Chemical characteristics of surface colour of birch veneer (Betula pendula)
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School of Chemical Technology |
Doctoral thesis (article-based)
| Defence date: 2015-11-20
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Authors
Date
2015
Major/Subject
Mcode
Degree programme
Language
en
Pages
62 + app. 60
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 182/2015
Abstract
This thesis investigates the discoloration of veneer produced from silver birch (Betula pendula) logs by means of biochemical and chemical analyses on the veneer and sap obtained from wood which was soaked at varying temperatures (20-70 ˚C). Drastic colour development was confirmed from the sap squeezed from green birch wood. The results from biochemical tests on the sap by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed the presence of polyphenol oxidases (PPO) which might form quinonoid intermediates in sap. Further chemical analysis by gas chromatography coupled with mass spectrometry revealed that the major phenol, which acts as a substrate for PPO, was epicatechin (EC). Control of the discoloration by either sodium sulphite (Na2SO3), or ethylenediaminetetraacetic acid (EDTA) was demonstrated. This thesis also investigates the chemical impact of elevated soaking temperature on the birch log being soaked. The results from spectrophotometric analysis on the veneer showed a significant increase in lightness (L*) and a decrease in yellowness (b*) in the veneer produced from logs soaked at 70 ˚C. Conversely, the effect of long-term storage resulted in a significant reduction in L* and an increase in b*. The results from the chemical analysis of squeezed sap revealed that the physical interaction between the core part of log and soaking water is limited when soaking at elevated temperatures. Assessment of the soaking water quality showed an increase of organic loading in water as soaking temperature increases. Bark seemed to be the major source of the organic substances. The results from the analysis of the squeezed sap from the soaked log showed that glucose and fructose were dominant free monosaccharides and their concentration was increased during soaking. The concentration of carboxylates, sulphite and sulphate had a positive correlation with soaking time at 70 ˚C. EC in the sap was diminished under soaking. In addition, the proanthocyanidins (PAs) contents had a moderate negative correlation between the contents and the soaking temperature. It was observed that phenolic compounds including EC and PAs played a major role in the colour change of the veneer, and their concentration was altered by elevated temperature.Description
Julkaistu vain painettuna, saatavuus katso Bibid. Published only in printed form, availability see Bibid
Supervising professor
Vuorinen, Tapani, Prof., Aalto University, Department of Forest Products Technology, FinlandThesis advisor
Kontturi, Eero, Prof., Aalto University, Department of Forest Products Technology, FinlandKeywords
Silver birch, Plywood, Veneer, Proanthocyanidins, Soaking, Colour change
Other note
Parts
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[Publication 1]: Yamamoto A, Rohumaa A, Kontturi E, Hughes M, Saranpää P, Andberg M, Vuorinen T (2013). Colorimetric behaviour and seasonal characteristic of xylem sap obtained by mechanical compression from silver birch (betula pendula). ACS Sustainable Chemistry & Engineering 1:1075-1082.
DOI: 10.1021/sc400090a View at publisher
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[Publication 2]: Yamamoto A, Rohumaa A, Kontturi E, Hughes M, Vuorinen T (2015). Chemical characteristics of squeezable sap of hydrothermally treated silver birch logs (Betula pendula): effect of treatment time and the quality of the soaking water in pilot scale experiment. Wood Science and Technology 49:289-302.
DOI: 10.1007/s00226-014-0693-5 View at publisher
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[Publication 3]: Yamamoto A, Rohumaa A, Kontturi E, Hughes M, Vuorinen T (2015). The chemical characteristics of squeezable sap from silver birch (Betula pendula) logs hydrothermally treated at 70 °C. The effect of treatment time on the concentration of water extracts. Wood Science and Technology.
DOI: 10.1007/s00226-015-0758-0 View at publisher
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[Publication 4]: Yamamoto A, Rohumaa A, Kontturi E, Hughes M, Vuorinen T (2015). The effect of hydrothermal treatment on the colour stability and chemical properties of birch veneer surfaces. BioResources.
DOI: 10.15376/biores.10.4.6610-6623 View at publisher