Surface modification of wood with

functionalized alkoxysilanes

Elisa Cappelletto, Rosa di Maggio

Department of Materials Engineering and Industrial Technology

University of Trento

Workshop “Basics for Chemistry of Wood SurfaceModification" 25 April-Kuchl

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

WOOD

COATING

Why? Enhancing wood durability

What? Alkoxysilanes different functionalized

How? Surface modification of wood throught immersion

Lignin

Hemicellulose

Cellulose

Material and Method

Sol-gel precursors

Solvents

Ethanol, Chloride acid and Ammonium solutions as catalytic agent

Substrate

Larch and Pine

Application by immersion

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Tetraethoxysilane

Si(OC2H5)4

Dimethyldiethoxysilane

(CH3)2Si(OC2H5)

Perfluorooctyltriethoxysilane

(C14H19F13O3Si) Phenyltriethoxysilane

(C6H5)Si(OC2H5)3

Preparation of Samples

Substrate: Larch and Pine

Coatings: wT, wM2, wPhtes

Residential Time: 3, 5,10, 20 min

Characterization: SEM-EDX

Time of deposition 20 min: presence of cracks

Conclusion:

Residential Time

single layer: 10 min

double layer: 3 min First Layer on Larch

5 min Fisrt Layer on Pine

10 min Second Layer

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

List of the SAMPLES

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Samples Substrate First Layer Second Layer Weight of coating per unit of surface g/m2

wM2 wood (CH3)2Si(OC2H5) 33

wTM2 wood Si(OC2H5)4 (CH3)2Si(OC2H5) 41

wTM2b wood Si(OC2H5)4 (CH3)2Si(OC2H5) 30

wTPFOS wood Si(OC2H5)4 (C14H19F13O3Si) 56

wTPhtes wood Si(OC2H5)4 (C6H5)Si(OC2H5)3 37

b= basic catalysis

Characterization of Treated Wood

SEM-EDX

FT-IR

NMR

Contact Angle Measurement

Fire Test

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Distribution on the surface

Coated wood

Untreated wood

Profile

EDX spectrum of Silicon

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

SEM-EDX

EDX spectra of Silicon

FT-IR (ATR)

IR spectra of treated samples show the strong Si-O-Si stretching band (1029 cm-1).

The treatments decrease the amount of –OH on the surface

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Solid State NMR investigation

Evaluation of the degree of condensation of

siloxane coatings

Structural Unit:

Q4 (Si(OSi)4), Q3 ROSi(OSi)3), Q2 (RO)2Si(OSi)2)

T3 RSi(OSi)3), T2 RSi(OSi)2OR’, T1 RSi(OSi)2(OR’)2

D2 R2Si(OSi)2, D1 R2Si(OSi)R’

High Degree of Condensation (DOC), matrix are

stable

DOC≈90

Deconvolution of Peaks

29Si CPMAS spectrum of treated samples

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

DOC=((4xQ4+3xQ3+2xQ2+Q1)/4+(3xT3+2xT2+T)/3+(2xD2+D1)/2+M)

where capital letters are the areas under the peaks obtained by

deconvolution

T2 T3

CONTACT ANGLE TEST(Vieca Method*)

The treatments increase hydrophobic behaviour of wood. Double layer

samples have higher equilibrium CA values respect to monolayer (≈90°)

0

20

40

60

80

100

120

untr

.woo

d

wM

2

wTM

2

wTM

2b

WTP

FOS

wTP

HTE

S

Theta STATIC CONTACT ANGLE

EQUILIBRIUM CONTACTANGLE

Untreated wood

vibration

Coated sample

*C. Della Volpe, D. Maniglio, M. Morra, S. Siboni, The determination of a “stable-equilibrium” contact

angle on heterogeneous and rough surfaces, Colloids Surf. A 206 (2002) 46–6

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Reaction to Fire (Cone Calorimeter Test)

s (MJ/m²) MLR t

Sample Time of ignition Total Heat Release Mass Loss rate

Untreated wood 13,33 156,65 445,000

Commercial prod. 14,00 156,51 235,000

WM2 13,33 157,33 428,333

WTM2a 15,33 145,22 30,000

WTM2b 16,67 151,75 31,667

WTPFOS 14,67 151,92 185,000

WTPHTES 18,00 148,46 35,00

Cone Calorimeter

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Time of ignition

Total Heat Release Mass Loss rate

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

SEM-EDX and FT-IR OF BURNED SAMPLES

SEM images of burned samples

EDX spectrum of burned sample

FT-IR (ATR) Treated wood and burned samples

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Conclusion

- The Modification of wood surface through immersion improves some properties of material

- Increase of the hydrophobic barrier

- Good Fire retardant properties ( taking into account the small amount of material deposited)

- Stable matrix on surface, and partial penetration on the bulk of wood

- No alteration of optical properties

- The results obtain with fluorinated treatments are comparable to those obtained with methylated

series. Methylated compounds are cheaper

- Good results with phenyltriethoxysilane

Work in Progress

- Biological test against fungi

- Application by impregnation

CNR-Ivalsa (Istituto per la Valorizzazione del Legno e delle Specie Arboree)

- Sesto Fiorentino (FI): Biological Test

- S.Michele all’Adige (TN): Flame Retardant Test

Acknowledgment The Trento Provincial Authority is gratefully acknowledged for funding (PAT – CENACOLI

project).

Collaborations

Elisa Cappelletto, Surface modification of wood with functionalized alkoxysilanes, University of Trento

Thanks for your attention

Elisa Cappelletto

elisa.cappelletto@ing.unitn.it