Influence of Magnesium Oxide Nanoparticles on the Compressive Strength of Urea Formaldehyde Resin

Abstract

Urea Formaldehyde (UF) resins have good chemical resistivity and high thermal stability, making them an excellent choice in the construction industry. They, however, pulverize quickly and have low strength and toughness. In this work, magnesium oxide (MgO) nanoparticles were added to UF as nanofillers to influence its compressive strength. MgO nanoparticles were synthesized by reducing magnesium nitrate at different concentrations, using orange peel extract. X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) techniques were used to confirm the formation of MgO nanoparticles. XRD results showed the formation of 43 nm, 35.28 nm, and 32.5 nm sized nanoparticles for 0.1 M, 0.2 M, and 0.4 M concentrations respectively. The varying-sized MgO nanoparticles were used for the preparation of UF/MgOnanocomposite at different weight-percentage (wt-%) ratios. A comparative study on the compressive strength of Urea Formaldehyde resins and UF/MgO was performed. From the results, it was found that the addition of MgO nanoparticles to UF resin enhances the compressive strength at certain wt-% ratios.

Full text

Journal of Nepal Chemical Society, June/July 2022, Vol. 43, No. 1 K.P. Sharma, P. Ghimire and U. Neupane
95 https://www.nepjol.info/index.php/JNCS
Introduction
Nanostructured crystalline particles have caught
the interest of researchers attributable to the wide
range of applications made possible by their particle
size-dependent properties, as well as their scientic
and industrial signicance [1]. Nano-sized particles
of metal oxide materials have received attention
in various industrial, medical, environmental, and
agricultural applications [2]. Recently, metal oxide
nanoparticles are also used as antibacterial agent
[3]. These nanomaterials have distinct thermal,
structural, and electronic properties that entrust
them with a high level of scientic interest in both
basic and applied elds [4]. One metal oxide, i.e.,
magnesium oxide (MgO), has high thermodynamic
stability, low dielectric constant, and large band gap,
making it a material of magnicent technological
importance in the construction industry [5]. MgO
has non-combustible properties, high stability, a
high specic surface area, and a higher specic heat
capacity, making it effective toughening ller without
compromising the properties on which they are added.
Researchers are currently investigating materials with
the properties of high thermal stability, good chemical
resistivity and excellent ame retardancy for the use
in construction materials to increase the safety.
UF has been promoted as a suitable choice for
satisfying the aforementioned construction industry
demands[6].This increases the wide application range
of UF composite. However, UF lacks active functional
groups due to which it is brittle, pulverizes quickly, and
Inuence of MagnesiumOxide Nanoparticlesonthe Compressive Strengthof
Urea Formaldehyde Resin
Susma KC1, Nelson Rai2, Sambridhi Shah1, Rajendra Joshi1, Naresh Raut1,
Situ Shrestha Pradhanang1, Rajesh Pandit1, *
1Department of Chemistry, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu, Nepal
2Central Department of Chemistry, Tribhuvan University, Kathmandu, Nepal
*email: panditrajesh02@gmail.com
Submitted : 12 June 2022, Revised 23 June 2022, Accepted 24 June 2022
Abstract
Urea Formaldehyde (UF) resins have good chemical resistivity and high thermal stability, making them
an excellent choice in the construction industry. They, however, pulverize quickly and have low strength
and toughness. In this work, magnesium oxide (MgO) nanoparticles were added to UF as nanollers to
inuence its compressive strength. MgO nanoparticles were synthesized by reducing magnesium nitrate at
different concentration, using orange peel extract. X-ray Diffraction (XRD) and Fourier Transform Infrared
(FTIR) techniques were used to conrm the formation of MgO nanoparticles. XRD results showed the formation
of 43 nm, 35.28 nm, and 32.5 nm sized nanoparticles for 0.1 M, 0.2 M, and 0.4 M concentrations respectively.
The varying-sized MgO nanoparticles were used for the preparation of UF/MgO nanocomposite at different
weight-percentage (wt-%) ratios. The comparative study on the compressive strength of Urea Formaldehyde
resins and UF/MgO was performed. From the results it was found that the addition of MgO nanoparticles to
UF resin enhances the compressive strength at certain wt-% ratios.
Keywords: Magnesium oxide, XRD, FTIR, urea-formaldehyde, nanocomposites
June/July 2022, Vol. 43, No. 1, 95-101
ISSN: 2091-0304 (print)
https://doi.org/10.3126/jncs.v43i1.46959
RESEARCH ARTICLE

Journal of Nepal Chemical Society, June/July 2022, Vol. 43, No. 1 S.KC, N. Rai,S.Shah, R. Joshi, N. Raut, S.S. Pradhanang, R. Pandit
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has low strength and toughness[7]. For these reasons,
it is crucial to focus on improving the mechanical
properties of UF, such as compressive and bending
strength, friability, and pulverization rate. Thus, to
improve the mechanical strength of UF, research has
recently emphasized incorporating reinforcing agents.
The toughness of UF can be improved by two methods:
physical and chemical. Flexible groups are integrated
into the macromolecular chains of polymers using
the chemical technique, which impacts UF’s strong
performance due to the inclusion of other polymers
[8]. External toughening agents are directly absorbed
into UF by producing a mixture in the physical
approach, which is believed to be a better method
to improve the mechanical properties of UF resin
[9]. Toughening agents are classied as organic or
inorganic. In order to improve mechanical properties,
organic toughening agents such as polyvinyl alcohol
(PVA) [10] polyethylene glycol (PEG) [11] ber[12],
cellulose [13] and inorganic toughening agents such
as MgO nanoparticles [14], silica gel [15], zirconium
[16] ,are widely used. Inorganic nanoparticles have
larger specic surface areas, more defects, and
more surface atoms than organic toughening agents,
which could combine closely with UF and improve
its ability to bear a load. Furthermore, nanoparticles
can effectively pass external stress and absorb a large
amount of energy when subjected to external force
[17]. As a result, inorganic nanoparticles have
received a lot of attention to improve the toughness of
polymers. However, no studies have been conducted
on the effect of MgO nanoparticles on the compressive
strength of UF resin. It would be good constructive
materials with improvised the brittle properties of UF
resin with nanoparticles. Therefore, this study focuses
on the synthesis of MgO NPs from green route and
using the synthesized NPs for developing a UF/
MgO nanocomposite. Furthermore, this work focuses
on the investigation of the compressive strength of
UF/MgO nanocomposite prepared at different wt-%
ratios and comparing it with the compressive strength
of pure UF resin.
Materials and Methods
Materials
Citrus sinensis (sweet orange) peels were collected
from fruit shops in Kathmandu. The chemicals used in
the experiments were magnesium nitrate Mg(NO3)2,
sodium hydroxide NaOH, urea, and formaldehyde
manufactured by Merck-India Pvt. Ltd. and obtained
from a local supplier in Kathmandu. All of the
chemicals were of analytical grade and were used
without further purication.
Methods
Preparation of Extract from Orange Peels
Dried orange peels were ground into powder and
40 gm of the powder was mixed with 400 mL of
deionised water in an R.B ask; the mixture was then
reuxed for 1 hour. The extract was ltered through
Whatman lter paper no. 41 [18].
Preparation of MgO Nanoparticles
Three different magnesium nitrate Mg(NO3)2 solution
was used as an initial precursor having 0.1 M, 0.2 M,
and 0.4 M concentrations. Peel extract was added
into various magnesium nitrate solutions which were
stirred for 4 hours continuously by using magnetic
stirrer. The pH of the solution was maintained 12
by adding NaOH solution drop wisely. The particles
formation occurs during stirring process where
magnesium nitrate was reduced to magnesium oxide
[18].
Preparation of Urea Formaldehyde (UF) Resin
and UF/MgOnanocomposite
UF was prepared by combining its precursors, urea
and formaldehyde, in a 1:2 ratio. The reaction mixture
was stirred in a water bath at 60 - 70 °C. The 20 %
NaOH solution was added drop wise to maintain
the basic conditions, i.e., pH 10. The prepared UF
resin was poured into a 2 cm cubical wooden mould.
The UF/MgOnanocomposites with various weight-
percentage ratios of MgO (i.e., 1 %, 2 %, 3 %, 5 %,
and 10 %) were prepared following same procedure as
mentioned above. Finally, the UF resin was pre-cured
in an oven at 60 °C for 12 hours. After that, it was
post-cured for 12 hours at 120 °C[19].The reaction of
urea and formaldehyde is shown in scheme 1.

Journal of Nepal Chemical Society, June/July 2022, Vol. 43, No. 1 S.KC, N. Rai,S.Shah, R. Joshi, N. Raut, S.S. Pradhanang, R. Pandit
97 https://www.nepjol.info/index.php/JNCS
Scheme 1. The polymerization reaction of UF-resin
Characterization technique
X-ray diffraction (XRD) and Fourier- Transform
Infrared (FTIR) analysis
XRD technique was used to calculate the crystalline
size and structure of the synthesized MgO
nanoparticles. The crystal phase and structure
of the prepared samples were determined by
using Bruker D2 PhaserDiffractometer (USA), with
a monochromatic CuKα radiation source (λ= 0.15418
nm) at angle 2θ ranging from 10° - 80°.
The FTIR spectroscopic technique analysed the
vibration frequency of the molecules’ stretching and
bending modes of synthesized MgO NPs and UF
resin. The formation of synthesized MgO NPs and UF
resin was conrmed using the instrument IR Afnity-
1S FTIR Spectrometer (SHIMADZU, Japan), where
spectra were analysed using the KBr pellet method in
the spectral range of 4000 – 400 cm−1.
Compressibility Test
The compressive strength test was performed
to determine the maximum compressive load
that a material can withstand before breaking.
The following equation is used to calculate the
compressive strength of synthesized MgO/UF
nanocomposites[20]. The equation used for the
calculation is
........ (1)
The compressive strength of the prepared sample
block was tested by using Compression Testing
Machine (C.T.M.), Harrish and Terrish, India, having
factor 0.14.
Results and Discussion
XRD Analysis of MgO Nanoparticles
The crystalline phase and structure of synthesized
MgO nanoparticles from sweet orange were
determined using the XRD analysis technique, where
the crystalline size was calculated using the Debye-
Scherrer equation[21]. The XRD pattern of MgO
nanoparticles produced with 0.1 M, 0.2 M, and 0.4
M magnesium nitrate and 0.2 M sodium hydroxideis
shown in Figure 1.
Figure 1. XRD pattern of MgO NPs synthesized using 0.1
M, 0.2 M, and 0.4 M Mg(NO3)2
The diffraction pattern (Figure 1) shows various
peaks, corresponding to (111), (200), and (220)
refection planes assigned to an angle 30°, 40°, and 60°
respectively as per the JCPDS No. 78-430representing
the cubic structure of MgO[22]. The average
crystallite size of synthesized MgO nanoparticles
from 0.1 M, 0.2 M, and 0.4 M Mg(NO3)2 was 43 nm,
35.28 nm, and 32.5 nm respectively.
Fourier Transform Infrared (FTIR) analysis
of synthesized MgO nanoparticles and Urea-
Formaldehyde (UF) resin
The FTIR spectroscopic analysis was done
to analyse the functional group present in the
synthesized samples. Figure 2 represents the FTIR
spectra of synthesized MgO nanoparticles with 0.1
M, 0.2 M, and 0.4 M Mg(NO3)2.

Journal of Nepal Chemical Society, June/July 2022, Vol. 43, No. 1 S.KC, N. Rai,S.Shah, R. Joshi, N. Raut, S.S. Pradhanang, R. Pandit
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Figure 2. FTIR spectra of MgO NPs synthesized using 0.1 M,
0.2 M, and 0.4 M Mg(NO3)2
The spectra of the synthesized MgO nanoparticles
are illustrated in Figure 2. The peaks at 3340.71cm-
1, represented the stretching vibration of the O-H
group due to water molecules present in the precursor
solution. The peak at 1643.35cm-1 corresponds to the
bending vibration of a surface hydroxyl group (-OH)
[23].The peaks at 1373.32cm-1 and 1026.13cm-1 are
assigned to O-C=O bending and bending vibration of
water molecules[24]. The vibrations at 2924.09cm-
1, and 2862.36cm-1 are due to C-H bond.The peak
observed at 524.64cm-1 indicates the formation of
MgO nanoparticles[25][26].
Moreover, the FTIR spectrum of pure urea-
formaldehyde (UF) is shown in Figure 3.
Figure 3. FTIR Spectrum of Urea-formaldehyde (UF) resin
The spectrum of prepared UF resin shows the peak at
3332.99cm-1, 2924.09 cm-1, 1627.92cm-1, 1535.34cm-
1, 1002.98cm-1 and 601.79cm-1. The peak at 3332.99cm-
1 corresponded to N-H stretching of primary aliphatic
amines, and the peak at 2924.09cm-1 represented
C-H stretching of UF. The peak at 1627.92cm-1 and
1535.34cm-1 attributed to the presence of –NH-CO-
NH- and –CO-NH- groups. The peak at 1002.98cm-
1 corresponded at the –CH2OH group [27]. The
FTIR spectrum conrmed the formation of urea-
formaldehyde resin using precursors, urea, and
formaldehyde.
Compressive Strength Analysis of UF/
MgONanocomposites
The compressive strength test of pure UF resin and
UF/MgO nanocomposites prepared by varying
the wt-% (1 %, 2 %, 3 %, 5 %, and 10 %) ratios of
MgO was investigated by using the equation (1) at
room temperature of 25 °C.
The prepared UF and UF/MgO nanocompositeswere
compressed between the platens of the Universal
Compressive Strength Testing Machine with a factor
of 0.14 by a gradually applied load. The obtained data
are presented in Table 1.
Table1. Compressive Strength of UF/
MgOnanocompositesat different composition
S.N.
MgO
NPs
(wt.-%)
Breaking Load(N)
in concentrations
Compressive
Strength (MPa) in
concentrations
0.1 M 0.2 M 0.4 M 0.1 M 0.2 M 0.4M
1 1% 280 285 292 70 71.25 73
2 2% 289 295 300 72.25 73.75 75
3 3% 305 311 315 76.25 77.75 78.85
4 5% 325 340 340 81.25 85 85
5 10% 282 285 290 70.5 71.25 72.5
The compressive strength of pure UF resin was
calculated to be 28 MPa. The results of our work
showed that UF/MgO nanocomposites have higher
compressive strength than pure UF resin. The
compressive strength of the UF/MgO nanocomposites
increased as the wt-% ratio of MgO nanoparticles
increased. It means that the addition of MgO
nanoparticles to UF resin resulted in a signicant
improvement of compressive strength. This is due to
dispersion of MgO nanoparticles.
The highest compressive strength of 85 MPa was
recorded in a nanocomposite containing 5 % MgO in

Journal of Nepal Chemical Society, June/July 2022, Vol. 43, No. 1 S.KC, N. Rai,S.Shah, R. Joshi, N. Raut, S.S. Pradhanang, R. Pandit
99 https://www.nepjol.info/index.php/JNCS
both 0.2 M and 0.4 concentrations. The compressive
strength of nanocomposites increased up to 5 %
(wt- %) of MgO nanoparticles, while compressive
strength decreased beyond that. This may be due to
the effect of agglomeration resulting from a higher
percentage of MgO nanoparticles on the cross-
linking of UF resin. The compressive strength of the
UF resin was found to be increased with the addition
of MgO nanoparticles. This explains the use of MgO
nanoparticles to improve the strength of materials
like UF resin, which is widely used in manufacturing
plastics, adhesives, hinges, etc. Similar results were
recorded in the previous article when nanoparticles
were incorporated in resins [16][28][29].
4. Conclusion
Magnesium oxide (MgO) nanoparticles were
synthesized using sweet orange peel extract and
different concentrations of magnesium nitrate
solution, i.e., 0.1 M, 0.2 M, and 0.4 M. The synthesized
MgO nanoparticles were characterized using XRD
and FTIR spectroscopic analysis techniques. The
XRD pattern showed that the synthesized MgO
nanoparticles prepared from 0.1 M, 0.2 M, and 0.4
M Mg(NO3)2 were cubic structures with an average
crystallite size of 43 nm, 35.28 nm, and 32.5 nm,
respectively. As the concentration of precursor was
increased, the average crystallite size was found
to be slightly decreasing. Likewise, UF resin was
prepared by using pure urea and formaldehyde
resin. The FTIR spectra conrmed the formation of
MgO nanoparticles and UF resin. Furthermore, UF/
MgO nanocomposites were synthesized by varying
the MgO weight percentage of nanoparticles (1 %,
2 %, 3 %, 5 %, and 10 %), and their compressive
strength was investigated. It was found that adding
MgO nanoparticles to the UF resin increases
its compressive strength as the compressive strength
of a nanocomposite containing MgO (5 wt.-%)
nanoparticles was found to be the highest at 85
MPa. However, the additional increment of MgO (10
wt.-%) nanoparticles showed lower the compressive
strength in all UF/MgO nanocomposite.
Acknowledgments
The author would like to acknowledge the
National Academy of Science and Technology
(NAST) Khumaltar, Lalitpur for XRD
analysis, Department of Plant Resources, Thapathali,
Kathmandu, Nepal for FTIR analysis and Central
Material Testing Laboratory, Pulchowk Campus,
Lalitpur for compressive strength test.
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