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Polyflavonoid tannins - From a cause of CCA soft-rot failure to the "missing link" between lignin and microdistribution theories
1986 - IRG/WP 3359
Polyflavonoid tannins are proven to be fast-reacting with CCA solutions and hence, to be strong competitors of the structural wood constituents for fixation of CCA preservatives. The consequence of this effect is that even relatively small amounts of tannin cause severe undertreatment of the structural wood constituents which in turn badly affects the long term durability of CCA-treated timber. The effect is compounded by heavy disproportionation between tannins and structural wood constituents of Cu, Cr and As. This leads to the well-known high susceptibility to soft-rot attack in Eucalyptus species and in vineyard posts even experienced with some susceptible softwoods. Relationships found by other authors between soft-rot incidence and lignin content in CCA-treated timber are shown here to be only part of the total failure mechanism. The total mechanism of resistance and failure is due to the balance of distribution of reactions among the various proportions of highly reactive tannins and more abundant but less reactive lignin and carbohydrates present in any wood. As a consequence of the clarification of these mechanisms the liability of different woods to soft-rot attack may then be determined. Solutions to the problem are presented and discussed. Lignin and microdistribution theories are shown to be both correct and different facets of a single unified theory. Better-performing CCA formulations for tannin-containing softwoods are proposed and proved to be effective. Directions under investigations for better performing CCA formulations for hardwoods are discussed. Inorganic waterborne preservatives formulations "precipitating", not "fixing", such as simple CrIII arsenates or ammoniacal copper arsenites, can be deduced to be better suited for Eucalyptus preservation than CCA itself.
A Pizzi, W E Conradie, M Bariska
Antifeedant activities of flavonoids and their related compounds against the subterranean termite, Coptotermes formosanus Shiraki
1999 - IRG/WP 99-10305
Antifeedant activities of some flavonoids and their related compounds against the subterranean termite, Coptotermes formosanus Shiraki were examined with no-choice and two-choice tests. The activities of these compounds were considered in relation to their chemical structures. All flavonoids tested showed antifeedant activities whereas catechinic acid without A-ring and pyran ring in the molecule showed attractant activity. As to the chemical structure-activity relationships, it was found that compounds containing two hydroxyl groups at C-5 and C-7 in A-rings showed the significant antifeedant activities. The presence of carbonyl group at C-4 in pyran rings was necessary for the occurrence of extreme activities. Flavonols and flavanonols with 3', 4'-dihydroxylated B-rings exhibited activities higher than those with 4'-hydroxylated or with 3',4',5'-trihydroxylated B-rings.
W Ohmura, S Doi, M Aoyama, S Ohara
The Effect of Flavonoids on Colour and Spectral Changes of the Wood Surface Caused by Heat Treatment or Ultra-violet Irradiation
2006 - IRG/WP 06-40341
Both heat treatment and UV irradiation can cause discolouration and change in the spectral properties of wood surface. Some of the characteristic flavonols have significant role on colour and spectral changes, despite of their relative small quantities in wood. Colour changes and spectral properties of natural and extracted black locust (Robinia pseudoacacia L.) and poplar (Populus nigra L.) were investigated by CIELAB colour measurement system, FTIR and UV/Vis spectrophotometry. Spectral properties of representative flavonols, impregnated on inert silica gel thin layer, were studied in addition to the two types of wood samples. Chemical structure of flavonols was established to have both influence on the colour and spectral changes of woods and close connection with their thermal and photo stability. A slow but continuous decrease of lightness was observed in the case of quercetin and its homologous compounds. Chemical reaction of robinetin was detected by thermal analysis and differential scanning calorimetry under 200 °C and both oxidative and inert conditions. The colour changes of quercetin homolog compounds, kaempferol and fisetin, which contain one and two hydroxyl group on their “B” ring, are similar to quercetin; while myricetin with three hydroxyl groups on its “B” ring shows “robinetin-type” changes. The colour changes of the hardwoods are depended on the time and temperature of heating, as well as on the time of light irradiation. The character of spectral changes of black locust can be classified on the type of robinetin, in contrast with the “quercetin-type” of poplar.
R Csonka-Rákosa, L Molnár-Hamvas, E Börcsök, J Molnár, K Németh