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Ultrasonication Technique: A Method for Dispersing Nanoclay in Wood Adhesives

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The efficiency of ultrasonication technique to disperse nanoclay in polyvinyl acetate (PVA) was examined. A hydrophilic nanoclay was added to PVA, and its effects on bond strength of wood joints were determined. The results of bond strength measured on block shear tests showed that nanoclay increased the bond strength of wood joints, especially in humid conditions. Atomic force microscopy (AFM) proved that it can be used to examine the quality of nanoclay dispersion in a matrix very precisely. The results of this study showed that ultrasonication technique is efficient in mixing nanoclay with the PVA matrix.
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Journal of Nanomaterials
Volume , Article ID , pages
http://dx.doi.org/.//
Research Article
Ultrasonication Technique: A Method for
Dispersing Nanoclay in Wood Adhesives
Alireza Kaboorani, Bernard Riedl, and Pierre Blanchet
D´
epartement des Sciences du Bois et de la Forˆ
et, Facult´
edeForesterie,deG
´
eographie et de G´
eomatique, Universit´
eLaval,
2425 Rue de la Terrasse, QC, Canada G1V 0A6
Correspondence should be addressed to Bernard Riedl; bernard.riedl@sbf.ulaval.ca
Received  May ; Revised  July ; Accepted  August 
Academic Editor: Gaurav Mago
Copyright ©  Alireza Kaboorani et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
e eciency of ultrasonication technique to disperse nanoclay in polyvinyl acetate (PVA) was examined. A hydrophilic nanoclay
was added to PVA, and its eects on bond strength of wood joints were determined. e results of bond strength measured on
block shear tests showed that nanoclay increased the bond strength of wood joints, especially in humid conditions. Atomic force
microscopy (AFM) proved that it can be used to examine the quality of nanoclay dispersion in a matrix very precisely. e results
of this study showed that ultrasonication technique is ecient in mixing nanoclay with the PVA matrix.
1. Introduction
Adhesives are among some of the most widely used com-
ponentsinstructuralmaterialsduetothewiderangeof
formulations that can be realized, providing a range of prop-
erties under conditions that other joining techniques cannot
oer. Commercialization of wood adhesives in the mid s
generated a momentum for wood industries to diversify their
products and enter into wider markets. Construction eld
was one of the markets which became more accessible to
wood industries. Using adhesives allowed the manufacturers
to fabricate wood composites with dierent sizes and shapes
for the construction while maximizing resource utilization.
epriceofwoodadhesivescoversanimportantpart
of production cost of wood products. As like any other
industries, wood industries wish to bring down production
costs in order to maximize prots. One of the means to cut the
cost is to use low-cost adhesives in fabrication of the products.
Low-cost adhesives usually have inferior properties. One of
the examples of low-cost adhesives is polyvinyl acetate (PVA)
which has been traditionally used for furniture assembly. As
a wood adhesive, PVA has many advantages: nontoxic, with
low negative impact on the environment, easy to use, and with
low volatile organic compounds (VOCs) emissions. However,
PVA has low performance towards water ingress and high
temperatures as well as low creep resistance. e vulnerability
stems from the fact that PVA is a linear amorphous polymer
with weak polar interaction among the molecular chains,
which results in a relatively low glass-transition temperature
(𝑔),near
C.
Low-cost and simplicity of the application of PVA have
convinced some wood products manufacturers to use PVA
as an adhesive in the production of wood components for
structures, despite the fact that PVA is not a heat-resistant
adhesive. Using PVA as a structural adhesive puts the safety
of home owners and re ghters at risk as there is a higher
probability of creep and sudden collapse of wood structures
at high temperatures. In the past research, water resistance
of PVA was mostly addressed, and little work has been done
aboutheatresistanceofPVA.Researchershaveproposed
some solutions to improve the properties of PVA. e
solutions can be divided to two groups: (1)copolymerizing
PVA with more hydrophobic or functional monomers []
and (2)blending PVA with other adhesives or hardeners [
].
Introduction of nanotechnology has opened a new oppor-
tunity to develop new generation of adhesives with prop-
erties that cannot be gained by conventional methods. e
Journal of Nanomaterials
incorporation of nanoparticles into a polymer matrix can lead
to a simultaneous improvement of dierent material prop-
erties [,]. e development of nanoparticles-reinforced
adhesive materials is presently one of the most explored
areas in materials science and engineering. e exceptional
properties of nanoparticles have led to widespread research in
this area. Nanollers provide many advantages over classical
microreinforcements for adhesive materials; for example,
they allow thin bond lines and consequently lower the risk
of embrittlement within the bulk adhesive material, resulting
in improved adhesive tensile strength [].
Nanocomposites, with dispersed nanoparticles, have
been studied extensively due to their capability to improve
mechanical, physical, thermal, and barrier properties with
very low nanoparticles loading of – wt% []. For such
composites, montmorillonite (MMT) and other clay nano-
particles have been used by many researchers []. With
a structure of stacked platelets and one dimension of the
platelet in the nanometer scale, MMT has a high aspect
ratio and specic surface when exfoliated. If the platelets
are dispersed properly, its nanosize can provide a signicant
amountofinterfacebetweentheclayandthematrixresin
with only a small weight percentage of MMT, thus contribut-
ing to the excellent mechanical and physical properties of the
nanocomposites.
Exfoliating the layered structure of the MMT within a
given matrix is crucial to improving the properties of a poly-
mer. Usually dispersing the layered structure of the MMT is a
challenge. Nanocomposite formation involves the migration
or diusion of the polymer into the interlayer galleries of the
layered silicate which push apart or swell the silicate layers.
ere are some techniques to disperse MMT into polymers.
For thermosetting polymer, mechanical mixing is the most
common of the techniques to disperse MMT to a matrix,
while heating is excluded. Mechanical technique includes
several methods such as mechanical mixing, shear mixing,
and ultrasonic mixing.
Ultrasonic irradiation, as a new technology, has been
widely used in chemical reactions. When ultrasonic waves
pass through a liquid medium, a large number of microbub-
blesform,grow,andcollapseinveryshorttimes,abouta
few microseconds. Ultrasonication generates alternating low-
pressure and high-pressure waves in liquids, leading to the
formation and violent collapse of small vacuum bubbles.
is phenomenon is termed cavitation and causes high-speed
impinging liquid jets and strong hydrodynamic shear-forces.
ese eects are used for the deagglomeration of nanometer-
size materials. In this aspect, ultrasonication is an alternative
to high-speed mixers and agitator bead mills. Ultrasonication
hasbeenusedasatechniquetodispersenanomaterialsin
dierent matrices [].
In this study, ultrasonication was used to disperse the
layered structures of MMT and develop MMT-reinforced
PVA adhesives. Such reinforced adhesives can have improved
properties. e main objective of this research is to study the
feasibility of using ultrasonication as a technique to delam-
inate MMT layers and use delaminated, that is, exfoliated,
MMT as nanoreinforcing ller for PVA. e bond strength of
joints glued with newly formulated adhesives was examined
under dierent conditions. Also structures of MMT/PVA
composites (lm) were evaluated as well.
2. Experimental
2.1. Materials. A commercial polyvinyl acetate (PVA) was
received in liquid form. Nanoclay which is low-cost and the
most widely studied nanoller was used as nanoller in this
st u dy. A hyd roph i l ic nanocl ay, name ly, Lit. G-  (polym e r-
grade (PG) montmorillonite) was supplied by Nanocor,
Inc., Arlington Heights, IL, USA. e specic gravity and
cation-exchange capacity (CEC) of the nanoclay were .
and  (meq/ g), respectively. is commercial brand of
nanoclay was chosen as nanoparticles because the past expe-
rience [] has shown that dispersing this type of nanoclay
bythehighshearmixerinPVAisdicultanddidnotresult
in good dispersion. Black spruce (Picea mariana)obtained
from trees grown in Qu´
ebec province was used as a substrate
for wood joints.
2.2. Preparation of Nanoclay/PVA Nanocomposites. Disper-
sion of nanoclay was conducted by a high-intensity ultrasonic
horn ( kHz, maximum amplitude nm from tip to tip,
Branson PG). One-gram nanoclay was added to  grams of
water, and then the solution was ultrasonicated for – min.
e temperature of the solution was kept below Cto
ensure high temperatures due to ultrasonication does not
interfere with the results. To maintain the temperature of the
mixture below C, the vessel with the mixture was cooled
by means of recirculating ethylene glycol bath. Sonication
experiments were carried out with % amplitude and a
volume of  mL of the nanoparticle-water mixture. During
ultrasonication, the sonication power was gradually raised
while maintaining the temperature of the mixture below
C. A certain amount of the ultrasonicated solution was
added to PVA, depending on the percentage of nanoclay in
PVA. Percentage of nanoclay in PVA (ranging from % to
%) was based on solid mass of PVA. e mixtures of PVA
with nanoclay were mixed for min. For X-ray diraction
(XRD), vapor sorption test, atomic force microscopy (AFM),
and transmission electron microscopy (TEM), samples of
nanocomposites were prepared by casting the PVA/nanoclay
composites on Teon sheets. Prior to further analyses, the
sheets of nanocomposites were allowed to dry at room tem-
perature for two weeks.
2.3. Fabrications and Tests of Wood Joints. Mixed solutions
of PVA and nanoclay were used to bond wood samples. A
wood species, black spruce, was used as substrate. Prior to
gluing,themoisturecontentofwoodwasxedat%by
conditioning wood to Cand%relativehumidityfor
twomonths.Aerapplyingglueonthesurfaceofwood,the
samples were pressed in an MTS hydraulic test machine with
 kN capacity at . kg/cm2pressure for two hours. Before
testing, glued samples were conditioned to Cand%
relative humidity (RH) for two weeks. Twenty samples were
tested for each set of formulation.
Journal of Nanomaterials
To evaluate the impact of nanoclay on performance of
wood joints, the shear strength of wood joints was measured
in dry and wet states, and at an elevated temperature. An
MTS hydraulic test machine with  kN capacity was used for
load application, and the data were acquired by a computer.
Wood failure and maximum load were recorded for each test.
Bond strength of adhesive in dry-state was studied on wood
joints made of black spruce. e block shear tests were carried
out according to ASTM D-. e sizes of samples for
“wet-state” tests were the same as those for dry-state tests.
For “wet-state” tests, the samples were taken directly out
of the water aer being immersed in water for  hours.
Before the tests, excess water was wiped o from the samples.
During the water immersion period, temperature of water
was maintained at 23±1C.
Block shear tests at the elevated temperature were car-
ried out according to ASTM -. Samples made of
blacksprucewereheatedinanoven,havingatemperature
controller with an integral and derivative (PID) control
algorithm, until the temperature in the middle of samples
reached C. On average, it took  min to reach Cin
the middle of samples. Aer reaching Cinthemiddle
of samples, the samples were kept at C for  min more,
followed by immediate block shear tests. e shear strength
of samples was measured by an MTS hydraulic test machine.
2.4. Characterization of the Nanoclay/PVA Nanocomposites
2.4.1. Water-Vapor Sorption Analysis. One of main drawbacks
of PVA as a wood adhesive is its vulnerability towards water
and high humidity. PVA has low resistance towards water
becauseoftworeasons.Firstreasonistheformationof
hydrophilic hydroxyl and carboxyl groups during emulsion
polymerization. PVA is usually partially hydrolyzed at the
polymer branches to form hydrophilic hydroxyl and carboxyl
groups appended to the polymer backbone. Second reason
for the poor water resistance is the microscopic pores and
water-soluble surfactant molecules which remain in the lm
allowing water-vapor to penetrate into the adhesive lm
easily []. Any decrease in water-vapor absorption of PVA by
adding nanoclay results in more durable PVA adhesives. In
order to nd out the eect of adding nanoclay on response
of nanoclay/PVA composites to humid environment, lms
of pure PVA and its composites were exposed to various
humidity levels, and weight gain was monitored. e vapor
sorption measurements were carried out at CwithaVTI-
SA symmetrical vapor sorption analyzer, TA Instruments.
e vapor sorption test was conducted in several steps.
Between  and  mg of sample was placed in the chamber.
First, the samples dried at % humidity and C. As the
sample weight equilibrated, the sample was exposed to %,
%, %, %, and % RH, in a stepwise fashion, as the
sample reached its maximum weight in each humidity level.
Overall, the process took about  hrs.
2.4.2. X-Ray Diraction (XRD). Small-angle X-ray scatter-
ing was used to examine eciency of the ultrasonication
technique to increase the distance between the nanoclay
platelets. XRD experiments were conducted by an X-ray
diractometer (Siemens/Bruker) ( kV,  mA) using Cu (
=.˚
A)astheradiationsource.einstrumentconsists
of a Kristalloex  generator, a -circle goniometer, and
a Hi-Star area detector, and it was equipped with GADDS
soware. To measure the distance between nanoclay platelets
before blending with PVA (powder form), the nanoclay
powder was inserted in thin-walled (. mm) glass capillary
tubes (. mm diameter). Increasing interlayer spacing is
identied by a shi of the diraction peak to lower angles,
according to Bragg’s law ( = 2sin ), leading eventually
to featureless patterns (exfoliated structures).
2.4.3. Transmission Electron Microscopy (TEM). Trans m i s -
sion electron microscopy (TEM) allows a qualitative under-
standing of the internal structure, spatial distribution and
dispersion of the nanoparticles within the polymer matrix,
and views of the defect structure through direct visualization.
Analyses were performed on a JEOL JEM-, transmis-
sion electron microscope at kV. TEM specimens, having
– nm thickness, were prepared by ultramicrotoming the
nanocomposite samples encapsulated in an epoxy matrix.
2.4.4. Atomic Force Microscopy (AFM). Atomic force mi-
croscopy (AFM) observations were carried out using a
NanoScope IIIa, an atomic force microscope (Veeco Instru-
ments, Inc.). AFM measurements were done under ambient
air conditions in tapping mode. e sensitivity of the tip devi-
ation and the scanner resolution was .nm. e resolution
was set to  lines by  pixels for all observations. Two
topographicandphaseimageswereobtainedwithineach
sample for scan areas of m× mandm× m.
Surfaceroughnesswascalculatedinm× mscan
areas, using the classical mean surface roughness parameters
𝑎and 𝑞(RMS). e parameters were calculated by the
Nanoscope .rsr soware as follows:
𝑎=1
𝑛
𝑖=1 𝑖−ave,
𝑞=RMS =∑𝑖−ave 2
,
()
where 𝑎isthemeanroughness,thearithmeticaverageofthe
absolute values of the surface height deviations, and 𝑞is the
root mean square of the height, and in both equations 𝑖is
the current value, ave is the average of the values within
the given area, and isthenumberofpointswithinthegiven
area.
2.5. Statistical Analyses. A one-way analysis of variance
model was used to study the eect of nanoclay content on
shear strength of wood joints. e general linear model
(GLM) procedure of the SAS program was used, and pairwise
comparisons were then made using the protected Fisher LSD
(least signicant dierence).
Journal of Nanomaterials
0
20
40
60
80
100
0
2
4
6
8
10
12
Pure PVA 1% nanoclay 2% nanoclay 4% nanoclay
Shear stress (MPa)
Stress
Wood failure
Wood failure (%)
Blend name
F : Bond strength for PVA and its nanocomposites in dry-
state at room temperature. Twenty samples were tested for each data
point.
T : Tabular summary of wood joints tests at various
conditions.
Samples Pure PVA PVA and %
nanoclay
PVA and %
nanoclay
PVA and %
nanoclay
Dry .
(%)
.
(%)
.
(%)
.
(%)
Wet .
(%)
.
(%)
.
(%)
.
(%)
e elevated
temperature
.
(%)
.
(%)
.
(%)
.
(%)
e values given in the brackets are coecient variations (%).
3. Results
3.1. Bond Strength. Results of measuring shear strength of
wood joints in dry tests are shown in Figure and Table .
Although uctuations caused by varying loading of nanoclay
on bond strength were not found signicant, all joints with
nanoclay in their formulations had improved shear strength.
e increase in wood joints strength was between % and
%.estrengthofjointsshowedimprovementsasnanoclay
content increased in the matrix. An increase in bond strength
of wood joints could be measured not only in terms of shear
strength but also in terms of wood failure under shear load.
Inclusion of nanoclay to PVA increased wood failure of wood
joints under shear load (Figure ). Higher wood failure in
joints having nanoclay in their adhesives means that nanoclay
increased the strength of glue line to a level that the strength
of glue line surpassed the strength of wood. It has been
reported that nanoclay improves the mechanical properties of
polymersbyoptimizingthenumberofavailablereinforcing
elements for carrying an applied load and deecting cracks.
Also the coupling between the tremendous surface area of
the clay and the polymer matrix facilitates stress transfer to
Pure PVA 1% nanoclay 2% nanoclay 4% nanoclay
Stress
Wood failure
Shear stress (MPa)
0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
5
Wood failure (%)
Blend name
6
7
8
F : Shear strength of wood joints bonded by PVA and its
nanocomposites aer -hour water exposure. Twenty samples were
tested for each data point.
the reinforcement phase, allowing for mechanical property
improvements [].
Figure and Table give the values of shear strength aer
-hour exposure of wood joints to water. Water exposure
decreased the shear strength of wood joints. e shear
strength of joints made of pure PVA decreased drastically,
dropping down to one-sixth of dry-state. Adding nanoclay
to PVA improved the resistance of glue line towards water.
e extent of improvement was between % and %.
Anyincreaseinnanoclayloadinginthematrixgavea
boost to water resistance of wood joints (at all levels of
loading). Positive eects of nanoclay on water resistance can
be attributed to better barrier properties of glue line.
Past research shows that nanomaterials can improve the
barrier properties of polymers []. e better barrier
properties are associated to the fact that permeate molecules
areforcedtofollowtortuouspathways,reducingthediusion
coecients [,]. In addition, the inclusion of nanoclay
with layered structures and their adhesion to the polymer
generate additional free volume, more likely aecting the
polymeric chains located near interfacial regions [].
Wood failure of joints was aected by adding nanoclay as
well. Wood joints bonded with PVA and % nanoclay showed
small percentage of wood failure under the shear load. e
wood failure could be related to good dispersion of nanoclay
in PVA matrix.
Values of shear strength of wood joints at Care
given in Figure and Table . Nanoclay had a positive eect
on heat resistance of wood joints. e eects were more
pronounced at % loading (resulting in % increase in
shear strength at C). As nanoclay content in the PVA
matrix increased, shear strength of wood joints improved at
the elevated temperature. e extent of improvement was
very signicant at % nanoclay loading. e PVA with %
nanoclay had . times higher shear strength. In our past
Journal of Nanomaterials
Pure PVA 1% nanoclay 2% nanoclay 4% nanoclay
Shear stress (MPa)
Stress
Wood failure
0
000 0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
Wood failure (%)
Blend name
F : Shear strength of wood joints at the elevated temperature
(C). Twenty samples were tested for each data point.
experience [] with a high shear mixer, a decrease in shear
strength of wood occurred at % nanoclay loading because
of poor dispersion of nanoclay in the PVA matrix. Such a
reduction did not occur in this study where an ultrasonic
technique was used to disperse nanoclay particles in PVA.
us, the results showed that using ultrasonic technique to
disperse nanoclay particles in the matrix can enhance the
eectiveness of nanoclay particles in the matrix.
Connement of polymer chains in nanoclay galleries,
restricting the mobility of polymer chains, and the ability of
nanostructure materials to redistribute the deforming action
overthevolumeofthematerialshaveprominentimpactson
improving the bond strength at high temperatures [].
No wood failure was observed in the joints at the elevated
temperature.
3.2. Water-Vapor Sorption. Results of vapor sorption tests are
given in Figure . e negative values of vapor sorption at the
beginning of the tests were related to the fact that the samples
lost weight as they were conditioned at % RH in the rst
step of the tests. Such a conditioning continued until the mass
lossofsamplesleveledo.esameprocedurewasapplied
to other RH levels. e nal values of vapor sorption at %
RH in which the samples reached saturation points were used
to compare the samples performance in the vapor sorption
tests. As nanoclay was introduced to the formulation, values
of vapor sorption decreased. e extent of decrease in vapor
sorption was proportional to nanoclay loading, as the lowest
value of vapor sorption was observed at a formulation with
% nanoclay. e results of vapor sorption tests can explain
the water resistance of nanoclay/PVA composites when used
a wood adhesive.
3.3. X-Ray Diraction (XRD). Generally, the crystalline
structure of nanoparticles has typically been established
using X-ray diraction (XRD) analysis and transmission
5
0
5
10
15
20
25
1 10 100 1000 10000
Vapor sorption (%)
Time (min)
Pure PVA
1% nanoclay 2% nanoclay
4% nanoclay
F : Vapor sorption of PVA/nanoclay composite lm at differ-
ent RH levels.
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Intensity
2𝜃
(A) Nanoclay (1%)
(B) Nanoclay (2%)
(D) Pure PVA
(C) Nanoclay (4%)
(E) Pure nanoclay
(E)
(A)
(D) (C)
(B)
F : X-ray diraction (XRD) patterns of pure PVA, pure na-
noclay, and their nanocomposites.
electron microscopy (TEM). Due to its relative easiness
and availability, XRD is most commonly used to probe
the nanocomposite structure and occasionally to study the
kinetics of the polymer melt intercalation. XRD is used to
probe alterations in the order of silicates by monitoring the
position, shape, and intensity of their basal reections. For an
intercalated structure, the (  ) characteristic peak tends to
shi to lower-angle regime due to the expansion of the basal
spacing. Although the layer spacing increases, there still exists
an attractive force between the silicate layers to stack them in
an ordered structure. In contrast, no peaks are observed in
the XRD pattern of exfoliated polymer nanocomposites due
to loss of the structural registry of the layers.
Figure presents the X-ray diraction proles of pure
PVA, pure nanoclay, and their nanocomposites prepared at
dierent nanoclay loadings. Bragg’s equation was used to
calculate basal spacings of nanoclay from the XRD peak
position. Nanoclay in pure forms had two peaks at .and
Journal of Nanomaterials
..eintensityofpeakat.
is higher than the other.
According to Braggs equation, the distances between clay
platelets were . nm and . nm. Aer mixing nanoclay
with PVA at dierent loadings, both peaks disappeared.
In fact, X-ray diraction proles of PVA nanocomposites
with dierent amounts of nanoclay are like those of pure
PVA. According to the denition of exfoliated structure,
exfoliation is achieved when the individual montmorillonite
platelets no longer exhibit an XRD deection; it can be
concluded that an exfoliated structure was achieved in all
studied cases. It should be noted that it is very hard to
draw any conclusion on structures of nanocomposites solely
according to the results of XRD as some layered silicates
initially do not exhibit well-dened basal reections. us,
peak broadening and intensity decreases are very dicult to
study systematically. erefore, conclusions concerning the
mechanism of nanocomposites formation and their structure
based solely on XRD patterns are only tentative. On the
other hand, TEM allows a qualitative understanding of the
internal structure, spatial distribution and dispersion of the
nanoparticles within the polymer matrix, and views of the
defect structure through direct visualization.
3.4. Transmission Electron Microscopy (TEM). Figure shows
the TEM images for nanocomposites containing nanoclay.
Adding nanoclay at % and % loadings led to good disper-
sion of nanoclay in matrix. e distance between nanoclay
platelets was increased, and the polymer chains entered
between the platelets space. is nanostructure is referred to
as exfoliated structure, giving superior properties to nano-
composites. As can be seen in Figure (c),nanocomposite
with % is composed mostly of intercalated structure with
very large aggregates or tactoids in the order of several tens
of silicate layers. Intercalated structure is not considered an
ideal structure for a nanocomposite, and it does not grant
the nanocomposites with superior properties as exfoliated
structure does. As observed in measuring bond strength
(in dry condition and at the elevated temperature), adding
nanoclay at % and % loadings gave a signicant boost to the
properties, but improvement of the properties at % content
was not much dierent than with nanocomposites with %
and%nanoclays.isphenomenonshouldberelatedto
diculty of dispersing nanoclay in matrix at high loadings.
Past research has shown that there is a direct linkage
between properties of nanocomposites and quality of nan-
oclay dispersion []. In fact, the extent of improvement,
as result of adding nanoclay, cannot be solely proportional
to nanoclay loading because of diculty in obtaining good
dispersion at high loading.
3.5. Atomic Force Microscopy (AFM). Although XRD and
TEMareusedtostudythequalityofnanoclaydispersion
in the polymer, problems involving XRD measurements (for
example, some layered silicates initially do not exhibit well-
dened basal reections) and subjectivity of TEM observa-
tions raise some questions regarding the results obtained
by XRD and TEM. In order to draw a rm conclusion on
structure of nanocomposites, a quantitative technique should
(a)
(b)
(c)
F : Images of PVA/nanoclay composites with dierent
nanoclay loadings ((a) %, (b) %, and (c) %). Scale bar is  nm.
be used. In this study, atomic force microscopy (AFM) was
used to determine the eects of adding nanoclay on PVA
surfacestructure.eAFMimagesforpurePVAandits
composites are presented in Figure .PurePVAhadasmooth
surface as it had low roughness values. As nanoclay was
added to the matrix, a reorganized surface was observed. e
reorganization became more notable as nanoclay loading in
thematrixincreased.At%nanoclayloading,thesurfaceof
PVA lm totally reorganized as a big increase in roughness
values was detected although this roughness is still too small
to be detected by human eye or resulted in light diusion.
eresultsofthisstudyshowthattheultrasonication
techniqueisaneectivewaytodispersenanoclayinthe
Journal of Nanomaterials
2
4
6
8
(𝜇m)
X2𝜇m/div
Z 450 nm/div
(a)
2
4
6
8
(𝜇m)
X2𝜇m/div
Z 450 nm/div
(b)
2
4
6
8
(𝜇m)
X2𝜇m/div
Z 450 nm/div
(c)
10
20
(𝜇m)
X10𝜇m/div
Z450nm/div
(d)
F : AFM images of pure PVA and its composites with dierent nanoclay loadings: (a) pure PVA, (b) % nanoclay, (c) % nanoclay, and
(d) % nanoclay.
PVA matrix. e extent of improvement on PVA per formance
as a wood adhesive was superior or at least similar to that
obtained by high-speed mixing []. When a high-speed
mixer was used to disperse nanoclay at a high loading
(%) in the matrix, a remarkable reduction was observed
in the improvement gained by adding nanoclay. Such a
reduction was not observed in the case of ultrasonic tech-
nique. Although adding % nanoclay to the PVA matrix
resulted in an intercalated structure, nanoclay did increase
the shear strength of wood joints in humid conditions and
at the elevated temperature. e results show that ultrasonic
technique is very ecient in dispersing nanoclay especially at
high loadings, contrary to the high shear speed mixer. High-
speedmixingcoulddispersenanoclayinthePVAonlyatlow
loadings and increased bond strength of PVA in dierent con-
ditions. High-speed mixing has some disadvantages: possible
damage to PVA emulsion (because of strong shear force used
during the mixing), high cost, and high energy consump-
tion. By contrast, ultrasonication technique has minimum
negative impact on PVA emulsion. Moreover, ultrasonication
technique is economical as ultrasonic mixing could take
place before production of PVA and the solution containing
nanoclaycanbeaddedtoPVAduringtheproductionprocess.
By considering the results obtained from this paper and our
previous work [] and by considering the advantages of
ultrasonication technique over high-speed mixing, adding
nanoclay to PVA in an industrial scale seems feasible and can
be recommended to wood adhesive manufacturers.
4. Conclusions
e results of this study showed that ultrasonication tech-
nique is ecient in dispersing nanoclay in PVA at low (% and
%) and high (%) loadings. Bond strength of newly formu-
lated adhesives measured on block shear samples increased
in wet conditions and at the elevated temperature. In dry-
state, the positive eects of nanoclay on strength of glue
line could be observed in terms of wood failure percentage.
e strength of glue line was so high that some failure
occurred in wood rather than in glue line. Improved barrier
properties strengthened the resistance of glue line towards
water, and subsequently signicant increase was observed
in bond strength in the wet-state. Contrary to the results
obtained from dry condition, the extent of improvement
Journal of Nanomaterials
on bond strength in wet-state was proportional to nanoclay
loading. Bond strength of PVA at the elevated temperature
was also aected by adding nanoclay. As nanoclay loading
in the PVA matrix increased, the shear strength of wood
joints at the elevated temperature improved, despite the fact
that the biggest gain in the shear strength was observed
at % nanoclay loading. Vapor sorption tests displayed that
nanoclay reduced vapor sorption of the matrix, explaining
higher water resistance of glue line having nanoclay in their
formulations. e morphological studies of nanocomposites
revealed that the uctuations observed in bond strength
tests were related to dispersion quality of nanoclay in the
matrix (PVA). AFM proved that it is a credible technique to
examine the quality of dispersion as the results of AFM fully
conformed to the TEM observations. At low loadings (% and
%), an exfoliated structure is achieved, causing a signicant
improvement on PVA properties. At high loading (%), a
coexistence of exfoliation and intercalation was observed, and
so improvements on the shear strength of wood joints were
achieved to a lesser extent.
Acknowledgments
e authors acknowledge the nancial support from Natural
Sciences and Engineering Research Council of Canada.
anks are also extended to FPInnovations for their assis-
tance.
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rene,Polymer,vol.,no.,pp.,.
... mm -2 at which, according to EN 314-2 (1992), there is no necessity to specify the percentage of wood failure. The reason for the increase in investigated bonding quality was probably the optimized number of available reinforcing elements for carrying the load and reduction in the presence of cracks (Kaboorani et al. 2013). It was confirmed by Kawalerczyk et al. (2021) that limiting the occurrence of microcracks in the plywood bond lines is one of the crucial factors influencing their strength. ...
... It was confirmed by Kawalerczyk et al. (2021) that limiting the occurrence of microcracks in the plywood bond lines is one of the crucial factors influencing their strength. Moreover, the coupling between the polymer matrix and the tremendous surface area of clay nanoparticles assist the stress transfer to the reinforcement phase (Kaboorani et al. 2013). However, as the concentration of nanofiller increased to 7 pbw, the reinforcing effect was no longer visible and it was probably due to the formation of agglomerates. ...
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The conducted study was aimed at finding the phenol-formaldehyde adhesive formulation containing both the nanoclay and the tannin filler which allows to manufacture water-resistant plywood characterized by the improved properties. The research assumed the application of six experimental variants having a different proportions of the mentioned components which were compared with the mixture prepared according to the industrial recipe. Properties of liquid mixtures such as their gelation time and viscosity were investigated. Moreover, thedifferential scanning calorimetry (DSC) was performed. The manufactured plywood panels were tested in terms of bonding quality, bending strength and modulus of elasticity. Studies have shown that after the adjustment in components proportions it is possible to achieve the proper viscosity level of adhesive mixtures. The results also indicated that thesuitable amount of nanoclay can contribute to the acceleration of resin gel time, however, the DSC analysis showed no effect on its reactivity. The nanoclay concentrations ranging from 2 to 4 pbw (parts by weight) per 100 g of adhesive positively influenced the bonding quality of plywood. Furthermore, there was no clear tendency in case of the effect of applied formulation on the modulus of elasticity and bending strength of plywood. The mixture containing 3 pbw of nanoclay and 5.3 pbw of tannin filler was distinguished as the most beneficial taking intoaccount the improvement in theproperties of manufactured plywood.
... Then, an appropriate amount of PEG as the pore-forming agent was added under constant stirring followed by PES addition into the binary solution at the temperature of 50 • . The introduction of ultrasonic waves into suspension creates small vacuum bubbles in the liquid and then collapse as they reach saturation level in the high-pressure cycle (cavitation) (Kaboorani et al., 2013). This cavitation process from sound energy will agitate the nanoparticles and prevent the aggregation of nanoparticles. ...
Article
Wastewater is inevitably generated from human activities as part of the life cycle chain that potentially damages the environment. The integration of photocatalytic reaction and membrane separation for wastewater treatment has gained great attention in recent studies. However, there are still many technical limitations for its application such as toxic metal release, catalyst deactivation, fouling/biofouling, polymer disintegration, and separation performance decline. Different types, combinations, and modifications of photocatalysts material combined with membranes such as semiconductor metal oxides, binary/ternary hybrid metal oxides, elemental doped semiconductors, and metal-organic frameworks (MOFs) for improving the performance and compatibility are presented and discussed. The strategies of incorporating photocatalysts into membrane matrix for pursuing the most stable membrane integrity, high photocatalytic efficiency, and excellent perm-selectivity performance in the very recent studies were discussed. This review also outlines the performance enhancement of photocatalytic membranes (PMs) in wastewater treatment and its potential for water reclamation. Photocatalysts enhanced membrane separation by inducing anti-fouling and self-cleaning properties as well as antibacterial activity. Based on the reviewed study, PMs are possible to achieve complete removal of emerging contaminants and ∼99% reduction of bacterial colony that leading on the zero liquid discharge (ZLD). However, the intensive exposure of photo-induced radicals potentially damages the polymeric membrane. Therefore, future studies should be focused on fabricating chemically stable host-membrane material. Moreover, the light source and the membrane module design for the practical application by considering the hydrodynamic and cost-efficiency should be a concern for technology diffusion to the industrial-scale application.
... This phenomenon is called cavitation and formed a strong hydrodynamic shear-forces. Therefore, here the ultrasound was created a reinforced interaction between CuWO 4 hollow spheres and layered Sg-C 3 N 4 (Kaboorani et al., 2013). As a result, to form strong interaction between them. ...
Article
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We report a highly selective and sensitive electrochemical sensor for the determination of nitrofurazone (NZ) based on sulfur-doped graphitic carbon nitride anchored with copper tungstate hollow spheres (Sg–C3N4/CuWO4). Here, a Sg–C3N4/CuWO4 composite was synthesized by a facile ultrasonic method. The physicochemical properties of the composite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Then, the surface morphology of the composite material was investigated by field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). Moreover, the electrochemical activity of the as-synthesized composite material was initially tested using electrochemical impedance spectroscopy (EIS). The electroanalytical techniques namely cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were carried out for the electrochemical studies. The proposed sensor exhibits lower LOD and good sensitivity of about 3 nM and 1.24 μAμM⁻¹ cm⁻² to NZ. In addition, the Sg–C3N4/CuWO4 modified electrode showed excellent repeatability, reproducibility, long-term storage stability and excellent selectivity. The developed sensor was successfully applied for the determination of NZ in human urine and serum samples and achieved good recovery results.
... The mechanism of sonication relies on a phenomenon known as cavitation where ultrasonic waves create bubbles within a medium that grows until it collapses violently under the influence of high-and low-pressure waves [38,39]. Richards et al. [40,41] have reported the use of ultrasound to improve chemical reactions. Ultra-sonication makes it possible to work at low temperature and pressure in a one-pot process whilst achieving high yield and reaction rates. ...
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Electromagnetic interference (EMI) shielding has potential importance due to rapid growth in electronic technology. In recent days, carbon nanomaterials and conducting polymer nanocomposites grab much attention for EMI shielding applications. Nanocomposites of polyaniline (PANI) and single-walled carbon nanotubes (SWCNTs) were synthesized by ultrasonically induced in situ polymerization technique. The content of the SWCNT filler is varied as 1, 2, 3, 4 and 5 wt%. Fourier transform infrared spectroscopy was used to quantitatively analyse the functional groups of nanocomposites. Raman spectra revealed good compatibility between PANI and SWCNTs phases. The surface morphology of nanocomposites was analysed by field emission scanning electron microscope. The microwave absorption ability of the nanocomposites was estimated by determining shielding effectiveness in the range of 8.2–12.4 GHz (X-band). The total shielding effectiveness was found to increase with increase of SWCNT phase in PANI matrix and the maximum value of − 32.80 dB at 11 GHz with 99.999% absorption was obtained for 3 wt% of SWCNT sample. Dynamic mechanical properties were studied as a function of temperature. The complex permittivity and electrical conductivity of PANI-SWCNT nanocomposites are also studied. The complex permittivity (ɛ′ and ɛ″) and AC conductivity were found to be higher in PANI-SWCNTs nanocomposites as compared to the PANI. The increasing behaviour has been attributed to the good interaction between SWCNTs and PANI molecular chains. The present results reveal that the current sample materials are suitable for shielding the devices from EMI in X-band frequency region.
... These can cause high local temperature, high speed impinging liquid jets and strong hydrodynamic shear-forces. De-agglomeration of particles can be achieved through these effects [14][15][16]. Thus, large particles size due to agglomeration can be reduced. ...
Article
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The combination of the organic and inorganic materials to fabricate a new form of material called ‘composite’ has been performed since several decades ago. However, the strategy to improve the homogeneity of the resultant composite system is still being the main focus of current research. In this study, dolomite and poly (ethylene-co-vinyl acetate) (PEVAc) were employed as filler and matrix, respectively. Dolomite was ground and ultrasonicated before being used as filler. It can be observed that the size of dolomite particles has been reduced significantly upon the grinding and ultrasonication processes. The effect of ground and ultrasonicated dolomite (GUD) addition on the mechanical performance of the PEVAc copolymer was investigated. Results indicate that the GUD filler has successfully increased the tensile strength, elongation at break, modulus of elasticity and tensile toughness of the PEVAc copolymer when being employed in 1 wt%. However, the use of higher content of GUD resulted in the decreasing trend of those properties. This shows that the ground and ultrasonicated dolomite with smaller and higher surface area particles than its pristine form could bring improvement to the mechanical performance of the copolymer when being used in low loading as it can be more easily dispersed in the copolymer matrix.
Article
The strategic design of energy storage materials from renewable sources has been a keen interest for researchers, especially for energy storage applications. In the present study, ZnCo2O4 and its nanostructures were fabricated along with cellulose nanocrystals (ZnCo2O4@CNC) using the green ultrasonication technique. Structural and morphological examination of composite materials have been investigated by the aid of Field-emission transmission electron microscopy (FE-TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Surface Brunauer-Emmett-Teller (BET) analysis revealing the existence of spherical particles arranged in a controlled nanoscale range (i.e., < 10 nm). The electrochemical properties of ZnCo2O4 and ZnCo2O4@CNC nanocomposites were performed by CV, GCD, and EIS measurements. The ZnCo2O4@CNC electrode reveals a higher specific capacitance value of 346 F/g than its pristine ZnCo2O4 (236 F/g) at 0.5 A/g (current density) in a three-electrode cell assembly. The ZnCo2O4@CNC nanocomposite electrode shows exceptional capacitance with 97 % cyclic retention straight after 5000 cycles at 0.5 A/g with an energy density of 15.8 Wh kg⁻¹ at a power density of 138.4 W kg⁻¹, significantly superior to its pristine ZnCo2O4 composite. The increased specific capacitance of nanocomposite materials manifested by the improved surface and morphological properties convince it as capable materials for high-performance electrochemical capacitors.
Article
DNA solutions were prepared by ultrasonication and purification to compare the characteristics between DNA solutions different in size, purity, or both. Ultrasonication effectively minimized the size variation in native DNA, while purification enhanced the transparency of fabricated DNA thin film. Each DNA solution was used to fabricate water-soluble or organic-soluble thin film. According to the electrical measurement of DNA and CTMA-modified DNA thin films and the fluorescence measurement of PicoGreen-embedded DNA thin films, ultrasonication and purification affect the electrical characteristics and intercalating efficiency of DNA thin films. The electrical properties of the water-soluble thin film and the organic-dissolved thin film were predominantly affected by purification, but opposite tendencies were observed. The highest resistance was observed in water-soluble DNA thin film fabricated from ultra-pure DNA, whereas organic-soluble DNA thin film from ultra-pure DNA showed the lowest resistance. Ultrasonication showed a synergistic effect on PicoGreen-DNA insertion, whereas purification suppressed the fluorescence signal.
Chapter
This chapter evaluated the effect of material formulation and processing parameters on mechanical properties of bioepoxy/clay nanocomposites using Taguchi design of experiments (DoEs). This study was motivated to employ a sophisticated statistical Taguchi DoE approach in a systematic manner for understanding significant material formulation and processing parameters on mechanical properties of bioepoxy/clay nanocomposites and further determining the optimum conditions. The identification of preferred combination of factors in term of material formulation and processing parameters were investigated via Pareto analysis of variance (ANOVA) and then more details regarding the correlation of optimum mechanical properties and morphological structures were elaborated accordingly.
Chapter
This chapter elaborates the material fabrication of both conventional epoxy/clay nanocomposites and bioepoxy/clay nanocomposites, as well as major characterisation techniques used for the holistic analysis of morphological structures, mechanical and thermal properties of such nanocomposites.
Chapter
Despite the popularity of using polymer/clay nanocomposites nowadays, more and more researchers and technologists in wide scientific communities have realised the importance of incorporating biodegradable polymers or biopolymers in nanocomposites systems reinforced with clay nanoparticles due to the urgent requirement of United Nations’ sustainable development goals, climate change, as well as plastic waste crisis. This chapter reviews the most recent advances in biopolymer/clay nanocomposites with respect to material selection, fabrication, optimisation technique in material processing, as well as their mechanical, thermal, biodegradable and barrier properties in order to establish a clear processing-structure–property relationship for such an advanced material system.
Article
To evaluate the feasibility of controlling polymer flammability via a nanocomposite approach, we have examined the flammability properties of nylon-6 clay-nanocomposites. The fire retardant (FR) properties of this new class of materials, organic-inorganic nanocomposites, are reported. The cone calorimeter data show that the peak heat release rate (HRR), the most important parameter for predicting fire hazard, is reduced by 63 percent in a nylon-6 clay-nanocomposite containing a clay mass fraction of only five percent. Not only is this a very efficient FR system, but, it does not have the usual drawbacks associated with other FR additives. That is, the physical properties are not degraded by the additive (clay), instead they are greatly improved. Furthermore, this system does not increase the carbon monoxide or soot produced during the combustion, as many commercial fire retardants do. The nanocomposite structure appears to enhance the performance of the char through reinforcement of the char layer. Indeed, transmission electron microscopy (TEM) of a section of the combustion char from the nylon-6 clay-nanocomposite (five percent) shows a multilayered silicate structure. This layer may act as an insulator and a mass transport barrier slowing the escape of the volatile products generated as the nylon-6 decomposes.
Article
Polymer nanocomposites with layered silicates as the inorganic phase (reinforcement) are discussed. The materials design and synthesis rely on the ability of layered silicates to intercalate in the galleries between their layers a wide range of monomers and polymers. Special emphasis is placed on a new, versatile and environmentally benign synthesis approach by polymer melt intercalation. In contrast to in-situ polymerization and solution intercalation, melt intercalation involves mixing the layered silicate with the polymer and heating the mixture above the softening point of the polymer. Compatibility with various polymers is accomplished by derivatizing the silicates with alkyl ammonium cations via an ion exchange reaction. By fine-tuning the surface characteristics nanodispersion (i. e. intercalation or delamination) can be accomplished. The resulting polymer layered silicate (PLS) nanocomposites exhibit properties dramatically different from their more conventional counterparts. For example, PLS nanocomposites can attain a particular degree of stiffness, strength and barrier properties with far less inorganic content than comparable glass- or mineral reinforced polymers and, therefore, they are far lighter in weight. In addition, PLS nanocomposites exhibit significant increase in thermal stability as well as self-extinguishing characteristics. The combination of improved properties, convenient processing and low cost has already led to a few commercial applications with more currently under development.
Article
Nylon-6−organoclay nanocomposites were prepared by melt processing via twin-screw extrusion for the purpose of comparing the effect of the number alkyl groups attached to the nitrogen of the organic modifier on the level of organoclay exfoliation. Wide-angle X-ray scattering and transmission electron microscopy techniques were employed to assess the morphology developed in each type of nanocomposite, while stress−strain diagrams were used to evaluate mechanical property performance. Nanocomposites derived from an organoclay having no alkyl tails in the quaternary cation result in an immiscible morphology, consisting primarily of unexfoliated clay particles, whereas those derived from an organoclay having one alkyl tail in the quaternary cation lead to a well-exfoliated morphology. Increasing the number of alkyl tails to two produced a mixed structure comprised of a large fraction of clay stacks intercalated with polymer as well as a fraction of dispersed clay platelets. The extent of mechanical reinforcement parallels the degree of exfoliation. Overall, the results may be explained by the competition between the effects of platelet−platelet interactions and the interaction of the polymer with the organoclay platelet.
Article
Mode I fracture cleavage testing was conducted on wood bonded with poly(vinyl acetate-co-NMA) latex adhesive containing two types/degrees of cross-linking: (1) cross-linking through AlCl3 catalysis of N-methylolacrylamide (NMA) comonomer; and (2) additional cross-linking using a phenol-formaldehyde resol additive, in addition to AlCl3 catalysis. The formulation lacking the phenolic additive performed well under dry conditions; but it completely failed during testing as a result of accelerated weathering. In contrast, fortification with the phenolic additive provided durability against accelerated weathering. In an effort to understand the effects of accelerated weathering, parallel-plate dynamic mechanical analysis was applied to freestanding neat adhesive films and to wood-bonded films (composites). Accelerated weathering dramatically altered the viscoelastic response of films and composites that lacked the phenolic additive; weathering caused a second, broad and reversible relaxation near 100 degrees C, which might be because of softening of the poly(vinyl alcohol) interfacial agent used during emulsion polymerization. In contrast, samples formulated with the phenolic additive only displayed the typical base-polymer glass transition. Correlation of the fracture testing and the rheological analysis suggests that the phenolic additive promotes adhesive durability by cross-linking the interparticle boundaries, where poly(vinyl alcohol) is believed to reside.