THERMO VACUUM MODIFICATION OF SOME EUROPEAN SOFTWOOD AND HARDWOOD

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1 THERMO VACUUM MODIFICATION OF SOME EUROPEAN SOFTWOOD AND HARDWOOD S. Ferrari, O. Allegretti, I. Cuccui, J. Sandak, A. Sandak 1

2 LABESS The laboratory of wood drying at IVALSA 2

3 THERMO-VACUUM SYSTEM 3

4 THERMO-VACUUM SYSTEM 4

5 THERMO-VACUUM SYSTEM Atmosphere: partial vacuum (200 mbar, O 2 : 2%) Convection heat transfer by means of high efficiency fans Dry process no use of water or steam Open system gas from wood removed by vacuum pump Vacuum drying (to 0%) + thermal treatment 5

6 Industrial Thermo-Vacuum plant (6-12 m 3 ) 6

7 THE PROCESS 1. Drying phase in vacuum conditions (until 0% MC) 2. Temperature increase up to set value ( C) 3. HT phase at constant conditions (T-pressure) 4. Cooling phase 7

8 METHODS 8

9 TEST PERFORMED T air C T: air temperature from 160 to 220 C t: treatment duration from 0.75 to 5 hours p: vacuum pressure mbar (0 2 conc. 2-7%) time (hours) Treat. n T [ C] t [h] p [mbar] species all a no black locust all all all all all all no cherry 9

10 SPECIES Spruce Fir Larch (Picea abies) (Abies alba) (Larix decidua) Oak Ash Beech Cherry Black locust (Quercus Petraea) (Fraxinus excelsior) (Fagus sylvatica) (Prunus avium) (Robinia pseudoacacia) 10

11 MEASURED PROPERTIES Mass Loss (ML) Equilibrium Moisture Content (EMC) (T=20 C; RH=65%) Color coordinates (L*, a*, b*) 11

12 MEASURED PROPERTIES Mass Loss (ML) Equilibrium Moisture Content (EMC) (T=20 C; RH=65%) Color coordinates (L*, a*, b*) Swelling (ASE65%) Durability Mechanical properties (only for SPRUCE and FIR)* (only for SPRUCE and FIR)* (only for SPRUCE and FIR)* * Allegretti, et alii, 2012, Thermo-vacuum Modification of spruce (Picea abies karst.) and fir (abies alba mill.) wood, BioResources 7(3),

13 MEASURED PROPERTIES Mass Loss (ML) Equilibrium Moisture Content (EMC) (T=20 C; RH=65%) Color coordinates (L*, a*, b*) Swelling (ASE65%) Durability Mechanical properties (only for SPRUCE and FIR)* (only for SPRUCE and FIR)* (only for SPRUCE and FIR)* FT-NIR spectra * Allegretti, et alii, 2012, Thermo-vacuum Modification of spruce (Picea abies karst.) and fir (abies alba mill.) wood, BioResources 7(3),

treatment test 0,5 m3 of sawn boards (thickness 32 mm).

14 CHARACTERIZATION TESTS Matching samples method was adopted to minimize wood variability NT T Each treatment test 0,5 m3 of sawn boards (thickness 32 mm). 3 sawn boards for each species selected for characterization tests 14

15 RESULTS 15

16 MASS LOSS Mass loss: influence of T at constant time (3 hours) and pressure (210 mbar) 16

17 MASS LOSS Mass loss: influence of T at constant time (3 hours) and pressure (210 mbar) ML higher for hardwoods than softwoods; ML vs. T: exponential growth trend 17

18 MASS LOSS Mass loss: influence of t at constant T (180 C) and pressure (210 mbar) ML vs. t: asymptotic trend 18

19 MASS LOSS Mass loss: influence of p at constant T (190 C) and time (3 hours) 19

20 COLOR 20

21 COLOR Color: influence of T and t T t hardwood softwood 21

22 COLOR Color: influence of ML 22

23 EMC (rh 65%, t 20 c) NT* 160 C 180 C 200 C 220 C EMC EMC var% EMC var% EMC var% EMC var% fir larch spruce black l n.a. n.a ash beech cherry oak

24 MODEL 24

25 ML% DEMC% DL% ASH B. LOCUST SPRUCE 25

26 QUALITY 26

DURABILITY of Spruce and Fir (treated at 220 C- 2.5h) Tr. versicolor Gl. trabeum Growth of GL. Trabeum totally suppressed: ML<2% Most aggressive fungus: P.

27 DURABILITY of Spruce and Fir (treated at 220 C- 2.5h) Tr. versicolor Gl. trabeum Growth of GL. Trabeum totally suppressed: ML<2% Most aggressive fungus: P. placenta (ground contact) ML 10-20% P. placenta Con. puteana From: Allegretti, et alii, 2012, Thermo-vacuum Modification of spruce (Picea abies karst.) and fir (abies alba mill.) wood, BioResources 7(3),

28 MECHANICAL PROPERTIES of Spruce and Fir (treated at 220 C- 2.5h) Fir Spruce HT (T-t) ± ± ± ±2139 E dyn σ b σ c (Mpa) (Mpa) (Mpa) Utr Tr var% Utr Tr var% Utr Tr var% ± ± ± ± ns 74.3 ± ns 74.3 ± ns 70.2 ± ns 70.2 ± ± ± ± ± ns 38.5 ± ns 38.5 ± ns 39.1 ± ns 39.1 ± ± ± ± ± ns ns: not significant variation From: Allegretti, et alii, 2012, Thermo-vacuum Modification of spruce (Picea abies karst.) and fir (abies alba mill.) wood, BioResources 7(3),

29 CONCLUSIONS 1. An analytical model for determination of ML color, EMC, and ASE by the process parameters T, t, and p has been assessed C for 2.5 h. improves the wood durability of Spruce from class 4 to class Mechanical tests did not show any significant change in bending strength and stiffness for Spruce treated up to 200 C; 4. In general good quality with no internal tension, deformations, and very few end- or pith checks after the thermo-vacuum treatments. Internal checks were observed in black locust treated at temperatures higher than 160 C 5. Properties of wood are uniform within the treatment stack. This means that the temperature in the cylinder is uniform and the heating convection under vacuum is efficient. Similar features were observed in a full-scale industrial plant. 6. total absence of odor. 29

30 Thanks for your attention 30

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