# The Dependence of the XRD Morphology of Some Bionanocomposites on the Silicate Treatment

Authors: Doina Dimonie; Radovici Constantin; Gabriel Vasilievici; Maria Cristina Popescu; Sorina Garea
Journal: Journal of Nanomaterials
 (2008)

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## Abstract

The degree of intercalation of the polyvinyl alcohol-starch blend with the layered silicate is increased if the silicates is untreated or intercalated with ammonium ions that contain small radicals. If untreated silicate like NaMMT is used, it is possible to obtain exfoliated-intercalated nanocomposites. The materials based on PVOH, starch, and Nanocor I 28, Nanocor I 33, or Cloisite 15 A can be intercalated nanocomposites. If the blend of PVOH and starch is reinforced with Cloisite 93 A, microcomposites can result. The study will continue with the analysis of the new morphologies considering the transmission electron microscopy (TEM).


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## Body

## 1. Introduction

The materials obtained based on
layered silicates and polymers can be of the following types: microcomposites when the polymer
is not intercalated between the silicate layers, intercalated nanocomposites when
the polymer chains are intercalated between the clay layers, and exfoliated nanocomposites
when the clay layers are completely distributed into the polymer matrix (Figure1). These materials can be obtained based on chemical, mechanical (melt
processing), and/or chemical/mechanical methods [1, 2].Figure 1
Possible nanocomposite morphologies dependent on the
dispersion and distribution into the polymeric matrix of the silicate lamellas
(a) microcomposites, (b) exfoliated nanocomposites, and (c) intercalated
nanocomposites.The main problems in the exfoliated polymeric nanocomposites obtaining
are the silicate lamellas separation and orientation, lamellas
compatibilization with the polymers, and the avoiding of the lamellas reaggregation
[1–3].The layered silicate montmorilonite
(MMT) has a little affinity with the hydrophobic polymers because of its
hydrophilicity. The diffusion of the polymers into the MMT galleries is
possible if proper anions are intercalated within the silicate galleries. Following
the stress carried out by the polymer inserted within the silicate galleries
and the mechanical shear that acts during the melt processing, it is possible to delaminate the
silicate and to disperse the resulted lamellas, at nanoscale, into the polymer
matrix [1, 2, 4, 5]. The performance of the subsequent silicate lamellas or
tectoides dispersion and distribution within the polymer matrix will control,
near the nanocomposite performances, the reproducibility of the obtained results.The theoretical approaches of the
modified layered silicate intercalation within a polymeric matrix, at the melt
processing, in [1], were approached.The nanocomposite obtaining method
depends on the request of the desired application. Many applications do not require
the silicate exfoliation. For this reason, before choosing the silicate exfoliation
method, a careful analysis of the application performances must be done.The morphology of the material based
on the layered silicate and polymer can be appreciated also based on the XRD diffractograms (Figure2 [1]).
The exfoliated nanocomposites are obtained when the XRD diffractograms do not contain anymore the diffraction
peak of the silicates. The intercalated nanocomposites are realized when the diffraction peak is shifted
toward small angles. The microcomposites appear in case of  the immiscibility of the polymer with the silicate. In this situation,
the blend peak is overlaped with those of the silicate [2].Figure 2
XRD diffractograms of (a) phase-separated microcomposite,
(b) intercalated nanocomposites, and (c) exfoliated nanocomposites [1].The XRD diffractograms
give also information about the morphologies of the polymer-silicate materials if
the following blend diffractogram characteristics are compared with those of
the silicate: number of the diffraction peaks, shifted degree of the
diffraction peaks, diffraction peak intensity, and silicate galleries swelling
degree.The nanocomposites based on polyvinyl
alcohol (PVOH), starch, and layered silicates are not very well studied [6–18]. These
materials have a practical importance because they can be entirely destroyed in
the environment as a consequence of the starch biodegradability and of the PVOH
water solubility. There are known works
about the nanocomposites of PVOH with cellulose [6, 7, 17] and polyoxometalates
[11]. In [8] the thermal stability of
nanocomposites based on PVOH and montmorilonite (MMT) and in [9] the
nanocomposites based on PVOH and bioactive glass or PVOH with chitosan and
bioactive glass considering the biomedical applications are studied.On the other hand, there are known a
lot of studies concerning the materials based on starch: with poly (ε-caprolactone) [12], with MMT [13, 14, 18],
proteins [15], and cyclodextrines [16].The dependence of the morphology of
the biodegradable materials based on polyvinyl alcohol, starch, and layered
silicates by the silicate galleries treatment, in this paper, will be presented.


## 2. Experimental

The nanocomposites based on polyvinyl
alcohol (PVOH), starch, and multilayered silicates were obtained by the melt processing
technique [19–21]. It was studied PVOH-starch blends with the 1/1 blending
ratio and 1–5% silicate loading
level. The blend composition respects the rules proper to the polymeric blends through the
melt processing techniques.


### 2.1. Materials

The following materials were used:(i)
polyvinyl alcohol with 99 moles% hydrolysis degree;(ii)
native starch from corn;(iii)
silicates: treated and untreated montmorilonite (MMT) (Table1);(iv)
melt processing additives (plasticizers, stabilizers);(v)
“entanglement” compatibility agents (polar compounds with small molecular weight).Table 1
The used layered silicates.


### 2.2. Characterization

The new blend morphology was studied based on and X-ray diffraction. On
a DRON 2, 0 X-ray diffractometer, the variation,
at the room temperature, of the radial diffraction intensity dependence on the
diffraction angle (2 teta) was
recorded. The working conditions were:  step size by 0.03° (2 teta),
scanning rate = 8 s/step, filter with λ=1.7921 Å, and diffraction range 2–15° (2
teta). The interbasal spacing was calculated based on the Bragg law (nλ=2dsinθ, where n is an integer; λ  is the
wavelength of X-ray; d is the spacing
between the planes in the atomic lattice; and θ  is the
angle between the incident ray and the scattering planes).


## 2.1. Materials

The following materials were used:(i)
polyvinyl alcohol with 99 moles% hydrolysis degree;(ii)
native starch from corn;(iii)
silicates: treated and untreated montmorilonite (MMT) (Table1);(iv)
melt processing additives (plasticizers, stabilizers);(v)
“entanglement” compatibility agents (polar compounds with small molecular weight).Table 1
The used layered silicates.


## 2.2. Characterization

The new blend morphology was studied based on and X-ray diffraction. On
a DRON 2, 0 X-ray diffractometer, the variation,
at the room temperature, of the radial diffraction intensity dependence on the
diffraction angle (2 teta) was
recorded. The working conditions were:  step size by 0.03° (2 teta),
scanning rate = 8 s/step, filter with λ=1.7921 Å, and diffraction range 2–15° (2
teta). The interbasal spacing was calculated based on the Bragg law (nλ=2dsinθ, where n is an integer; λ  is the
wavelength of X-ray; d is the spacing
between the planes in the atomic lattice; and θ  is the
angle between the incident ray and the scattering planes).


## 3. Results and Discussions

Nanocor I 28 is a layered silicate modified with trimethyl-dodecadecyl-ammonium ions. It has an inhomogeneous
structure because its galleries do not have the same size (Figure3—16.1 Ǻ  for that  from 1.76°,
24.4 Ǻ  for that from 4.2°, and
58 Ǻ for the diffraction from 6.36°). The
main diffraction peak is that from 4.2° which has an intensity of
30 counts/s.Figure 3
The XRD diffractograms of Nanocor
I 28 and of the PVOH-starch blend with 4% Nanocor I 28.The shape of the diffractogram of the
blend based on PVOH, starch, and 3% Nanocor I 28 is different
from that of the silicate alone
because the diffraction peaks are shifted toward small angles (2,02°; 4,53°) and have
different intensities (120 and 50 counts/s). The resulted morphology is more
homogeneous because the silicate galleries have relatively the same size (43.7 Ǻ for the main diffraction peak from 2.02°).
The peak intensity is 110 counts/s. All the studied PVOH-starch blends with 1–5% Nanocor I 28
have a basal spacing enlarged with approximately 20 Ǻ  (Table 2, Figure 4). These results
illustrate an interaction degree between the hydroxylic oxygen from the two
polymers and the ammonium ions from the silicate galleries. The electrostatic forces,
on the one hand, and the mechanical shear that acts during the melt processing,
on the other hand, interpose the polymer with the silicate and enlarge the
silicate galleries with approximately the same values. Because the diffraction
peak of the blend is smaller than that of the silicate alone, it can be
supposed that the order degree of the resulted blend morphology is smaller.
Because the diffraction peak is shifted toward small angles, the resulted
materials can be an intercalated nanocomposite.Table 2
The diffraction angles and the interbasal spacing of the PVOH-starch blends with
(1–5)% Nanocor I 28.
PVOH/starch/Nanocor I 282 tetad,Ǻ1%4,20212%2,2; 4,4240,1; 203%2,13; 2; 4,3241,4;  41; 20,54%2,16; 4,3640,9; 20,65%2,08; 4,3042,4; 20,6The XRD diffractograms of the
PVOH-starch blends with (1–4)% Nanocor I 28 ((a) 1, 2%; (b) 3, 4%).
(a)(b)Nanocor I 33 is modified with dodecylpyrrolidone
ions and has also an inhomogeneous morphology because it contains galleries of different
sizes (Figure 5—30,6 Ǻ  for that
from 10.8°, 30,29 Ǻ  for that from
6.64°,
and 30,23 Ǻ. for the diffraction from
3.35°). The main diffraction peak is at 3.35° and has an intensity by approximately 170
counts/s.Figure 5
The XRD diffractogram of Nanocor
I 33 and of the PVOH-starch blend with 4% Nanocor I 33.The diffractogram of the blend of
PVOH and starch with 4% Nanocor I 33 has two diffraction peaks by smaller intensity,
both of them shifted toward small angles (Figure5—50 counts/s of
the peak from 5.13°, and approximately 120 counts/s of those from 2.5°).
The smaller diffraction peak can be a sign that the morphological order of the resulted
blend is lower. The silicate interbasal spacing has the same size as that of the silicate. These
results proved that the electrostatic interactions between the hydroxylic
oxygen from PVOH, starch, and the dodecyl pyrrolidone ions from the silicate galleries are by small intensity. Because the
diffraction peak is shifted toward small angles, it seems that the resulted
materials can be an intercalated nanocomposite.The Cloisite 93 A galleries contain the ammonium ions, each of them with a methyl and three
hydrogenated tallow radicals (~ 65% C18; ~ 30% C16; ~ 5% C14) [10]. This silicate has a
rather inhomogeneous morphological structure because
it contains galleries of
different sizes (Figure 6—13 Ǻ  for the diffraction from 7.9°, 25, 3 Ǻ  for that from 4.86°, and
57.6 Ǻ  for that from 1.78°).
The main diffraction peak is that from 4.86° which has an intensity
by approximately 110 counts/s. The blend of 4% Cloisite 93 with PVOH and starch
seems to have a relatively more homogenous morphology
because it shows only two peaks, one at 4.05° and a large one
at approximately 5°. Because the blend diffraction and that of the silicate
too take place at approximately the same angle, the diffraction peaks intensity
is the same and the galleries are enlarged only with 5 Ǻ, it seems that
there is no compatibility between PVOH, starch, and the Cloisite 93 A. This
means that between the hydroxyl groups from the two polymers and the ammonium
ions substituted with three radicals HT and a methyl one from the galleries no attractions
are settled up. Because the blend diffraction peak is overlaped with those of
the silicate, the resulted material can be  a microcomposites.Figure 6
The XRD diffractograms of
Cloisite 93 A and of the PVOH-starch blend with 4% Cloisite 93 A.Cloisite 15 A is modifiedwith ammonium ions that contain two methyl and two hydrogenated tallow radicals. This
silicate has also an inhomogeneous structure because it contains galleries of
different sizes (Figure 7—8,24 Ǻ  for the diffraction from 3.41° and 12,5 Ǻ  for that from 8.24° 7). If the diffraction maximum
from 8.24° has a low intensity by approximately 30 counts/s, those from the 3.21° are by 95 counts/s. The blend diffractogram is totally different from that of the silicate and
contains two peaks, one at 4.5° by approximately 65 counts/s and the
other at 2.32° with a high intensity by 150 counts/s. The blend interbasal
spacings are by 38,1 Ǻ  and 10 Ǻ.Figure 7
The XRD diffractogram of
Cloisite 15 A and of the PVOH-starch-4% Cloisite 15 A blend.The possible interactions
between the two polymers and the ions from the silicate galleries enlarge the galleries
by approximately 9Ǻ. These results can be a sign that the settled interactions
between the silicate and the two polymers are of low intensity. The order degree of the resulted
materials is higher because the blend diffraction peak is higher than that of
the silicate. Since the diffraction peaks of the blends are shifted toward
small diffraction angles, it is possible that the obtained material can be an
intercalated nanocomposite.Bentonite has an
interbasal spacing by 12.42 Ǻ  (diffraction peak at 5.56°). The PVOH-starch blend with 4% bentonite
has galleries by 20,3 Ǻ  (diffraction peak at 5,13°) (Figure 8). Because the diffraction peak of the obtained material is shifted
toward small angle, it is possible to exist a degree of intercalation
between the PVOH, starch, and the bentonite that determines a bentonite swelling degree by 7,88 Ǻ. For this reason,
it is possible that the resulted material can be intercalated nanocomposite.Figure 8
The XRD diffractogram of the bentonite and of the PVOH-starch-4% bentonite blends.Natrium montmorilonite has an inhomogeneous morphology
because it contains galleries of different sizes (Figure 9—25,6 Ǻ  for the diffraction from 2,93° and 12,43 Ǻ  for that from 6,85°).
The XRD diffractogram of the blend of PVOH and starch with NaMMT has totally another
shape than that of the silicate alone. On the blend diffractogram, only a very
small diffraction peak appears at 4.92° that means a gallery
by 18 Ǻ. The silicate
galleries enlargement is by approximately 6 Ǻ. Because the
diffraction peak is almost absent, it is possible that the resulted materials to be exfoliated-intercalated
nanocomposites.Figure 9
The XRD diffractogram of NaMMT and of the PVOH-starch-3% NaMMT blend.All the above-presented results are summarized in Table3. In 4
cases from 5, the blend diffraction peaks have different intensities than the silicate
and the galleries are enlarged with 10–20 Ǻ. The order
degree of the resulted materials is smaller or higher because the blends
diffraction peaks have different intensities than the silicates alone. With the
exception of Cloisite 93 A, in all analyzed situation, the diffraction peaks
are shifted toward small angles with (1, 09–3, 8)°. Considering
the greatest shifting value of the blends diffraction peak, it seems that the better
intercalation was registered effects in case of an untreated silicate, NaMMT. If the silicate
enlargement size is
considered, it seems that better intercalation is produced in case of
Nanocor I 28. All these observations
seem to lead to the conclusion that in case of the PVOH and starch blends, the
degree of intercalation of the two polymers with the layered silicate is
increased if layered silicates,  untreated or intercalated with ammonium ions that contain
small radicals, are used.Table 3
The comparison of the XRD diffractograms of the layered silicates with those
of the blends PVOH-starch-layered silicates.
PVOH-starch withNo. of theShifted degree of theGalleries swelling sizeǺDiffraction peaks intensity,Type ofdiffraction peaksdiffraction angle,blend/silicate counts/s/counts/sthe resultedblend/silicate°peak no.1/2/3peak no.1/2/3materialNanocor I 282/21,83/2,18201. 20/60Intercalated/2. 40/150Nanocor I 332/31,64/0,85The same1.70/70Intercalated2.170/120Cloisite 93 A2/3The same5110/110MicrocompositesCloisite 15 A2/24,8/2,1891.30/0; 2.60/100Intercalated3.150/0Bentonite1/13,807,8850/100IntercalatedNaMMT1/21,931850/70Exfoliated-intercalatedBased on the above-mentioned results,
neither the silicate exfoliation degree nor the silicate/lamellas dispersion into
the polymeric matrix of the new obtained materials can be estimated. The TEM micrographs will
bring the necessary information for making estimation about the importance of
the silicate galleries treatment, the silicate exfoliation degree, and dispersion
within the polymeric matrix and on the nature of the resulted nanocomposites
morphology. The TEM micrographs of these blends will be presented in a future
paper.


## 4. Conclusions

The morphology of the material based
on the layered silicate and polymer can be appreciated also based on the XRD diffractograms.
The exfoliated nanocomposites are obtained when the XRD diffractograms do not
contain anymore the diffraction peaks of the silicates. The intercalated
nanocomposites are realized when the diffraction peaks are shifted toward small
angles. The microcomposites appear in case of immiscibility of the polymer with
the silicate. In this situation, the blend peak is overlaped with that of the silicate.The XRD diffractogram also gives
information about the morphologies of the polymer-silicate materials if the
following blend diffractogram characteristics are compared with those of the
silicates: number of the diffraction peaks, shifted degree of the diffraction
peaks, diffraction peak intensity, and silicate galleries swollen degree.In case of the PVOH-starch blends, the
degree of intercalation of the two polymers with the layered silicate is
increased if the layered silicates is untreated or intercalated with ammonium ions that contain small
radicals. If untreated silicate like NaMMT, it is possible to
obtain exfoliated nanocomposites. The materials that contain Nanocor I 28 or
Nanocor I 33 or Cloisite 15 A are of intercalated nanocomposites type. If the blend of PVOH and
starch is reinforced with Cloisite 93 A, microcomposites can be obtained.



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*Source: 538421-2008-12-16.xml*