Atmosphere and dose effects on the irradiation at high LET of polystyrene

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Atmosphere and dose effects on the irradiation at high LET of polystyrene

M. Ferry, M. Cornaton, D. Durand, V. Dauvois, S. Esnouf, Jl. Roujou, C. Aymes-Chodur, Y. Ravache

To cite this version:

M. Ferry, M. Cornaton, D. Durand, V. Dauvois, S. Esnouf, et al.. Atmosphere and dose effects on the irradiation at high LET of polystyrene. IRaP 20108 (the Ionizing Radiation and Polymers symposium), Aug 2018, Moscow, Russia. �cea-02339102�

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Atmosphere and dose effects on the

irradiation at high LET of polystyrene

M. Ferry1_{, M. Cornaton}1_{, D. Durand}1_{, V. Dauvois}1_{, S. Esnouf}1

,J.L. Roujou1,

C. Aymes-Chodur2_{and Y. Ngono-Ravache}3

1_{Den-Service d’Étude du Comportement des Radionucléides (SECR), CEA, Université}

Paris-Saclay, F-91191, Gif-sur-Yvette, France.

2_{Université Paris-Sud, SM2B/ICMMO, UMR CNRS 8182, F-91405, Orsay, France.} 3_{CIMAP (CEA/CNRS/ENSICaen/UNICaen), CIMAP site GANIL, Caen, France.}

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Introduction & context

Polystyrene

Very resistant under irradiation

Radiation protection conferred by the side-chain aromatic ring Phenomenon assigned to “sponge-type” mechanism

-Energy dispersion by conjugated double bonds delocalization

LET effect on G

₀

from PS irradiated under inert atmosphere/vacuum

LET ↗ <=> radiation resistance ↘

Literature

Polymer studied at different LET but always at low doses No study on the atmosphere & dose effects ?

Influence of radiation-induced defects accumulation?

Influence of reactions with oxygen?

| Page 2

Schoepfle & Fellows, Ind. Eng. Chem. 23 (1931), 1396

Alexander & Charlesby, Proc. R. Soc. London, Ser. A 230 (1955), 136 Chang & LaVerne, J. Polym. Sci.: Part A: Polym. Chem. 38 (2000),1656

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Gas radiation chemical yields determination

A two steps irradiation

Pre-ageing step in closed containers in large excess of gas

SME line of GANIL

-16_{O ions irradiation (E}

i ≈ 7 MeV/A)

-LET ∼ 6.5 MeV.mg-1_.cm-2

-Atmosphere: nitrogen / oxygen

-Doses : 2 – 4 – 10 MGy

Second step in closed glass ampoules

HE line of GANIL to go through thin glass walls

-36_{Ar ions irradiation (E}

i ≈ 95 MeV/A)

-LET ∼ 2.5 MeV.mg-1_.cm-2

-Atmosphere: helium / reconstituted air (with tracer)

-Doses : 500 – 1000 kGy

Masses estimated to reach in closed containers

Final hydrogen content < 1 %_vol to avoid readdition If present, final oxygen content > 10 %_vol

-To ensure homogeneous oxidation conditions

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Results

1. Crosslinking vs Scissions

2. Molecular evolution

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Materials evolution

Soluble fraction in THF

| Page 5 0 2000 4000 6000 8000 10000 12000 0 20 40 60 80 100 120

Irradiation under air

Irradiation under inert atmosphere

Soluble we ight (% w ) Dose (kGy)

Under inert atmosphere

Insoluble gel formation Confirmation of

crosslinking as the

predominant mechanism

Under oxidative atmosphere

Solubility remains important

Scission predominant mechanism

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Materials evolution

Average Molecular Weights

Average molecular weights of the soluble fractions

Under inert atmosphere, SEC peaks almost disappear at the highest doses

Confirmation of crosslinking as predominant mechanism

At low doses, application of the Saito’s equation

Under inert atmosphere: a part of polymer already insoluble

-Saito’s equation hypothesis not verified

=> Results given for information purposes only

| Page 6 10 15 20 25 30 35 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 10 15 20 25 30 350.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Intensi ty (µRI)

Irradiation under inert atmosphere Unirradiated (signal / 3) Irradiation 0.9 MGy Irradiation 3.0 MGy Irradiation 5.2 MGy Irradiation 11.4 MGy Intensi ty (µRI)

Retention time (min)

Unirradiated (signal / 2) Irradiation 0.9 MGy Irradiation 2.9 MGy Irradiation 5.1 MGy Irradiation 11.0 MGy 0 2000 4000 6000 8000 100001200010 3 104 105 106 0 2000 4000 6000 8000 1000012000 103 104 105 106 Aver age mo lecular wei gh t (g.mol -1 )

Irradiation under oxidative atmosphere Mn

Mw Irradiation under inert atmosphere

Mn Mw Aver age mole cula r we ight (g.mol -1 ) Dose (kGy)

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Materials evolution

Scissions vs crosslinking

Under inert atmosphere

From literature : G(S) << 4 * G(X)

=> Predominant mechanism: crosslinking

Insoluble fraction already formed at low doses

=> G(S) overestimated (about one order of magnitude)

Under oxidative atmosphere

This work: G(S) > 4 * G(X)

=> Predominant mechanism: chain scissions

| Page 7 G(X) (10-7 mol.J-1₎ G(S) (10-7 mol.J-1₎ G(S) / 4 G(X) Oxidative atmosphere 0.02 0.12 1.5 Inert atmosphere 0.03 0.16 -Inert atmosphere / Literature 0.03 0.02 0.17

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Materials evolution

Deconvolution of the FTIR massif (C=O area)

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ATR mode infrared spectra with subtraction of

the pristine PS spectrum

1850 1800 1750 1700 1650 1600 Experiment Fit 1840 cm-1 1800 cm-1 1764 cm-1 1741 cm-1 1724 cm-1 1706 cm-1 1688 cm-1 1663 cm-1 1633 cm-1 1616 cm-1 1596 cm-1 Absorbanc e (a .u.) Wavenumber (cm-1)

4 MGy under oxidative atmosphere

Liang & Krimm, J. Polym. Sci. 27 (1958), 241 Luongo, J. Polym. Sci. 42 (1960), 139

Ngono-Ravache et al., Polym. Deg. Stab. 111 (2015), 89

Wavenumber (cm-1₎ Attribution 1840 Anhydrid 1800 Anhydrid 1764 Peracid + perester 1741 Ester 1724 Ketone 1706 Carboxylic acid 1688 Conjugated ketone 1663 Asymetric alkene 1633 Asymetric alkene 1616 Conjugated alkene 1596 Aromatic alkene

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Materials evolution

At a molecular level

| Page 9 1850 1800 1750 1700 1650 1600 1850 1800 1750 1700 1650 1600 1850 1800 1750 1700 1650 1600 Experiment Fit Anhydrid Anhydrid Peracid + perester Ester Ketone Carboxylic acid Unsaturated ketone Asymetric alkene Asymetric alkene Conjugated alkene Aromatic alkene 10 MGy 04 MGy Absorbance (a.u.) Wavenumber (cm-1) 02 MGy

No dose threshold

Defects probably equivalent under low LET ionizing rays and SHI

Very important ketone contribution whatever D

Saturated ketones

Conjugated ketones

OO P OO O O₂ PO O C O C H₂ O C + + +  fragm entations + +

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Gases evolution

Hydrogen and benzene emission

Under inert atmosphere

Hydrogen release ≈ and benzene release

↗

Energy transfers

-Efficient in the dose range studied

-At the expense of the side-chain

Under oxidative atmosphere

Hydrogen release ↗ from 2 MGy : G(H₂)_ox ∼ 2 * G(H₂)_inert at 10 MGy

Benzene release

↗ 2 times faster

-In-chain reactions strongly sensitize polystyrene

-Oxygen ↘ radiation-induced protection: attack on the tertiary carbon | Page 10

0 2000 4000 6000 8000 10000 12000 0.0 4.0x10-9 8.0x10-9 1.2x10-8 1.6x10-8 2.0x10-8

G (H 2 ) (mol.J -1 ) Dose (kGy) 0 2000 4000 6000 8000 10000 12000 0.0 2.0x10-9 4.0x10-9 6.0x10-9 8.0x10-9 1.0x10-8

G (C 6 H 6 ) (mol.J -1 ) Dose (kGy)

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Gases evolution

Oxidized specific gases

0 2000 4000 6000 8000 10000 12000 0.0 5.0x10-8 1.0x10-7 1.5x10-7 2.0x10-7 2.5x10-7 3.0x10-7 3.5x10-7 O₂ consumption CO₂ formation CO formation Radia tion chem ica l y iel ds (mol.J -1 ) Dose (kGy)

Rabek, Photodegradation of Polymers, Physical

Characteristics and Applications, Springer (1996), 60

Matsuo & Dole, J. Phys. Chem. 63 (1959),837

From benzene release

From literature

CH CH OO O₂ CH₃ CO₂ CH₂ C O₂ OO O C C O CH2 CO CH2 H H C O O O O2 PH _C O O OH P C O O CO₂ CH₂ O HO O h scission + + + h  fragmentation (slide 9) + h + scission  + + + + + +

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Conclusion

Under inert atmosphere: crosslinking

Via the aromatic ring, i.e. without loss of benzene / conjugated C=C

No hydrogen release

Protection active up to high doses (10 MGy)

Under oxidative atmosphere: scissions

Radical’s formation on the tertiary carbon

-Subsequent O₂ consumption and in-chain oxidation reactions

-Loss of benzene => loss of radiation protection

Preliminary mechanism to be completed

Loss of radiation protection begins at lower doses (2 MGy)

-Atmosphere is of high importance to evaluate the loss of radiation protection

with dose ↗

| PAGE 12

Puglisi et al., Radiat. Eff. Defects Solids 98 (1986), 161

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