24 th icnts, bologna, 1-5 september 2008 radiation induced damage electron, gamma photon and ion...

24th ICNTS, Bologna, 1-5 September 2008

Radiation Induced Damage

Electron, Gamma Photon and Ion Irradiation Effects in PP/EPR/HDPE

Christelle Bergeon 1, Christophe Mavon 1, Franck Berger 1, Zohra Lounis-Mokrani 2, Patrick Delobelle 3, Michel Fromm 1

This paper mainly deals with changes in surface properties of an industrial polymer due to irradiations with gamma photons, electrons and alpha particles.

In the second part of the presentation a discussion is presented that aims at comparing the dose (electrons, photons) effects with the fluence (alphas) effects, based on simple track structure theory.

1: Laboratoire de Chimie-Physique et Rayonnement - Alain Chambaudet (LCPR-AC)UMR CEA E4, Université de Franche-Comté. 16 route de Gray. F-25030 Besançon Cedex

2 : Laboratoire de Dosimétrie, Centre de Recherche Nucléaire d’Alger, BP 399, Alger Gare 16000, Algeria

3 : FEMTO ST-LMARC. UMR 6174. 24, chemin de l’épitaphe. 25030 Besançon cedexFrance.




The Polymer Under Study : PP / EPR / HDPE

Plastics have become an important material for industrial applications, particularly in the automobile sector. Nowadays, plastics make up on average

more than 15% of a vehicles’ weight.

Polypropylene is the most commonly used polymer base. This material is the object of this study. Plastic parts are usually coated with paint and/or varnish. Workers in the industry have been trying to improve the coatings’ adherence properties for years.

They often try to improve adherence by using a

flaming treatment or a plasma technology.

What are the effects of ionizing radiations onPP / EPR / HDPE surface and bulk properties ?

is a ternary blend : isotactic polypropylene / ethylene-propylene rubber / high density polyethylene




The Polymer Under Study : PP / EPR / HDPE

Brandon JP, Ph-D Thesis, University of Besançon, N° 245, 1991.

Scanning Electron Microscopy of the PP/EPR chemically etched in potassium permanganate in an acid medium

isotactic polypropylenepolyethylene

http://upload.wikimedia.org/wikipedia/commons/5/57/Isotactic-polypropylene-plan-3D-balls.png

http://upload.wikimedia.org/wikipedia/commons/2/27/Polypropylene.jpg

http://upload.wikimedia.org/wikipedia/commons/9/9b/Polyethylene-3D-vdW.png

http://upload.wikimedia.org/wikipedia/commons/f/f7/Polyethylene-repeat-2D-flat.png




Irradiations

Electrons: 10 to 106 Gy, 2 MeV, In air (Van de Graaf accelerator, Aerial, Strasbourg, France)

Gammas: 10 to 106 Gy, 1.17 et 1.33 MeV, In air (60Co source, Alger, Algeria )

Alphas : 1011 to 1016 He+.cm-2, 400 keV, Under vacuum (Ion implantation, Lyon, France)

The samples are exposed to electrons and gamma photons in air, as for the alpha particles, irradiation is performed under vacuum !

Electron and gamma photon irradiations can be considered as uniform which is not the case for alpha particles (track structure

and dependance on the fluence)

The depth at which the incomming particles deposit their energy is very different as well as their stopping power :

Radiation Quality

Oxygenation




Analytical methods

-FT-IR / ATR (Functional groups)

-Contact angle (Surface energy, polarity, dispertion, … )

- Nano-Indentation (Young’s modulus & Hardness)

Surface properties

-Differential Scanning Calorimetry (Melting enthalpy & temperature)

Swelling (Swelling ratio and soluble fraction)

Bulk properties

Irradiated samples have been analysed by means of:




1630 cm-1 : vinylic function

1709 cm-1 :Carbonyl bond

Results :Surface chemical modifications: FT-IR/ATR spectroscopy

110015001900230027003100

Absorbance

Wavenumbers (cm -1)

0.05

2839 cm-1

2871 cm-1

2916 cm-1

2950 cm-1

1165 cm-1

1375 cm-1

1456 cm-1

Spectrum of the pristine material

11001300150017001900210023002500270029003100

He+ (1014 He+.cm-2)

Electrons (9*10 5 Gy)

Gamma (9*10 5 Gy)

Wavenumbers (cm -1)

O2

Vacuum

H2C

CH3 H2C

C

O2H2C

CH3 H2C

C

OO

HOH CH3

H2C

H2C

C

O

++

Gedde et al., J. Appl. Polym. 1990

H2C

H2C

-H2 HC

HC

HC

HC

A. Chapiro, NIM B. 1988




Results (alphas only) :Surface modifications: Contact angle

Surface free energy versus fluence

There is a correlation between the increase in surface free energy and the loss of hydrogen (vinylic bond formation).

35

37

39

41

43

45

47

10 11 12 13 14 15 16log(fluence (He+.cm-2))

S (mJ .m-2)

Untreated

Untreated




Results :Electrons and photons: Hardness & Young’s Modulus.

Whatever electrons or photons were used the results obtained are similar when compared as a function of Dose

30

40

50

60

70

80

90

100

0 500 1000 1500 2000 2500 3000 3500

h (nm)

H (MPa)

Untreated

9×105 Gy

1

1.2

1.4

1.6

1.8

2

2.2

0 500 1000 1500 2000 2500 3000 3500

h (nm)

E (GPa)

9×105 Gy

Untreated

Hardness and Young ’s modulus measured on the untreated and electron-irradiated (D = 9×105 Gy) sample’s surface.




Results :Nano-indentation curves for alpha & electron -irradiated samples.

0

2

4

6

8

10

12

14

0 500 1000 1500 2000

h (nm)

P (mN)

Untreated

1014 He+.cm-2

1015 He+.cm-2

1016 He+.cm-2

0

2

4

6

8

10

12

14

0 500 1000 1500 2000 2500 3000 3500

h (nm)

P (mN)

Untreated

9×104 Gy

9×105 Gy

The material was more fragile after the ion treatment since the analyzed surface is a hard film (the irradiated part is 2.3 µm) on a soft substrate (the untreated part).

Alpha particles gradually lose their energy as they penetrate the PP/EPR up to about 2.3 µm. For samples irradiated with electrons, H and E remain constant within the domain of the studied indentation depth. Indeed, in this case, we can consider that the electrons regularly lose their energy up to h = 3000 nm.

The visco-elastic behaviour remainsThe visco-elastic behaviourdoes not remain after irradiation




Results :Swelling for gamma & electron -irradiated samples.

In order to study the crosslinking of the PP/EPR, the samples were analyzed using the swelling technique. Swelling was performed in two different liquids. First, the studied samples were dipped into 1,2-dichorobenzene, a PP/EPR solvent, at 130°C for about one hour. Thus, the crosslinking network, insoluble in the solvent, could be studied. Some samples were also dipped into hexane in order to obtain information about the PP/EPR samples that were either untreated or irradiated at weak doses and fluences. This liquid is not a PP/EPR solvent but it has a good affinity with him.

Immersion in 1,2 -dichlorobenzene after irradiation at an electron dose of 9 . 105 Gy.

We observe the crosslinking effect.




Results :Swelling in hexane for gamma & electron -irradiated samples.

0.15

0.16

0.17

0.18

0.19

0.2

0.21

0.22

0.23

0 1 2 3 4 5 6 7

log(Dose (Gy))

τ

ElectronGamma

Untreated

211mmm−τ=

m1 is the sample’s mass after one day of swelling and hexane evaporation; and m2 is the sample’s mass after a second swelling in hexane during a period of 46 days.

provides information on the crosslinking part of the sample.




Results :Differential Scanning Calorimetry

-1,8-1,6-1,4-1,2-1-0,8-0,6-0,4-0,20

80 100 120 140 160 180Temperature (°C)

mW/mgPEHD PPEndo0 Gy4×105 Gy9.4×105 Gy

Thermogramms of untreated and -irradiated PP/EPR

Melting peaks for the two main components of the compound, i.e. PP and HDPE

140

145

150

155

160

165

170

0 1 2 3 4 5 6 7

log(Dose (Gy))

Untreated

Tmelting PP (°C)

ElectronGamma

158

159

160

161

162

163

164

165

13 13 .5 14 14 .5 15 15 .5

log(flue nce (He +.cm -2))

Tme lting P P (°C)

Untre ate d

50

55

60

65

70

75

80

0 1 2 3 4 5 6 7

log(Dos e (Gy))

ΔHmelting PP (J .g-1)

ElectronGamma

Untreated

15

25

35

45

55

65

75

13 13.5 14 14 .5 15 15 .5

log(fluence (He+.cm-2))

ΔHmelting PP (J .g-1)

Untreated




Results :Differential Scanning Calorimetry




Comparison :

0 1 2 3 4 5 6 7

lo g ( D o s e (G y ) )

F T - IR /A T R

M e lt in g t e m p e r a tu re

S w e ll in g

H a rd n e s s

Y o u n g 's m o d u lu s

1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7

lo g (F lu e n c e (H e+

. c m- 2

) )

F T - IR / A T R

M e lt in g t e m p e ra t u r e

S w e llin g

H a r d n e s s

Y o u n g 's m o d u lu s

Critical doses and fluences where the studied properties are greatly modified (ò : electrons, ô : gamma photons, p : alpha particles).




Dose & Fluence :The changes in the compound properties were observed from a critical dose (≈ 105 Gy) or a critical fluence (≈ 5×10 13 He+.cm-2).

For the ion irradiation, the track overlapping can explain most of the observed effects:

See the work by Yamauchi

But, is there a way to transform a dose into a fluence or reciprocally ?

scale: 20 nm/division

1011

i ons. c m- 2

1012

i ons. c m- 2

1013

i ons. c m- 2




Dose - Fluence Relation ?

Equivalent Dose Calculation for = 5 .1013 He+.cm-2

In Polyethylene

D = ρφRE × 1000

⟨LET⟩ = 199 keV.µm-1, or 1.99×106 keV.c m-1

050

100150200250300

0 100 200 300 400Energy (keV)

TEL (keV.µm-1)

1.5×107 .J kg-1

D = ρφ×LET 1.8×107 .J kg-1

With electrons and gammas

in air, we find

D = 105 Gy





100

r (nm)

x (µm)

1 10 102 103 104 0

20 40 60 80

C o r e t r a c k

R

rt

(a) (b)

halo

The latent track

Vareille, J.C. PhD Thesis, University of Limoges, Limoges, France, 1982.

Dose(× 106 Gy)

r (nm)

4321051015 0 100 E (keV)

200300400

Deposited dose by an helium ion (400 keV) in the polypropylene versus the distance to the track center r and versus the particle energy E.

Waligorski, M.P.R. ; Hamm, R.N.; Katz, R. Nucl Tracks Radiat Meas 1986, 11(6), 309-319.

Matlab calculation based on:





Dose inside the latent track

30 40 50 60 70 80 90 100 110

0 1 2 3 4 5 6 7 8 9 r (nm)

Deposited total dose (%)

With the MATLAB software, the deposited total dose along the ion’s range can be estimated: D ≈ 3×107 Gy.

r = 5 nm

0

0.2

0.4

0.6

0.8

1

9 10 11 12 13 14 15

log(fluence (He+.cm -2))

Covered surface fraction

= 5 .1013 He+.cm-2

To be compared with D = 105 Gy !




Conclusions

Creation of carbonyl bonds in the case of a treatment under air (electrons and ) and the formation of vinylic groups after irradiation with ions under vacuum

For similar doses, the studied effects are equivalent after electron or irradiation.

For the three kind of irradiation used (electrons, , He+), the studied properties are notably modified for fluences above 5×10 13 He+.cm-2 in the case of alpha particles and for doses i nthe orderof 10 5 - 10 6 Gy in the case of electrons and gamm aphotons.

The difference in the irradiation atmosphere (vacuum for alpha particles and air for electro ns and ) and in the nature of th e transformations induced by radiations (high LET for alpha particles and low LET for el ectrons and ) seem to b e responsible for the observed differences.

24 th icnts, bologna, 1-5 september 2008 radiation induced damage electron, gamma photon and ion...

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