Materials Sciences and Applicatio n s , 2011, 2, 453-457
doi:10.4236/msa.2011.25060 Published Online May 2011 (
Copyright © 2011 SciRes. MSA
The Evaluation of Polyethylene /Cla y Comp osite
from Solid State NMR
Regina F. Nogueira1, Maria Inês B. Tavares1,2, Rosane A. S. San Gil3, Antônio G. Ferrei ra1
1Departamento de Química, Universidade Federal de São Carlos, São Carlos, Brasil; 2Laboratório de Nanocompósitos Poliméricos,
Instituto de Macromoléculas Professora Eloisa Mano da Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil;
3Departamento de Química, Orgânica da Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil.
Received September 30th, 2010; revised November 12th, 2010; accepted May 6th, 2011.
Polymeric nanocomposites based on polyethylene (PE) and Brazilian natural montmorillonite clay (MN) were obtained
by melt processing, using a twin-screw extruder. The main objective of this work is focusing on the characterization of
composites materials by solid -state nuclear magnetic resonance (NMR). The solid-sta te NMR measurements were used
to observe both polymer matrix (through carbon-13 and hydrogen nuclei) and the clay (silicon-29 and aluminum-27).
The polymer matrix analyses were carried out applying solid state techniques, such as: cross-polarization magic angle
spinning (CPMAS), variable contact time (VCT) and by the proton spin-lattice relaxation time in the rotating frame
parameter (T1
H), detected from the resolved carbon-13 decay of the VCT experiment and through the determination of
spin-lattice relaxation time, T1H (using low field NMR). The clay was analyzed by 29Si and 27Al, employing MAS NMR
technique. From those techniques we can have principally response on clay dispersion in the polyethylene matrix, as
well as the interactions between both components in the nanostructured material. The T1H response was an important
result which showed, that the materials formed, presented different molecular domains (according to the domain size
that varied from 25 to 50 nm, measured by relaxation), considering the clay dispersion mode in terms of intercalation
and/or exfoliation in the polymer matrix.
Keywords: NMR, Polymer, Polyethylene, Clay, Montmo rillonite
1. Introduction
Polymeric composites are class of materials that employ
a mixing of polymer and fibers or inorganic compounds.
According to the type, size and form of inorganic filler
incorporated in the polymeric matrix, polymer compo-
sites possess particular properties, i.e., polymeric nano-
composite. The polymeric nanocomposite morphologies
are a consequence of the formed nanostructure, which
influences directly the final properties of these materials
that are depended on the dispersion mode of the inor-
ganic nanoparticle in the matrix [1-6]. Thus, the know-
ledge of filler dispersion is the key to understand the ma-
terial application and it is also an important point to be
evaluated. Several conventional techniques are normally
used to characterize the filler dispersion, such as: elec-
tronic microscopy (SEM), X-ray diffraction (XRD), Fou-
rier transform infrared spectroscopy (FTIR) and thermal
analyses (DSC and TG). More recently solid-state nu-
clear magnetic resonance has been employed, with suc-
cess, to better understand the nanostructure formed in the
polymeric nanocomposite [7-12]. The success comes to
the fact that solid-state NMR spectroscopy allows ob-
taining information on chemical molecular structure;
components interaction and filler homogeneity dispersion
at molecular level [7-16].
Solid-state NMR has become an indispensable ana-
lytical tool for the study of crystalline and amorphous
materials as silicates; zeolites; concretes and glasses, for
instance [17]. Nuclear magnetic resonance spectroscopy
is the most powerful method to obtain information about
the local environment of the aluminum; 27Al, NMR sig-
nals from 0 to 14 ppm are attributed to octahedral coor-
dinated aluminum [17] and the peaks between 50 and 60
ppm correspond to tetrahedral coordinated 27Al.
It is known that solid state 29Si NMR has been suc-
cessfully applied to the study of a wide range of crystal-
line and amorphous silicates or other related materials
[11]. There are five types of SiO4 tetrahedral units de-
The Evaluation of Polyethylene/Clay Composite from Solid State NMR
Copyright © 2011 SciRes. MSA
signated as Q region (Q0, Q1, Q2, Q3 and Q4) that can be
assigned in the 29Si NMR spectrum. Typical chemical
shift values can be associated to Q region characteristic,
such as: Q0 = 72 to −82 ppm; Q1 = 82 to −89 ppm; Q2 =
92 to −96 ppm; Q3 = 100 to −104 ppm; and Q4 = 110
ppm. Q0 is designated as a single tetrahedron, Q1 as end
group, Q2 a middle group, Q3 a branching site, and Q4 a
cross-linking group [18,19].
The main objective of this work was to study PE/MN
nanocomposites by solid state NMR through 13C (ana-
lyzing the polymer matrix), 27Al and 29Si nuclei (evalua-
ting the clay structure), focusing to understand the dis-
persion and/or interaction between clay and PE poly-
meric chains.
2. Experimental
2.1. Materials
The polyethylene sample used in this study was supplied
by Polibrasil, Camaçari, Bahia, Brazil, with Melt Flow
Index: MFI = 7.0 g/10 mi n, 190˚C/2.16 kg and melting
temperature was 160˚C.
The commercial montmorillonite clay (MMT) was
supplied by Bentonite União Nordeste, Paraíba, Brasil.
2.2. Sample Preparation
The composite of polythene/montmorillonite, prepared at
different ratios (1%, 3%, 5%, 7% and 10%), were ob-
tained by melting in HAAKE 9000 plastograph, coupled
with chamber of mixture Rheomix 600, equipped with a
conical counter-rotate twin scr ew extrud er (TW), at shear
rate of 60 rpm, for 10 minutes at 180˚C.
2.3. Solid State NMR Characterization
High-resolution solid-state 13C NMR spectroscopy ex-
periments were carried out at room temperature in rotor
of 7 mm of Zirconium using a VARIAN, model UNIT-
Plus, 9.4 Tesla, spectrometer operating at resonance fre-
quencies of 100.47 MHz, 104.3 MHz and 79.49 MHz for
13C, 27Al and 29Si, respectively. The 13C CPMAS spectra
were measured with a 6 µs 90˚ pulse, a 2 s pulse delay
time, an acquisition time of 20 ms, and 512 scans. All
NMR spectra were taken at 300 K using broad-band
proton decoupling and a normal cross-polarization pulse
sequence. A magic angle sample-spinning (MAS) rate 6
kHz was used to avoid absorption overlapping. The pro-
ton spin-lattice relaxation time in the rotating frame was
determined indirectly through the decay of each resolved
carbon nucleus using the range of contact time estab-
lished from 200 to 8000 µs, hexamethyl benzene (HMB)
was used as external standard, the methyl carbons were
assigned as 17.3 ppm. The 29Si CPMAS NMR spectra
were recorded with 4 µs 1H 90˚ pulses, 1 ms of contact
time, spinning rate of 6 kHz, and 10 s of recycle delay.
Kaolin was used as external standard. 27Al MAS NMR
experiments were recorded at MAS with 8 kHz spinning
frequency, with 0.2 s of recycle delay and AlCl3(H2O)6
was used as external standard.
3. Results and Discussion
From the resolved 13C nucleus decay pattern from a se-
ries of 13C CPMAS NMR spectra of PE and their hybrids
with MN, we can obtain information on carbon intermo-
lecular interactions and molecular mobility due to its
environmental. The decay profile of PE NMR signal is
typical for one semi-crystalline material. Therefore, for
its composites the profile decay changed to similar be-
havior of amorphous material, which is attributed to MN
incorporation in the polymer matrix due to the changes
promoted in the molecular organization, which gives us
the first indication of some interaction between both
composite components. The changes in the molecular
organization after clay incorporation in the PE matrix
come s f ro m th e fact that the clay could act as a nucleante,
which causes changes in the chains organization from the
morphology created in the new materials, containing
intercalated and some exfoliated clay, even in low con-
centration. From the variable contact time experiment
T1ρH values were determined for each resolved carbon,
and in this case only a signal from PE, at 33 ppm, was
detected. From this NMR signal we could extract infor-
mation on polymer matrix organization and intermolecu-
lar interactions after clay incorporation, because this pa-
rameter is sensitive to local motions in a molecular range
due to its observation in the tens of kilohertz, and then
domains with 1 to 4 nm size are observed since that their
molecular motion s are identical. Ta ble 1 summarizes the
H values determ ined for PE a nd its composites.
From the relaxation values determined for the com-
posites present a higher molecular rigidity comparing to
PE due to the decrease of this parameter, compared to PE
itself. From uniform values of this parameter, it can be
evaluated that these materials have the nanoparticles
homogeneously dispersed, and the molecular domains
have a similar size, this relaxation parameter shows do-
mains in the range of 4 nm. Because T1ρH evaluates in
the rotating frame i.e. it is measured in the tens of kilo-
hertz and it also has contributions from both proton
spin-spin relaxation time and spin-lattice relax ation time,
which makes their values be interpreted in relation to the
homogeneity in the lower scale comparing to the other
two relaxation parameter. Another important point is
related to the TCH time of cross-polarization transfer, only
3% of nanoclay presented lower time to cross-polarize,
which suggests that this clay proportion was better dis-
tributed in relation to the others, showing to be the best
clay ratio for this system. According to the relaxation
The Evaluation of Polyethylene/Clay Composite from Solid State NMR
Copyright © 2011 SciRes. MSA
Table 1. T1
H values and the TCH (time for cross-pola-
rization) determined for each resolved carbons through
variable contact time, for PE and its PE/MN hybrids with
Amo stra TCH
(ppm) T1
PE 207 35 18
PE1%MN 206 33 12
PE3%MN 191 33 11
PE5%MN 201 35 11
PE7%MN 222 33 10
PE10%MN 198 33 10
parameter, good intermolecular interactions are formed
in the nanocomposites components, since the relaxation
parameter decreases the spatial proximity also decreases,
making the chains closer.
Th e op ti mu m 13C CPMAS spectra of PE and its hybrid
composites were recorded to observe changes in the
chemical shift and signal forms. In all spectra just one
NMR signal located at 33 ppm was detected. No signifi-
cant change was found in the chemical shift; however,
significant changes in the signal form are evident, which
supports the modifications in the molecular organizations
after clay incorporation in the polymer matrix. The 13C
CPMAS spectrum for 3% of clay incorporation presented
the base line narrow than the other, which is another in-
dication of the formation of a material with good nano-
particle distribution.
Figure 1 exhibits the 27Al MAS NMR of the hybrid
composites with MN. The 27Al nucleus inform on clay
structural changes, after being dispersed in the polymer
matrix. In this Figure the 27Al MAS hybrid spectrum with
5% of natural clay showed a different profile comparing
to the others, showing strong changes in the clay struc-
ture due to the interaction between both hybrid compo-
nents, which was promoted by a formation of nanomate-
rials with part exfoliated and part intercalated. Then, 27Al
nucleus can be probe to accompany the clay dispersion
and the morphology formed in the nanomaterials. The
same behavior was already observed, using this nucleus
as a probe to evaluate nanocomposite formation for the
polypropylene and organoclay system [6].
Figu re 2 shows the 29Si MAS NMR spectra of PE hy-
brids with MN. Analyzing the solid state 29Si MAS N MR
spectra for the natural clay and its hybrids with PE at
different ratios, it was verified that the natural clay pre-
sented an intensity NMR signal located at 95 ppm (Q2)
and another one less intense in –110 ppm (Q4) [18,19].
For the hybrids with 1 to 5% of clay only a broad signal
centered at 95 ppm were detected, showing strong
changes in the clay organization due to the polymer in-
sertion among the clay lamellae, which would promote
an exfoliated and/or intercalated nanomaterial. The nano-
structured mixed material presents a disorder of clay
structure, which is characteristic of nanomaterial forma-
tion. Therefore, for samples with higher ratio of clay
(from 7% to 15%), they presented narrow signals as was
found for lower clay ratio, suggesting a phase separation,
and consequently no nanocomposite formation. This re-
Figure 1. 27Al MAS NMR of hybrid composites with MN.
The Evaluation of Polyethylene/Clay Composite from Solid State NMR
Copyright © 2011 SciRes. MSA
Figure 2. 29Si MAS NMR of MN and its hybrid c omposites wit h P E.
sult indicates that high quantity of clay cannot be well
dispersed in the polymeric matrix, as it was obtained for
the low ratios, both situations behavior differently the
first one has this behavior because high quantity of clay
are to much to be well dispersed, while low quantity of
clay make them to small to be dispersed due to the local
interactions making th e clay lamellae be together.
4. Conclusions
The work proves that the use of solid state NMR can be
considered an important tool to evaluate the changes in
both polymer and clay. It also permits to infer on nano-
material homogeneity in terms of clay dispersion in the
hybrid material.
This method permitted us to have a view from polymer
matrix and from nanoparticule.
The employment of 27Al and 29Si nuclei, to have re-
sponse from the clay, was good source of information.
Therefore, 29Si nucleus was more sensitive to changes in
the clay organization and was effective to show changes
The Evaluation of Polyethylene/Clay Composite from Solid State NMR
Copyright © 2011 SciRes. MSA
in the clay particle, which proved to be a best source of
information on nanoparticule.
According to the results we can conclude that the main
purpose of this work was achieved.
5. Acknowledgements
The authors would like to thank you FAPESP to support
this research.
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