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Progress in Organic Coatings 61 (2008) 76–82
Alumina and zirconia acrylate nanocomposites coatings for
wood flooring: Photocalorimetric characterization
V´
eronic Landry a, Bernard Riedl a,∗, Pierre Blanchet b,a
aUniversit´e Laval, D´epartement des sciences du bois et de la forˆet, Qu´ebec, Canada G1P 7P4
bForintek Canada Corp., Value-Added Products Department, Qu´ebec, Canada G1P 4R4
Received 22 March 2007; accepted 10 September 2007
Abstract
Radiation curable coatings are presently the standard in wood flooring industries, although important improvements can still be brought to these
coatings. In this work, nanocomposites coatings for wood flooring were prepared from various acrylate reactives. Nanoparticles were added in
the neat acrylate formulation prepared from two acrylate monomers, two acrylate oligomers, a defoaming agent and a photoinitiator. Particle size
characterization was performed by a dynamic light scattering technique. Reinforcing agents and coupling agents addition effects on acrylate resin
conversion were studied by photo-calorimetry (photo-DSC). For each nanocomposite sample, heat of reaction and induction time were determined
from exotherms and these datas were used to study the effects of reinforcing agents and coupling agents on curing kinetics of radiation curable
nanocomposite coatings. Photo-DSC studies show that nanoparticles and coupling agent clearly affect coatings polymerization. In fact, zirconia
nanoparticles tend to decrease polymerization. Alumina nanoparticles do not affect negatively curing coatings. Silane coupling agent affects
positively the curing of acrylate coatings, although zirconate coupling agent tends to decrease it.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Nanocomposites; UV curing; Acrylates; Photopolymerization; Wood flooring coatings
1. Introduction
Many nanocomposites studies were published in the last
decade. Thermoplastic polymers like polyolefins (PP and PE),
polyurethanes, polyimides and nylons are among the most stud-
ied matrices [1]. Their uses in the automotive and aerospace
industries explain the widespread interest for new and improved
products. In many cases, fillers and coupling agents are added
in polymers to enhance properties. The most used fillers are
aluminum oxide (Al2O3), clay, calcium carbonate (CaCO3), sil-
ica (SiO2) and titanium dioxide (TiO2). Studies show that their
addition in polymers is often related to a great improvement
of mechanical properties. Improved scratch and impact resis-
tance, Young’s modulus, modulus of rupture are among the
most researched properties for thermoplastic nanocomposites.
Flame, fire and moisture resistance seem to be improved by
clay introduction and exfoliation in thermoplastic polymers [2].
Thermoset nanocomposites studies are fewer than those per-
∗Corresponding author. Tel.: +1 418 656 2437; fax: +1 418 656 5262.
E-mail address: bernard.riedl@sbf.ulaval.ca (B. Riedl).
formed for thermoplastic matrices. Processes with the first ones
are more difficult to develop and applications, even if they cover
a wide range of industries, are less diversified than for ther-
moplastics. Adhesives and coatings are two very widespread
industries which are both under continuous development and use
large quantities of thermoset polymers, especially epoxies and
acrylates. The uses of reinforcing agents in these industries are
quite important and this is one of the reasons why nanocompos-
ite studies are popular presently. Epoxy nanocomposites studies
in the last few years shown a strong increase. Montmorillonite
exfoliation in epoxy polymer was one of the major interest [3,4].
Exfoliated nanocomposites were shown to increase the Young’s
modulus [5] and fracture toughness [6]. Nanocomposites were
also prepared with carbon fiber and silica [7]. Those prepared
with carbon nanofiber presented higher temperature perfor-
mance capability, better mechanical performance, an extreme
environment corrosion resistance and an improved dimensional
control compared to neat epoxy. Epoxy–silica nanocomposites
showed elastic modulus improvement and epoxy glass transition
increased.
Acrylate thermoset nanocomposites studies started to be pub-
lished in 2000 [8]. These studies are largely due to the growth of
0300-9440/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.porgcoat.2007.09.013
V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82 77
UV radiation curable coatings in many industries. These coat-
ings, developed in the last 1970s, now have a wide market share
in all the important coatings areas (metal, plastic and wood) and
are still under development. UV curing is an important tech-
nology for printing inks, overprint varnishes, adhesives, food
packaging and in the electronic devices industries. UV coatings
present an important advance for the finishing technology. In
fact, their curing rate and mechanical performance make the UV
coating technology very popular for many wood industries [9].
While wood flooring industries have switched to UV technol-
ogy 10 years ago, they are still looking for mechanical resistance
improvement, especially with regard to scratch and wear resis-
tance. To obtain a strong and resistant coatings, curing has to be
well done. The photo-calorimetry technique is certainly among
the best ways to evaluate and to quantify UV curing.
In the last 5 years this technique appeared to be a state of the
art technique to study radiation curable coatings. A small number
of studies have been published on photo-DSC technique, and the
technique already has shown a great analytical potential. Popular
topics studied with photo-DSC are oxygen inhibition [10–12]
of photocured systems, acrylate polymerization kinetics [13],
influence of monomers and oligomers structure on photocur-
ing rate and new photoinitiators efficiency [14,15]. Recently, a
few studies on acrylate nanocomposite were reported. Cho et
al. [16] have studied the effects of different loadings of silica
nanoparticles in acrylate formulations. They studied the heat of
reaction and curing rate as a function of silica loading. Similar
studies were performed for clay nanocomposites coatings [17].
In this study, nanoclay particles were added in the formulation
as well as alumina and zirconia nanoparticles in a typical wood
UV curing formulation. Coupling agents were also considered
in those formulations. Photo-DSC was used to study the effect
on polymerization rate and amount. The effects of nanoparticles
and coupling agents introduction on curing of radiation curable
coatings were investigate by the aim of Photo-DSC.
2. Materials and methods
2.1. Materials
Basic formulation was prepared from two acrylate monomers
and oligomers. The acrylate monomers which were used are 1,6
hexanediol diacrylate (HDODA, SR 238, 9 cps) and tripropylene
glycol diacrylate (TRPGDA, SR 306, 15 cps), two bifunctional
monomers. HDODA is a low viscosity and fast curing monomer.
TRPGDA has a low volatility and viscosity. The oligomers
chosen are an aliphatic polyester-based urethane hexaacrylate
oligomer (CN 968, 18,000 cps) and a difunctional bisphenol
A-based epoxy acrylate blended with TRPGDA (CN 104A80,
36,000 cps). CN 968, an hexafunctional oligomer which shows
good abrasion and heat resistance, is also a fast cure response
monomer. CN 104A80, a high reactivity bifunctional acrylate,
is the lowest color bisphenol A-based epoxy acrylate. More-
over, it provides a good balance of water properties and high
reactivity. All acrylate products were provided by Sartomer.
The free-radical photoinitiator chosen is 2-hydroxy-2-methyl-
1-phenyl-1-propanone (Darocur 1173) from Ciba Specialty
Table 1
Properties of the three different nanofillers used in this study: mean particle size,
surface area and refractive index
Properties 1-Al2O32-Al2O3ZrO2
Hardness (Mohs scale) 9 9 6.5
Surface area (m2g−1) 100 ±15 Unknown 15–40
Mean particle size (nm) 13 40 30–60
Refractive index 1.7–1.8 1.7–1.8 2.13–2.20
Chemicals. This one decomposes in a benzoyl radical and an iso-
propanol radical, both able to initiate and propagate quickly the
free radical polymerization. Darocur 1173 is a liquid photoini-
tiator with good solvency properties so is easy to incorporate
in acrylate formulation and is recommended for minimal yel-
lowing. This photoinitiator presents UV absorption peaks in
methanol at 245, 280 and 331 nm.
Four different reinforcing agents were added in the basic for-
mulation, three nanofillers and one comparative micrometric
filler. The last was a 5m alumina, mostly used in UV top-
coat for wood flooring applications. The three nanofillers chosen
were two aluminas and one zirconia. The first nanometric alu-
mina was received in powder form and the second was received
already dispersed at 30% (w/w) in one of the acrylate monomers
used in this study, TRPGDA. Zirconia was also received in pow-
der form. Table 1 compares the properties of the nanofillers:
mean particle size, surface area and refractive index in visible
light.
Two coupling agents were also added into the different formu-
lations in order to enhance the coupling between the metal oxide
fillers and the acrylate matrix. Silanes are the most used coupling
agents in radiation curable coatings and in paint and coatings
in general. A methacrylfunctional silane that can be used as
adhesion promoter, surface modifier, co-monomer for polymer
systhesis and crosslinker was our first choice (a trimethoxysi-
lylpropylmethacrylate, Dynasylan MEMO, from Degussa). The
alkoxy group undergoes hydrolysis then reactive silanol groups
produced can bond to a variety of inorganic substrates with
hydroxyl groups, like alumina. A zirconate coupling agent
was also used, neopentyl(diallyl)oxytriacrylatezirconate, NZ 39,
from Kenrich Petrochemicals. Due to proton reactivity of zir-
conate, mixer and all laboratory accessories were beforehand
washed with isopropanol solution of zirconate. Silane coupling
agent was added at 1% (w/w) of nanoparticles and zirconate
coupling agent at 2% (w/w) of nanoparticles, following man-
ufacturer’s specifications. These coupling agent were added in
two different ways in the neat acrylate formulation, as described
in the following section. Fig. 1 shows the structure of both
coupling agents.
2.1.1. Neat acrylate formulation
Basic acrylate formulation was prepared from acrylate
monomers and oligomers, defoming agent and photoinitiator.
The two acrylate oligomers were first mixed together, then
defoming agent was added. Mixing was performed for 5 min.
Then, monomers were added and mixed again for 5 min. If
needed, fillers and coupling agent can be added, as explained
78 V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82
Fig. 1. (a) Silane coupling agent: 3-(trimethoxysilyl)propyl methacrylate; (b)
zirconate coupling agent: neopentyl(diallyl)oxytriacrylate.
in the following section. Photoinitiator was always added at the
end of the mixing process to prevent as much as possible the
evaporation of this reactant.
2.1.2. Nanocomposites preparation
Nanocomposites were prepared by in situ and ex situ method.
Both methods are presented in the literature, despite only the
first one being used in industry. In the first case, nanoparticles
were added into basic acrylate formulation, and then coupling
agent was added. Formulations were mixed for 10 min with high-
speed mixer in order to favorise coupling between filler and
coupling agent. Photoinitiator was the last component added.
For ex situ method, fillers were first refluxed under nitrogen
atmosphere for 8 h in ethanol. Coupling agents were added at
the beginning of the reflux. Once this treatment was completed,
solvent was evaporated and the treated particles were washed
three times with fresh ethanol. Table 2 presents the composition
of the different formulations.
2.2. Methods
Metal oxide dispersion was assessed by a particle analyser,
Zetasizer Nano ZS, from Malvern instruments. This apparatus
allows the determination at higher particle concentration then
Fig. 2. Spectral distribution of the Hamamatsu UV light source (02 type).
conventional light scattering techniques. Back scatter technol-
ogy increased the concentration limits and the sensitivity of the
technique. In a conventional light scattering apparatus, detec-
tion angle is 90◦, the maximum sample concentration is affected
by the multiple scattering. NIBS detection is performed at 173◦
which is very helpful to decrease multiple scattering. Then, sam-
ple concentrations can be as high as 5% (w/w), depending of
particle size. Zetasizer Nano ZS allows to determine particle
size distribution of highly concentrated solutions. Metal oxide
dispersions were prepared in HDODA in a ball mill for 2 h. Z-
average diameter and polydispersity index (PDI) are presented
in this paper.
The impact of nanoparticles addition on curing behavior
was evaluated with a Photo-DSC (DSC822e from METTLER-
Toledo). The UV source used is LightningcureTM L8333, which
is a Mercury–Xenon lamp (240–400 nm) from Hamamatsu with
a maximum absorption at 360 nm. Fig. 2 presents the output
curve of the UV lamp used. Nanocomposites samples pre-
pared for these experiments were prepared at 2.0 ±0.1 mg and
they were cured at an intensity of 40 mW cm−2at a thick-
ness of 200 m. Experiments were performed under air flow
of 50 ml min−1at 30 ◦C. Heat of reaction and induction times
are obtained from exotherms. Kinetic parameters of the dif-
Table 2
Composition of the different formulations
Name Monomer Oligomer Filler Coupling agents
g±0.1 g±0.1 g±0.1 Filler Addition Type g±0.01
B 27.7 68 0 0.00
A1 26.3 64.7 8 Al2O35m In situ 0.00
A2 26.3 64.7 8 2-Al2O3In situ 0.00
A3 26.3 64.7 8 1-Al2O3In situ 0.00
A4 26.3 64.7 8 1-Al2O3In situ Silane 0.08
A5 26.3 64.7 8 1-Al2O3Ex situ Silane 0.08
A6 26.3 64.6 8 1-Al2O3In situ Zirconate 0.16
A7 26.3 64.6 8 1-Al2O3Ex situ Zirconate 0.16
Z1 26.3 64.7 8 ZrO2In situ 0.00
Z2 26.3 64.7 8 ZrO2In situ Silane 0.08
Z3 26.3 64.6 8 ZrO2In situ Zirconate 0.16
V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82 79
ferent formulations like reaction orders and rate constant were
determined.
3. Data reduction
Photo-DSC allows the obtention of an exotherm related to the
radiation curing of the acrylate coatings. Thermosetting resins
have two general kinetics models: nth-order and autocatalytic
models. The first one can be expressed by the following equation:
dα
dt=k(1 −α)n(1)
where dα/dtis the reaction rate given in s−1,αthe extent of
reaction or the fraction conversion after time t,kthe specific
rate constant and nis the reaction order. The radiation curable
coatings studied here follow an autocatalytic model. This model
was first introduced by Kamal [18], processes following the auto-
catalytic model can be represented by the following equation:
dα
dt=(k1+k2αm)(1 −α)n(2)
k1is the externally catalyzed rate constant and k2is the autocat-
alyzed rate constant with Arrhenius temperature dependency.
The reaction orders m and n represented, respectively the
initiation and propagation step. If the initial rate of the reaction
is negligible, Eq. (2) can be reduced to
dα
dt=kαm(1 −α)n(3)
For both models, temperature dependence of the specific
constant rate, k, was assumed to follow the Arrhenius equation
presented below:
k=Aexp −Ea
RT (4)
where Ais the frequency or the pre-exponential factor which is a
constant, Eathe activation energy of the system, Rthe universal
gas constant (8.31 J mol−1K−1) and Tis the temperature.
Parameters dα/dtand αcan be both obtained from the DSC
curves. The reaction rate, dα/dt, is given by (dH/dt)/H0and α,
the extent of reaction, by Hp/H0.Hpis the curing enthalpy
after time tand H0is the maximum enthalpy, calculated from
the area under the DSC curve.
Fig. 3. Representation of autocatalytic model and experimental cure for formu-
lation.
Fig. 4. Size distribution of nanoparticles for HDDA with 30% (w/w) of Nanobyk
3602.
Autocatalytic model data fit is presented in Fig. 3. Points rep-
resent the experimental data obtained for our basic formulation
and full line is for the autocatalytic model.
4. Results and discussion
4.1. Zetasiser experiments
Fig. 4 presents an example of the results obtained with Zeta-
sizer Nano ZS for a dispersion of Nanobyk in HDODA, one of
the monomer used in this study. In this case, particle size dis-
tribution is relatively sharp so only one peak is present on the
resulting graph and the absence of peaks at higher sizes show
absence of aggregation. Table 3 presents the results obtained for
the different nanofillers in HDODA monomer at different con-
centrations. Mean particle size (nm) are presented in this table.
Dispersions of 2-Al2O3were done from 0.5% to 30% (w/w)
and no aggregation was observed, even at 30% (w/w). 2-Al2O3
is a commercial dispersion of nanometric alumina. Particle size
given by the manufacturer for those nanoparticles is 40 nm. Zeta-
sizer studies give particle size (Z) from 35.5 to 37.2 nm, which
are very close to company values. This means that aggregation
is not important in this case. 1-Al2O3and ZrO2dispersions con-
centrations are 0.1, 1 and 1.5% (w/w). Zetasizer apparatus allows
analysis of very concentrated samples, up to 30% (w/w), but
strong aggregation prevents good analysis and results obtained
are often incorrect. Polydispersity index (PDI) is a measure of
the width of the particles dispersion. Polydispersity index (PDI)
inferior at 0.2 is related of a narrow dispersion and PDI val-
ues superior at 0.2 represents a broad dispersion. Polydispersity
indexes of 1 were found for concentration dispersions up to 1.5%
Table 3
Mean particle size (Z) of the alumina zirconia dispersions in HDODA
Name % (w/w) Z(nm)
2-Al2O30.5 35.5
2-Al2O31 35.6
2-Al2O35 36.7
2-Al2O310 35.7
2-Al2O320 37.7
2-Al2O330 37.2
1-Al2O30.1 40.8
1-Al2O31 42.2
1-Al2O31.5 129.9
ZrO20.1 62.8
ZrO21 101.5
ZrO21.5 210.0
80 V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82
Table 4
Heat of reaction, conversion percentage and induction time of the formulations
Formulations H(J g−1)%
conv. tind (s)
A1 379 87.1 0.21
A2 333 76.5 0.27
A3 372 85.5 0.27
A4 401 92.18 0.21
A5 361 82.9 0.24
A6 369 84.8 0.22
A7 359 82.5 0.24
Z1 341 78.4 0.26
Z2 350 80.5 0.25
Z3 329 75.6 0.25
Neat 370
(w/w) of nanoparticles. These results mean that strong aggrega-
tion occurred for Al2O3and ZrO2dispersions as performed in
our laboratory. PDI values of 1 also revealed that the distribu-
tion of particle size in those formulations is very broad, single
nanoparticle and aggregates of different sizes being both present.
Zetasizer experiments showed that for a concentration of more
than 1.5% (w/w), the nanoparticles can easily form aggregates in
acrylate formulations. As the formulations studied in photo-DSC
were prepared at 4% (w/w) of nanoparticles, aggregates and also
nanoparticles at single state were present in formulation.
4.2. Photo-DSC studies
Table 4 shows the results obtained from the exotherms of
the different formulations. Heats of reaction, induction times
and conversion percentages are presented in this table. For a
thermoset material, the heat of reaction represents the curing
amount which is proportional to consumption of double acry-
late bonds and crosslinking density. Heats of reaction obtained
for the different formulations go from 329 to 401 J g−1. For-
mulation A2, prepared with Nanobyk 3602, present poor heat
of reaction. It means that a higher percentage of acrylate moi-
eties in formulation remains unreacted. Zirconia nanocomposite
coatings showed poor heats of reaction compared to neat acry-
late formulation and alumina nanocomposite coatings. The high
value of zirconia refractive index can explain these results. In
fact, light scattering by zirconia can decrease the reactivity of
the formulations.
The formulations prepared with 1-Al2O3(A3–A7) gave bet-
ter results but the heat of reaction values vary a lot depending of
the coupling agent used and the addition technique employed.
In fact, in situ preparation gives better results then ex situ prepa-
ration for both coupling agent. For DYNASYLAN MEMO, the
silane coupling agent used, heat of reaction drops from 401 to
361Jg
−1and for NZ 39, the zirconate coupling agent, from 369
to 359 J g−1. For the same preparation technique, silane cou-
pling agent shows better results than zirconate. This situation
is observed for alumina and also for zirconia nanocompos-
ites. Silane and zirconate coupling agents have different ways
to form bonds between molecules, although silanes are some-
times preferred because their chemistry is more simple than
zirconates. Although some comparative studies were performed
Fig. 5. Exotherms obtained from alumina–acrylate nanocomposites (a) with the
different aluminas used in this study (b) with the silane and zirconate coupling
agent with in situ and ex situ methods.
between silanes and titanates/zirconates coupling agent, in some
cases, titanates and zirconates have shown good results. Like
silica, alumina and zirconia used in this study are two metal
oxides who can easily react with silane. Exotherms obtained
for all the formulations prepared in this study are shown in
Figs. 5(a and b) and 6, respectively for the alumina and the zirco-
nia nanocomposites. It is possible to see the difference between
the curing of the different formulations.
The induction time is the time necessary to attain 1% of con-
version. The induction time can be influenced by many factors
including photoinitiator efficiency and oxygen inhibition. In this
study, experiments were performed under air flow, so oxygen
Fig. 6. Exotherms obtained from zirconia–acrylate nanocomposites.
V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82 81
Table 5
Kinetic parameters (k,m,n) of the autocatalytic model for each nanocomposite
formulations
Formulations mn k(s−1)
Neat formulation 0.53 1.46 0.92
A1 0.53 1.42 0.92
A2 0.48 1.5 0.74
A3 0.52 1.47 0.94
A4 0.57 1.47 0.99
A5 0.53 1.44 0.96
A6 0.52 1.52 0.97
A7 0.53 1.44 0.94
Z1 0.47 1.55 0.73
Z2 0.52 1.48 0.80
Z3 0.51 1.50 0.85
inhibition occurs. Still, results presented in Table 4 show that
filler and additive type can also influence the induction time.
Induction times found here are related to heat of reaction. In
fact, the more complete is the reaction, the higher the heat of
reaction and the shorter the induction time are. It means that the
length of the induction period is closely related to the final state
of the coatings.
Table 5 presents the reaction orders and the rate constant
of the autocatalytic model for the different nanocomposite for-
mulations. Main differences between formulations came from
the rate constant. Neat formulation present a rate constant of
0.92 s−1. Addition of 4% (w/w) of micrometric alumina (A1)
did not change the rate constant of the radiation curing. Nanobyk
addition, though, changes drastically the curing rate of the coat-
ings. In fact, reaction is highly slowed down by the addition of
4% (w/w) of these nanoparticles which were already dispersed.
Formulations prepared from nanoparticles powder showed a
completely different behavior. In fact, no decrease in the reaction
rate was observed. A slight increase was actually observed for
all the samples. The higher rate constant value is for A4 sample,
where silane coupling agent was added by in situ technique. This
sample also shows the higher conversion percentage and heat of
reaction. Sample prepared with silane coupling agent by ex situ
technique shows a reaction rate slightly inferior than A4 sam-
ple. The same situation was observed for the heat of reaction
and conversion percentage. Zirconate coupling agent addition
shows basically the same behavior than silane. In fact, in situ
preparation technique gives higher reaction rate and conversion
than ex situ preparation.
According to results obtained for aluminum oxide formula-
tions, in situ preparation method only was used for formulations
prepared with zirconium oxide only. In this case, silane still
shows a conversion and reaction rate higher than zirconate cou-
pling agent. If we compare the zirconium oxide formulation with
silane with any others formulations prepared with aluminium
oxide, except the one with Nanobyk, the rate constant is very low.
An hypothesis for the explication of this result is the increase
of light scattering caused by the high refractive index of zir-
conia, around 2.14. This one is really high compared to those
of alumina and acrylate resin. In order to keep transparency of
the acrylate coatings, particles added have to present a refractive
index close to the one of the acrylate resin. The different acrylate
components of the formulation used in this study present refrac-
tive index from 1.456 to 1.534. These values are smaller then the
refractive index of zirconia. On the other hand, alumina presents
a refractive index near that of the acrylate products. In fact, the
alumina refractive index is between 1.7 and 1.8, depending of
the particle size of alumina. Thus, refractive indexes values can
explain the lower curing of the radiation curable coatings studied
here.
However, refractive index hypothesis cannot explain the
rate constant reduction observed for formulation prepared from
Nanobyk dispersion. Silane and zirconate coupling agents give
very different results. For zirconia and alumina nanocomposites,
silane improves the heat of reaction. Silanes are the most studied
and used coupling agents in the paint and coatings industry. They
have been used in the past majoritarely with silica particles, even
if some studies reported enhancement of mechanical properties
when silanes are added to alumina and zirconia composites. Sil-
ica shows a higher density of hydroxyl groups then alumina and
zirconia and good improvement have been observed in this study.
Zirconate molecules are highly different from silane. Accord-
ing to literature, zirconate could react in different ways with
fillers. Neoalkoxy type titanate, like the one used in this study,
have been reported to react with surface protons at the inorganic
interface of the particles resulting in the formation of matrix
compatible/reactive monomolecular layers on the inorganic sur-
face. Although, results obtain in this study did not show curing
improvement with zirconates addition.
5. Conclusion
Coatings formulations were prepared with 4% (w/w) alumina
and zirconia nanoparticles. Two coupling agents were added
in these formulations, silane and zirconate. They were added
by in situ and ex situ technique. Zetasizer experiments show
that commercial dispersion of alumina nanoparticles present a
very narrow particle size distribution compared to dispersions
performed in our laboratory. From the exotherms obtained for
each formulation, heat of reaction and induction times were
determined. They follow the same trend, a higher conversion
associated with a shorter induction time. Photo-DSC shows that
acrylate coatings of this study follow the autocatalytic model.
The kinetic paramaters (k,m,n) of the autocatalytic model allow
the comparison of the rate consumption of the acrylate bond
for the different formulations. In situ preparation clearly shows
better results in terms of rate of reaction and conversion than
results obtained with ex situ preparation. The formulation which
has presented the higher level of curing and the higher rate of
reaction is the formulation A4, prepared with alumina nanopar-
ticles with silane in situ preparation. Silane addition gives better
results than zirconate addition. For both alumina and zirconia
nanocomposites, conversion of acrylate resin is faster and more
important with silane. Addition of zirconia decreased the quality
of the curing. The conversion and the rate are both decreased
by this filler. Silane improves slightly the curing quality but the
heat of reaction and the rate constant remains lower than for neat
formulation and the major part of the formulation prepared from
alumina.
82 V. Landry et al. / Progress in Organic Coatings 61 (2008) 76–82
Acknowledgements
Authors wish to thank Economic Development Canada,
Forintek Canada Corp., the National Sciences and Engineering
Research Council of Canada trough its industry-university grant
program and Chemcraft International.
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