Anti-UV waterborne nanocomposite coatings for exterior wood
Anti-UV waterborne nanocomposite coatings for exterior wood
1Université Laval2 FPInnovations
Mirela Vlad 1,2 prof. Bernard Riedl 1 dr. ing. Pierre Blanchet 2,1
2009 International Conference on Nanotechnology for the Forest Products Industry
June 23-26, Edmonton, Alberta
Wood Coatings Demand by Application & End Use (million dollars)
Year 1996 2001 2006 2011 2016
Global Wood Coatings Demand 1660 1958 2390 2790 3370
INTRODUCTION
Source: The Freedonia Group, Inc.
World demand for Architectural Paints is forecast to rise 3,9% per years through 2011 to a total of 21,5 million metric tons, valued at 47$ billion (US).
Water-based paints will expand their share of the global market to 73%.
0100
200300
400500
600700
800900
Siding Furniture Decking Flooring Windows &Doors
OtherApplications
19962001200620112016
Effects of UV on wooden substrates and wood coatings
Wooden substrates Wood coatings
Lignin degradation Embrittlement, cracking
Destruction of cell structure Yellowing of resins
Discoloration Loss of adhesion, delamination
Cracking Discoloration
Increase of water retention Loss of gloss, chalking
Decay attack Environmental etching
Photostabilization using nanosized UV absorbers
Zinc oxide (broad absorption spectrum from UVA to UVC)
Titanium oxide (absorption edge 350 nm)
Cerium oxide (broad absorption spectrum from UVA to UVC)
MOTIVATION
AGGREGATION TENDENCY OF NANOPARTICLEShigh specific surface area => high surface energySurface modification involve dispersants which stabilize the colloidal dispersion of nanoparticles.
A. Steric stabilization - this involves polymers added to the system adsorbing onto the particle surface and preventing the particle surfaces coming into close contact.
B. Electrostatic or charge stabilization - this is the effect on particle interaction due to the distribution of charged species in the system.
Factors affecting Zeta Potential:1. pH;2. Conductivity (particles with zeta potentials
> +30 mV or < -30 mV are considered stable);3. Concentration of a formulation component.
Waterborne nanocomposites
Pote
ntie
l (m
V)
Distance from particle surface
Zêta potentiel
Stern potentielSurface potentiel
0 mV
-100 mV
Slipping plan
Particle with negative surface
charge
Diffuse layer
Stern layer
PROBLEMATIC
MATERIALS
Exterior acrylic latex paint (SICO)
Nanoparticles of ZnO:Hydrophilic version (Degussa, 20 nm)Silanized version (Degussa-Evonik, 20 nm)
Nanoparticles of TiO2 :Uncoated (Sigma, 20 nm)Coated with Si and Al (Sachtleben, 10 nm)
Commercial water-based dispersions :Predispersed nano-CeO2, 10 nm (Byk Chemie) Predispersed nano-ZnO, 20 nm (Byk Chemie) Predispersed nano-ZnO, 40 nm (Byk Chemie) Predispersed nano-ZnO, 60 nm (Byk Chemie)Predispersed nano-ZnO, 20 nm (Degussa)
Dispersants:Poly(acrylic acid) sodium salt PAA (M=2100 and 5000)Poly(methacrylic acid) PMAAPolyacrylamide PAM (M=17000)Copolymer of acrylic acid and sulfonated monomers
High Speed Disperser Ragogna Custom Machinery
(source: FPInnovations)
Horizontal bead mill MULTILAB (source: FPInnovations)
Roller coater(source: CRB)
Substrate
Black Spruce (Picea mariana):
softwood used for the production of structural timber
(frames, lining, roofs, scaffolding, forgery - floors,
skirting, decking);
easy to dry;
good quality of machining;
weak aptitude to impregnation with preservatives;
low natural durability (decay attack).
Surface preparation prior to coating:
conditioning at 8% humidity (2 weeks);
final sanding was made with the sandpaper 150 (average particle diameter=92 μm)
Db , kg/m3 D0 , kg/m3 βr , % βt , % βv , %
406 445 3,8 7,5 11,1
www.wynnspainting.com
High speed mixing
High-frequency sonication
Nanocompositepaint
Acrylic resin (latex)
Additives
(wetting agent, pigment dispersant,
defoamer, levelling, thickener,
rheologic and plasticizer agent, filler,
surfactants, biocide etc.)
Pigment (TiO2 , rutile, 250 nm)
Nanoparticles (ZnO, TiO2 , CeO2)
(powder or aqueous dispersions)
Water & co-solvent
Application & air drying
Colloïdal dispersion of nanoparticles
Dispersion
Nanocompositecoating
Cole-Parmer ® 750-Watt Ultrasonic Processors with
Temperature Controller
Nanoparticles
Dispersant
Water
Flat-sawn
Black Spruce
EXPERIMENTAL
Weather-Ometer ATLAS Ci3000+
Water cooled Xenon lampInner and outer filter: BorosilicateWavelength: 340 nmIrradiance: 0.35 W/m2
Temperature on black panel : 63oC
Cycle A (400 hours): 100% UV exposure
Cycle B (400 hours): 108 minutes UV and 12 minutes
UV and water spray.
Gloss, 60o
(ASTM D523)48 hours or more
Colorimeter
BYK-GARDNER
Micro-TRI-glossmeter
BYK-GARDNER
Color: L*, a*, b*(ASTM E2366)every 48 hours
Accelerated weathering (ASTM G155, ASTM D6695, ISO 11341)
Adhesion strength by pull-off method (ASTM D4541) before and after the weathering
EXPERIMENTAL
Time, h0 100 200 300 400
Δ L*
-0,4
-0,3
-0,2
-0,1
0,0
0,1
0,2
Time, h0 100 200 300 400
Δa*
-0,2
0,0
0,2
0,4
Color changesCycle A
RESULTS
80 μm
CIE L*a*b* system
1% nano-ZnO (pH=10.5)2% nano-ZnO predispersed in PAA0% nano5% nano-ZnO (pH=10.5)5% nano-ZnO predispersed in PAA7% nano-ZnO (pH=10.5)2% nano-ZnO (pH=10.5)
1% nano-ZnO (pH=10.5)2% nano-ZnO predispersed in PAA0% nano5% nano-ZnO (pH=10.5)5% nano-ZnO predispersed in PAA7% nano-ZnO (pH=10.5)2% nano-ZnO (pH=10.5) ( ) ( ) ( )222 **** baLE Δ+Δ+Δ=Δ
Color changes
Cycle A
Time, h0 100 200 300 400
Δb*
-3
-2
-1
0
1
Time, h0 100 200 300 400
ΔE
*
0,0
0,5
1,0
1,5
2,0
2,5
3,0
2% predispersed nano-ZnO (40 nm)1% nano-TiO22% nano-TiO20% nano0.4% predispersed nano-ZnO (40 nm) +0.54 nano-CeO2 (10 nm)1% predispersed nano-ZnO in PMAA2% predispersed nano-ZnO (60 nm)
Time, h0 100 200 300 400
Δ L*
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
Time, h0 100 200 300 400
ΔE
*
0,5
1,0
1,5
2,0
2,5
3,0
3,5
Time, h0 100 200 300 400
Δ b*
-2
-1
0
1
2
Cycle B
70 μm
Color changes
1% nano-ZnO (pH=10.5)2% nano-ZnO predispersed in PAA0% nano5% nano-ZnO (pH=10.5)5% nano-ZnO predispersed in PAA7% nano-ZnO (pH=10.5)2% nano-ZnO (pH=10.5)
Time, h0 100 200 300 400
Glo
ss, 6
0o
3,0
3,5
4,0
4,5
5,0
5,5
6,0
6,5
Cycle A
Gloss changes
Definition of gloss
Time, h0 100 200 300 400
Glo
ss, 6
0o
3,5
4,0
4,5
5,0
1% nano-ZnO predispersed in PAA (2100)5% nano-ZnO predispersed in PAA (2100)2% nano-ZnO predispersed in PAA (2100)0% nano1% nano-ZnO predispersed in PAA (5000)1% predispersed nano-ZnO (40 nm)
Cycle B
* predispersed nano-ZnO (20 nm) in polyacrylamide (PAM, M=17000);
** predispersed nano-ZnO (20 nm) in copolymer of acrylic acid and sulfonated monomers;
*** water-based commercial dispersion of nano-ZnO (20 nm).
Cycle B
Color and gloss changes
Initial gloss, 60o 4,49 5,89 5,75 4,43 4,83 4,04 5,55
Final gloss, 60o 4,10 4,64 4,37 4,76 4,85 3,75 4,37
0% nano 1%silanized
ZnO
2%silanized
ZnO
2%predisp.ZnO*
2%predisp.ZnO**
2% predisp.ZnO***
1% coatedTiO2-2,00
-1,50
-1,00
-0,50
0,00
0,50
1,00
1,50
2,00ΔL*
Δa*
Δb*
ΔE*
Positest Adhesion Tester
Cycle A
0
0,51
1,52
2,53
3,54
4,5
A B C D E F
Before weatheringAfter weathering
Adhesion measurement by the pull-off methodA
dhes
ion
stre
ngth
, MPa
Adhesion strength = max. tensile strength
[H=F/A]
ABCDE
F
0% nano2% predispersed nano-ZnO (60 nm)5% predispersed nano-ZnO (20 nm)2% predispersed nano-ZnO (20 nm)1% nano-ZnO predispersed in linseed oil emulsion1% nano-ZnO predispersed in PMAA
Actuator
Cross-Sectional View of Actuator
Dolly
Pull-off tests
Cycle B
A’B’GHI
0% nano2% predispersed nano-ZnO (60 nm)2% predispersed nano-ZnO (40 nm)1% nano-TiO2
2% nano-TiO2
Adh
esio
nst
reng
th, M
Pa
K
LMN
0,4% predispersed nano-ZnO (40 nm)+0,54% predispersed nano-CeO2 (10 nm)1% nano-ZnO predispersed in PAA (5000)2% nano-ZnO predispersed in PAA (2100)5% nano-ZnO predispersed in PAA (2100)
00,5
11,5
22,5
33,5
44,5
5
A' B' G H I K L M N
Before weatheringAfter weathering
0% nano
2% predispersed nano-ZnO (60 nm)
2% nano-ZnO (pH=9)
3% nano-ZnO (pH=10.5)
JEOL 840A (Tokyo, Japan) microscope equipped with EDX (energy dispersive X-ray analysis)
1 μm
1 μm
Images of Scanning Electron Microscopy
1% nano-ZnO predispersed in linseed oil emulsion
1 μm
1 μm
2% predispersed nano-ZnO (40 nm)
1 μm
1 μm
1% nano-ZnO predispersed in aqueous sol. of PAA
1% nano-ZnO predispersed in aqueous sol. of PMAA
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00
Color changes ΔE*
Without coating0% nano (acrylic latex paint) (A)
5% nano-TiO2 (20 nm) (B)
2% nano-TiO2 (20 nm)
5% predispersed nano-ZnO (40 nm)
2% predispersed nano-ZnO (40 nm)
2% nano-ZnO (20 nm) predispersed in aqueous sol. of PAA (C)
5% nano-ZnO (20 nm)
2% nano-ZnO (20 nm)
OUTDOOR EXPOSURE (118 days)
A
B
C
before
after
after
after
Nanoparticles size distribution by DLS
Zetasizer Nano ZS(Malvern Instruments)
Principe of DynamicLight Scattering
Aqueous dispersion of 20% nano-ZnO (20 nm)
with PAA (M=5000)
Aqueous dispersion of 20% nano-ZnO (20 nm)with a polyacrylamide
Commercial aqueous dispersion 40%
nano-ZnO (40 nm)
CONCLUSIONS
Nanocomposites coatings prepared with ZnO nanoparticles hydrophilic and silanized version (in
powder form and predispersed) showed higher protection against UV radiations (accelerated
weathering and outdoor exposure) and antibacterial properties (outdoor exposure) compared
with the acrylic latex paint;
Nanocomposites coatings prepared with uncoated TiO2 nanoparticles showed anti-UV and self-
cleaning properties in outdoor exposure;
Nanocomposites coatings prepared with coated TiO2 nanoparticles showed anti-UV properties in
accelerated weathering;
High durability against UV radiations demand an efficient nanoparticles dispersion (without
aggregation or flocculation);
The dispersant must not accelerate the polymer matrix degradation by yellowing (Δb*).
The nanoparticles protect the coatings against photodegradation caused by UV radiations,
therefore adhesion strength values were slightly improved after the accelerated weathering.
ACKNOWLEDGEMENTS
FP Innovations
NanoQuébec
FQRNT
SICO
American Coatings Show Daily, June 2008: 25-26.
A. Goldschmidt, H.-J. Streitberger. BASF handbook on Basics of Coating Technology. VincentzNetwork, Germany, 2003.
C. Hegedus (Air Products and Chemicals Inc.). The use of Nano Zinc Oxide in Coatings. ICE 2007 – Preshow Short Course, Toronto.
J. Wildeson, A. Smith, X. Gong, H. T. Davis. JCT Coatings Tech, July 2008: 32-33.
Zetasizer Nano series technical note. Malvern Instruments. http://www.malvern.com.
BIBLIOGRAPHY
