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Chemical and ultrastructural aspects of thermally modified wood with emphasis on durability

Gao, Jie (2017). Chemical and ultrastructural aspects of thermally modified wood with emphasis on durability. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis agriculturae Sueciae, 1652-6880 ; 2017:112
ISBN 978-91-7760-114-2
eISBN 978-91-7760-115-9
[Doctoral thesis]

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Abstract

The Termovuoto (thermo-vacuum) process is an environmental friendly industrial approach to modify wood by combining efficient vacuum drying and thermo-treatment. In this thesis, chemical and ultrastructural aspects of two softwoods (spruce and fir for 4 h at 160−220℃) and two hardwoods (ash and beech for 3 h at 190−220℃) thermally modified using the Termovuoto process were studied by light- and electron microscopy with emphasis on durability.

Histochemical staining indicated an increasing amount of acidic groups in thermally modified woods (TMWs), particularly in the compound middle lamella (CML) including middle lamella cell corner (MLcc) (CMLcc) regions of TMWs treated at 220℃ (TMW220℃). TEM observations showed significantly increased KMnO4 staining intensity of lignin in TMW220℃, presence of electron dense particles in CMLcc regions of softwood TMW220℃, and large lignin aggregates and disordered lamellar structure in the fibre S2 layer of hardwood TMW220℃.

The durability of TMWs against two white rot (Phlebia radiata, Pycnoporous sanguineus)-, two brown rot (Postia placenta, Gloeophyllum trabeum)- and three soft rot (Chaetomium globosum, Phialophora mutabilis, Phialophora malorum) fungi was evaluated by the soil block test. For brown- and white-rot fungi, Termovuoto treatment showed considerable improvement in durability class (i.e. class 1−3) for soft- and hardwoods at 220℃ against all fungal species tested. Softwood TMWs showed an overall lower decay resistance than hardwood TMWs, among which ash TMWs showed greater durability than beech TMWs. For soft rot fungi, softwood TMWs were more durable than hardwood TMWs, irrespective of fungal species. Ash showed lower durability than beech in untreated reference wood, while ash TMWs showed greater durability than beech TMWs during one year decay test. Behavior of thermal modification (TM) differed significantly between ash (ring-porous hardwood) and beech (diffuse-porous hardwood) against brown-, white- and soft-rot fungi, indicating importance of the native wood anatomy.

Decay patterns and morphological changes of TMWs were examined by light- and electron microscopy. The white rot fungus P. sanguineus did not show significant differences in characteristic features of decay in tracheids and fibres of TMWs compared to those in untreated reference. However, the delignification process in tracheids and fibres by P. sanguineus was delayed in TMWs, particularly at high treatment temperatures as evidenced by narrower transition zones from delignified and lignified areas than untreated reference. The soft rot fungus P. mutabilis produced typical soft rot Type-I cavities in fibres of hardwood TMWs at low temperature (190−200℃). However, soft rot cavity formation was greatly inhibited and/or delayed in fibres at high treatment temperatures (i.e. 210−220℃). Ash TMW200℃ showed a radial-like distribution of electron dense materials in cavities and lack of fibrillar-like materials within degraded fibre walls, which differed from reference.

The fungal durability of Termovuoto TMWs differed in terms of treatments, wood and fungal species. The Termovuoto process did not change the patterns of decay caused by white-, brown- and soft-rot fungi used, but rather slowed down the decay process at certain treatment temperatures for certain wood species. Understanding of the decay patterns in TMWs is essential for further optimization of the Termovuoto process for improving the durability of specific wood species for specific purposes.

Authors/Creators:Gao, Jie
Title:Chemical and ultrastructural aspects of thermally modified wood with emphasis on durability
Series/Journal:Acta Universitatis agriculturae Sueciae (1652-6880)
Year of publishing :November 2017
Depositing date:23 November 2017
Volume:2017:112
Number of Pages:70
Papers/manuscripts:
NumberReferences
IGao, J., Kim, J.S., Terziev, N., Allegretti, O. and Daniel, G. 2014. Chemical and ultrastructural changes in compound middle lamella (CML) regions of softwoods thermally modified by the Termovuoto process. Holzforschung68 (7):849−859.
IIKim, J.S., Gao, J., Terziev, N., Cuccui, I. and Daniel, G. 2015. Chemical and ultrastructural changes of ash wood thermally modified using the thermo-vacuum process: I. Histo/cytochemical studies on changes in the structure and lignin chemistry. Holzforschung 69(5): 603−613.
IIIGao, J., Kim, J.S., Terziev, N. and Daniel, G. 2016. Decay resistance of softwoods and hardwoods thermally modified by the Termovouto type thermo-vacuum process to brown rot and white rot fungi. Holzforschung 70 (9): 877−884
IVGao, J., Kim, J.S., Terziev, N. and Daniel, G.2017. Effect of thermal modification on the fungal durability and decay patterns of hardwoods and softwoods against soft rot fungi. International Biodeterioration & Biodegradation.(In press)
VGao, J., Kim, J.S. and Daniel, G. 2017. Effect of thermal modification on the micromorphology of decay of hardwoods and softwoods by the white rot fungus Pycnoporus sanguineus (Holzforschung; Submitted).
VIKim, J.S., Gao, J., Terziev, N., Allegretti, O. and Daniel, G. 2015. Chemical and ultrastructural changes of ash wood thermally modified (TMW) using the thermo-vacuum process: II. Immunocytochemical study of the distribution of noncellulosic polysaccharides. Holzforschung 69(5): 615−625.
VIIKim, J.S., Gao, J. and Daniel, G. 2015. Ultrastructure and immunocytochemistry of degradation in spruce and ash sapwood by the brown rot fungus Postia placenta: Characterization of incipient stages of decay and variation in decay process. International Biodeterioration & Biodegradation103: 161−178.
VIIIKim, J.S., Gao, J.and Daniel, G. 2015. Cytochemical and immunocytochemical characterization of wood decayed by the whiterot fungus Pycnoporus sanguineus I.preferential lignin degradation prior to hemicelluloses in Norway spruce wood. International Biodeterioration & Biodegradation 105: 30−40.
IXKim, J.S., Gao, J. and Daniel, G. 2015. Cytochemical and immunocytochemical characterization of wood decayed by the white rot fungus Pycnoporus sanguineusII. Degradation of lignin and non-cellulosic polysaccharides in European ash wood. International Biodeterioration & Biodegradation 105: 41−50.
Place of Publication:Uppsala
Publisher:Department of Forest Products, Swedish University of Agricultural Sciences
Associated Programs and Other Stakeholders:SLU/LTJ - Partnership Alnarp
SLU/LTJ - Tillväxt Trädgård
Wildlife Damage Centre
Euroscapes
ISBN for printed version:978-91-7760-114-2
ISBN for electronic version:978-91-7760-115-9
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:J Handling, transport, storage and protection of agricultural products > J12 Handling, transport, storage and protection of forest products
K Forestry > K50 Processing of forest products
Subjects:Obsolete subject words > NATURAL SCIENCES > Biology
Obsolete subject words > FORESTRY, AGRICULTURAL SCIENCES and LANDSCAPE PLANNING > Product science > Wood fibre and forest products
(A) Swedish standard research categories 2011 > 2 Engineering and Technology > 205 Materials Engineering > Paper, Pulp and Fiber Technology
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Wood Science
Agrovoc terms:wood, improved wood, softwood, hardwood, rots, wood preservation, resistance to fungicides, scanning microscopy, electron microscopy, analytical methods, ultrastructure
Keywords:brown rot, decay resistance, light microscopy (LM), scanning electron microscopy (SEM), soft rot, thermo-vacuum (Termovuoto) process, thermally modified wood (TMW), transmission electron microscopy (TEM), ultrastructure, white rot
URN:NBN:urn:nbn:se:slu:epsilon-e-4502
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-4502
ID Code:14743
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Forest Products
Deposited By: Jie Gao
Deposited On:23 Nov 2017 12:51
Metadata Last Modified:23 Nov 2017 12:51

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