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Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

48th Annual Convention48th Annual ConventionSociety of Wood Science and TechnologySociety of Wood Science and Technology

New Protection Systems With New Protection Systems With Silicones and Silicones and SilanesSilanes

C. Mai, S. Donath, O. Weigenand, H. Militz

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

General AspectsGeneral Aspects

• Si is the second most frequent element on earth– Makes up 27.5% of the earth‘s crust– Is predominantly found as polymeric SiO2 :

m SiO2.n H2O - [Si(OH)4]

• Si occurs in higher concentration in tropical wood species

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

General Aspects of SiliconGeneral Aspects of Silicon

Natural process of Natural process of silificationsilification::

Petrified woodPetrified wood

From: Museum of natural history, Vienna

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Chemistry and NomenclatureChemistry and Nomenclature

•• SilanesSilanes: Hydrogen compounds of silicon: Hydrogen compounds of siliconSiSinnHH2n+2 2n+2 (n=1(n=1--15)15)

•• Halogen Halogen silanessilanes: : SiHSiH33Cl; SiHCl; SiH22ClCl22, SiHCl, SiHCl33

•• SilicicSilicic acidacid::

Monosilane

H S i

H

H

H S iS i

H H

H

H H

H

Disilane

H O Si

OH

OH

OH

n S iO2 + 2n H 2O

Silicate

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Chemistry and Nomenclature of Silicon CompoundsChemistry and Nomenclature of Silicon Compounds

• Silanol: H3SiOH Silanediol: H2Si(OH)2 etc.

• Silicone (polyalkylsiloxane): Organic derivatives of poly(silicic acid)

– Si-C bond is stable towards acids and bases

R = AlkylR OS i S i O S i etc.

R R R R

RRRR

OS i

n HOH2O-n

HO

H

H

O SiSi etc.

H

Si

H

OH

H

OSi

H

SiloxaneSiloxane

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Aims of SiliconAims of Silicon--TreatmentTreatment

1. Protection against degrading and staining fungi and insects

Basidionmycetes / MouldsNo biocide

2. Improvement of properties related to moisture and weathering

Swelling /shrinkageadhesion of coatings and varnishUV degradation

Incorporation of silicon compounds into the cell Incorporation of silicon compounds into the cell wallwall

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

3. Improvement of elasto-mechanical properties

hardnesstensile strengthfire resistance

Can be achieved by deposition of silicon Can be achieved by deposition of silicon compounds into the compounds into the luminalumina of the wood cellsof the wood cells

Aims of SiliconAims of Silicon--TreatmentTreatment

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

TreatmentsTreatments

•• Inorganic silicates (“water Inorganic silicates (“water glass”) glass”)

•• SilanesSilanes (sol(sol--gel process)gel process)

•• SiliconesSilicones

•• MicroMicro--emulsionemulsion technologytechnology

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

““Water glass”Water glass”

What is “water glass”?What is “water glass”?•• WaterWater--soluble K or Nasoluble K or Na--silicates or their solutionssilicates or their solutions•• Alkaline (pH over 12)Alkaline (pH over 12)

•• Problem: Fixation:Problem: Fixation:–– Precipitation in the wood through acids Precipitation in the wood through acids

–– Precipitation with salts (CaClPrecipitation with salts (CaCl22, Al, Al22(SO(SO44))33, borax), borax)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

““Water glass”Water glass”

Fixation:Fixation:MatthesMatthes et al., et al., ErfurtErfurt (1998 (1998 –– 2003)2003)

–– Precipitation through COPrecipitation through CO22 from airfrom air–– Needs several weeks for curingNeeds several weeks for curing

FurunoFuruno et al. (1991 et al. (1991 -- 2001)2001)–– Precipitation through salts (2 impregnation steps)Precipitation through salts (2 impregnation steps)

•• E.g. boron compounds, AlE.g. boron compounds, Al22(SO(SO44))33 or CaClor CaCl22, BaCl, BaCl2 2

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

0 5 10

Si

Penetration of Penetration of waterwater glassglass

Penetration was determined by means of SEM-EDX

• x-ray mapping of Si

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

• Precipitation of silicate within wood by gaseous acetic acid

• Biocidal leachable compounds are formed

„„Water glass“: white / brown rotWater glass“: white / brown rot

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

„„Water glass“: white / brown rotWater glass“: white / brown rot

T. versicolor (Beech)

0

10

20

30

40

50

60

70

neutralized untreated (n) alkaline untreated (a)

Wei

ght l

oss

[%]

10%20%30%

0

10

20

30

40

50

60

70

neutralized untreated (n) alkaline untreated (a)

10%20%30%

C. puteana (Pine)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

““Water glass”Water glass”

ResultsResults•• Decay resistance (EN 113)Decay resistance (EN 113)

–– HighHigh•• Because of high pHBecause of high pH

•• Enhanced fire resistanceEnhanced fire resistance•• Increased Increased hygroscopicityhygroscopicity•• High pH (problems at high drying temperature)High pH (problems at high drying temperature)•• MechanicalMechanical

–– ASE low increaseASE low increase–– Hardness unchanged or increased Hardness unchanged or increased –– Strength is significantly reducedStrength is significantly reduced–– Dynamic Dynamic MoEMoE unun--changedchanged

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

““Water glass”Water glass”

MASID MASID umwelterhaltendeumwelterhaltende ProdukteProdukte GmbHGmbH•• ““WoodblissWoodbliss”: (aqueous solution, pH >12)”: (aqueous solution, pH >12)

–– More than 10% silicate (water glass), More than 10% silicate (water glass), up to 10% up to 10% silicicsilicic acid (to improve penetration)acid (to improve penetration)

TimbersilTimbersil (Springfield, VA)(Springfield, VA)•• „„SodiumSodium Silicate Technology (SST)“Silicate Technology (SST)“

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

TreatmentsTreatments

•• Inorganic silicates (“water glass”) Inorganic silicates (“water glass”)

•• SilanesSilanes (sol(sol--gel process)gel process)•• SiliconesSilicones

•• MicroMicro--emulsionemulsion technologytechnology

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

OEt

etc.+ H2O

2 HO ..... (SiO2)nSi

OEt

OEt

HO O OH

OEt

OEt

SiSi

OEt

OH- H2O

WoodWood--inorganic composites by solinorganic composites by sol--gel processgel process

•• Two stage processTwo stage process–– Hydrolysis Hydrolysis (here (here SilicicSilicic Acid Esters)Acid Esters)

–– CondensationCondensation

•• End product is an amorphous silicate (glass)End product is an amorphous silicate (glass)

Silicate

Si

OEt

EtO OEt Si

OEt

HO OH- 2 EtOH

+ 2 H2OOE Et O tTTetraetraeeththooxyxy

ssilaneilane (TEOS)(TEOS)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SilaneSilane TypesTypes

Y = “Y = “OrganoOrgano--functional groupfunctional group””OX = “OX = “SiliconSilicon--functional groupfunctional group, OCH, OCH33, OC, OC22HH55 etcetc.

TEOS SiO2 MTES Me-SiO3/2

Si

OX

OXOXY

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

WoodWood--inorganic composites by solinorganic composites by sol--gel processgel process

SakaSaka et al. (1992 et al. (1992 -- 2001)2001)How to treat?How to treat?SiSi must incorporated into the cell wall!!must incorporated into the cell wall!!•• PrePre--conditioning of wood to fibre saturation pointconditioning of wood to fibre saturation point

–– Impregnation with TEOS in ethanol (free of water)Impregnation with TEOS in ethanol (free of water)–– Condensation in the cell wallCondensation in the cell wall

•• ASE: about 42%ASE: about 42%

•• Water uptake is reducedWater uptake is reduced

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

WoodWood--inorganic composites by solinorganic composites by sol--gel processgel process

BöckerBöcker et al. (2001), et al. (2001), BöttcherBöttcher et al. (1999)et al. (1999)

SilanesSilanes are hydrolysed before the impregnation.are hydrolysed before the impregnation.Impregnation is performed with preImpregnation is performed with pre--condensed condensed sols (in ethanol)sols (in ethanol)• Properties:

–– WPG: 5 WPG: 5 –– 50%50%–– Reduced moisture contentReduced moisture content–– ASE: 60% (at 45% WPG)ASE: 60% (at 45% WPG)–– Low decay resistanceLow decay resistance

•• Enhanced by boron addition (“controlled release”)Enhanced by boron addition (“controlled release”)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

AlkoxysilanesAlkoxysilanes

SiOEt

OEtOEt

EtO

TEOS

Tetraethoxysilane

SiCH3

OEtOEt

EtO

MTEOS

Methyl-Triethoxysilane

SiC3H7

OEtOEt

EtO

PTEOS

Propyl-Triethoxysilane

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Impregnation MethodsImpregnation Methods

““Sol impregnation”Sol impregnation”

1. Conditioning of Wood Samples at 65% r.H.

2. Hydrolysis of the silane(Pre-hydrolysis)

3. Impregnation with Sol

4. Curing at 103°C

““SilaneSilane impregnation”impregnation”

1. Conditioning of wood samples at 100% r.H. (fibre saturation)

2. Impregnation with silane/catalyst mixture

3. Curing at 103°C

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

5 x 10 x 30 mmBeechPine Sapwood

Basidiomycete Test (Mini-block)(T. versicolor, C. puteana)

5 x 10 x 100 mmPine SapwoodSoil Bed Test(ENV 807)

25 x 25 x 10 mm(rad x tang x long)

BeechWater Uptake,Dimensional stabilization

Sample SizeWood SpeciesExamination

Wood SamplesWood Samples

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Penetration of Penetration of SilanesSilanes

Sol (pre-hydrolysed) Silane (monomer)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

WPG (WPG (beechbeech))

TEOS Sol

MTES Sol

PTEO Sol

TEOS Silane

MTES Silane

PTEO Silane

0

5

10

15

20

25

30

35

WP

G [%

] After curing After aging

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Dimensional stabilisation (beech)Dimensional stabilisation (beech)

TEOS Sol

MTES Sol

PTEO Sol

TEOS Silane

MTES Silane

PTEO Silane

0

5

10

15

20

25

30

35

AS

E [%

] After curing After aging

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Water Immersion TestWater Immersion Test

0

60

120

180

240

300

360

0 2 4 6 8 10 12 14 16 18 20 22 24Immersion Time [h]

Wat

er U

ptak

e of

Woo

d C

ompo

site

[mg/

cm³]

ControlTEOSMTEOSPTEOSTEOSMTEOSPTEOS

Sols

Silanes

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Soil Bed Test (Soil Bed Test (ENvENv 807)807)

16,7

1,3

10,4

25,6

9,8 9,6

-2,4

2,7

12,6

4,8

55,5

28,5

46,750,0

32,2

18,3

2,3

6,9

26,3

10,6

66,9

33,5

55,9

47,7

31,3

13,6 15,0

45,8

23,8

-5,0

5,0

15,0

25,0

35,0

45,0

55,0

65,0

75,0

TEOS MTEOS PTEOS Pine SW Pine HW TEOS MTEOS PTEOS Pine SW Pine HW

Sols Silanes

MO

E lo

ss [%

]

after 8 weeksafter 16 weeksafter 24 weeks

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

BasidiomyceteBasidiomycete Test (miniTest (mini--block)block)Mass Loss of Beech after 6 Weeks Exposure to Mass Loss of Beech after 6 Weeks Exposure to TrametesTrametes versicolorversicolor

36,4 37,0

14,0

8,9

38,0

7,5

4,7 4,5

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

40,0

Control TEOS MTEOS PTEOS Control TEOS MTEOS PTEOS

Sols (conc. 50%) Silanes (conc. 100%)

mas

s lo

ss [%

]

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

WeatheringWeathering

control Silane 1 Silane 2

Artificial weathering of pine wood in a QUV (2 weeks)

untreated oligomeric silane systems

Reverse sides of wood samples after 1 year of weathering in Göttingen

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Conclusions (Conclusions (SilanesSilanes))

• Good penetration of monomeric silane in pine and beech

• Ageing during several weeks

• Slight or no reduction of moisture uptake

• Slight dimensional stabilisation

• Good hydrophobation effects with alkyl-silanes

• Alkyl-silanes improved resistance against fungal attack only initially

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SilanesSilanes –– TwoTwo--step Processesstep Processes

Covalent Fixation to the cell wallCovalent Fixation to the cell wall1. Reaction with organo-silanes2. Reaction with TEOS

3-Isocyanatpropyl triethoxysilane

β-(3,4 epoxycyclohexyl) ethyl trimethoxysilane

vinyl trimethoxysilane

High ASE !High ASE !

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

TreatmentsTreatments

•• Inorganic silicates (“water glass”) Inorganic silicates (“water glass”)

•• SilanesSilanes (sol(sol--gel process)gel process)

•• SiliconesSilicones•• MicroMicro--emulsionemulsion technologytechnology

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SiliconesSilicones

Si O

CH3

A

CH3

Si O

R

CH3

Si O

CH3

CH3

Si

CH3

CH3

A

nm

Silicones are Silicones are polydimethylpolydimethyl siloxanessiloxanes!!

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SEM-EDX: x-ray mapping of Silicon

0 5 10 15

Si

SiliconesSilicones EmulsionsEmulsions -- PenetrationPenetration

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Dimensional Dimensional stabilitystability ((PinePine))

-5

5

15

25

35

45

55

65

Micro 1(30%)

Micro 1(15%)

Micro 1(7.5%)

Micro 2(30%)

control

WPG

and

ASE

vol (

%)

WPGASE 0-20/65ASE 0-fs

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SiliconesSilicones -- DecayDecay FungiFungi (12 (12 weeksweeks))

T. versicolorC. puteana

0

10

20

30

40

50

60

70

silicone 1 silcone 2 silicone 3 control

Wei

ght l

oss

[%]

0

10

20

30

40

50

60

70

silicone 1 silcone 2 silicone 3 control

Wei

ght l

oss

[%]

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

SiliconesSilicones -- Outside WeatheringOutside Weathering

0

10

20

30

40

50

60

0 5 10 15 20

Exposure time [weeks]

Woo

d m

oist

ure

[%]

silicone 1silicone 2control

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Silicones Silicones -- Outside Weathering (6 month)Outside Weathering (6 month)

untreated treated

Front Front sideside

treateduntreated

Reverse Reverse sideside

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Conclusions (Conclusions (SiliconsSilicons))

• Penetration was dependent on the particle size of silicone emulsions

• Micro-emulsions enhanced the dimensional stability

• Reduction of moisture uptake and increase in weathering stability

• Decay resistance was dependent on functional groups on the siloxane backbone

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

TreatmentsTreatments

•• Inorganic silicates (“water glass”) Inorganic silicates (“water glass”)

•• SilanesSilanes (sol(sol--gel process)gel process)

•• SiliconesSilicones

•• MicroMicro--emulsionemulsion technologytechnology

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

WACKER SMKWACKER SMK®® TechnologyTechnology

MicroMicro--emulsions of some 10 nm diameteremulsions of some 10 nm diameter

•• Emulsifier:Emulsifier:–– NN--(2(2--aminoethyl)aminoethyl)--33--aminopropyl aminopropyl trimethoxysilanetrimethoxysilane + +

α,ωα,ω--dihydroxydihydroxy--methylpolymethylpoly siloxanesiloxane +KOH+KOH

•• CoCo--Emulsifier:Emulsifier:–– IsooctyltriethoxyIsooctyltriethoxy silanesilane

[15g + 80g A + 4g [15g + 80g A + 4g propionicpropionic acid]acid]

•• Hydrophobic compound:Hydrophobic compound:–– SilaneSilane, , siloxanesiloxane, , polysiloxanepolysiloxane

Good water repellent effect, but no increase of ASEGood water repellent effect, but no increase of ASE

30 nm

Silane, siloxane, polysiloxaneSilane, siloxaneFunctional polysiloxane

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Conclusions (general) Conclusions (general)

• Wide variety of chemicals is available

• Various wood properties can be improved

• Improvement of decay resistance is low

• Decay resistance can be enhance by combination with other compounds (“controlled release”)

• High water repellence

• Application in use-class III (EN 335)

Institute of Wood Biology and Wood TechnologyUniversity of Göttingen

Thank you for yourattention!