Applied Chemistry,

Vol. 12, No.2, November 2008, 앙7-때

Thermal decomposition kinetics of y-ray irradiated

DGEBAlJeffamine epoxy resin

Kvouna-Yona Lee • Ki-Yup Kim· In-Ra Hwang

Advanced Radiation Technology Institute , Korea Atomic Energy Research Institute ,

1266 Sinjeongdong , Jeongupsi , Chonbukdo 580-195 , South Korea

1. Introduction

Epoxy resin is widely used in a variety of fields. Especially , epoxy resin has

been used as paint in extreme environments such as nuclear power plants and

ships. As such , epoxy resin has been considered an essential material for the last

forty years in a variety of fields. Especially in a nuclear power plant , epoxy resin

has been used in about 26 parts in diverse forms , playing a critical role as a final

safety valve in the case of an acciden t. Nevertheless , the changes in characteristics

according to the usage conditions generated at the time of a system application or

drop in properties have not been sufficiently studied so far. It can be attributed to

the limitations of the experimental analysis in that it is virtually impossible to

exactly reproduce an actual working environment, along with the complicated

operative system and environmental histories [l, 2]. Unpredicted incidents in

nuclear power plants are caused by a physical or chemical external stimulus.

Maintaining the safety requirements of these factors is critical for a safety control

of a nuclear power plan t. Especially , the aging of facilities and the unsoundness of

materials increase the probability of a failure according to the safety criteria inside

a nuclear power plan t. Hence , prompt response and early mitigation of an accident

during an operation are critica l. Nevertheless , there is an insufficient amount of

useful information about a safety test and an actual system regarding the probable

incidents inside a nuclear power plant caused by the properties of the used

materials [3 , 4 J. Consequently , in order to satisfy the high level of the safety

criteria in a system, it is important to understand a new system by estimating

correlations among the physical and chemical changes , and further to understand

the feature of a final hardener through an investigation of the thermal

characteristics of a resin system. In this study , we measure the thermal

decomposition kinetics by a gamma-ray irradiation on an epoxy resin system , which

is applied to the paints for the iron-surfaced containment buildings of nuclear

power plants.

2. Experimental

2. 1. Materials

As for an epoxy resin , YD-128 CDiglycidyl Ether of Bisphenol A type , Epoxy

Equivalent Weight (E.E. W.) = 184-190 g/eq , viscosity (at 25°C) = 11500-13500

277

278 Kyoung-Yong Lee' Ki-Yup Kim' In-Ra Hwang

cps , specific gravity = 1. 17) from Kukdo Chemical Co. Ltd was used. while D-230

Oeffamine) an amine system from the same company was used as a hardener. The

epoxy and hardener were combined at a ratio of 2.3 1 (216 g 93.9 g) until a

transparent compound was obtained. The mixed compound was inserted in a silicon

molder , which was fabricated in our lab. The mixed compound was put into an oven

at 80°C for four hours for the initial hardening process. After the initial hardening

process , the samples underwent a second hardening process by being placed in an

oven at 60 °C for twelve hours. The fabricated samples were irradiated by

gamma-ray at room temperature , using the 60Co gamma-ray sources at the

radioactive ray irradiation facility at the Korea Atomic Energy Research Institute.

The radioactive rays of 500 kGy , 1000 kGy , and 2000 kGy were irradiated at a

dose rate of 8 KGy/hr , with 2000 kGy as the standard. which is the lowest dose

with negligible damage for the epoxy resin ends.

2.2 TGA analysis

A TGA (TA instrument , Mode 2950) was used to perform a thermogravimetric

analysis of the samples and evaluate their activation energy based on ASTM E

1641 [5 ], First , the TGA was heated from 50°C to 800°C at rates of 1 °C/min , 2

。C/min ， 5 °C/min , and 10 °C/min to obtain the TG and DTG curves.

Thermogravimetric analysis is generally conducted to evaluate how thermolysis

affects the mass of volatile solids , liquids , and flammable materials. The analysis

can also be used to evaluate the thermal degradation of a polymer according to

thermolysis. Among numerous thermogravimetric analytic approaches for explaining

an evaluation model , the Flynn-Wall-Ozawa method will be used in this study

because this method is based on statistics and involves simple equations [6 ],

Additionally , the kinetic parameters were obtained using the Kissinger method. The

activation energy was computed from the slope of the first-degree equation by

applying the four peak values of the given DTG curve and the heating rate

conditions to the Kissinger method [7 ],

3. Result and discussion

3.1 TGA

Fig. 1 show the TG-DTG curve of the samples at 1 °C Imin , 2 °C/min , 5 °C/min ,

and 10 °C/min. As is shown in the TG graph. the Initial Decomposition Temperature

(IDT) decreases as the irradiation dose and temperature increase. and the heating

rate decreases , which can be attributed to the increased amount of peroxides

following the oxidative reaction of the gamma-ray and oxygen. As is shown in the

DTG graph in Fig. 1, the DTG peak temperature of the samples decreases as the

irradiation dose increases. and as the heating rate decreases. The peak of the DTG

curve indicates a point where the decomposition takes place most vigorously in the

domain of the TG curve. The curve shows that the oxidative reaction becomes

웅용화학， 제 12 권 제 2 호， 2008

Thermal decomposition kinetics of of 'i-ray irradiated DGEBA/Jeffamine epoxy resin 279

more active as the irradiation dose increases and as the heating rate decreases ,

which reduces the DTG peak temperature [8 , 9J.

겐l. 5”‘••‘π’“n tn" 1f

-TGcu

UTG ‘:or‘'"~ .......-

--OICt:Jhli..,‘ t ’JIlI I,,) I~ 씨‘。，‘'Cllnla)

’”‘"C/lftla 、~

la)’∞ 2.6

.。

(μxs:￡·‘-*·i호】

”“

“

내

%

ω

(A;)

등강-ytt

?。 0.'

00’∞ 200 300 ‘00 500 eoo

Tem""nlure (1::)

(a) non-irradiated epoxy

Ie) ’@ f !”c. ,---·-TG c.

l nTG ωn-•• _

OJ ('Chub:!)

Xξ'rl-o,('‘'min)

0l5o (‘ttIlm·iniIn

‘

20

%

‘‘

“

(S:sμ-‘--

'"0

’00 200 3-∞ ‘00 ‘@ ‘아Tpmpera‘ure ee)

(이1야 2.0

‘·‘:야…I 빼‘·…rv... i’ 6“ν(i흘)、흘--;-’‘|’-←샤 -ei

@딘떨 iO~ ~‘~ • -::""-----'o 。

100 200 300 ‘。o ... eo。

(b) 500 kGy irradiated epoxy

(이100

1.5.V

;

...，。 풍,o. 효

z 。

(은

얻)

@

뻐

애

(S)-aMZ

‘tt

-흘-‘‘·>-;a

--01 ('C:min~

mμ--씨 ("ell'l l매

_··_--u~ ("(;/ml.)l

-느낀.l.!O민~~o 。

일XI eo。100 '"。

(c) 1000kGy irradiated epoxy (d) 2000kGy irradiated epoxy

Fig. 1 TG-DTG curves of the samples by the irradiation dose and temperature.

In Fig. 2. a conversion level at 5% was set for the TG curves that was obtained

at various heating rates , in order to calculate the activation energy of the samples

according to the ASTM E 1641 standard. The activation energy of the samples was

computed by applying the DTG peak temperature to the Kissinger method.

• Non-....rad“ a ’• 500 kG、 πradiattd

.. tooo kOy iπadblt찌

’ 1000 kOy irnd“”’0:. 0.8。ι

。

0 ...

’0.2

0.0

” ’ 7 1.8 1.S 2.0 2 ’ 2.2 2.3lrr(XIO')

• :'iQD-i rT'adillll f't'’• ’“IkG‘ Irro’“ad

‘ 11‘>O kG‘ Irr‘’10‘ad,. 11)(10 ‘Gylrndlal얘

r .. '2.0

g도

11.5

11 。

lO.!

1.68 160 162 1.6‘ ,.‘ ’ ..I fT(xIO')

(a) Flynn-Wall-Ozawa method (b) Kissinger method

Fig. 2 Arrhenius plots for the activation energy of the samples

Fig. 2 summarizes the slope of the samples obtained from an application of the

Flynn-Wall-Ozawa method of ASTM E 1641 along with the outcomes from the

Applied Chemistry, Vol. 12, No.2, 2αB

280 Kyoung-Yang Lee' Ki-Yup Kim' ln-Ra Hwang

Kissinger method. Clearly , all the samples in Fig. 2 and Table 1 reveal a linearity

with a regression coefficient (r2) value in the range from 0.95 to 1. Table 1 lists

the activation energy obtained from Fig. 2. In Table 1. the activation energy of the

samples decreases as the irradiation dose increases , which can be attributed to the

fact that the peroxides of the samples created from the oxidation of the gamma-ray

and oxygen increased [10 J.

Table 1 Activation energy of the samples

FWO method Kissinger method

Dose Er2 E

r 2

(kJ/mo\)slope

(kJ/mo\)slope

Non-irradiated 159 .4 -8.8 204.9 24.6 0.99500 kGy-irradiated 145.3 -8.1 0.99 179.1 2 1.5 0.99

1000 kGy-irradiated 132 .4 -7 .4 0.99 167.7 20.2 0.982000 kGy-irradiated 64.5 -3.8 0.95 164.7 19.8 0.99

4. Conclusion

In this paper, the characteristics of a kinetic thermal decomposition was

investigated through a gamma-ray irradiation of DGEBAlJeffamine epoxy resins.

According to the TGA experiment results , the oxidative reaction becomes more

active as the irradiation dose increases , which is represented by a DTG peak

temperature and activation energy. The activation energy value turned out to

depend largely on which one of the two methods , either the Flynn-Wall-Ozawa or

Kissinger method , was used.

Acknowledgements

This research is carried out under the Nuclear R&D Program by MOST of Korea. we are

grateful for their support. This work is a part of a project "Study of the establishment of

Good Irradiation Practice (GIP) system"

References[1] T. Ozdemir , A. Usanmaz , Radia t. Phys. Chern. 77 (2008) 799.

[2] H.S. Yoon , J. Korean Soc. Dye. Finish. 6 (999) 7.

[3] D.W. Chung , KIEE. J. Electr. Eng. Techno I. 2 (2007) 386.

[4] E. Friesen , J. Meseth. S. Guentay , D. Suckow, J.L. Jimeez , L. Herranz. V. Peyres, G.F.D. Santi ,

A. Krasenbrink , M. Valisi. L. Mazzocchi. Nucl. Eng. Des. 209 (200 1) 253.

[5] Annual Book of ASTM Standards E 1641 14.02 (1 998) 104 1.

[6] J.H. Flynn , L.A. Wall. Polym. Lett. 4 (966) 323

[7] L. Nunez. F. Fraga. M. R. Nunez , M. Villanueva. Polymer 41 (2000) 4635.

[8] J. Li , L.Tong. Z. Fang. A.Gu , Z. XU,Polym. Degrad. Stab. 91 (2006) 2046.

[9] D. Rosu. C.N. Cascava f, C. Ciobanu , L. Rosu. J. Ana l. App I. Pyrolysis. 72 (2004) 191

[10] J.Y. Lee. Y. Liao , R. Nagahata. S. Horiuchi. Polymer 47 (2006) 7970.

응용화학， 제 12 권 제 2 호， 2008