organic modification of bulgarian bentonite by … · materials, paints, varnishes, adhesives,...

Albena Yoleva, Stoyan Djambazov, Georgi Michailov

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Journal of Chemical Technology and Metallurgy, 51, 3, 2016, 275-280

ORGANIC MODIFICATION OF BULGARIAN BENTONITE BY AN EASY LOW COST METHOD


Department of Silicate Technology University of Chemical Technology and Metallurgy8 Kl. Ohridski Blvd., 1756 Sofia, BulgariaE-mail: [email protected]

ABSTRACT

Bentonite is hydrophilic in nature due to the cations within its interlayer space. This makes natural bentonites ineffec-tive sorbents of organic compounds. The modification of their surfaces by surfactants is an option to prepare bentonite-based sorbents of organic pollutants and bentonite fillers used for polymer nanocomposites production. The present study reports the formation of organobentonites on the ground of Bulgarian bentonite following an easy and cost-effective cation exchange methodology. Octadecylamine is the surfactant used. All reactions are carried out in a single vessel. No drying and grinding of the bentonite’s is required prior to the organic modification. The organobentonites obtained are studied by XRD, IR, DTA and TGA. Different organic solvents as ethanol, toluene and xylene are used to investigate their sorption and swelling properties. It is found better organic ions intercalation is obtained that with increase of the amount of the organic modifier. This is evidenced by the increase of the spacing d (001) (Å) from 13,20 (Å) to 20,50 (Å). The best organic cations intercalation is achieved in a bentonite containing 20 mass % of octadecylamine. The organobentonites obtained are hydrophobic in water and hydrophilic in organic media. The organobentonite modified by 20 mass % of octadecylamine shows the best swelling capacity in xylene.

Keywords: natural bentonite, organo-modification, octadecylamine, cation exchange.

Received 25 January 2016Accepted 11 April 2016

INTRODUCTION

The application of bentonite to polymer industry as well as to the production of different types of packaging materials, paints, varnishes, adhesives, building materi-als, etc. is growing. It is so because the numerous studies of the bentonite’s mineralogy, crystal chemistry and physico-chemical properties indicate that the primary mineral in bentonite - montmorillonite, belonging to the class of natural nanoparticles, can serve as a buffer between the plastics’ organic polymer and the inor-ganic silicate. The treatment of bentonite by surfactants, represented mainly by quaternary alkyl ammonium compounds, results in a new variety of bentonite called organo-bentonite. The surface modification achieved improves the compatibility of the inorganic and organic

components which are inherently incompatible in the polymer nanocomposites [1 - 8].

Nanocomposite polymer materials filled with organo-bentonite are finding growing development. The addition of an organo-bentonite to the polymer matrix leads to increase of the mechanical strength, thermal stability, gas permeability and water-repellent properties of the polymers [9 - 14].

Bentonite is a kind of clay composed primarily of montmorillonite. The latter consists of platelets with an inner octahedral layer sandwiched between two silicate tetrahedral layers. The octahedral layer may be thought of as an aluminum oxide sheet where some of the alu-minum atoms have been replaced with magnesium; the difference in Al and Mg ions valences creates negative charges distributed within the plane of the platelets that

Journal of Chemical Technology and Metallurgy, 51, 3, 2016

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are balanced by positive counterions, typically sodium ions, located between the platelets or in the galleries. In its natural state, this clay exists as stacks of many platelets. Hydration of the sodium ions causes the gal-leries expansion and hence clay’s swelling; indeed, these platelets can be fully dispersed in water. The sodium ions can be exchanged with organic cations to form an organo-bentonite. When the sodium is replaced with much larger organic surfactants, the gallery expands and the X-ray basal spacing increases [1 - 5].

The present study reports the production of organo-bentonites containing different amounts of octadecylamine on the ground of Bulgarian bentonite. An easy and cost-effective cation exchange methodology is used. The organo-bentonitess prepared are characterized by XRD, IR, DTA and TGA.

EXPERIMENTAL

MaterialsBulgarian bentonite from Stambolovo deposit,

Haskovo area was used for the experiments. The for-mation of bentonite there was associated with “in situ” acids’ argillization to acidic layered tuffs deposited in shallow-sea lagoon environment. The averached chemi-cal composition of the bentonite is as follows: 15,08 mass % of Al2O3, 2,34 mass % of Fe2O3, 2,86 mass % of MgO, 5,65 mass % of CaO, 0,23 mass % of TiO2, 0,50 mass % of Na2O, 1,14 mass % of K2O, and 60,03 of mass % SiO2. The mineral composition of bentonite refers mainly to monmorilonite (ca 80 %) and small amounts of quartz, calcite and impurities of mica and clinoptilo-lite. Sodium carbonate (PA) was used for the bentonite’s alkaline activation. Octadecyleamine (ODA), C18H39N, provided by Aldrich, USA (Mw 269.51 g mol-1) was used as a surfactant for the organic modification. Its protonation was achieved by acetic acid use. Xylene, toluene and ethanol (PA) were used for determination of the organo-bentonites’ sorption properties.

Organobentonite preparation The Bulgarian bentonite was modified by ODA on

the ground of an ion exchange. Different quantities of octadecylamine varying from 5 mass % to 20 mass % in respect to the bentonite’s amount were used. An easy and cost-effective methodology for organic modification of the bentonite was used. It refers to the following: 100

g of natural bentonite was placed in 1000 ml of distilled water and stirred for 1 hour; then 3 mass % sodium carbonate solution was slowly added and stirred around 1 hour to obtain sodium modification of the bentonite; subsequently amounts referring to 5 mass %, 10 mass %, 15 mass % and 20 mass % of ODA (dissolved in water and protonated by acetic acid introduction to pH 2-3) were slowly added to the sodium bentonite and stirred for 4 hours to full organic modification of the bentonite. The resulting organo-bentonites were dried at 60°C in an air dryer and then milled in a ball mill to a powder of a particle size below 63 microns.

Methods of characterizationChemical analysis: a classical silicate analysis and

ICP-AES were carried out after alkali fusion and dis-solution in an acid.

XRD: It was performed on Diffractometer ”TUR-M62” with CoKα radiation in the range of 2θ from 5 to 60o.

DTA and TGA: they were performed on “Stunton Redcroft” (England) in the temperature range 20°C - 1000°C with a heating rate of 10°C/min; the sample weight was 10,00 mg.

IR spectroscopy: Spectrophotometer “Perkin-Elmer Spectrum 1000” was used in the range of 4000 cm-1 - 400 cm-1.

RESULTS AND DISCUSSION

Fig. 1 shows the diffraction patterns of unmodified bentonite, sodium bentonite and organo-bentonites containing different surfactant amounts. Sodium ben-tonite has a basal spacing d (001) at 12,39 Å (2q - 7,13). The d (001) spacing of the organobentonites increases with ODA quantity increase. The basal spacing in the organobentonites increases from 13.20 Å to 20.50 Å in case of 5 mass % ODA and 20 mass % ODA presence, correspondingly. This verifies the intercalation of the surfactant quaternary ammonium cation in the bentonite. The basal spacing displacement increases with ODA content increase.

The IR spectra of sodium bentonite and the or-ganobentonites obtained are shown in Fig. 2. Those of the organobentonite show well outlined peaks at 2920 cm-1 and 2851 cm-1. They are related to the asymmetric us (CH2) vibrations. A peak at 1449 cm-1 refers to the asymmetric


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deformation of the (CH3) group. The presence of (CH2) and (CH3) groups peaks in the organobentonites’ spectra evidence the intercalation of the organic modifier qua-ternary ammonium cations in the interlayer space of the

bentonite. There is a peak at 3627 cm-1 which refers to the presence of a hydroxyl group in the bentonite’s structure.

The peak recorded at 3443 cm-1 is linked to the water molecules in the bentonite structure and as can

Fig. 1. XRD of a natural bentonite, a sodium bentonite and organobentonites.

Fig. 2. IR spectra of a sodium bentonite and organobentonites.


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Fig. 3. DTA and TG of a natural bentonite.

Fig. 4. DTA and TG of a sodium bentonite.

Fig. 5. DTA and TG of an organobentonite modified by 20 mass % of ODA.


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be seen from the figure it decreases and shifts in or-ganobenonites spectra. This is attributed to the removal of some hydroxyl groups of the structural Si-OH, Al-OH and H2O located in the interlayer space upon organic cations insertion. The peak at 1636 cm-1 is attributed to the presence of adsorbed water. It decreases also in the organobentonites’ spectra. The peak at 1039 cm-1 and those in the range between 900 cm-1 and 700 cm-1 are due to Si-O group vibration. The peak at 520 cm-1 cor-responds to the vibrations of Al-Si-O group, while that at 466 cm-1 refers to those of Si-O-Si group.

Figs. 3, 4 and 5 show the DTA and TG curves of unmodified bentonite, sodium bentonite and orga-nomodified bentonite containing 20 mass % of octa-decylamine. The weight loss between 30°C and 150°C in the unmodified bentonite (Fig. 3) and sodium bentonite (Fig. 4) is apparently due to evaporation of water from the hydrated inorganic cations and those adsorbed at the silicate surfaces. The weight loss of the unmodified bentonite decreases above 150°C until it becomes stable at temperatures above 700oC. The weight loss in this case is accompanied by a change in the bentonite’s crystal structure. There is a permanent weight loss in case of the organically modified bentonite (Fig. 5) which results from the decomposition of the organic compounds ob-tained in the course of modification. This is in agreement with the results of the IR analysis verifying the presence of the various functional groups attached to the surface of the bentonite. The TG analysis of Na-bentonite shows two thermal transitions of degradation (Fig. 4). The first transition is observed at about 120oC with 5.1 % weight loss due to desorption of water molecules. These water molecules are linked to the cations in the bentonite’s interlayer and evaporate at low temperatures. The sec-ond transition connected with 13 % weight loss at about 750oC refers to the elimination of crystallisation water. It is seen that the first weight loss observed in case of Na-bentonite, connected with the removal of the water of hydration in the bentonite interlayer, is missing in the organobentonite’s curve (Fig. 5). This demonstrates the complete removal of water and associated cations in the interlayer. The second thermal transition does not exist in this case. In fact the TG curve of organobentonite shows a smooth continuous thermal transition up to 750oC with a weight loss depending on the octadecylamine content. It is 45.26 % in case of 20 mass % ODA presence. It is related to the organic matter decomposition. It is worth

noting that there the organobentonite contains a mini-mal amount of adsorbed water (1 % - 2 %) in the in the temperature range of 20°C - 200°C, while the natural bentonite contains 12 %. The large endothermic effect of the organobentonite at 400°C - 450°C is related to organic matter decomposition.

The sorption capacity of the organobentonite in water and organic media is studied. Fig. 6 shows that organobentonite is not dispersed in water and remains on the water surface. It is sorbed in xylene. It has the ability to form gels in organic solvents.

The swelling index of organobentonite modified by 20 mass % ODA is determined in xylene, toluene and ethanol media. In these cases 2.00 grams of the organobentonite sample are added to 100 ml xylene, toluene and ethanol and after 24 the volume of sedi-ment is measured. The best sorption ability is observed in xylene, followed by that in toluene, which in turn is followed by that in ethanol (Fig. 7). The best perform-ing modified organobentonite (containing 20 mass % of ODA) has swelling index of 25 ml/2g in xylene, 15 ml/2g in toluene and 10 ml/2g in ethanol.

Fig. 6. An illustration of the organobentonite’s organo-phobicity in water and its organophilicity in an organic medium.

Fig. 7. An organobentonite swelling capacity in organic solvents.


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CONCLUSIONS

Organobentonites are obtained on the ground of a Bulgarian bentonite by the introduction of different amounts of octadecylamine following an easy and cost-effective methodology. The organic modification and the resulting structural changes are verified by XRD, IR DTA and TGA. It is found that better organic ions intercalation is obtained by increase of the amount of organic modifier. This is evidenced by the increase of the spacing d (001) (Å) from 13,20 (Å) to 20,50 (Å). The first peak (2q) shifts to smaller angles with the surfactant content increase. The best intercalation of organic cations is achieved in the bentonite containing 20 mass % of ODA. The presence of (CH2) and (CH3) groups in organobentonite spectra is a verification of the intercalation of the quaternary ammonium cations of the organic modifier in the interlayer space of the bentonite. The organobentonite has a minimal amount of adsorbed water (1 % - 2 %) in the temperature range of 20°C - 200°C when compared to that of the natural bentonite (12 %) and is characterized by a large endo-thermic effect at 400°C - 450°C determined by organic matter decomposition.

The organobentonites obtained are hydrophobic in water and hydrophilic in organic media. The best swell-ing capacity shows the organobentonite modified by 20 mass % of octadecylamine in xylene. It can be applied to removal from water of oils, fats and other organic substances of a high molecular weight and as a filler in polymeric nanocomposite.

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