effects of nano-silica addition on water absorption of glass fiber/epoxy composite
TRANSCRIPT
Effects of Nano-silica Addition on Water Absorption of Glass Fiber/Epoxy Composite
Huey-Ling Chang*1a, Chih-Ming Chen2b, Cheng-Ho Chen2c
1Department of Chemical and Materials Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan, R.O.C.
2Department of Mechanical Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan, R.O.C.
E-mail: [email protected], [email protected], [email protected]
Keywords: Nanoparticle; Nanocomposite; Epoxy resin; Dynamic mechanical analysis
Abstract. Nanocomposite samples containing epoxy resin, glass fiber and 0~2 wt.% SiO2
nanopowder are prepared. The effects of SiO2 addition on the water absorption rate, glass transition
temperature (Tg) and dynamic mechanical properties of the various samples are then observed. The
water absorption of the nanocomposite specimens is then compared with that of pure glass
fiber/epoxy composite specimens when tested in water. The results show that the addition of 2 wt.%
SiO2 reduces the water absorption from 0.0704% to 0.0573%. The storage modulus with adding
2wt.% silica nano-composite compared to the neat composite raises up 13.82%. Following the
water absorption test, the mechanical properties of the samples are not obvious change. Therefore,
the experimental results indicate that 2wt.% SiO2 addition is beneficial to the water resistance and
dynamic mechanical properties of epoxy resin / glass fiber nanocomposites.
Introduction
The application of composites has in recent years extended from the military and aerospace to
various different areas. Composites are composed primarily of reinforcement and matrix materials.
Reinforcement materials are divided into two classes of glass fibers and carbon fibers, and the
matrix materials are primarily thermoplastic and thermosetting resins. However, the effect of
mixing fibers in the matrix has reached its limit of enhancing mechanical properties. In order to
further enhance the properties, nanopowders are added to improve the strength between the matrix
and fibers. Therefore, adding powders into epoxy has become a popular research topic.[1]
As nanocomposites become widely used, it is discovered that adding nanoparticles in epoxy
enhances its properties [2-5]. From the literature, it is found that adding silica particles in epoxy can
improve the mechanical, thermal properties and wear resistance [6]. Mechanical properties include
tensile modulus, bending strength and fracture toughness; and thermal properties include the glass
transition temperature and thermal cracking temperature. Wear resistance represents the friction loss
value.
Chen et al. [7] add spherical silica in bisphenol F diglycidyl ether epoxy and hardeners to
improve the fracture toughness and elastic modulus simultaneously without changing the strength
and Tg at low silica content. When silica content is above 5wt.%, Tg drops significantly. Chen et al.
contribute the obvious drops to the possible high heat generated at the tip of the ultrasonic probe.
Local high temperature triggers the homopolymerization of epoxy or decomposition of epoxy
monomer; particularly in high content level, silica become catalysts for self-polymerization. These
polymerization phenomena affect the measurement number of epoxy and amines, further influence
the cross-linking density and lead to the drops of Tg’s. Therefore, too much addition of silica will
lead to the deteriorated properties. Mahrholz et al. [8] use liquid composite molding (LCM) to study
the applicability of silica/epoxy in fiber reinforced polymers (F.R.P.). After adding nano-silica, the
stiffness, strength, and toughness are all significantly higher than pure epoxy.
With the decrease of global energy sources, renewable energy is in focus. Composite materials
are widely used in this area. Windmill blades are currently 100% of composite materials; therefore,
the composites industry is now at the center of wind power generation equipment. Because water
Advanced Materials Research Vol. 853 (2014) pp 40-45Online available since 2013/Dec/24 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.853.40
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 136.186.1.81, Swinburne University, Hawthorn, Australia-07/09/14,04:27:53)
vapor is abundant in the environment, windmill blades exposed in the open air will experience
weight increase or shape changes if they have high water absorption. The efficiency of power
generation will be decreased; even the blade structure may be damaged. Therefore, the
water-absorbing properties of composites are very important.
In this paper, laminates made from adding nano-silica powders and glass fibers in the epoxy are
tested for the relationship between water absorption and silica content. The samples are analyzed by
a dynamic mechanical analyzer. A dynamic mechanical analyzer places the specimen under
particular conditions and detects the changes in mechanical properties due to temperature, force or
frequency changes. The characteristics of the materials are then judged, therefore the machine can
be used to study the property changes of the samples after water-absorption tests.
Experimental
Materials. The diglycidyl ether of bisphenol-A type epoxy resin (an epoxide equivalent weight of
180 g/equiv.) was purchased from Chang Chun Plastics Co. Ltd. Taiwan. The epoxy resin was cured
with the incorporation of an amine type epoxy curing agent (the amine hydrogen weight of 65
g/equiv. and amine value 430g/equiv.). The silica nanoparticle used was a silicon dioxide powder.
The surface of the fumed silica was chemically modified with poly(dimethylsiloxane) coupling
agents. The hydrophobic fumed silica with a specific surface area (BET) of 100 m2/g, and original
particle diameter of 14 nm and a tapped density 60 g/L(acc. to DIN ISO 787/XI, Aug. 1983). Glass
fiber (SK3600) was purchased from Korea. Note that all the purchased materials were used
as-received without further purification.
Sample preparation. Samples were prepared in the following fashion:
(1) Mix until uniform a preset ratio of resin and nanoparticle in the wet ball mill.
(2) Use the centrifugal machine and vacuum to degas the mixture.
(3) Add in hardener according to ratio and mix and degas like before.
(4) Uniformly cast the mixed resin onto the glass fiber cloth.
(5) Place into molding machine to form the sample (120℃,120min,500psi).
(6) Post-curing process (150℃,180min).
(7) Perform analysis.
Measurement. The dynamic mechanical properties of the composites were determined by DMA
(TA Instruments DMA 2980) at a frequency of 1Hz, temperature range from 30 to 200℃, and
heating rate of 5℃/min. Water-absorption tests: Grind smooth the cut surfaces of the specimen,
place in the 50℃ oven and heat 24 hours to remove the moisture. Weigh after dry and record the
weight W0. Immerse the specimen completely in a 23℃distilled water container and record the
weight after the specimen is immersed 0, 24, 48, 72, 96, 120, 144 and 168 hours. The samples were
quickly dried with cloth and measured. The water-absorption ratio is calculated according to the
following formula.
Waterabsorption % =
× 100% (1)
Results and Discussion
Nano-silica is used as filler, added in epoxy and then coated on glass fibers to form nanocomposites.
Detailed ingredient weight percentages and dimensions are shown in Table 1. Nano-composites are
made according to the manufacturing processes; water absorption tests are then performed.
Specimen are placed in distilled water by 168 hours, weight measurements are taken once every 24
hours, the results are presented in Table 2 and Figure 1. The results show that, after 168 hours water
absorption test, the samples with 0wt.%, 1wt.%, and 2wt.% addition have water absorption ratio of
0.0704%, 0.0598%, and 0.0573% respectively. The lower water absorption ratios should be
contributed to the characteristic silica itself does not absorb water in the mixed sample.
Advanced Materials Research Vol. 853 41
Table 1 The weight percentage of detailed ingredients of the composites
Table 2 The water absorption of composite (immersed in 23℃water)
0 24 48 72 96 120 144 168
0.00
0.05
0.10
0.15
0.20
Wat
er A
bso
rpti
on
(%)
Time(hr)
(a)
(b)
(c)
100 110 120 130 140 150 160
0.06
0.09
0.12
0.15
Wat
er A
bso
rpti
on(%
)
Time
Figure 1 The water absorption vs. time of composite (a) GEHP0 (b) GEHP1 (c) GEHP2
Next, a dynamic mechanical analyzer (DMA) is used to analyze glass fiber/epoxy. The effects of
different silica content and the dynamic mechanical property changes after water absorption tests
are examined. The results are shown in Table 3. The properties of the samples before
water-absorption tests are examined first. The storage modulus of glass fiber/epoxy without silica is
11912MPa, 1wt.% is 12614MPa, and 2wt.% is 13558MPa. The storage modulus rise as the content
of silica increases as shown in Figure 2. The 2 wt.% SiO2 addition increases the value of storage
modulus by 13.82% compared to that of the sample with no silica nanopowder. The loss modulus of
glass fiber/epoxy without silica is 144.40MPa, 1wt.% is 173.00MPa, and 2wt.% is 199.10MPa. The
Tg of glass fiber/epoxy without silica is 87.05℃, 1wt.% is 88.90℃, 2wt.% is 88.01℃ as shown in
Figure 3. The loss modulus and Tg do not have significant changes. The results show that adding
silica not only increases the storage modulus but also does not affect the loss modulus and Tg.
Table 3 Glass transition temperature and modulus of composite obtained from DMA results
a modulus at 32°C.
b the sample were tested after immersed in water for 168 hours.
Sample Epoxy (wt.%) Hardener (wt.%) SiO2
(wt.%)
Dispersing
Agent (wt.%)
Antifoaming
Agent (wt.%)
GEHP0 74.60 24.90 0.00 0.00 0.50
GEHP1 73.66 24.76 0.99 0.10 0.49
GEHP2 72.51 24.81 1.98 0.20 0.50
Sample Weight increment (%)
24hrs 48hrs 72hrs 96hrs 120hrs 144hrs 168hrs
GEHP0 0.0377 0.0528 0.0603 0.0653 0.0679 0.0704 0.0704
GEHP1 0.0299 0.0473 0.0523 0.0548 0.0573 0.0598 0.0598
GEHP2 0.0274 0.0374 0.0474 0.0524 0.0548 0.0573 0.0573
Sample E’ (MPa)a E” (MPa)
a Tg (℃)
GEHP0 11912 144.40 87.05
GEHP1 12614 173.00 88.90
GEHP2 13558 199.10 88.01
GEHP0-wb 11937 180.56 88.82
GEHP1-wb 12582 203.30 89.54
GEHP2-wb 13505 228.80 89.90
42 Materials Science, Machinery and Energy Engineering
Figure 2 Storage modulus of (a) GEHP0 (b) GEHP1 (c) GEHP2
Figure 3 Tan Delta of (a) GEHP0 (b)GEHP1 (c) GEHP2
The properties of the samples after water-absorption tests are then examined. The storage
modulus of glass fiber/epoxy without silica is 11937MPa, 1wt.% is 12582MPa, and 2wt.% is
13505MPa as shown in Figure 4. The results show that there are no significant changes in the
storage modulus after water-absorption tests, and the peak shape coincides with that of before tests.
It can be seen that water has little effect on the samples. The results are also consistent with the
aforementioned sample low water-absorption ratio; therefore, the sample has good water resistance.
The loss modulus of glass fiber/epoxy without silica is 180.56MPa, 1wt.% is 203.30MPa, and
2wt.%is 228.80MPa. The Tg of glass fiber/epoxy without silica is 88.82℃, 1wt.% is 89.54℃,
2wt.% is 89.90℃, shows no obvious changes, as in Figure 5. From these tests, we know there are
no significant changes in all the properties after water-absorption tests. The peak shapes of DMA
figures before and after water absorption are quite consistent, indicating little change in dynamic
mechanical properties.
20 40 60 80 100 120 140 160 180 200 220
2000
4000
6000
8000
10000
12000
14000
Sto
rage M
odu
lus(
MP
a)
Temperature(℃)
(a)
(b)
(c)
20 40 60 80 100 120 140 160 180 200 220
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Tan
Del
ta
Temperature(℃)
(a)
(b)
(c)
Advanced Materials Research Vol. 853 43
20 40 60 80 100 120 140 160 180 200 220
2000
4000
6000
8000
10000
12000
14000
Sto
rag
e M
od
ulu
s(M
Pa)
Temperature(℃)
(a)
(b)
(c)
Figure 4 Sample Storage Modulus of (a) GEHP0-w (b) GEHP1-w (c) GEHP2-w
20 40 60 80 100 120 140 160 180 200 220
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Tan D
elta
Temperature(℃)
(a)
(b)
(c)
Figure 5 Tan Delta (a) GEHP0-w (b) GEHP1-w (c) GEHP2-w
Summary
Effects of nano-silica addition on water absorption of glass fiber/epoxy composites are studied. The
dynamic mechanical properties after water-absorption tests are also investigated. The samples are
placed in water and nano-silica addition is found to reduce the sample water-absorption ratios. For
the dynamic mechanical properties before water-absorption tests, the storage modulus rise as the
amount of added nano-silica increases. The 2 wt.% SiO2 addition sample increases the value of
storage modulus by 13.82% compared to that of the sample with no silica nanopowder. For Tg,
silica addition has no significant changes. The DMA figures after water-absorption tests are quite
consistent with those before tests. Therefore, the samples have good water resistance and adding
nano-silica helps to improve the storage modulus and lower water-absorption ratios.
Acknowledgement
The authors are grateful to the National Science Council of Taiwan for financial support of this
work.
44 Materials Science, Machinery and Energy Engineering
References
[1] W. Jiang, F. L. Jin, S. J. Park: J. Ind. Eng. Chem., Vol.18 (2012), p.594.
[2] C.G. Chen, R. S. Justice, D.W. Schaefer, J. W. Baur: Polymer, Vol.49 (2008), p.3805.
[3] S. S. Ray, M. Okamoto: Progress in Polymer Science, Vol.28 (2003), p.1539.
[4] F. Hussain, M. Hojjati, M. Okamoto, R. E. Gorga: Journal of Composite Materials, Vol.40
(2006), p.1511.
[5] H. Zou, S.Wu, J. Shen: Chem Rev., Vol.108 (2008), p.3893.
[6] B. Wetzel, F. Haupert, K Friedrich, M.Q. Zhang, M.Z. Rong: Polymer Engineering and
Science, Vol.42 (2002), p.1919.
[7] C. G. Chen, Alexander B. Morgan: Journal of Polymer, Vol.50 (2009), p.6265.
[8] T. Mahrholz, J. Stängle, M. Sinapius: Journal of Composites: Part A, Vol.40 (2009), p.235.
Advanced Materials Research Vol. 853 45
Materials Science, Machinery and Energy Engineering 10.4028/www.scientific.net/AMR.853 Effects of Nano-Silica Addition on Water Absorption of Glass Fiber/Epoxy Composite 10.4028/www.scientific.net/AMR.853.40
DOI References
[1] W. Jiang, F. L. Jin, S. J. Park: J. Ind. Eng. Chem., Vol. 18 (2012), p.594.
http://dx.doi.org/10.1016/j.jiec.2011.11.140 [2] C.G. Chen, R. S. Justice, D.W. Schaefer, J. W. Baur: Polymer, Vol. 49 (2008), p.3805.
http://dx.doi.org/10.1016/j.polymer.2008.06.023 [3] S. S. Ray, M. Okamoto: Progress in Polymer Science, Vol. 28 (2003), p.1539.
http://dx.doi.org/10.1016/j.progpolymsci.2003.08.002 [4] F. Hussain, M. Hojjati, M. Okamoto, R. E. Gorga: Journal of Composite Materials, Vol. 40 (2006),
p.1511.
http://dx.doi.org/10.1177/0021998306067321 [5] H. Zou, S. Wu, J. Shen: Chem Rev., Vol. 108 (2008), p.3893.
http://dx.doi.org/10.1021/cr068035q [7] C. G. Chen, Alexander B. Morgan: Journal of Polymer, Vol. 50 (2009), p.6265.
http://dx.doi.org/10.1016/j.polymer.2009.11.002 [8] T. Mahrholz, J. Stängle, M. Sinapius: Journal of Composites: Part A, Vol. 40 (2009), p.235.
http://dx.doi.org/10.1016/j.compositesa.2008.11.008