difficulties to combine biological degradation factors with artificial weathering

Difficulties to combine biological degradation factors with artificial

weatheringFocussing on how to measure and

evaluate

Difficulties to combine biological degradation factors with artificial weathering - focussing on how to measure and evaluate

COST E18 SymposiumCopenhagen 16-02-2004

ConclusionsBlue stain testingBiological factorsWeathering and assessmentIntro

Joris Van Acker – Imke De Windt – Jan Van den Bulcke

IntroductionIntroduction

Standardised methods:

• European: EN 927

• International: ISO

Problems: critical values

performance assessment






Natural weathering, CEN/TC139/WG2:• accelerated natural exposure• Climatic Index

+ mimicry - transfer of biological

degradation patterns

Artificial ageing:• UVS equipment (UV-CON, QUV with spray option)• Wheater-O-meter (WOM)

+ fast - physico-mechanical






Solution:

combined or sequential testing of physico-mechanical and biological ageing

• short-term• critical levels• special focus on biological performance





Weathering and assessmentWeathering and assessment

Natural weathering:

- mimicrydisadvantages:• weather• sample variability

- harmonisation of specimens and expositiondisadvantages:

• macro- and microclimate






Artificial weathering:

• higher reproducibility• more confidence in:

machines ageing cycles

• less time consuming• better control

dark & dry

cold period

water spray

UV light






Assessment parameters:

• chalking• flaking• blistering• cracking• adhesion

Not necessary critical for all coatings

degradation phenomena on wood ‘missing’:

• biological• erosion• additional






Needs for methodology:

• optimisation• prioriy of parameters• substrate:

hardwood softwood porosity, vessel grouping dimensional stability extractives

• sample size: boards window frame corners





Biological factorsBiological factors

Biological factors can be essential part of paint degradation:






Standard tests: prEN927 3-5, EN152

artificial weathering

Alternative tests: • susceptibility• fungal growth on, through, in the coating and the substrate• impact analysis






Additional parameters:

• film thickness• water and water vapour permeability• porosity• surface roughness





Blue stain testingBlue stain testing

Blue stain testing basics EN152: + WOM

• coating not on the vermiculite medium (contact with uncoated side)• Aureobasidium pullullans and Sclerophoma pithyophila• evaluation of surface blue staining and zone free of blue stain






Reversed method:

• coating on the vermiculite medium, other sides sealed• Aureobasidium pullullans and Sclerophoma pithyophila• evaluation of surface blue staining and interior presence of blue stain






Internal presence of blue stain in service:not just a blue free zone





ConclusionsConclusions

- Modern coatings: low VOC + low biocidal content- Increased impact of biological factors- Yearly changes in impact of biological coating degradation- Reproducible testing: artificial ageing + laboratory test method- Artificial ageing should be specific for wood - Wood coatings mainly fail due to moisture impact (swelling / shrinkage)- Blue stain in service testing of coatings differs testing fungicidal impact- Modern water- borne wood coatings should be able to

resist biological factors...by means non-biocidal components or parameters...

difficulties to combine biological degradation factors with artificial weathering

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