Improving the Performance of Heat Insulation
Polyurethane Foams by Silica Nanoparticles
M.M. Alavi Nikje, A. Bagheri Garmarudi, M. Haghshenas, and Z. Mazaheri
1
Abstract. Heat insulation polyurethane foam materials were doped by silica nano
particles, to investigate the probable improving effects. In order to achieve the best
dispersion condition and compatibility of silica nanoparticles in the polymer
matrix a modification step was performed by 3-aminopropyltriethoxysilane
(APTS) as coupling agent. Then, thermal and mechanical properties of
polyurethane rigid foam were investigated. Thermal and mechanical properties
were studied by tensile machine, thermogravimetric analysis and dynamic
mechanical analysis.
1 Introduction
Polyurethanes are one of the most versatile groups of plastic materials. The variety
of polyurethane types reaches from flexible and rigid foams over thermoplastic
elastomers to adhesives, paints and varnishes. Rigid polyurethane foams are
highly applied in construction industry as heat insulator and also shock-noise absorber. The thermal characteristics of these polymeric materials had made them as
a very useful product for decrement in energy loss in buildings and constructions
[1,2]. Their low thermal conductivity is due to a unique combination of blowing
agent properties, cell size, and closed cell morphology. However, PUs also have
some disadvantages, such as low thermal stability and low mechanical strength,
etc. There is an interest to improve the physical and thermal properties of these
polymers. To overcome these disadvantages, great deals of effort have been devoted to the development of nanocomposites in recent years [1]. One route is to
utilize nano technology to modify them. In this research it has been tried to introduce silica nano particles in polyurethane rigid foam formulation in order to investigate its probable improving effect on foam samples. This would produce high
performance composites. There are also many reports, indicating the physical mixing of nano material and polyol as the synthesis route. The main problem in this
M.M. Alavi Nikje, A. Bagheri Garmarudi, and Z. Mazaheri
Chemistry Department, Faculty of Science, IKIU, Qazvin, Iran
M.M. Alavi Nikje, A. Bagheri Garmarudi, and M. Haghshenas
Department of Chemistry & Polymer Laboratories, Engineering Research Institute,
Tehran, Iran
150
M.M.A. Nikje et al.
kind of prepared nanocomposites is the heterogeneous dispersion of nano particles
[3-7]. While it can be expected that the nano silica, with extremely large surface
area would affect the PU properties much more than regular fillers, it is noticeable
that how the dispersion of nano filler in polyol matrix is homogenized. The main
objective of this research was to examine the effect of nano silica on the properties
of rigid PU foams. In addition, silane based agent was applied to play the role of
coupling agent between polyol media and nano phase surface. Effect of well dispersed nano filled on thermal and physical properties of PU was monitored.
2 Experimental
2.1 Materials and Apparatus
DatloFoam TA® 14066 polyether polyol containing all of required additives, MDI
(Suprasec®5005) for rigid polyurethane foam were from HUNTSMAN Co. Technical data are listed in tables 1 and 2. Nano silica (Particle size 12 nm,
AEROSIL®, surface area 200 m2g-1) from Degussa, 3-aminopropyltriethoxysilane
(Amino A-100) from Silquest® chemicals (wetting area 353 m2g-1) and toluene
from MERCK.
Table 1 Technical data for MDI
Suprasec®5005
Appearance
Dark brown liquid
Viskosity
220 cps @ 25ºC
Specific gravity
1.23 g.cm-3@ 25 ºC
Flash point
233 ºC
Fire point
245 ºC
Table 2 Technical data for polyether polyol
DatoFoamTA®14066
Appearance
Viscous yellow liquid
Viskosity
5260 cps @ 25ºC
Specific gravity
1.06 g.cm-3@ 25 ºC
Water kontent
2.3%
pH
12
Infrared spectra were obtained by a Tensor 27 Brucker Infrared spectrometer.
Thermal properties of nanocomposites were analyzed by using Dupont 2000
instrument under nitrogen flows from room temperature to 700 ºC at heating rate
of 10ºC/min. tensile strength and elongation at break of these foams were
Improving the Performance of Heat Insulation Polyurethane Foams
151
measured using by INSTRON 1122 tensometer at a test speed 5 mm/min. Dynamic mechanical analysis was carried out by Dupont 2000 instrument at a frequency 1Hz and heating rate of 5 ºC/min from -50 to 150 ºC.
2.2 Sample Preparation
Five grams of nano-silica in 200 ml toluene was refluxed with mechanical stirring
(1000 rpm) at 80-90°C for 2h. Then 2.83 g 3-aminopropyltriethoxysilane (APTS)
was added to this mixture. The mixture was refluxed for 12h under same condition. After isolation and washing with methanol the free APTS was removed. Finally, modified nano-SiO2 powder was dried in an oven at 70°C for 24h and resulted powder was dried and sieved. Figure 1 shows the schemoatic process of
modification. Then polyether polyol (200 g) was mixed with modified nano silica
in acetone media. High shear mechanical stirrer (15 min) and ultrasonic homogenizer (20 min) were used to perform the mixing process. In the next step, acetone
was removed under vacuum at 20 ºC. MDI portion was then added to the mixture,
being well homogenized during the fast curing step.
Fig. 1 Schematic structure of modified nanosilica
Fig. 2 FT-IR spectra
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M.M.A. Nikje et al.
3 Result and Discussions
3.1 Monotoring of Modification Process
Comparison of FTIR spectra obtained form nono silica and modification's product
made some useful information. Aerosil A200 spectrum absorption peak at 3442
cm-1 is attributed to silanol group on to Aerosil surface and the signal due to Si-O
band would appeare at 1107 cm-1. In the modification product's spectrum it was
observed that the absorbance peaks of the C-H stretching vibrations would appeare below 3000 cm-1. This would indicate the covalent band between silanol
group on the nano-silica surface and APTS (Figure 2).
3.2 Thermomechanical Studies
The results of tensile strength, elongation at break and elasticity modulus are
shown in table 3.
Table 3 The results of mechanical and thermal tests and glass transition temperature
Nano silica content
Elasticity Modulus
Tensile strength
Elongation at break
(%w)
(MPa)
(MPa)
(%)
0.0
3.7
0.5
31.2
0.5
3.6
0.50
22.1
1.0
4.3
0.45
17.9
1.5
3.4
0.4
24.2
2.0
3.5
0.6
24.5
2.5
5.1
0.5
27.4
3.0
2.5
0.3
21.7
Tensile strength in 2 wt% loaded sample 2.5% sample was the highest of all.
This result indicated that with increasing of nano silica up to 2% loading, an interfacial interaction between the functionalized silica surface and the nearby polymer
chains is strong. Silica nano particles inherently possess high module and would
strengthen the PU matrix when dispersed in the nano scale. In the other hand, surface modification of nano silica by coupling agent would reduce the possible heterogeneity of network which is also effective as a negative effective parameter.
Finally in 3 wt% sample it was reduced to 0.3 MPa. Decrement in the tensile
strength at high concentration 3 wt% was attributed to the aggregation nanosilica
due to additional hydrogen bonding between silica surface, that result in increasing number of voids in the polymer layer next to the filler surface. The elongation
at break at nanocomposites was decreased comparing to those of pure PU foam.
Because the functionalized silica surface would act as crosslinker and not as a
Improving the Performance of Heat Insulation Polyurethane Foams
153
chain extender which leads to decrease of elongation at break. But whitin the nanofilled PU, in 2.5% sample, the highest elongation at break was seen. Perhaps it
could be assumed that in 2.5% loaded sample, a part of amino group on nanosilica
surface acted as chain extender to some extent.
Also with infusion of nano silica in polymer matrix, the glass transition temperatures (Tg) were increased to 2% loading and in higher nano silica content were
decreased. The increasing in Tg up to 2% nanocomposites may be attributed to decrease in phase separation between soft and hard segment in presence of nano silica. Increment in the Tg of soft segments, indicates that silica nanoparticles have
been in a very tight correlation with polymer network because of their high surface area. In the other hand, as shown in figure 1 the surface activity of nano silica
would interact with crosslinking polymer network in presence of silane coupling
agent strongly which leads to hindered relaxational mobility in the polymer segments near the interface, increasing the Tg. TGA data are also shown in Table 3. It
is observed that temperature corresponding to 50% decomposition with increasing
of nano silica would shift to higher temperatures. This means that the incorporation of SIAP in to PU foam offers a stabilizing effect against decomposition.
Table 4 TGA data
Nano silica content
Tg
Td at 50%w
(%w)
(°C)
(°C)
0
85
307
0.5
95
311
1
85
313
1.5
95
310
2
95
320
2.5
80
337
3
57
315
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