatogr., 549:273-281. Fukushima, Y. and Inagaki, S., 1987. Synthesisof an intercalatedcompoundof montmorilloniteand 6-polyamide. J. Incl. Phenom., 5: 473-482. Fukushima, Y., Okada, A., Kawasumi, M., Kurauchi, T. and Kamigaito, O., 1988. Swelling behaviour of montmorilloniteby poly-6-amide. Clay Miner., 23: 27-34. Hlavaty, V. and Oya, A., 1992. Proc. 36th Meeting of the Clay Society of Japan, pp. 82-83. Jager, P. and Waight, E.S., 1963. Solid state polymerization of methacrylamideand N-arylmethacrylamides.J. Polym. Sci., Part A, I: 1909-1927. Kuchta, L., Jesen(ik, K., Hlavat~, V. and Fajnor, V.~, 1991. Termick~t charakteristika produktov interakcie oktadecylaminu s montmorillonitom.Zbor. ~si. konf. Termanai, pp. 163-164. Lagaly, G. and Weiss, A., 1973. Conformationai changes of long chain molecules in the interlayer space of swelling mica-type layer silicates. Proc. Int. Clay Conf. 1972, pp. 637--649. Lagaly, G., Stange, H. and Weiss, A., 1973. Adaptation of long chain molecules onto aromatic swelling liquids in mica type layer silicates. Proc. Int. Clay Conf. 1972, pp. 693-704. Lara, A.S. and Eiceman, G.A., 1991. Gas chromatographicproperties of organoammoniumexchanged montmorillonites II. J. Chromatogr., 549: 283-295. Ogawa, M., Kuroda, K. and Kato, C., 1989. Preparation of montmorillonite-organicintercalationcompounds by solid-solid reactions. Chem. Lett., 1659-1662. Okada, A., 1991. Abstr. 12th Symp. Inorg. Polym., pp. 7-12.

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Restanio, A.J., Mesrobian, R.B., Morawetz, H., Ballantine, D.S., Dienes, G.J. and Metz, [).J., 1956. Gamma-ray initiated polymerization of crystalline monomers. J. Am. Chem. Soc., 78: 2939-2943. Theng, B.K.G., 1974. The Chemistry of Clay-Organic Reactions. Adam Hilger, London, 343 pp. Yariv, S., Kahr, G. and Rub, A., 1988. Thermal analysis of the adsorption of rhodamine 6G by smectite minerals. Thermochim. Acta, 135: 299-306.