Absorption of Liquid Water in Pine, Birch and Spruce and the Effect of Heat Treatment on the Microstructure.

Transcription

1 Absorption of Liquid Water in Pine, Birch and Spruce and the Effect of Heat Treatment on the Microstructure. Margot Sehlstedt-Persson, Dennis Johansson, Tom Morén Luleå University of Technology Skellefteå Campus Division of Wood Science and Technology Sweden

2 Effect of heat treatment on capillary water absorption of heattreated pine, spruce and birch Dennis Johansson, Margot Sehlstedt-Persson, Tom Morén Luleå University of Technology Skellefteå Campus Division of Wood Science and Technology Sweden Effect of Heat Treatment on the Microstructure of Pine, Spruce and Birch and the Influence on Capillary Absorption Margot Sehlstedt-Persson, Dennis Johansson, Tom Morén Luleå University of Technology Skellefteå Campus Division of Wood Science and Technology Sweden

3 Purpose Dynamics of longitudinal capillary absorption of free water in heat-treated and dried wood CT-Scanning Physical changes of anatomical microstructure SEM-studies

4 Species Material Scots pine (Pinus sylvestris) 50 x 100 x 300 mm; sap- and heartwood Norway spruce (Picea abies) 50 x 100 x 300 mm; sap- and heartwood Birch (Betula pubescens) 50 x 90 x 300 mm Treatment Industrial drying max 60 C Heat treatment 170 and 200 C (Thermowood process) Test Capillary absorption, 15 days Intermittently CT-scanning Water level 25 mm

5 CT-Scanning At 0, 1, 3, 5, 8, 12, and 15 days of absorption Scan width 5 mm along the length axis

6 Calculation of MC Voxel size = 0.63 x 0.63 x 5 mm 3 Uniform moisture distribution No consideration of volume swelling FSP 30%

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10 Conclusions from absorption test Birch heat treatment decreased absorption height Pine sapwood - deviant behaviour Spruce small difference between sap and heartwood Pine heartwood comparable to spruce sap heartwood Focus on pine and spruce special attention to crossfield pits and bordered pits

11 Transport passages in softwood 2.4 rays/ longitudinal tracheid Effective 3-dimensional transport system

12 Spruce and pine Picea abies Pinus sylvestris 20-25% unaspirated up to 50% unaspirated Average diameter 2 μm Average size 12 x 31 μm overall pit area 10 x larger Bordered pits in latewood:

13 SEM studies Split areas no cutting Radial view Areas 15 x 20 mm

14 Results: Pine sapwood 60 C

15 Results: Pine sapwood 170 C

16 Results: Pine sapwood 170 C Membranes partly ruptured

17 Results: Pine sapwood 200 C

18 Pine sapwood No visible difference between 60 C 170 C and 200

19 Green Pine sapwood

20 Results: Pine heartwood 170 C

21 Discussion Open structures in crossfield pits in pine sapwood - effective water uptake Frequently in LT-dried and heat treated pine sapwood not in green sapwood Not common in pine heartwood! Hypothesis: Initial capillary drying process?! Heartwood formation mortification of parenchyma cells Rapid emptying of parenchyma cells in sapwood

22 Results: Spruce sapwood 60 C

23 Results: Spruce sapwood 170 C

24 Results: Spruce sapwood 200 C

25 Results: Spruce sapwood 170 C Green

26 Results: Bordered pits Pine sapwood

27 Pine sapwood: Conclusions SEM studies Open structures crossfield pits in rays- rapid water uptake No visible difference between 60 C, 170 C 200 C! Pine heartwood - no visible changes Hypothesis: Rapid emptying of parenchyma cells in sapwood during initial capillary drying?! Ruptured membranes in bordered pits occur Spruce no visible changes Birch no visible changes

28 Thank You for listening!