effects of nano-silica addition on water absorption of glass fiber/epoxy composite

7
Effects of Nano-silica Addition on Water Absorption of Glass Fiber/Epoxy Composite Huey-Ling Chang* 1a , Chih-Ming Chen 2b , Cheng-Ho Chen 2c 1 Department of Chemical and Materials Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan, R.O.C. 2 Department of Mechanical Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan, R.O.C. E-mail: a [email protected], b [email protected], c [email protected] Keywords: Nanoparticle; Nanocomposite; Epoxy resin; Dynamic mechanical analysis Abstract. Nanocomposite samples containing epoxy resin, glass fiber and 0~2 wt.% SiO 2 nanopowder are prepared. The effects of SiO 2 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.% SiO 2 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.% SiO 2 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 40-45 Online available since 2013/Dec/24 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi: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)

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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