Outdoors, wood degrades due to weathering from factors such as solar radiation (ultraviolet, visible and infrared light), water (rain, dew, snow, humidity), temperature and atmospheric pollution (sulphur dioxide, nitrogen dioxide, ozone, dust, etc.). Among these factors, solar radiation, especially ultraviolet light, has the most damaging effect by the formation of free radicals and depolymerizing lignin in the wood cell walls, followed by water, which leaches the degradation products, causing surface erosion.
This study examined three species of soft deciduous wood – aspen (Populus tremula), birch (Betula pendula) and grey alder (Alnus incana), all of which were weathered untreated and hydrothermally modified (HTM-d) at 160oC for 3 h and at 170oC for 1 h. The artificial weathering period was 1000 h and consisted of cycles of condensation, irradiation with UV light and water spray. Because the photodegradation of wood is essentially a surface phenomenon, the ATR FTIR method was applied to examine the changes in the chemical structure of wood. The spectra showed that the characteristic peaks of lignin in all examined wood species (untreated and after hydrothermal modification (HTM) significantly decreased or practically disappeared after weathering, which means that lignin becomes most degraded. Cellulose, which consists of amorphous and crystalline regions, is also affected by weathering, and the amorphous part of cellulose is more degraded. The results show that the HTM-d wood surface after weathering also becomes damaged and needs to be protected; therefore, the next aim of the work will be to find coatings with the best protection properties.
Keywords: HTM-d wood, artificial weathering, ATR FTIR
Authors
Kapaca E.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Cirule D.
Grinins J.
Bikovens O.
Andersons B
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