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COST Action FP1006“Bringing new functions to wood through surface modification”
Boris Forsthuber, Vjekoslav Živković,Gerhard Grüll, Hrvoje Turkulin
Photoprotection of wood against theinfluence of visible light
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300 350 400 450 500 550 600 650 700 7500
10
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Window glass - easy glazing Window glass - double glazing Window glass - double glazing
+ UV-coating
Tra
nsm
issi
on [%
]
Wavelength [nm]
UV Vis
UV-Vis Transmission throughwindow glass
2(-2‘-hydroxy-phenyl)-benzotriazole class
UV-filtering →
e.g. by UV-absorber:
2(-2‘-hydroxy-phenyl) -s-triazine class
or
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� Xenon arc light exposure of clearcoated pear-tree veneer (behindwindow-glass)
Influence of visible light
0 6 24 48 72 96Xenon arc light exposure [h]
WithUV Absorber
WithoutUV Absorber
→ Influence of visible light!
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Possibilities of wood visible light photostabilization
� Use of micronized pigments- e.g. micronized TiO2 (Rutile)
� Use of semi-transparent coatings- e.g. Iron Oxide Pigments
� Use of photo-antioxidants- e.g. HALS radical scavengers
Visible light Photostabilization
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UV-Vis Spectra
300 400 500 600 7000
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20
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without UV absorber/screener with UV absorber micronized TiO
2
semi-transparent ironoxide
Tra
nsm
issi
on [%
]
Wavelength [nm]
UV Vis
Semi-transp.ironoxide
Micron.TiO2
UV-absorber
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Colour stabilization– micronized pigments
Highest Absorbancein the visible region
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� Influence of Pigment concentration
� Influence of Pigment particlesize
Colour stabilization– semi-transparent coatings
Schauwecker et al. (2014)
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� HALS radical scavengers
Denisov-cycle:
Scavenging radicals
Ganna Gryn‘ova et al. (2012)
Non-radicalproducts
UV-Absorber+
Monomeric HALS primer
TiO
2
Monomeric HALS impregnation
BT
Z
HP
T
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� Acid/Base interaction
→ Interaction with acidic compounds
HALS – Possible Interactions
pKb ~ 4-6 pKb ~ 5-7 pKb ~ 8-10
BasicitySchaller et al. (2009)
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HALS can show antagonistic effects with phenolicantioxidants
� Hydrogen Abstraction:
� Coupling reaction:
� Increased formation free radicals by homolytic decomposition ofhydroperoxide
� → Might lead to an increased discolouration/bleaching on dark wood species
HALS – possible Interactions
Lucki et al. (1984)
(Yamashita and Ohkatsu, 2002)
Prieto et al. (2014)
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� Volatilty of HALS α (molecular weight)-1
� Certain Mobility is needed
� Grafting of HALS onto the wood surface
HALS - Volatility
Grelier et al. (1997)
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� Photoprotection of wood against visible light can be done, using � UV-Absorber/Pigments with a certain absorbance in the visible area
� Semi-transparent coatings
� Sterically hindered radical scavengers (e.g. HALS)
� Absorbance in the visible area leads to an alteration of the woods colour in the initial state
� HALS are effective in visible light protection
� Several properties might limit the effectiveness of HALS� Basicity
� Interaction with phenolics
� Volatility
Conclusion
Standort Stetten Standort Arsenal
Boris Forsthuberb.forsthuber@holzforschung.at
Tel. +43/1/798 26 23-20
www.holzforschung.at
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