Investigation of chemical changes in the structure of thermally modified wood

Transcription

1 Investigation of chemical changes in the structure of thermally modified wood Peter Niemz, ETH Zürich - Institute for Building Materials (Wood Physics); Tamas Hofmann and Tamas Rétfalvi, Institute of Chemistry and Soil Science, Faculty of Forestry, University of West Hungary 11th International IUFRO Wood Drying Conference, Skellefteå, Sweden Content 1. Introduction 2. Materials and Methods Physical and Mechanical Properties Chemical Properties 3. Results 4. Conclusions 2

2 1. Introduction More and more wood is used in constructions Thermally treated wood gains more and more importance (constructions, furniture) Higher fungi resistance from treated wood Dark wood gains more and more importance Different treatment methods are used (in steam atmosphere, autoclave, vacuum-press drying) 3 Change in colour: influence: temperature-time-method untreated 12h 180 o C 24h 180 o C

3 Treated spruce used as aged wood 5 Heat treated ash in the interior (Thermoholz Spreewald, Germany) 6

4 Thermally treated spruce after 3 years of weathering 7 Influence of the method The use of a closed system for treatment (autoclave, saturated steam atmosphere) results in a higher concentration of formic acid and acetic acid (10 times higher) than in Vacuum Press Drying (Roffael, Niemz, Kraft 2008) 8

5 Emission of acetic components from thermally treated wood Species Acetic acid (mg/100g) Formic acid (mg/100g) Vacuum Press Drying Autoclave spruce beech spruce beech Roffael, E.; Kraft, R.; Niemz, P. : Formaldehyd- und Säureabgabe aus Thermoholz. Holz-Zentralblatt, Stuttgart (2008) 50,S Content 1. Introduction 2. Materials and Methods Physical and Mechanical Properties Chemical Properties 3. Results 4. Conclusions 10

6 Industrial plant for heat treatment with autoclave in nitrogen atmosphere Pressure 7 bar 11 SEM pictures of treated wood (Steam; Vacuum Press) drying) Method 1 Method 2 12

7 Tested wood Species Symbol Treatment steps Hardwoods Beech I Bu 0, 2, 3 Beech II Bu 0, 2, 3 Softwoods Spruce Fi 0, 2 0-untreated, 2 and 3 treated (3 is more intensive than 2) Content 1. Introduction 2. Materials and Methods Physical and Mechanical Properties Chemical Properties 3. Results 4. Conclusions 14

8 Physical and Mechanical properties Density: DIN MOE/MOR: DIN Moisture content: DIN Colour measurements (Minolta Chroma-Meter CR 200) 15 Chemical properties ph: Method of Roffael and Kossatz (1961) Ethanol-Toluene extract: Tappi standard: T 254 cm-97 Tappi standard: T 204 cm-97 Total phenol determination: spectrometry according to Folin-Ciocâltău Soluble Carbohydrate content: Method of Dubois et al. (1956) using glucose as standard Hemicellulose determination: hemicellulose content using the method of Polyak (1948) 16

9 Content 1. Introduction 2. Materials and Methods Physical and Mechanical Properties Chemical Properties 3. Results 4. Conclusions 17 Mechanical properties (20 o C/65%) Sample Density (g/cm 3 ) Moisture content (%) L-value Bending strength (N/mm 2 ) MOE (N/mm 2 ) Beech Beech Beech Spruce Spruce

10 Sorption of beech Beech 0 Beech 2 Beech 3 20/35 20/50 20/65 20/80 20/93 19 Sorption of spruce Spruce 0 Spruce 2 20

11 Chemical composition of beech Treatment ph Ethanol-Toluene extract (%) Totalphenol (mmol/100g dw.) Hemicellulose (%) Chemical composition of spruce Treatment 0 2 ph Ethanol-Toluene extract (%) Totalphenol (mmol/100g dw.) Soluble Carbohydrates (mg/g dw.)

12 Linear correlations between chemical parameters for hardwood Parameter 1 Parameter 2 R Ethanol-Toluene extract Totalphenol Totalphenol Bending strength Totalphenol Moisture content Totalphenol Hemicellulose Hemicellulose Bending strength Totalphenol Density Hemicellulose Moisture content Correlation for hardwood samples Ethanol-Toluene soluble fraction (%) high correlation (higher variation from treatment have an influence too, 3 steps) y = x R 2 = Totalphenol (mmol quercetin/100g dw) 24

13 Linear Correlations between physical and chemical parameters softwood Parameter 1 Parameter 2 R Soluble Carbohydrates MOE Soluble Carbohydrates Bending strength Totalphenol Bending strength Totalphenol L-value Content 1. Introduction 2. Materials and Methods Physical and Mechanical Properties Chemical Properties 3. Results 4. Conclusions 26

14 4. Conclusions Softwood and hardwood samples behave differently during the thermal modification process in an autoclave under N 2 atmosphere. The different behaviour can be assigned to the distinct composition of the wood species. The correlations between the tested parameters are different for softwood and hardwood species. 27 Thanks for your attention! ETH, Campus ZürichZ rich-hönggerberg IfB, Wood Physics 28