ICARST 2017

IAEA-Vienna 24 to 28 April 2017

Development of styrene-free unsaturated resins and acrylic

monomers for the consolidation of wooden cultural heritage

artefacts by radiation-curing

Khôi TRAN, Senior Researcher CEA

ARC-Nucléart, Grenoble, France

47 years of gamma irradiation for conservation of

cultural heritage artefacts

Ramses II mummy in Musée

de l’Homme, Paris

1977

Sculpture in the irradiation chamber,

2000

Frozen baby mammoth Siberia, 2010

Cobalt 60 sources Irradiation facility

Statues: insect eradication Consolidation with radiation-curing resin

Resin impregnation facility: vacuum/pressure tanks

Radical coplymerization of styrene-unsaturated polyester resin

Liquid state:

48% styrene

52% U-Polyester

Gelification under

gamma irradiation

Solid by cross-linking

of polyesters by poly

styrene

Dose : 30-50 kGy at 0.5 to 1kGy/hour

Drawbacks of Styrene UP resins: irreversibility, unsoluble,

and safety regulations more severe on styrene monomer

Alternative to Styrene-UP resins:

1) Styrene-free resins such as :

Advalite® resins from Reichhold Co. : vinyl hybrid resin

Atlac® resins from DSM Co. : vinyl ester resin

Viscosity : 200 to 300 mPa.s or cp

but still crosslinked after radiation-curing !

2) Acrylic monomers with low vapour pressure

Viscosity : 15 mPa.s

2-Hydroxy-ethyl-methacrylate

2-Hydroxy-propyl-methacrylate

in principle reversible, forming a gel in contact with water

Acrylic resins and acrylic monomers are very

sensitive to oxygen inhibition : sticky surface, degraded wooden

surface not well consolidated

Radical polymerization in inert atmosphere, as nitrogen, or surface barrier

Radiation-curing of monomers in current solvents such as

isopropanol, ethyl acetate,… : partial consolidation of the wood

after solvent evaporation, more deontological respect than total

or full filling of the wood porosity by the resin

Radiation-curing control by FTIR

DSC Advalite à 20°C/min

Tg = 55°C

DSC HEMA à 20°C/min

Tg = 66°C

DSC HPMA à 20°C/min

Tg = 55°C

DSC HPMA 80 4HBA 20

Tg = 50°C

DSC Analysis of resins and monomers

Solid state NMR spectroscopy of radiation-cured HPMA monomer

Carbons assigned to vinylic carbons in the range 110-120 ppm vanish and give rise

to two new signals in the range 60-40 ppm : complete polymerization

No change in other signals or no new ones : No crosslinking

Sound wooden samples for consolidation by resins and monomers

fir samplesbeech samples

Colorimetry analysis of consolidated samples

Fir

Beech

0

2

4

6

8

10

12

14

16

18

20

PARALO ÏDE B72 20%

STYRÈNE POLYESTER

ADVAL ITE 2 ,0

ATLAC 80 HPMA 20

HEMA HPMA HPMA 80 4HBA 20

HPMA 40 2BUTANOL

60

HPMA 40 IPA 60

HPMA 80 ACE 20

ΔE

Sapin Hêtre

beech

Delta E values obtained from colorimetry measurements on consolidated

samples

fir

0

10

20

30

40

50

60

70

80

Styrènepolyester Paraloïde

B72

Advalite ATLAC 80HPMA 20

HEMA HPMA HPMA 804HBA 20

HPMA 40IPA 60

HPMA 402Butanol

60

HPMA 80ACE 20

Resi

n c

onte

nt

in w

ood (

%)

Sapin Hêtre

% 𝐼𝑚𝑝𝑟e𝑔𝑛𝑎𝑡𝑖𝑜𝑛= ( 𝐹𝑖𝑛𝑎𝑙 weight − 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 weight )/( 𝐹𝑖𝑛𝑎𝑙 weight)

fir beech

Impregnation rate : resin or monomer content in wood

Volumic changes of treated samples

-3

-2

-1

0

1

2

3

4

5

Paraloïd B72 20ACE 80

Styrene polyester Advalite HPMA HPMA 40 IPA 60 HPMA 80 ACE 20

Volu

me c

hange

(Fin

al V

olu

me

-in

itia

l volu

me

)/In

itia

l V

olu

me (

%) Fir Beech

0

500

1000

1500

2000

2500

Bois brut Paraloïde Styrènepolyester

Advalite ATLAC 80HPMA 20

HEMA HPMA HPMA 804HBA 20

HPMA 40IPA 60

HPMA 402Butanol60

HPMA 80ACE 20

Ela

stic

Modulu

s (M

pa) Sapin Hêtre

𝑀𝑜𝑑𝑢𝑙𝑒 𝑠𝑝é𝑐𝑖𝑓𝑖𝑞𝑢𝑒=(𝑀𝑜𝑑𝑢𝑙𝑒 é𝑙𝑎𝑠𝑡𝑖𝑞𝑢𝑒 𝑒𝑛 𝑓𝑙𝑒𝑥𝑖𝑜𝑛)/𝐷𝑒𝑛𝑠𝑖𝑡é

fir beech

Mechanical Testing on consolidated samples

Wood Styrene Polyester Advalite HPMA HPMA40ACE60

fir

beech

X-ray radiography of impregnated samples

SEM Observations on consolidated samples

Full filling of the pores by HEMA or

HPMA Partial filling of the pores

by HPMA at 40% in solvent

-3

-2

-1

0

1

2

3

4

5

6

Cycle humide 1 Cycle sec 1 Cycle humide 2 Cycle sec 2 Cycle humide 3

ΔV

(%

)

Bois brut Paraloïd B72 20 ACE 80 Styrène polyester Advalite 2,0

ATLAC 80 HPMA 20 HEMA HPMA pur HPMA 80 4HBA 20

HPMA 40 IPA 60 HPMA 40 2Butanol 60 HPMA 80 ACE 20

Ageing of consolidated samples in humid and dry atmospheres

Application on

historical artefacts

HPMA HPMA 40 IPA 60 Advalite

HPMA HPMA 40 IPA 60 Advalite

before after

HPMA-EtAc 80/20

Conclusion

Advalite resin can be an alternative to styrene-UP resin, but

irradiation in inert atmosphere

HPMA acrylic monomer is more promising than HEMA for :

less sensitive to humidity

acrylic polymer : better durability

possibility of partial consolidation using solution of

monomer in solvent

possibility of radiation-curing in air by using

solutions of monomer

Deontological criteria in conservation of cultural heritage

(reversibility-solubility; durability; partial consolidation; product

availability; implementation on artefacts) are more satisfied by

application of acrylic monomers such as hydroxy-acrylates

• Other process (additives) for radiation-curing of acrylic

monomers/resins in air ?

• More hydrophobic momomers such as butyl-methacrylayte

• Mixture of monomers and acrylic polymers (Paraloid B72) to increase

viscosity and less shrinkage upon polymerization.

• Development of flexible, elastomer resins for consolidation of

degraded leather or other soft materials. Use of 2-ethyl-hexyl

methacrylate for instance

• Research on aqueous colloidal, dispersions of monomers/oligomers

cured by irradiation, for archaeological waterlogged artefact

consolidation

• Grafting by irradiation of monomers on cellulosic materials? wood,

paper ?

Perspectives

Thank you for your attention