new protection systems with silicones and silanes · 2007. 4. 24. · institute of wood biology and...
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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!