NdCl3-schiff base complex as catalyst for formation of water-blown semi-rigid polyurethane foam

Article abstract of DOI:10.14233/ajchem.2015.18793

Neodymium chloride Schiff base complex was synthesized and characterized by scanning electron microscopy, elemental analysis, 1H NMR, FT-IR and complexometric titration. This complex, combined with triethylenediamine, was used as a catalytic composite for

Full text of DOI:10.14233/ajchem.2015.18793

Asian Journal of Chemistry; Vol. 27, No. 9 (2015), 3361-3364
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.18793
NdCl
3
-Schiff Base Complex as Catalyst for Formation
of Water-Blown Semi-Rigid Polyurethane Foam
*
ANPING LIAO , LEILEI QIAO, RIMEI HE, PING LAN, LIHONG LAN, YANYUE LU and MEI LI
School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Guangxi Colleges and Universities, Key Laboratory of
Chemical and Biological Transformation Process Technology, Nanning 530006, P.R. China
*Corresponding author: Tel: +86 771 3260558; E-mail: gxanping@sina.com
Received: 6 October 2014; Accepted: 27 January 2015;
Published online: 26 May 2015;
AJC-17256
1
Neodymium chloride Schiff base complex was synthesized and characterized by scanning electron microscopy, elemental analysis, H
NMR, FT-IR and complexometric titration. This complex, combined with triethylenediamine, was used as a catalytic composite for the
foaming reaction of all-water blown semi-rigid polyurethane foam. The effect of ratio of the complex to triethylenediamine on the
properties of reaction product was investigated. This catalytic composite can be in place of organic tin catalyst such as stannous octoate,
dibutyl tin dilaurate and other conventional polyurethane foam catalyst, which are usually unstable and toxic, leading to environmental
hazards.
Keywords: Schiff base complexes of neodymium chloride, Catalyst, Water foaming, Polyurethane foam.
polyurethane foam. The one-step method is employed for the
preparation.
INTRODUCTION
In recent years, great progress has been made in the field
1
-6
of polymer with rare earth metals as catalyst . It is shown
that rare earth catalysts possess excellent catalytic performance
EXPERIMENTAL
7
for the formation of polymers . Novel rare earth catalysts have
Polyether polyols MA–4110 (Changzhou Mid-Asia Chemical
Co., Ltd., China); diphenylmethyl propane diisocyanate PM-
200 (MDI, Wanhua Chemical Group Co., Ltd., China); Silicone
oil SD-201 (Siltech New Materials Co., Ltd., China). Triethylene
attracted more and more attention. The complexes of Schiff
bases and rare earth metal are widely used as catalysts in
scientific research and industrial production . Polyurethane
8
(PU) foam is always synthesized by the reaction of a polyether/
diamine and stannous octoate [Sn(Oct) ] (Sinopharm Chemical
2
polyester-polyol and a polyisocyanatein with the presence
of catalyst and a series of additives. Polyurethane foam has
a special structure with alternate soft segments and hard
segments in the molecular chain. The aggregation structures
from micro-phase separation give unique properties for poly-
urethane foam. Because of its large-scale production and
mature manufacturing processes, semi-rigid polyurethane
foam is widely used in construction, automotive, decoration
Reagent Co., Ltd., China) was purified according to the method
described in literature. Tris(2-hydroxyethyl)amine and ethylene
glycol (Sinopharm Chemical Reagent Co., Ltd., China) were
treated by refluxing with phthalic anhydride. Mold discharging
agent and rare earth catalyst were homemade.
FT-IR (MAGNA-1R 550 FTIR,America); H NMR (Varian,
VNMRS600,America);FESEM(SUPRA55Sapphire, Germany);
Foaming mould (homemade).
Preparation and characterization of catalysts: 35 mL
of salicylaldehyde and 100 mL ethanol was added to a 500
mL flask. This mixture was stirred for 20 min, followed by
the addition of a solution of 10 mL of ethylenediamine and 50
mL of anhydrous ethanol. Then this resultant mixture was
heated at 78 °C for 2 h.After cooling to room temperature, the
reaction mixture was placed in an ice bath and the yellow preci-
pitate was collected by filtration and washed with anhydrous
ethanol, then the product was further purified by recystalliza-
1
9
-12
and other fields . There are many reports about semi-rigid
13
polyurethane water blown foam . But study on the Schiff base
complexes of rare earth as catalysts for water blown semi-
rigid polyurethane foam is still very limited. This work
investigated the use of neodymium chloride Schiff base
complexes mixed with ethylene diamine compound as a catalyst
for the preparation of water blown semi-rigid polyurethane
foam and explored the effect of different proportions of
complex to ethylene diamine on the performance of semi-rigid

3
362 Liao et al.
Asian J. Chem.
g
C
g
CH2
tion with ethanol and vacuum dried 2 h, as a result the yellow
crystals of Schiff-base ligand can be obtained.
H
2
b
g
CH
N
N
b
d
Anhydrous neodymium chloride (3.302 g), Schiff-base
ligand (7.12 g) and 40 mL anhydrous ethanol were added to a
flask. This mixture was heated, with stirring, at 80 °C for 3 h
and then cooled to room temperature. The precipitate was
collected by filtration and washed with anhydrous ethanol to
give product which was used as catalyst.
HC
a
HO
e
a
OH
d
c
f
e
f
c
ef
b
cd
Preparation of combination material and foaming process
Component A: The polyether polyol, catalyst, cross-
linking agent and foaming agent were mixed according to an
appropriate proportion given in Table-1 and stirred at room
temperature.
a
Component B: MDI: The component A was added to a
beaker with stirring, followed by the addition of component B
over 10 sec. This reaction mixture then was poured into a
mould which maintained at constant 50 °C. Foaming mold
was released after 4-6 min and the whole water foaming poly-
urethane foam was obtained.
1
4
12
10
8
6
4
2
0
1
Fig. 1. H NMR spectrum of Schiff base
100
TABLE-1
80
60
40
20
0
MASS RATIOS OF COMPONENT IN ONE STEP PREPARATION
Component
Proportion
100 pbw
2 pbw
0.5 pbw
0.1 pbw
1 pbw
1 pbw
1 pbw
100 pbw
Polyether polyols MA-4110
Triethylene-diamine
Silicone oil
–1
1635 cm
NdCl Schiff base complexes catalyst
3
Ethylene glycol
Distilled water
Triethanolamine
MDI PM-20
0
500 1000 1500 2000 2500 3000 3500 4000 4500
The whole water foaming polyurethane foam was cured
at room temperature for 72 h and then its bubble pore structure,
density, compressive strength and other performance indexes
were measured.
Determination of apparent density of foam: The foam
was shaped according to the Chinese national standards (GB/
T6343-2009) to measure the mass and volume and calculate
the apparent density of foam compression performance. The
test was carried out following Chinese national standards (GB/
T 8813-2008).
–1
Wavenumber (cm )
Fig. 2. FT-IR spectrum of Schiff base
NdCl
3
Schiff base complexes (catalyst): The catalyst
which was obtained by the reaction of neodymium chloride
with Schiff base ligand was vacuum dried after washing by
anhydrous ethanol, with yield of 86.3 %. Rare earth metal
element content was measured by complexometric titration
and neodymium content is shown at 16.9 % which is close to
the calculated value of 16.7 %. Halogen element content is
determined by silver nitrate precipitation, which shows that
the chloride ion content is 11.8% closed to the calculated value
of 12.1%. In infrared spectra, the C=N absorption moves from
647 cm (Schiff base ligand) to 1635 cm after the formation
of neodymium chloride Schiff base complexes (Fig. 3).
The complex was characterized by H NMR. The spectrum
was shown in Fig. 4 and the data are as following: δ: 13.37 (s,
H, Ar-OH), 8.26 (s, 2H, CH=N), 7.30, 6.89 (m, 10H, C
.84 (m, 4H, N-CH
(m, 2H, CH CH OH), 1.06 (t, 3H, CH CH OH). The complex
formula was deduced to be Nd(H
Effect of catalyst on the evaluation results of whole
water foaming semi-rigid polyurethane foam: The compa-
rison of semi-rigid foam prepared by the catalyst of NdCl
Schiff base complexes and prepared using stannous octoate
was shown in Table-2. The whole water foaming semi-rigid
Measurement of dimensional changes after Laundering:
The sample foam was kept in refrigerator and dryer at -3 and
5
3 °C for a month respectively, the dimensional changes was
measured by field emission scanning electron microscope
FESEM).
-
1
-1
1
(
1
RESULTS AND DISCUSSION
2
3
6 5
H -),
Schiff base: The Schiff base was recrystallized then
vacuum dried to constant weight, with yield of 93.1 %. Schiff
2
-CH
2
-N), 4.39 (t, 1H, CH
3
CH
2
OH), 3.43
1
1
3
2
3
2
base ligand was analyzed using H NMR shown in Fig. 1. H
NMR(CDCl ) data are as follows. δ: 13.19 (s, 2H, OH), 8.36
d, 2H, CH=N), 6.83-7.29 (m, 10H, C -), 3.93 (t, 4H, N-
CH -CH -N).
Infra spectroscopy of this Schiff base ligand was measured
by FT-IR (KBr background), as shown in Fig. 2. FT-IR data: ν
2
Salen)
2
Cl
3
·2C
2
5
H OH.
3
(
H
6 5
2
2
3
-1
=
1635 cm , C=N.

Vol. 27, No. 9 (2015)
NdCl
3
-Schiff Base Complex as Catalyst for Formation of Water-Blown Polyurethane Foam 3363
and stable density. Due to the unstable and oxidation properties
100
of Sn(Oct) catalyst and heat producing in foaming process,
2
the catalytic capability of stannous octylate is decreased,
leading to poor foaming process stability. Bubbles formed are
prone to collapse and shrinkage. Therefore the foam product
with rare earth catalyst has better quality because of more
uniform and stable bubble pore structure.
8
6
4
2
0
0
0
0
0
Influence of catalyst on mechanics properties of whole
water foaming semi-rigid polyurethane foam:The mechanical
property of polyurethane foam is mainly decided by the nature
of the polymer, volume ratio of gases in the products and
–
1
1647 cm
14
bubble size and other geometric properties . The catalyst will
decide the rate and content of gas produced to some extent in
the foaming process; thus affects the bubble pore shape and
pore size distribution directly. The experimental results shown
in Fig. 5 indicate that different mass ratio of rare earth catalyst
to triethylene diamine will influence mechanical properties of
the foam products.
0
500 1000 1500 2000 2500 3000 3500 4000 4500
–1
Wavenumber (cm )
Fig. 3. FT-IR spectrum of NdCl Schiff base complexes catalyst
3
Compressive strength
Dimensional stability (%) (-3, one month)
Dimensional stability (%) (-53, one month)
3
6
1.4
1.2
35
3
4
1.0
0.8
0.6
0.4
0.2
33
32
3
1
30
29
28
0.0
14
12
10
8
6
4
2
0
3:1
2:1
1:1
1:2
1:3
1
Rare earth catalyst:Triethylene-diamine (pbw)
Fig. 4. H NMR spectrum of NdCl
3
Schiff base complex catalyst
Fig. 5. Effect of catalyst on mechanical properties of foam products
polyurethane foam was obtained by using the composite
catalyst, NdCl Schiff base complexes and triethylene diamine,
Based on Fig. 5, with the increase of rare earth catalyst,
compression strength tends to decrease after the initial increase.
But the dimensional changes in different temperature show
increase after the initial decrease. In general, the performance of
the products is gradually improved and has better dimensional
stability, due to using the rare earth catalysts and triethylene
diamine in the foaming process. The rare earth can interact
with the carbonyl group in the polyurethane system, which
affects the hydrogen bonding structure of polyurethane system
and lead to structure change in polyurethane foam . There-
fore with the increase of the proportion of rare earth catalysts
in the catalytic system, the compression strength and dimensional
stability of the polyurethane foam increase.
3
stannous octoate and triethylene diamine, respectively.
Based on Table-2, with the increase of rare earth catalyst,
the whiteness, gelation and demoulding time increase as well
as the reaction rate is easy to control. In the process of foaming,
the chain growth and the foaming reaction reach a steady
balance. The foaming process will produce a large amount of
CO
2
and the addition of rare earth catalyst promotes the balance
producing rate. Strong
between foaming process and CO
2
1
5,16
bubble wall therefore will form while foaming, which assists
to hold the produced gas and lead to the more uniform foaming.
The foam has better solidification and the bubble is not easy
to collapse and shrink, as result the foam has good formability
TABLE-2
REACTION PROFILES OF WHOLE WATER FOAMING SEMI-RIGID POLYURETHANE FOAM IN DIFFERENT RATIOS OF CATALYST
Catalyst (pbw)
Cream time (s)
Gelation time (s)
Stripping time (s)
Foam density (kg/m )
Compatibility
A:B = 1:1
15
48
278
70.6
Common
A:B = 1:2
13
40
270
73.8
Preferably
A:B = 2:1
19
59
285
76.4
Good
C:B = 1:1
7
35
353
70.9
Common
C:B = 1:2
9
38
360
72.8
Common
C:B = 2:1
8
43
366
70.5
Errand
3
A: Rare earth catalyst, B: Triethylene-diamine, C: (Sn(Oct)2

3
364 Liao et al.
Asian J. Chem.
Influence of rare earth catalyst on bubble pore structure
Due to the unstable properties of stannous in foaming process,
the reaction has lower rate of gel and molecular chain growth.
As result it lead to the uneven of gas formation rate, the fracture
of bubble surface and the non-uniform of aperture size in reaction
process.
of all water foaming semi-rigid polyurethane foam: The
influence of catalysts on foam bubble pore structure is shown
in Fig. 6. The whole water foaming semi-rigid polyurethane
foam was prepared with a catalytic system of neodymium
chloride Schiff base complexes and triethylene diamine with
quality ratio of 2:1 and with the other one of stannous caprylate
and triethylene diamine on the base of the quality ratio of 1:1
respectively.
Conclusion
All water blown polyurethane semi-rigid foam was prepared
with neodymium chloride Schiff base complexes and ethylene
diamine as catalyst. The compression strength, cell structure
and other properties of foam were measured. It is found that,
with the ratio of 2:1 of neodymium chloride Schiff base comp-
lexes to triethylene-diamine, the foam product shows the best
formability, compression strength, dimensional stability at
different temperatures and cell structure. With its high catalytic
capability, catalyst composed of Schiff base complexes of
neodymium chloride and ethylene diamine will make good
contribution for the production of polyurethane foam with
excellent performance.
(a)
ACKNOWLEDGEMENTS
The Project Supported by Guangxi Higher Education
Institutes Talent Highland Innovation Team Scheme
(
GJR201147-12), Guangxi natural science foundation of key
projects (2011GXNSFD018015) and the Innovation Project
of Guangxi University for Nationalities (gxun-chx2013098)
of China.
(b)
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Fig. 6. Bubble figures with different catalyst systems measured by FESEM;
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3
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