new protection systems with silicones and silanes - swstswst.org/meetings/am05/mai.pdf · new...

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


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


General Aspects of SiliconGeneral Aspects of Silicon

Natural process of Natural process of silificationsilification::

Petrified woodPetrified wood

From: Museum of natural history, Vienna


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


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


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


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


TreatmentsTreatments

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

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

•• SiliconesSilicones

•• MicroMicro--emulsionemulsion technologytechnology


““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)



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


0 5 10

Si

Penetration of Penetration of waterwater glassglass

Penetration was determined by means of SEM-EDX

• x-ray mapping of Si


• Precipitation of silicate within wood by gaseous acetic acid

• Biocidal leachable compounds are formed

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


„„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)



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



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)“



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

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



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)


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



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



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”)


AlkoxysilanesAlkoxysilanes

SiOEt

OEtOEt

EtO

TEOS

Tetraethoxysilane

SiCH3

OEtOEt

EtO

MTEOS

Methyl-Triethoxysilane

SiC3H7

OEtOEt

EtO

PTEOS

Propyl-Triethoxysilane


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


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


Penetration of Penetration of SilanesSilanes

Sol (pre-hydrolysed) Silane (monomer)


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


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


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


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


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 [%

]


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


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


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 !





•• SiliconesSilicones•• MicroMicro--emulsionemulsion technologytechnology


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!!


SEM-EDX: x-ray mapping of Silicon

0 5 10 15

Si

SiliconesSilicones EmulsionsEmulsions -- PenetrationPenetration


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


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

[%]


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


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

untreated treated

Front Front sideside

treateduntreated

Reverse Reverse sideside


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





•• SiliconesSilicones



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


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)


Thank you for yourattention!

new protection systems with silicones and silanes - swstswst.org/meetings/am05/mai.pdf · new...

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