Properties and processing of Wood Densification by THM

Transcription

1 Thematic Session Modelling of THM treated wood, Joined Action FP0802, FP0904 August 24, 2011, Helsinki Properties and processing of Wood Densification by THM Parviz Navi

2 contents 1- Compression methods 1.1 Open systems (atmospheric pressure) 1.2 Closed systems (pressurized gas environment) 1.3 Mixed systems 1.4 unidirectional (platen press) 1.4 Compression forming (Two-directional compression) 1.5 Isobar (membrane press, 3D)

3 contents 2. Effects of THM processing on wood 2.1 Physical effects: Glass transition, Elasto-viscoplasticity, and shape memory or compression set-recovery 2.2 Chemical : TH wood degradation, fixation set-recovery 2.3 Effects of THM parameters on wood properties 3. Conclusions

4 1- Compression methods 1.1 Open systems (atmospheric pressure) Schema of the process THM densification with open-system process using an hydraulic press with heated plates, moisture content is 15% maximum

5 1.1 Open systems (atmospheric pressure) Production of a rolled wooden tube in a mold (courtesy from P. Haller) a) charging b) Closing c) Forming

6 1.1 Open systems Example of tube construction Tube Spruce, fabricated by densified bended wood panels, Photo P. Haller (2008) Filament winding of moulded tubes (Haller, 2009)

7 1- Compression methods 1.2 Closed systems (pressurized gas environment), THM treatment Densifying Apparatus (pressure vessel) up to 150 C and saturated steam: (a) closed condition, (b) open condition,1) chamber, 2) piston, 3) mould, 4) cover, 5) densified wood, (Navi & Girardet, 2000).

8 1.2 Closed systems (pressurized gas environment) Photograph of a THM (pressure vessel or reactor) together with control panels Schematic representation of a THM reactor showing ingoing and outgoing streams to cylindrical chambers

9 1.2 Closed systems Multi-layer THM reactor

10 Diagram of THM processing (Treatment chamber) 4 stages

11 Forming a trunk by THM closed system Photo of a two layered THM reactor, opened state. Diameter of the cylinder is 20 cm.

12 Densified trunk of pine (one dimensional) Two cross-sections of one directional radial densified trunk of pine after drying. The trunk after densificatin sawn into two parts and dried. This shows cracks formed on the wood during drying (Girardet and Navi, 2007)

13 1.3 unidirectional densification (a) (b) (c) (d) (a) Spruce before densification d= 430 kg/m 3 (b) After densification d= 1290 kg/m 3 degree of densification 68 % (c) Pine before densification d= 490 kg/m 3 (d) After densification d= 1300 kg/m 3 degree of densification 68 % (Navi and Girardet)

14 1.3 unidirectional (platen press), VTC, (Mixed system) Viscoelastic Thermal Compression device (VTC): Diagram showing the press inside to the chamber, platens and the specimen between the platens (F. Kamk)

15 1.3 unidirectional (platen press), VTC, (Mixed system) Large Viscoelastic Thermal Compression device (VTC): Photograph of the interior of the chamber (Courtesy of F. Kamk)

16 Viscoelastic thermal compression process (VTC) Phase 1 steaming Phase 2 venting Phase 3 compression Cooling specimens are cooled under compression

17 1.4 Compression forming (Two-directional compression) THM apparatus (pressure vessel or reactor) and the internal moulding block (Ito et al )

18 1.4 Compression forming (Two-directional compression) Transformation of a circular trunk to a square-section by twodimensional densification (Ito et al., 1998a)

19 1.4 Compression forming (Two-directional compression) Compressed Lumber Processing System Temperature in the THM chamber during the post-processing

20 1.4 Compression forming (multi-directional compression) Photo of two pieces of densified wood fabricated by Compressed Lumber Processing system

21 1.5 Isobar (membrane press - 3D) This is a 3D densification referring to the membrane press method (pressure vessel + a flexible membrane and steam) where compression occurs under three-dimensional uniform applied stress. Constant fluid pressure (isobaric) on the membrane causes compression of substrate in regions with least resistence, (F. Kamke).

22 2. Effects of THM processing parameters on wood 2.2 Chemical : TH wood degradation Samples are compressed at different temperatures between110 C and 200 C in a closed system. Degree of set-recovery of compressed samples measured under water soaking-drying cycles (Heger, 2004).

23 2.2 Chemical : TH wood degradation Set-Recovery (R) of samples compressed at different temperatures between 110 C and 200 C at a compression rate of 10 mm/min (Heger, 2004).

24 Sample of densified spruce compressed to 35 %; detail of a partially crushed earlywood zone. Sample of densified spruce compressed at140 C under saturated moisture conditions.

25 2.2 Chemical : degradation of wood constituents Chemical degradation of wood constituents is function of Temperature, Moisture Content and Processing Time. In both Heat-treatment and THM wood densification under the same T & H the degradation is similar. In THM densification the process needs water or (steam). High temperature steam, chemically degrades wood constituents (here only up to 200C considered)

26 The most important of degradation is wood hydrolysis (specially the hemicelluloses), function of T, MC and t In wood at high temperatures, water plays three important roles: it makes hydrolysis possible it ensures the mobility of the protons it participates in the acidification of the reactive medium Definition of hydrolysis : A chemical reaction in which water is used to break down a compound; this is achieved by breaking a covalent bond in the compound.

27 1- Hydrolysis of polysaccharides: Quantitative analysis of hemicelluloses by GPC (gas phase chromatography) Percentages of the different neutral sugars in treated wood after washing with water (the rest solved in water). Treatments Man Xyl Gal Ara Total Reference (natural) Densified Densified and post-treated (180 C, 30 min) notraces 8.1 Densified and post-treated (200 C, 5 min) notraces 8.6

28 2- Determination of the degree of polymerization of cellulose by capillary viscometer (according to the AFNOR (NF G06-037) Cellulose microfibrils are chemically more resistant to the hydrolysis. Degree of polymerization of three spruce samples Treatments: densification densification densification post-treatment at 180 C, 30 min post-treatment at 200 C, 4 min

29 4- Index of crystallinity (CrI) of the cellulose and diameter (L) of cellulose crystallites Treatment Temperatur e (oc) Time (minutes) CrI Diameter, L (Å) No treatment Densified Densified and posttreated under saturated moisture conditions `` `` Densified at 140 C and post-treated under saturated moisture conditions `` `` `` `` `` `` `` `` ``

30 5- Determination of the glass transition temperature (T g ) of lignin by DSC (Differential Sweeping Calorimetry with a single scan) Depending to temperature & time lignin condenses or depolymerises

31 What happens to wood after THM treatment

32 Unity or integrity of wood (cellulose-hemicelluloses-lignin) Covalent and hydrogen bands

33 2.3 Effects of THM parameters on wood properties The swelling of beech as a function of time (logarithmic scale) during humidification : (a) before densification, (b) after densification by open system (Huguenin & Navi, 1995).

34 Shear strength of the initial wood (black) and wood densified in a THM closed system (grey) for spruce and maritime pine (average values) (Navi & Girardet, 2000).

35 Brinel hardness of initial wood and densified wood in a THM closed system for spruce, beech and maritime pine (average values) (Navi & Girardet, 2000).

36 MOR and MOE of THM wood Natural wood, Wood densified at 140 C during 20 minutes post-treated at 140 C for 3 hours, post-treated at 160 C for 1 hour, post-treated at 180 C for 20 minutes, post-treated at 200 C for 4 minutes From each type of sample, at least 10 specimens were tested in tension. Photograph of a specimen after fracture under tensile testing (Navi & Heger, 2005).

37 20 mi. 3h. 1h. 20m. 4mi. Longitudinal tensile strength and Young s modulus of densified samples

38 Pressure or Stress [MPa] Kutnar and Kamke, 2010 Temperature [ o C] Influence of stress level on properties of THM wood Stress Steam Temperature Time [s] 0

39 Kutnar and Kamke, 2010 Test parameters of each THM treatment Load [MPa] Temperature [ C] Saturated steam pressure [psi] Compression loading steam environment Venting time prior to compression [s] Saturated steam 0 Superheated steam 180 Transient conditions Saturated steam 0 Superheated steam 180 Transient conditions Saturated steam 0 Superheated steam 180 Transient conditions 10

40 OD density [g/cm 3 ] 150 C 160 C 170 C Kutnar and Kamke, 2010 Oven dry density after THM treatment Transient Superheated steam Saturated steam

41 Moisture content [%] Moisture content of THM treated wood after conditioning at 20 C and RH 65% Transient Superheated steam Saturated steam 150 C 160 C 170 C Kutnar and Kamke, 2010

42 MOE and MOE/ρ emc of THM specimens Treatment Temperature [ C] MOE [GPa] MOE/ρ emc [GPa cm 3 /g] Untreated (1.06) 19.5 (1.35) Saturated steam (2.08) 20.3 (3.68) (4.90) 20.3 (4.26) (6.63) 24.8 (5.21) Transient conditions (4.80) 19.2 (4.34) (5.91) 20.8 (3.12) (3.01) 26.9 (2.92) Superheated steam (2.08) 15.8 (1.68) (4.83) 18.4 (4.04) (5.02) 18.2 (2.93) Kutnar and Kamke, 2010

43 Kutnar and Kamke, 2010 MOR and MOR/ρ emc of THM specimens Treatment Temperature [ C] MOR [MPa] MOR/ρ emc [MPa cm 3 /g] Untreated (10.9) 194 (9.60) Saturated steam (38.2) 193 (35.5) (45.1) 194 (39.9) (16.7) 215 (30.8) Transient conditions (42.0) 161 (36.7) (55.4) 170 (19.6) (16.7) 233 (16.3) Superheated steam (21.3) 137 (19.6) (40.8) 164 (41.9) (49.3) 158 (28.8)

44 Steam pressure [MPa], Compression stress [MPa] Kutnar and Kamke, 2010 Temperature [ C] Influence of post heat-treatment at 200 C on properties of THM wood Compression stress Steam pressure Temperature Time [s]

45 MOR/ density post heat-treated THM wood at 200 C Kutnar and Kamke, 2010

46 Viscoelastic thermal compression process (VTC) Phase 1 steaming Phase 2 venting Phase 3 compression Cooling specimens are cooled under compression Kutnar and Kamke, 2008

47 MOR [MPa] MOE [GPa] MOR and MOE of VTC wood 180,0 25,0 160,0 140,0 120,0 100,0 80,0 60,0 40,0 20,0 15,0 10,0 5,0 20,0 0,0 Control VTC 63% VTC 98% VTC 132% 0,0 MOR [MPa] MOE [GPa] Kutnar and Kamke, 2008

48 Effect of densification temperature on maximum bending strength (I) and tensile strength (II) Fang C.H., Mariotti N., Cloutier A., Koubaa A., Blanchet P Densification of wood veneers by compression combined with heat and steam. Eur. J. Wood Prod. DOI /s aspen (black) and hybrid poplar (grey).

49 Effect of densification temperature on MOE of bending (I) and tension (II) (?) Fang C.H., Mariotti N., Cloutier A., Koubaa A., Blanchet P Densification of wood veneers by compression combined with heat and steam. Eur. J. Wood Prod. DOI /s aspen (black) and hybrid poplar (grey).

50 3.Conclusions 1. Research on wood densification still needs the laboratory works 2. Few attempts has been made to commercialize the technology with open system 3. Domain is with high innovation because of T,H,M & t effects on mechanical and chemical degradation 4. Challenges exist on the moulding of large scale elements 5. Need for a Numerical simulation of Virtual processing of THM

51 Dr. Frederic Heger, Mr. Fred Girardet Dr. Andreja Kutnar Acknowledgment