Green and Sustainable Chemistry, 2012, 2, 21-25
http://dx.doi.org/10.4236/gsc.2012.21004 Published Online February 2012 (http://www.SciRP.org/journal/gsc)
Clay Modification by the Use of Organic Cations
Pankil Singla1, Rajeev Mehta2*, Siddh Nath Upadhyay3
1School of Chemistry and Biochemistry, Thapar University, Patiala, India
2Department of Chemical Engineering, Thapar University, Patiala, India
3Department of Chemical Engineering, IT-BHU, Varanasi, India
Received November 16, 2011; revised December 25, 2011; accepted January 5, 2012
To render layered silicates miscible with polymer matrices, one must convert the normally hydrophilic silicate surface
to an organophilic one, making the intercalation of polymeric chain between silicate layers possible. This can be done
by ion-exchange reactions with cationic surfactants. Sodium montmorillonite (Na-MMT) was modified with several
organic cationic surfactants. Organoclays with water soluble surfactants were prepared by the traditional cation ex-
change reaction. An alternative procedure was used to prepare organoclays with water insoluble salts. The basal spacing
and thermal behavior of organoclays were characterized by X-ray diffraction, XRD and Thermogravimetric analysis,
Keywords: Montmorillonite; Organo-Montmorillonite; Surfactant; Basal Spacing
In recent years polymer/layered silicates nanocomposites
have attracted great interest, both in industries and aca-
demia. Montmorillonite (Na-MMT) is commonly used as
a nanofiller in the preparation of polymer nanocomposite.
The possible application of generated organoclay is the
better intercalation of polymer chains between stacks of
MMT clay. The modified Na-MMT is used for making
eco-friendly polymer clay nanocomposite with improved
physical and mechanical properties.
Montmorillonite, and other layered silicate clays are na-
turally hydrophilic. This makes them poorly suited to mi-
xing and interacting with most polymer matrices which
are mostly hydrophobic [1-3]. Moreover, the stacks of clay
platelets are held tightly together by electrostatic forces.
For these reasons, the clay must be treated before it can
be used to make a nanocomposite. Making a composite
out of untreated clay would not be a very effective be-
cause most of the clay would be unable to interact with
the matrix. An easy method of modifying the clay surface
is traditional ion exchange method. The cations are not
strongly bound to the clay surface, so small molecule ca-
tions can replace the cations present in the clay. By ex-
changing ions present in between layers with various or-
ganic cations, montmorillonite clay can be compatibilized
with a wide variety of matrix polymers. At the same time,
this process helps to separate the clay platelets so that
they can be more easily intercalated and exfoliated.
By exchanging of sodium cations for organic cations that
are also called surfactants, the surface energy of MMT
decreases and the interlayer spacing expands. The result-
ing material is called organoclay. The basal spacing of the
resulting organoclays depends on the chemical structure
of the surfactant, the degree of cation exchange, and sili-
cate layer thickness . Organically modified montmoril-
lonites have been widely studied fundamentally and in
practical applications in the area of organic-inorganic hy-
brids, composites and nano-scale composites . Ammo-
nium surfactants used in commercially available organo-
clays usually incorporate short aliphatic chains and ben-
zyl groups [7-9]. Phosphonium surfactants have been used
in the preparation of organoclays [10-14]. Phosphonium
surfactants are thermally stable than ammonium surfac-
In this paper, we present preparation and characteriza-
tion of new organo-montmorillonite clays by using am-
monium surfactant and phosphonium surfactant which
contain one or more hydrophobic groups such as long
alkyl chains, phenyl and stearate. We report the basal
spacing by XRD measurements and thermal behavior by
2. Experimental Section
Unmodified montmorillonite clay with Cation Exchange
Capacity, CEC 86 meq/100 g was supplied by GM Che-
micals, Ahmadabad. The surfactants were purchased from
opyright © 2012 SciRes. GSC
P. SINGLA ET AL.
SD fine chemicals and used as received. The basal spac-
ing of MMT is 0.75nm. This MMT was used as such
without any further purification. The specification of clay
is given in Table 1. The solvent diethyl ether and petro-
leum ether were used without further purification. How-
ever realizing that these solvents are not ecofriendly, hence
almost all the solvent recovered by using rota-evaporator.
2.2. Choice of Organic Cations
The chemical composition of the surfactants is given in
Table 2. The surfactants were used on the basis of the
long hydrophobic carbon chains attached to the central
atom. It results in increasing surface area that will lead to
better intercalation of organic cation between the layers
of unmodified MMT clay. Phosphonium ion has four phe-
nyl rings attached to it. The rigidity of the phenyl groups
facilitates packing and elevates the melting point relative
to quaternary ammonium salts. Zinc Stearate is a fatty
acid which has hydrophobic effect. Its main application
areas are the plastics and rubber industry where it is used
as a releasing agent and lubricant which can be easily
incorporated. The potential application of surfactants
used is their role in biological system. They play a vital
role in drug delivery. Specifically quaternary ions are
used on skin for cleansing wounds or burns. They are
mostly used for their disinfectant and preservative prop-
Table 1. Specification of MMT clay.
Table 2. Main characteristics of surfactants.
Surfactant, MW (g/mol) Chemical structure % purity
bromide, 308.3 98%
Zinc Stearate, 632.2 -----
erties as they have good bactericidal properties. Hence
the used surfactants have wide potential applications.
2.3. Organoclay Preparation
Two procedures for modification of MMT clay were fol-
lowed, depending upon the solubility of salts in aqueous
phase, which are similar to the procedure reported .
The following procedure was used for the salts which
were soluble in aqueous phase. 5 g of sodium MMT were
dispersed in 500 mL of distilled water for 24 h at room
temperature, using a magnetic stirrer. Using an aqueous
solution of salt, the amount of surfactant added was equi-
valent to the CEC of clay. The cation exchange reaction
occurs rapidly. The resulting organoclay suspension was
mixed further for 12 h. The suspended organoclay was
filtered under vacuum, using whatman filter paper. The
resulting organoclay was dispersed into 50 mL of fresh
distilled water and mixed further for 4 h. No chloride
traces were detected by addition of silver nitrate, after
two washing. The resulting organoclay was dried at 60˚C
for 24 h under vacuum. Finally the resulting material was
ground, using a Pestle Mortar for 30 s, in order to obtain
a fine powder. The organoclay product was stored in de-
The procedure to produce organoclays with water in-
soluble salts was as follows. 5 g of sodium MMT were
dispersed into 500 mL of distilled water at room tem-
perature, using a magnetic stirrer. After 24 h, mixing was
stopped and 200 ml of diethyl ether solution of salt, con-
taining the stochiometric amount of salt corresponding to
the CEC of MMT, was slowly poured into the clay dis-
persion. The resulting system contained a clear upper or-
ganic phase and a turbid bottom mineral phase. After 12
h of moderate mixing, the mineral phase became transpa-
rent and the organic phases became turbid. Special care
was taken to avoid diethyl ether evaporation. At this point,
the system was warmed up to evaporate the diethyl ether
(60˚C), using a Rota-evaporator. After solvent evapora-
tion, the organic phase became a sticky solid precipitate.
The precipitated organoclay was filtered and dispersed in
hot water (80˚C) for 4 h. The washing was repeated three
times, until no chloride traces were detected with silver
nitrate after the third washing. The resulting organoclay
paste was manually mixed with 40 ml of petroleum ether
using a spatula. After free petroleum ether evaporation,
using Rota-evaporator, the organoclay was dried at 80˚C
for 24 h under vacuum. Then it was ground, using a Pes-
2.4.1. X-Ra y Diffr ac ti on
X-ray diffraction (XRD) was performed on dried powder
samples. The organoclays were grounded into a fine pow-
Copyright © 2012 SciRes. GSC
P. SINGLA ET AL. 23
der prior to XRD measurements using Pestle Mortar with
sufficient pressure so as to make a fine powder. The scans
were performed for each sample and the values are re-
ported for the basal spacing in Table 3 . The x-ray diffrac-
tion patterns were obtained using a XPERT-PRO x-ray
diffractomer with Cu Kα radiation (λ = 1.54 Å). The ex-
periments were run at room temperature with an angle
range (2θ) from 4˚ to 15˚ for Zinc Stearate and 2˚ to 70˚
for rest of the four ions at 4˚/min and step size of 0.02˚.
The machine was operated at 40 kV and 40 mA.
The weight loss arising from the degradation was studied
by TGA (Perkin Elmer Diamond TG/DTA instrument.
Samples of 5 - 7 mg were heated from 50˚C to 650˚C at a
rate of 10˚C/min. The TGA trace was used to determine
the % weight loss at 650˚C which is sufficient tempera-
ture to degrade the organic content present in modified
3. Results and Discussion
3.1. X-Ray Diffraction of the
XRD of different samples of modified MMT clay give
the values of basal spacing. The basal spacing of the dif-
ferent samples is given in Table 3. The diffraction pat-
terns of the different samples are given in Figure 1. The
basal spacing of unmodified MMT clay is termed as ini-
tial basal spacing (0.75 nm at 2θ = 11.64). After modify-
cation of clay the basal spacing increased, by treating it
with different organic cations. An increase of the interla-
yer distance, leads to a shift of the diffraction peak to-
ward lower angles. After treating the unmodified MMT
clay with Zinc Stearate, the diffraction peak shifts to lo-
wer angle i.e. 2θ = 6.32 and basal spacing increases from
0.75 nm to 1.39 nm. Similarly, when it is treated with
Tetraphenyl Phosphonium ion then the basal spacing in-
creases to 2.26 nm which is sufficiently large value for
its potential as reinforcement in a polymer nanocompo-
sites. The increase in basal spacing by Tetraphenyl phos-
phonium ion is due to the four phenyl groups attached to
phosphorous cation which helps in pulling apart the two
stacks of MMT clay. The XRD of pure organic cation such
as Zinc Stearate and Triphenyl Phosphonium bromide do
not show any peak at the angle where XRD of modified
MMT clay has shown after treating with the respective
ions. Hence the shift in angle to the lower angle shows
the increase in basal spacing. Increase in basal spacing is
successfully achieved by using Zinc Stearate which is a
known fatty acid. This opens up a great interest in the po-
tential of fatty acids for clay modification that are cheap
and easily available. One can easily increase the organic
content in fatty acids and it is quite possible that one
Table 3. Basal spacing of clay vs surfactants.
S.No.Organo-montmorillonite clay Final basal spacing, nm, (2θ)
1. Zn Stearate-MMT 1.39 (6.32)
2. TPP-MMT 2.26 (3.90)
3. DTMA-MMT 0.74 (11.80)
4. HDTMA-MMT 0.73 (12.04)
5. TDTMA-MMT 0.73 (11.96)
Figure 1. XRD pattern of modified MMT clay with differ-
ent organic cations.
should be able to tweak the interlayer spacing of MMT
clays. In case of ammonium ions treated MMT clay, no
effect on basal spacing was seen and it has not changed
The increase in value of basal spacing depends upon
two factors. One is the presence of large hydrophobic
groups on surfactants and second is the decrease in sur-
face energy of MMT. As the size of hydrophobic groups
increases, the basal spacing increases to a large extent.
The increase in basal spacing results in formation of bet-
ter intercalated or exfoliated polymer clay nanocompo-
site with improved physical and chemical properties.
The initial basal spacing in the organoclay is an im-
portant parameter for the determination of the potential
for polymer intercalation and clay mineral delamination
. Organoclays with smaller interlayer distances have
reduced probabilities for polymer intercalation.
3.2. Thermal Stability and Degradation Behavior
of Organo-Montmorillonite Clay
The low thermal stability of ammonium surfactants pre-
sents a problem for melt compounding and processing of
polymer nanocomposites. Thermal degradation during pro-
cessing could initiate/catalyze polymer degradation, in
addition to causing a variety of undesirable effects during
processing and in the final product. TGA gives us infor-
mation about the thermal stability of the organoclay. The
TGA curves for unmodified Na-MMT clay and organi-
cally modified clays are shown in Figure 2. It is noted
Copyright © 2012 SciRes. GSC
P. SINGLA ET AL.
Figure 2. TGA curves for unmodified NaMMT clay and or-
ganically modified montmorillonites. (a) Unmodified NaMMT
clay; (b) Triphenyl phosphonium-MMT clay; (c) Dodecyl-
trimethyl ammonium-MMT clay; (d) Tetradecyltrimethyl
that the TGA of the unmodified montmorillonite has three
mass loss steps: Between ambient and 100˚C, at 135˚C
and at 450˚C. These mass loss steps are attributed to de-
sorption of water from the clay, dehydration of the hy-
drated cation in the interlayer and the dehydroxylation of
the montmorillonite respectively.
The presence of organic cation increase the number of
decomposition steps. Four steps of the mass loss steps
are observed for the organoclays [17,18]. In case of TPP-
MMT, the first step is from the ambient to 66.9˚C tem-
perature range and is attributed to the desorption of water.
The second step occurs from 135.5˚C to 310˚C and is
assigned to the loss of hydration water from the Na+ ion.
The third mass loss step is attributed to the removal of
the surfactant at around 440˚C. The fourth mass loss step
in the TGA curves is assigned to the loss of structural
hydroxyl groups from within the clay. It is around 580˚C.
This is an indication of the thermal stability of modified
Further, the TGA curve of TDTMA-MMT and DTMA-
MMT clay shows first degradation step from ambient to
70˚C temperature range. The second step occurs from
245˚C to 326˚C and third step occurs at 490˚C. The
fourth step occurs at 560˚C.
The first and second decomposition steps are impor-
tant for utility of such organically modified montmoril-
lonites in polymer-based composite materials prepared
via melt state processing, as most polymers are processed
within this temperature range. Hence, these new OMMTs
can be used for preparing organic–inorganic hybrids by
melt processing with thermoplastic polymers such as po-
lypropylene (PP), polystyrene (PS), poly(methyl metha-
crylate) (PMMA) and others which are relatively polar,
as well as for other applications.
Montmorillonite has been successfully modified using
organic cationic surfactants. The XRD results show inter-
calation of the organic cations between the clay mineral
layers. Zinc Stearate is a fatty acid and is successfully
used for increasing basal spacing. Hence basal spacing is
also increased by using fatty acid with long hydrophobic
chains. They are cheap and easily available. The phos-
phonium-MMT clay shows increase in basal spacing but
the ammonium-MMT clay does not show increase in basal
spacing. One of the reasons can be the experimental pro-
cedure which is used for the ions that are soluble in aque-
The TGA curves for these organoclays show the deg-
radation due to residual water desorption, dehydration,
followed by decomposition of the organic modifier. These
organically modified montmorillonites have potential uti-
lity in the preparation of polymer nanocomposites and in
other applications. The organoclays prepared in this study
can be used to prepare nanocomposites with polar poly-
mers in order to render good level of dispersion, im-
proved mechanical and other properties.
We thank the School of Chemistry and Biochemistry,
Thapar University, GM Chemicals, Ahmedabad and ap-
preciate the generous gift of the clay.
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