Nanoobjects in wood-protective coatings - Christian Lehringer (EMPA)

Nanoobjects in wood-protective coatings

Christian Lehringer, Klaus RichterEmpa, Swiss Federal Laboratories for Materials Science and Technology

M. Ernst

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University College of London, 04.11.2010, Christian Lehringer and Klaus Richter

Topics

Nano – where size does matter Wood – a substrate with special

characteristics Application of engineered nanoobjects

(ENOs) in wood coatings Environmental, health and safety aspects Conclusions


Nano – where size does matter

"Nano" = 1 to 100 nm


ISO/TS-27687 (2008)

Disciplines of Nanotechnology


Topics





Wood – a substrate with special characteristics


Bio-Composite-Polymer Porous structure Heterogenous Anisotropic Combustible Hygroscopic Biodegradable Sensitive to UV-radiation Density depends on species

lon

gitu

din

al

Topics





Key areas of wood surface coating


UV-protection

HydrophobationEasy-to-clean Antimicrobial

HardnessScratch resistance

Some ENOs currently used for wood coatings and their application area


*with hydrophobic functionalization

Nanoobject Aluminum

oxide (Al2O3)

Iron(III) oxide

(Fe2O3)

Silver (Ag)

Titan dioxide (TiO2)

Zinc oxide (ZnO)

Silizium dioxide (SiO2)

Hardness x x

Abrasion resistance x x

Scratch resistance x x

UV-Protection x x x

Antimicrobial x x x

Hydrophobation/ Easy-to-clean

x*

UV-protection


Schilliger 2010

UV-protection

Nanoscaled pigments of TiO2, Fe2O3, ZnO for transparent systems

Absorption and scattering of UV light Substitute for organic UV-Absorbers (UVA) Combination with lignin stabilizers and

hindered amine light stabilizers (HALS) Photocatalytic activity of nanoparticles

requires combination with radical interceptors


UV-protection


www.nanobyk.com


Sol-gel-technology with organofunctional silanes or (poly)siloxanes

Effect: hydrophobic characteristic of substance + formation of hydrophobic nanostructure

Liquid water protection feasible, water vapor protection difficult


Wood-inorganic composites by sol-gel process Two stage process

Hydrolysis (here Silicic Acid Esters)

Condensation….


Si

OEt

EtO OEt Si

OEt

HO OH- 2 EtOH

+ 2 H2O

OE Et O tTetraethoxy silane (TEOS)

OEt

etc.

+ H2O2 HO ..... (SiO2)nSi

OEt

OEt

HO O OH

OEt

OEt

SiSi

OEt

OH- H2O

Silicate

3-Isocyanatpropyl triethoxysilane

β-(3,4 epoxycyclohexyl) ethyl trimethoxysilane

vinyl trimethoxy silane

Wood-inorganic composites by sol-gel process


… in the cell wall

Antimicrobials


Künniger 2010

Mold Blue stain Algae

Antimicrobials

Leach-resistance of Ag; TiO2; ZnO for long-term effect

Nanoobjects should be released systematically and preferably continuously in small amounts from an actively biocidal coating

Function possibly through ingestion, as contact poison, by photo-oxidative mechanism or binding to microbial DNA


Antimicrobials


Hochmannova 2010

Surface hardness/ scratch resistance

Silicones and nanosized alumina particles (Al2O3; SiO2) as additive

Surface modification of nanoparticles by trialkoxysilanes to improve the dispersibility of in acrylate media

In parquet industry, however, until now a broad application has not been realized




TEM picture of polyacrylate filled with 30 wt.-% nanosized silica.

Bauer 2005



www.nanobyk.com

Challenges and future research

Homogenous dispersion of nanoobjects in embedding matrix – avoid agglomeration

Long-term studies about leaching and mitigation

Balance between leach-resistance and systematic release of nanoobjects

Polymerization in the wood cell wall and covalent bonding


Challenges and future research

Avoid crack formation, yellowing, depolymerization, improve gloss retention

Commercial application of sol-gel-technologies for wood impregnation

Reactivity of nanoobjects (e.g. Ag Ag2S)

Renovation cycles (sanding, coating removal, new coating)


Design for minimal exposition of engineered nanoobjects (ENOs)


“Factors of stability” Stability of ENO integration into coating system

by trend higher by trend lower

Location of ENOs in façade coating system

in the bottom layers at the surface

Binding type between ENOs and coating matrix

covalent not covalent

Property of ENOs in organic coating matrix

not photocatalytic photocatalytic

Property of ENOs in organic or mineral coating matrix

wettability high wettability low

Property of façade coating system

resistance against exterior influ-ences (e.g. moisture, wind-abrasion, temperature changes)

low resistance against exte-rior influences

Som 2010

wettability low

wettability high

Topics






Life cycle of nanocoatings

Estimated influences of ENOs on the environment, modified after Som et al. (2010)


ENVIRONMENT Ag c)

ZnO c)

TiO2 b)

SiO2 a)

Al2O3

a) Indication for hazardous effects (with realistic con-centrations)

+ + + -- --

Solution in water increases the toxic effects (+), re-duces toxic effects (-)

++ ++ 0 -- ++

Tendency for agglomeration and sedimentation (-) or no sedimentation (+)

- - -- -/+ --

Waste water facility releases ENO into waters (+), does not release ENO into waters (-)

- n.i. - - -

Stable during waste incineration (+), burns during waste incineration (-)

+ + ++ ++ ++

legend: + applies; weak indices available; - does not apply; n.i, not investigated (high

degree of uncertainty)

The indices represent the overall evaluation of the ENOs: a) rather harmless; b) big uncertainty due to lack of data; c) biological effect traceable, effect on environment to be expected. These estimations do not represent the effects of nanoobjects that were generated by unintended actions (e.g. traffic) *: mostly dependent from contaminants in the samples (transition metals such as Iron, Nickel, Cobalt etc.) #: Aluminum oxide hydroxide (AlOOH) in the lung was investigated.

Estimated influences of ENOs on the health on basis of different biological studies, modified after Som et al. (2010)


HEALTH Ag

a) ZnO

c) TiO2

a) SiO2

a)

amorph Al2O3

#

b) Chronic toxicity (long term effects to be expected, PNEC, PEC), threshold values known n.i.

Acute toxicity

Impairment of DNA n.i.

Brain damage: damage of the central nervous sys-tem

n.i. n.i. n.i. n.i. n.i.

Crossing and damaging tissue barriers (e.g. blood-brain barrier, placenta, lung)

n.i. n.i. #

Skin n.i.

Gastrointestinal tract n.i.

Lung

legend: + applies; weak indices available; - does not apply; n.i, not investigated (high degree of uncertainty)

The indices represent the overall evaluation of the ENOs: a) rather harmless; b) big uncertainty due to lack of data; c) biological effect traceable, effect on environment to be expected. These estimations do not represent the effects of nanoobjects that were generated by unintended actions (e.g. traffic) *: mostly dependent from contaminants in the samples (transition metals such as Iron, Nickel, Cobalt etc.) #: Aluminum oxide hydroxide (AlOOH) in the lung was investigated.

The "Collingridge dilemma“ (Collingridge 1980)

Decision making in uncertainity


Early phase of development

Influence on

innovations

Technical "log-in effects"

Costs for correctio

ns

Socio-economic “lock-in” effects

Time and knowledgeLate phase of developmentEarly phase of development

Influence on

innovations

Costs for correctio

ns

Time and knowledgeLate phase of development

Summary

Wood coating systems with considerable market relevance

Thorough risk assessment, life-cycle-analysis, material characterization, standardized metrology required

Public acceptance strongly depends on transparent security systems, consistent labeling of nanoproducts and honest communication


Thank you very much for your attention


Nanoobjects in wood-protective coatings - Christian Lehringer (EMPA)

Technology

Transcript of Nanoobjects in wood-protective coatings - Christian Lehringer (EMPA)