Use of thermally modified wood in Use of thermally modified wood in building constructions building constructions

Prof.dr. Franc PohlevenProf.dr. Franc Pohlevenfranc.pohleven@bf.uni-lj.si

University of LjubljanaUniversity of LjubljanaBiotechnical Faculty,Biotechnical Faculty,

Department of Wood Science and Technology,Department of Wood Science and Technology,RoRožžna dolina, Cesta VIII/34na dolina, Cesta VIII/34SI1000 Ljubljana, SloveniaSI1000 Ljubljana, Slovenia

INTRODUCTIONINTRODUCTION

• Different wood modification process:• Thermal• Chemical• Enzimatic

INTRODUCTIONINTRODUCTION

• DIFFERENT HEATING MEDIA:nitrogen, steam, oilVACUUM – A SLOVENIAN METHOD

• Exposure to high temperatures cause severe degradation of cellulose and losses in mechanical properties

INTRODUCTIONINTRODUCTION

• Temperatures from 160 °C to 260 °C• Absence of oxygen• Process of wood modification• Chemical changes in wood cell walls• Changes of wood (=modified wood)

Phases of process (24 h)

drying at 103 °C

vacuuming up to 0,05 bar

heating to 150 °C

heating to T of modif. (3 h)

cooling down

MATERIALS AND METHODS - modificationMATERIALS AND METHODS - modification

SOFTWOOD or HARDWOOD

PROPERTIES OF THERMALLY MODIFIED PROPERTIES OF THERMALLY MODIFIED WOODWOOD

• Improvement of durability and dimensional stability

• Removing of resins• Improvement of resonant (acoustic) properties• Mass loss• Change of physical properties:

• Colour• Reduction of strength and stiffness• Bending strength 10 % – 50 %

Results - change of colourResults - change of colour

S B H

Elm wood

• MASS LOSSES

Spruce: 3 % (190 °C) – 24 % (230 °C)Larch: 5 % (190 °C) – 31 % (230 °C)

MATERIALS AND METHODS – decay testsMATERIALS AND METHODS – decay tests

• DECAY TESTS

mini-block test (Bravery)

cross-section: 10 mm × 5 mm

length: 30 mm

Gloeophyllum trabeum

Coniophora puteana

exposure: 8 weeks

Mass loss (%)

Gt Cp

Spruce untreated 35,2±5,4 56±12

treated 1,5±1,1 8,9±4,4

Larch untreated 34,2±7,7 29,0±2,9

treated 1,17±0,18 0,90±0,21

• DECAY – samples treated at 200 °C

RESULTS – decay testsRESULTS – decay tests

MATERIALS AND METHODS – dimensional stabilityMATERIALS AND METHODS – dimensional stability

• DIMENSIONAL STABILITY

ASE – soaking/ovendrying test (3 cycles)

shrinkage (α) in r, t dim.

20 mm × 20 mm × 20 mm

50 mm × 20 mm × 20 50 mm × 20 mm × 20 mmmm

unorientedunoriented

ABSORPTION OF WATER VAPOUR AT 83 ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITY% AIR HUMIDITY AND T = 25 °CAND T = 25 °C

Exposure atExposure at 83 % 83 % RH and RH and 25 °C 25 °C

RESULTS: absorption of RESULTS: absorption of water vapour – spruce water vapour – spruce

woodwood

RESULTS: absorption of RESULTS: absorption of water vapour – beech woodwater vapour – beech wood

RESULTS: absorption of RESULTS: absorption of water vapour – oak woodwater vapour – oak wood

DIMENSIONAL STABILITYDIMENSIONAL STABILITY (spruce) (spruce)

DIMENSIONAL STABILITY (beech)DIMENSIONAL STABILITY (beech)

DIMENSIONAL STABILITY (oak)DIMENSIONAL STABILITY (oak)

APPROXIMATIONAPPROXIMATION OF REDUCTION OF DIMENSIONOF REDUCTION OF DIMENSIONSS OF OF MODIFIED WOODMODIFIED WOOD SPECIMENS (spruce) SPECIMENS (spruce)

APPROXIMATIONAPPROXIMATION OF REDUCTION OF DIMENSIONOF REDUCTION OF DIMENSIONSS OF OF MODIFIED WOODMODIFIED WOOD SPECIMENS (beech) SPECIMENS (beech)

APPROXIMATIONAPPROXIMATION OF REDUCTION OF OF REDUCTION OF DIMENSIONDIMENSIONSS OF MODIFIED WOOD OF MODIFIED WOOD SPECIMENS SPECIMENS

(oak)(oak)

MATERIALS AND METHODS – MOE AND MATERIALS AND METHODS – MOE AND MORMOR

• MOE, MOR

static three-point bending test

300 mm × 20 mm x 20 mm, absolute dry

Zwick Z-100Zwick Z-100

10 mm/min

MATERIALS AND METHODS - MATERIALS AND METHODS - MOEMOE

• MOE non-destructively

natural vibration analysis in clamped-free conditions

300 × mm 20 mm × 10 mm, absolute dry

12

3

4

56

MATERIALS AND METHODS - MATERIALS AND METHODS - MOEMOE

• MOE non-destructively

inductive proximity sensor

0

2

4

6

8

10

0 0,2 0,4 0,6 0,8 1 1,2

čas (s)

nape

tost

(V

) FFT

νn

dynamic signal analyzerdynamic signal analyzer

• MOR AND MOE of absolute dry samples

0

2000

4000

6000

8000

10000

12000

14000

16000

100 x MOR(spruce-bending)

MOE (spruce-bending)

MOE (spruce-

vibration)

MOE (larch-

vibration)

MP

a

Untreated

Treated, 190 °C

Treated, 210 °C

Treated, 230 °C

RESULTS – MOE and RESULTS – MOE and MORMOR

Laboratory chamber for thermal wood modification

Industrial chamber for thermal wood modification

Silvaprodukt d.o.o., Ljubljana, Sovenia

The first product made from thermally modified wood, modified according to “our procedure”

CONCLUSIONSCONCLUSIONS

• The best characteristics of the products made of modified wood were achieved with wood, modified at temperatures between 180 °C and 210 °C

• In spite of the treatment, the mechanical properties of modified wood are still appropriate for wood to be used in constructions

• Wood modification process can ensure appropriate resistance for diverse ways of utilisation of wooden products, especially in in wet conditions