Progress in Organic Coatings 77 (2014) 24–29
Contents lists available at ScienceDirect
Progress in Organic Coatings
journal homepage: www.elsevier.com/locate/porgcoat
Development of bio-based hybrid resin, from natural lacquer
Shinji Kanehashi, Hiroki Oyagi, Rong Lu, Tetsuo Miyakoshi ∗
Department of Applied Chemistry, Meiji University, 1-1-1 Higashi-mita, Tama-ku, Kawasaki 214-8571, Japan
a r t i c l e
i n f o
Article history:
Received 11 May 2013
Received in revised form 26 June 2013
Accepted 15 July 2013
Available online 29 August 2013
Keywords:
Natural lacquer
Composite
Urushiol
Resin
Coating
Hybrid
a b s t r a c t
Preparation and structure analysis of a bio-based hybrid material composed of natural lacquer, epoxy,
and organic silane compounds were investigated using liquid and solid-state nuclear magnetic resonance. The good composition of additives in the hybrid was determined by the drying, hardness, and
resin-molding properties. Although natural lacquer alone cannot form thick resins, this bio-based hybrid
material showed good resin formation at room temperature without thermal treatment. This result could
be based on the enhancement of curing by the sol–gel reaction between natural lacquer and the organic
silane compound, and a crosslink reaction between organic silane and epoxy groups. At the same time,
oxidative polymerization at the unsaturated side chains in the urushiol was enhanced by the sol–gel reaction because the catechol hydroxyl groups, which have an antioxidative property, reacted with the organic
silane. In addition, this bio-based resin possesses a thermoset property because curing of the hybrid was
improved by thermal treatment. Based on the structure analyses, the sol–gel reaction between urushiol and organic silane compound proceeded immediately, indicating the high reactivity of this sol–gel
reaction. On the other hand, the reaction between bisphenol A-type epoxy resin and the organic silane
seems to progress slowly after the epoxy ring opening. In addition, a sol–gel reaction occurred between
the amine group in the organic silane and the hydroxyl group formed after the crosslink reaction of
the epoxy group. These results suggested that the improvement in drying and molding properties of
the hybrid was based on the chemical reactions among all components (i.e., natural lacquer, epoxy, and
organic silane).
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Many functional polymer materials such as film and resin have
been synthesized to make more comfortable and convenient in our
daily life. Most of these polymer materials are derived from oil and
require large amounts of energy to produce. Therefore, an alternative to oil-based industrial products using renewable resources
is desired due to recent environmental problems, global warming, and depletion of fossil fuels. Development of polymers from
natural products, such as plant oils and non-food materials, is one
of the very attractive ways to solve such environmental problems
economically and ecologically.
Natural lacquer (urushi) is one of the traditional natural polymers in Japan that has a beautiful glossy appearance and high
durability [1]. Lacquer sap consists of urushiol, which has C15
unsaturated hydrocarbons at 3 or 4 catechols, water, a gummy
substance, a nitrogenous material, and laccase [2,3]. One advantage
of natural lacquer is that it is polymerized enzymatically in the
presence of moisture and laccase without any organic solvent,
∗ Corresponding author. Tel.: +81 44 934 7203; fax: +81 44 934 7906.
E-mail address: miya@isc.meiji.ac.jp (T. Miyakoshi).
0300-9440/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.porgcoat.2013.07.013
making natural lacquer, bio-based coating material. Therefore,
polymer materials using natural lacquer have been investigated
for use as resins [4,5], hybrids [6–8], and composites [9,10].
The laccase in lacquer sap plays an important role in this
polymerization. The autoxidation of natural lacquer occurs at
unsaturated side chains of urushiol [1]. However, because these
reactions progress slowly, the curing of natural lacquer generally
takes longer than that of conventional organic coatings. The drying
of natural lacquer is strongly affected by the environmental conditions such as humidity and temperature. This enzymatic oxidation
reaction requires a highly moist environment (70–80% RH) for activation of laccase [11]. Furthermore, it is difficult to fabricate thick
resin products from natural lacquer alone. Therefore, fabrication
of thick resin material using natural lacquer is also important to
expand the use of natural lacquer application as effective utilization
of renewable resources.
We previously developed hybrid lacquers composed of natural lacquer and amine-functionalized organic silane compounds
that show good drying property at low relative humidity [8,12,13].
Hybridization by the sol–gel reaction between OH groups in the
lacquer and organic silane compounds considerably improves the
film properties such as drying speed and hardness [12,14]. In addition, we recently reported hybrid microwave-adsorption materials
S. Kanehashi et al. / Progress in Organic Coatings 77 (2014) 24–29
O
OH
O
O
O
OH
C15H25-31
Urushiol
H
N
H2N
O
O
Si
O
N-(2-aminoethyl)-3-aminopropyl
trimethoxysilane (AATMS)
Bisphenol-A epoxy (BPAE)
H
N
H2N
O
O
Si
O
N-(2-aminoethyl)-3-aminopropyl
triethoxysilane (AATES)
H2N
O
O
Si
O
3-aminopropyl
trimethoxysilane (APTMS)
Fig. 1. Chemical structure of urushiol, bisphenol-A epoxy (BPAE), and
silanes,
N-(2-aminomethyl)-3-aminopropyl
trimethoxysilane
organic
(AATMS),
N-(2-aminomethyl)-3-aminopropyltriethoxysilane
(AATES),
and
3-aminopropyltrimethoxysilane (APTMS).
prepared from natural lacquer, epoxy, and organic silane compounds [9]. However, the chemical structure of these hybrids has
not been described. Therefore, the chemical structure of a biobased hybrid resin fabricated by chemical reactions among natural
lacquer, epoxy, and organic silane compounds and optimization
of additive components were investigated in terms of the drying,
hardness, and molding properties of the hybrids.
2. Experimental
2.1. Chemicals
The natural lacquer used in this study was purchased from
Doityu Shoten, Co. Ltd., Osaka, Japan. Urushiol and lipid component of the lacquer were extracted from raw lacquer sap
according to the previous study [14]. Bisphenol A-type epoxy
resin (BPAE, Epoxyclear 305114) was purchased from I-Resin
Co., Ltd., Tokyo, Japan, and used without further purification.
Organic silane compounds, N-(2-aminomethyl)-3-aminopropyl
trimethoxysilane (AATMS), and 3-aminopropyltrimethoxysilane
(APTMS) were purchased from Tokyo Chemical Industry Co., Ltd.,
Tokyo, Japan. N-(2-aminomethyl)-3-aminopropyltriethoxysilane
(AATES) was kindly supplied by Shin-Etsu Polymer Co., Ltd., Tokyo,
Japan. These chemical structures of compounds used in this study
are presented in Fig. 1.
2.2. Preparation of hybrid lacquer and resin
Ten grams of natural lacquer and given ratios of additives
such as BPAE and organosilicon compounds were mixed for
5 min at room temperature. After fabrication of a hybrid lacquer, the mixture was uniformly coated on a square glass plate
(70 mm × 70 mm × 1.3 mm) at 23 ◦ C ± 1 ◦ C using a 76 ␮m thickness applicator (Yoshimitsu Seiki, Tokyo, Japan) which has ± 10 ␮m
deviation. This lacquer was stored in the dark at 25 ◦ C and 50% RH to
evaluate the drying and hardness properties. For preparation of the
thick resin, the mixture of natural lacquer, BPAE, and organosilicon
compounds was poured into a fluororesin tube (outside diameter:
16 mm, inside: 14 mm, and thickness: 20 mm) at room temperature. After three days, formed thick resin was taken from the tube.
The effect of thermal treatment on the curing property of hybrids
was also investigated.
2.3. Characterization
The molecular weight of the hybrid was determined at 40 ◦ C
by aqueous phase gel permeation chromatography (GPC; TSK-gel
column ␣-3000, ␣-4000 and ␣-M, ␾7.8 mm × 300 mm × 3, Tosoh
Co. Ltd., Tokyo, Japan) using dimethylformamide (DMF) as an eluent
with 0.01 mol LiBr on a high-performance liquid chromatography
25
system with an RI-8012 refractive-index detector with polystyrene
standards. The elution rate was 0.8 ml/min.
The drying process of the epoxy coatings at 23 ◦ C ± 1 ◦ C can be
divided into three stages: dust-free dry, touch-free dry, and harden
dry (HD). Each stage was measured using an automatic drying time
recorder (RC auto-recorder of painting drying time, TaiYu Co. Ltd.,
Osaka, Japan) at 23 ◦ C ± 1 ◦ C and 60% relative humidity.
The pencil hardness is performed based on the current national
standard of GB/T6739-1996. H and B indicate the hardness and softness, respectively, of tested coatings, and higher numbers express
the relative hardness or softness of the tested coatings. F and HB
indicate medium hardness. However, F is a slightly harder coating
than HB. In the present study, pencil lead hardness was determined
using a C-221 (Yoshimitsu Seiki, Tokyo, Japan) at 23 ◦ C ± 1 ◦ C.
The gel content of the epoxy coating was determined. Coatings
were immersed in acetone at 23 ◦ C ± 1 ◦ C for 24 h, and the nonsoluble parts were filtered and dried in a Taiyo muffle furnace
(Isuzu, Tokyo, Japan) for 1 h at 50 ◦ C, cooled, and subsequently
examined at room temperature to remove residual solvent before
weighing. The gel content was calculated using the following equation:
gel content(%) =
M1
× 100
M0
(1)
where M1 and M0 are the weight of the insoluble fraction and the
original weight of the completely dried epoxy coating, respectively.
The structural analysis was conducted via liquid-state proton
and carbon nuclear magnetic resonance (1 H- and 13 C-NMR) spectroscopies using a JNM-ECA500 spectrometer (JEOL Ltd., Tokyo,
Japan). Samples were dissolved in deuterated dimethyl sulfoxide
(DMSO) solution with chemical shifts referenced from tetramethylsilane (TMS). Cross-polarization/magic angle spinning (CPMAS)
solid-state 13 C-, 29 Si-, and 15 N-NMR experiments were performed
on a JNM-ECA400 NMR spectrometer (JEOL Ltd., Tokyo, Japan) using
a zirconium sample tube (␾6 mm).
3. Results and discussion
3.1. Molecular weight distribution
GPC was conducted to determine the molecular weight distribution of hybrids, and the results are summarized in Table 1. As the
organic silane content increased, the molecular weight and molecular weight distribution tended to increase. This result could be
based on the sol–gel reaction between organic silane and urushiol, as previously reported [12]. On the other hand, the increase
in the molecular weight for hybrids using AATES seemed to be
lower than that of other silane compounds such as AATMS and
APTMS. This result indicates that the organic silane reactivity of
the sol–gel reaction in the methoxy group seems to be higher than
that in ethoxy group. Therefore, the molecular weight of hybrids
was affected more by the use of organic silane compounds other
than BPAE.
3.2. Drying and hardness properties
To determine the suitable addition ratios of organic silane and
BPAE, we measured the drying and hardness properties of various
bio-based hybrid lacquers. The drying property of the lacquers is
summarized in Table 2. The addition of BPAE and silane compound
to the natural lacquer significantly improved the drying property
at room temperature. The hybrid lacquers prepared with 20 wt% of
BPAE (Entries 3, 6, and 9) dried more rapidly than natural lacquer
(Entry 1). On the other hand, an BPAE at higher concentration (i.e.,
30 wt%) decreased the drying property, indicating that the excess
BPAE could prevent the sol–gel reaction between urushiol and the
26
S. Kanehashi et al. / Progress in Organic Coatings 77 (2014) 24–29
Table 1
Molecular weight of bio-based hybrid lacquers.
Entry
1
2
3
4
5
6
7
8
9
10
a
Silane
None
AATMS
AATES
APTMS
Additive content (wt%)
Content ratio (%)a
Silane
BPAE
Monomer
Oligomer
Polymer
Mn
Mw
Mw /Mn
0
10
20
30
10
20
30
10
20
30
0
30
20
10
30
20
10
30
20
10
49.1
47.3
24.4
21.0
57.4
47.3
44.1
44.5
37.2
17.2
45.7
35.9
48.4
50.6
34.7
40.3
42.9
38.9
42.0
52.0
5.2
16.8
27.2
28.4
7.9
12.4
13.0
16.6
20.8
30.8
510
520
1070
1030
430
530
610
540
1260
1120
2140
3840
7560
8080
1670
3190
3360
3960
9240
9320
4.2
7.4
7.1
7.8
3.9
6.0
5.5
7.3
7.3
8.3
Molecular weight
Oligomer: dimer 5 molecular weight < 10,000 g/mol, polymer: molecular weight = 10,000 g/mol.
Table 2
Drying property and hardness of baio-based hybrid lacquers.
Entry
Silane
1
2
3
4
5
6
7
8
9
10
None
a
b
AATMS
AATES
APTMS
Additive content (wt%)
Drying property (h)a
Silane
BPAE
DF
TF
HD
1 day
2 days
3 days
7 days
14 days
0
10
20
30
10
20
30
10
20
30
0
30
20
10
30
20
10
30
20
10
18.5
6.9
0.9
0.5
17.7
1.4
1.2
7.5
0.2
1.5
23.1
20.0
4.6
1.9
24<
12.3
4.6
17.2
6.9
7.7
24<
24<
13.1
14.6
24<
23.9
16.9
23.6
13.1
20.0
TF
TF
HD
DF
HD
HD
HD
HD
HD
HD
HD
HD
6B
HD
DF
HD
HD
HD
HD
HD
HD
HD
6B
HD
TF
HD
HD
HD
HD
HD
HD
HD
6B
HD
HD
HD
HD
HD
6B
HD
6B
HD
4B
5B
HD
HD
HD
HD
6B
6B
DF: dust free dry, TF: touch free dry, and HD: harden dry (based on JIS-K-5400).
Pencil hardness: HD 6B < B < HB < F < H 9H.
organic silane compound. There is no obvious difference in the
hardness of bio-based hybrids, regardless of the kind of organic
silane compound and their ratios. Among them, the hybrids using
AATMS seem to be hard compared with the natural lacquer. Based
on these results, the better condition for preparation of hybrids
using BPAE and organic silane compound seems to be 20 wt% of
AATMS and 20 wt% of BPAE (Entry 3) in this study.
3.3. Molding property
The molding property of bio-based hybrids at room temperature is summarized in Table 3. The natural lacquer cannot cure
thick resin materials because of the slow oxidization reaction. The
hybrids composed of 20 wt% of organic silanes, AATMS and APTMS,
and 20 wt% of BPAE showed good molding property. This result
is in good agreement with the drying and hardness properties of
the hybrids. This is because the reactions among urushiol, BPAE,
and organic silane improved their molding property. However, the
Table 3
Molding property of bio-based hybrid resins.
Entry
Silane
1
2
3
4
5
6
7
8
9
10
None
a
Hardnessb
AATMS
AATES
APTMS
Additive content (wt%)
Silane
BPAE
0
10
20
30
10
20
30
10
20
30
0
30
20
10
30
20
10
30
20
10
: cured, : cured but brittle, and ×: uncured.
Molding propertya
×
hybrids using AATES cured but were very brittle. This result was
consistent with the GPC measurement. Therefore, the methoxy or
ethoxy groups in organic silane compounds affect the sol–gel reaction with urushiol or BPAE. In addition, the effect of excess organic
silane or BPAE on curing at room temperature could prevent the
enhancement of drying for thick resin and therefore reduce the
molding property.
Basically, thermal treatment enhances the curing time of thermosetting resin materials. The effects of temperature on curing of
the bio-based hybrids using AATMS and BPAE are summarized in
Table 4. The cured hybrid resins were obtained with more than
30 min at 70 ◦ C. As the temperature increased, the resins tended to
cure but were brittle. As mentioned before, the sol–gel reaction of
this system proceeded easily at room temperature. The rapid solgel reaction between urushiol and AATMS at high temperature (i.e.,
over 80 ◦ C) could make more rigid structure, indicating that this
rigidity could reduce the molding property. In addition, methanol
as a by-product in the sol-gel reaction between could erupt explosively from the resins at high temperature, suggesting that boiling
of the methanol in the resins may affect the brittleness. Therefore,
these results suggest that this bio-based hybrid can be used in thermosetting resin materials because the thermal treatment of this
hybrid enhanced the curing property.
3.4. Gel content
Fig. 2 presents the gel content of the natural and bio-based
hybrid lacquers. As expected from the drying and hardness properties of hybrids, the gel content of all hybrids were higher than that
of the natural lacquer, indicating that the hybrid lacquers prepared
from BPAE and organic silane had a higher crosslink density than
the natural lacquer. The detailed structure of the hybrid was analyzed using hybrids prepared from BPAE and AATMS because they
S. Kanehashi et al. / Progress in Organic Coatings 77 (2014) 24–29
27
Table 4
Effect of curing temperature and time in molding property of hybrid lacquer resins.
Entry
Silane
Silane
1
2
3
4
5
a
Temperature (◦ C)
Additive content (wt%)
BPAE
20
20
AATMS
60
70
80
90
100
Time (min)
10
20
30
40
×a
×
×
×
×
: cured, : cured but brittle, and ×: uncured.
100
AATMS 20wt%
BPAE 20 wt%
Gel content (wt%)
80
AATES 20wt%
BPAE 20 wt%
60
None
APTMS 20wt%
BPAE 20 wt%
40
20
0
0
2
4
6
Time (days)
8
10
Fig. 2. Gel content of natural lacquer and bio-based hybrid lacquers.
Fig. 4.
13
C-NMR spectra of BPAE, urushiol, and bio-based hybrid (solvent: DMSO).
seem to be good components to prepare the hybrid resin based on
the GPC, drying, and hardness properties.
3.5. Structure analysis
3.5.1. Liquid-state NMR
Fig. 3 presents liquid-state 1 H-NMR spectra of BPAE, urushiol,
and hybrids prepared from BPAE and AATMS. A decrease in the
peak at 7.3–6.8 ppm, which corresponds to the aromatic proton of
BPAE, was observed, whereas the peak at 6.7–6.5 ppm which corresponds to the aromatic proton of urushiol, decreased and was
shifted and broadened by the addition of AATMS [14]. In addition, the peaks at 2.69 and 2.81 ppm corresponding to the epoxy
group of BPAE decreased in the hybrid. On the other hand, a new
peak at 3.19 ppm could be based on the methanol produced by
Fig. 3.
1
H-NMR spectra of BPAE, urushiol, and bio-based hybrid (solvent: DMSO).
alcoholysis and the sol–gel reaction between urushiol and AATMS.
Based on these results, the sol–gel reaction between urushiol and
organic silane compound proceeded, and the epoxy crosslink reaction between BPAE and amine group occurred in the AATMS.
Fig. 4 presents liquid-state 13 C-NMR spectra of BPAE, urushiol,
and the hybrid. Similarly, the peaks at 41 and 44 ppm corresponding
to the epoxy group of BPAE were shifted. Furthermore, the urushiol aromatic carbons in hybrid detected at 145–141, 129–120, and
112 ppm were broadened. In addition, the aromatics of BPAE at 158
and 143 ppm decreased. Based on these results, the reaction proceeded among urushiol, BPAE, and silane. On the other hand, a new
broad peak at 150–145 ppm was detected in the hybrid. This peak
was assigned to silyloxy ( O Si ) units [14,15].
Fig. 5.
13
C CPMAS spectra of urushiol, urushiol + silane, and bio-based hybrid.
28
S. Kanehashi et al. / Progress in Organic Coatings 77 (2014) 24–29
Fig. 6.
29
Si CPMAS spectra of urushiol + silane and bio-based hybrid.
3.5.2. Solid-state NMR
Fig. 5 presents the solid-state 13 C-NMR spectra of urushiol,
urushiol + silane, and a hybrid. The hydroxyl-substituted carbon of
urushiol were detected at 142 ppm, while the peaks of these carbons were slightly shifted to the low magnetic field and appeared
at 148 ppm for urushiol-silane and the hybrid, implying that the
hydroxyl groups of urushiol have been replaced by the silyloxy
( O Si ) units [14]. The aromatic carbon of BPAE detected at
158 ppm as presented Fig. 4, disappeared in the hybrid, suggesting
that the reaction among these components proceeded.
Fig. 6 presents the solid-state 29 Si-NMR spectra of urushiol + silane and the hybrid. The peaks from −55 to −70 ppm which
belonging to highly condensed-siloxane ( Si O Si ) units were
detected in all hybrids [14,16,17]. This is because the sol–gel reaction among silane, urushiol, moisture in the natural lacquer, and
OH groups was produced by the epoxy reaction. It is considered
that predominantly the sol–gel reaction occurred and that a condensed inorganic network was formed in the hybrids [14,18,19].
Furthermore, from the disappearance of the methoxy carbon peak
seen at 50 ppm in the 13 C-NMR spectra, it can be surmised that the
other linkage units were connected to the urushiol and showed as
phenoxysilane [12,14].
3.5.3. Possible reaction
The 1 H- and 13 C-NMR analyses and GPC measurement of hybrids
showed the sol–gel reaction between urushiol and the organic
silane compound proceeded immediately, indicating the high
reactivity of this sol–gel reaction. On the other hand, the reaction
between BPAE and the organic silane progressed slowly after the
epoxy ring opening. These spectra also showed that the epoxy in
BPAE and amine group in organic silane had reacted almost completely after curing. Based on these results, the possible reaction
route is presented in Fig. 7. Firstly, the sol–gel reaction between
urushiol and organic silane compound proceeded, and then the
crosslink reaction between BPAE and organic silane occurred. A
decrease in the hydroxyl groups in the urushiol promoted the
autoxidation of urushiol. According to the solid-state NMR, almost
all primary and secondary amine groups reacted with the epoxy
of BPAE. Furthermore, the methoxy group of organic silane reacted
with not only urushiol but also with the hydroxyl group of BPAE
produced by a crosslink reaction. Therefore, this bio-based hybrid
could be based on the chemical reactions among all components
(i.e., natural lacquer, epoxy, and organic silane). In addition, this
bio-based hybrid material can be applied in industrial applications,
not only as coating materials but also resin molding.
4. Conclusions
Bio-based hybrid materials were prepared from natural lacquer,
epoxy, and organic silane compound. According to structure analysis, the sol–gel reaction between natural lacquer and organic silane
compound, and a crosslink reaction between organic silane and
epoxy groups proceeded. An excess of BPAE or organic silane prevented each chemical reaction (i.e., sol–gel and crosslink) based on
the GPC and the drying, hardness, and resin molding properties.
At the same time, the oxidative polymerization at the unsaturated
chains in the urushiol was enhanced by the sol–gel reaction because
the catechol hydroxyl group, which has an antioxidative property,
reacted with the organic silane. In addition, the curing time of the
hybrid was improved by thermal treatment, indicating that this
resin was thermosetting property. NMR spectra showed that almost
all primary and secondary amine groups reacted with BPAE. Furthermore, the methoxy group of organic silane reacted not only
with urushiol but also with the hydroxyl group of BPAE formed after
the crosslink reaction. These results suggest that the enhancement
of drying, hardness, and molding properties of the hybrid was based
on chemical reactions among all components (i.e., natural lacquer,
epoxy, and organic silane). Therefore, this bio-based hybrid material can be applied to industrial applications as not only a coating
but also to produce thick resin materials.
Fig. 7. Possible reactions among urushiol, BPAE, and organic silane compound.
S. Kanehashi et al. / Progress in Organic Coatings 77 (2014) 24–29
Acknowledgement
This research was partially supported by a Grant-in-Aid for
the Japan Society for the Promotion of Science (JSPS) Fellows
(2410856).
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