Abstract
The effects of short-term thermo-mechanical (STTM) densification by varying temperature and pressure regimes on the changes in anatomical structure of alder wood (Alnus glutinosa Gaertn.) veneers with low moisture content (~5 %) were investigated. Scanning electron microscopy (SEM) images of oblique cross and radial sections of non-densified and densified alder veneer were analysed. Veneer sheets were densified using pressure levels of 4, 8 and 12 MPa at three temperatures: 100, 150 and 200 °C for a short time of 4 min. The obtained results show that STTM densification of veneers causes irreversible changes in their morphology. Significant deformation of vessels and fibres and appearance of small spherical-like droplets (condensing compounds of lignin and degradation products of hemicelluloses) on the surface of the cell wall as well as pronounced thermo-mechanical wrinkling accompanied by the formation of axial cracks and rippled surface of the cell wall of the vessels were observed at higher temperatures and pressures. SEM images showed that the cell lumens collapsed and a certain amount of fractures in cell walls developed with increasing densification temperature and pressure. Moreover, densification of veneer with low moisture content at high temperatures and pressures causes a considerable fragility and occurrence of thermal erosion of the cell wall of vessel elements and fibres.






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Ahmed SA, Moren T, Hagman O, Cloutier A, Fang C-H, Elustondo D (2013) Anatomical properties and process parameters affecting blister/blow formation in densified European aspen and downy birch sapwood boards by thermo-hygro-mechanical compression. J Mater Sci 48:8571–8579
Arruda L, Del Menezzi CHS (2013) Effect of thermomechanical treatment on physical properties of wood veneers. Int Wood Prod J 4(4):217–224
Aydin I, Colakoglu G (2005) Effects of surface inactivation, high temperature drying and preservative treatment on surface roughness and colour of alder and beech wood. Appl Surf Sci 252:430–440
Bekhta PA (2003) Method of the plywood production. Patent of Ukraine, No. 62787A dated 15.12.03. Bulletin No. 12
Bekhta PA, Marutzky R (2007) Reduction of glue consumption in the plywood production by using previously compressed veneer. Holz Roh Werkst 65:87–88
Bekhta PA, Hiziroglu S, Shepelyuk O (2009) Properties of plywood manufactured from compressed veneer as building material. Mater Des 30:947–953
Bekhta PA, Niemz P, Sedliačik J (2012) Effect of pre-pressing of veneer on the glueability and properties of veneer-based products. Eur J Wood Prod 70:99–106
Bekhta P, Proszyk S, Krystofiak T (2014a) Colour in short-term thermo-mechanically densified veneer of various wood species. Eur J Wood Prod 72(6):785–797
Bekhta P, Proszyk S, Krystofiak T, Mamonova M, Pinkowski G, Lis B (2014b) Effect of thermomechanical densification on surface roughness of wood veneers. Wood Mater Sci Eng 9(4):233–245
Bekhta P, Proszyk S, Lis B, Krystofiak T (2014c) Gloss of thermally densified alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) wood veneers. Eur J Wood Prod 72(6):799–808
Buyuksari U, Hiziroglu S, Akkilic H, Ayrilmis N (2012) Mechanical and physical properties of medium density fibreboard panels laminated with thermally compressed veneer. Compos B 43:110–114
Candan Z, Korkut S, Unsal O (2013) Effect of thermal modification by hot pressing on performance properties of paulownia wood boards. Ind Crop Prod 45:461–464
Cīrule D, Alksne A, Lavnikoviča I, Antons A, Pavlovičs G, Dolacis J (2008) Comparison of the physical properties of grey alder (Alnus incana (L.) Moench) and black alder (Alnus glutinosa (L.) Gaertn.) wood in Latvia and elsewhere. Ann WULS SGGW For Wood Technol 63:129–132
Claessens H, Oosterbaan A, Savill P, Rondeux J (2010) A review of the characteristics of black alder (Alnus glutinosa (L.) Gaertn.) and their implications for silvicultural practices. Forestry 83(2):163–175
Donohoe BS, Decker SR, Tucker MP, Himmel ME, Vinzant TB (2008) Visualizing lignin coalescence and migration through maize cell walls following thermochemical pretreatment. Biotechnol Bioeng 101(5):913–925
Fang C-H, Mariotti N, Cloutier A, Koubaa A, Blanchet P (2012) Densification of wood veneers by compression combined with heat and steam. Eur J Wood Prod 70(1–3):155–163
Fengel D, Wegener G (1989) Wood: chemistry, ultrastructure, reactions. Walter de Gruyter, Berlin
Kajba D, Gracan J (2003) EUFORGEN Technical Guidelines for genetic conservation and use for Black Alder (Alnus glutinosa). International Plant Genetic Resources Institute, Rome 4 pp
Kutnar A, Kamke FA, Sernek M (2009) Density profile and morphology of viscoelastic thermal compressed wood. Wood Sci Technol 43:57–68
Lacić R, Hasan M, Trajković J, Šefc B, Šafran B, Despot R (2014) Biological durability of oil heat treated alder wood. Drvna Industrija 65(2):143–150
Mamoňová M (2013) Wood anatomy. Technical University in Zvolen, Zvolen 123 p
Mamoňová M, Laurová M, Nemčoková V (2002) Analysis of structure of beech wood subjected to hydrothermic treatment. Wood structures and properties ’02. Arbora Publishers, Zvolen, pp 51–55
Navi P, Girardet F (2000) Effects of thermo-hydro-mechanical treatment on the structure and properties of wood. Holzforschung 54(3):287–293
Pavlovičs G, Antons A, Alksne A, Lavnikoviča I, Cīrule D, Dolacis J, Daugavietis M, Daugaviete M (2009) Comparison of the anatomical structure elements and physical properties of the wood of different alder species growing in Latvia. Ann WULS SGGW For Wood Technol 69:173–177
Salca EA, Hiziroglu S (2014) Evaluation of hardness and surface quality of different wood species as function of heat treatment. Mater Des 62:416–423
Salca E, Cismaru I, Fotin A (2007) Effect of sunlight upon colour stability of alder and cherry veneers. PRO LIGNO 3(4):65–71
Salca EA, Gobakken LR, Gjerdrum P (2015) Progress of discoloration in green, freshly cut veneer sheets of black alder (Alnus glutinosa L.) wood. Wood. Mater Sci Eng 10(2):178–184
Selig MJ, Viamajala S, Decker SR, Tucker MP, Himmel ME, Vinzant TB (2007) Deposition of lignin droplets produced during dilute acid pretreatment of maize stems retards enzymatic hydrolysis of cellulose. Biotechnol Progr 23:1333–1339
Temiz A, Yildiz UC, Aydin I, Eikenes M, Alfredsen G, Colakoglu G (2005) Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test. Appl Surf Sci 250:35–42
Toksoy D, Colakoglu G, Aydin I, Colak S, Demirkir C (2006) Technological and economic comparison of the usage of beech and alder wood in plywood and laminated veneer lumber manufacturing. Build Environ 41:872–876
Tu D, Su X, Zhang T, Fan W, Zhou Q (2014) Thermo-mechanical densification of Populus tomentosa var. tomentosa with low moisture content. BioResources 9(3):3846–3856
Welzbacher CR, Wehsener J, Rapp AO, Haller P (2008) Thermo-mechanical densification combined with thermal modification of Norway spruce (Picea abies Karst) in industrial scale—dimensional stability and durability aspects. Holz Roh- Werkst 66:39–49
Yildiz S, Yildiz UC, Tomak ED (2011) The effects of natural weathering on the properties of heat-treated alder wood. BioResources 6:2504–2521
Acknowledgments
The authors are grateful to the COST Actions FP 0904 “Thermo-Hydro-Mechanical Wood Behaviour and Processing” and FP1006 “Bringing new functions to wood though surface modification” for the financial support within the frame of Short Term Scientific Missions (STSM). Special thanks are extended to Dr. Ortynska G. and Dr. Krystofiak T. for their technical support in preparing the samples and measurements of the size of vessels. This research was supported by Slovak Grant agencies SRDA Project No. APVV-14-0506; and VEGA Projects No. 1/0149/15 and No. 2/0199/14.
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Bekhta, P., Mamoňová, M., Sedliačik, J. et al. Anatomical study of short-term thermo-mechanically densified alder wood veneer with low moisture content. Eur. J. Wood Prod. 74, 643–652 (2016). https://doi.org/10.1007/s00107-016-1033-2
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DOI: https://doi.org/10.1007/s00107-016-1033-2


