Determination of Polyphenolic Content of Bark Extracts for Wood Adhesives
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P. Md. Tahir
Summary
The phenolic content of condensed tannins varies considerably, depending on the method of determination. Even though the Stiasny precipitation number has been commonly used to estimate the amount of reactive tannin towards formaldehyde, particularly in adhesive applications, this estimation alone is not sufficient. In this study two methods of determining the amount of reactive tannin towards formaldehyde were examined. These were (1) the reactivity towards formaldehyde or the Stiasny precipitation number, and (2) the formaldehyde uptake. Five different types of tannin were examined from Rhizophora mucronata, P. radiata, mimosa, quebracho and chestnut. The study indicates that the phenolic content in tannin can be better estimated by determining both the Stiasny number and the amount of formaldehyde uptake. High correlation (r2 = 0.905) was detected between the two methods. The study also revealed that hot water extracts of R. mucronata contain relatively small amounts of reactive polyphenols and are less reactive than sulfite extracts. The consumption of formaldehyde by this type of tannin was only 0.294 molecules per flavanoid unit. Similar to R. mucronata, the sulfite extracts of P. radiata contain relatively high amounts of reactive polyphenols and reacted with substantially higher amounts of formaldehyde per flavanoid unit, comparable to mimosa and quebracho tannins. Nonetheless, the reactivity towards formaldehyde (gel time) of the latter tannins is muchlower, despite their higher polyphenolic content. Of the two methods used to estimate the polyphenolic content of bark extracts, the Stiasny number had a relatively higher correlation (r2 = 0.518) with gel time than formaldehyde uptake (r2 = 0.345) did. The behaviour of these tannins in relation to their reactivity and chemical structures is discussed.
Copyright © 2002 by Walter de Gruyter GmbH & Co. KG
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Articles in the same Issue
- Weight Loss and Cell Wall Degradation in Rubberwood Caused by Sapstain Fungus Botryodiplodia theobromae
- Changes of EPR Spectra of Wood Impregnated with Copper-Based Preservatives during Exposure to Several Wood-Rotting Fungi
- Quantitative Analyses of Morphological Variation of Cross-Sectional Tracheids of Hinoki (Chamaecyparis obtusa Endl.) Near Knot by Image Processing
- Direct Effects of Wood Characteristics on Pulp and Handsheet Properties of Eucalyptus globulus
- Identification of the Lignan Nortrachelogenin in Knot and Branch Heartwood of Scots Pine (Pinus sylvestris L.)
- Chemical Composition of Lipophilic and Phenolic Constituents of Barks from Pinus nigra, Abies bornmülleriana and Castanea sativa
- Pinus pinaster Oleoresin in Plus Trees
- Determination of Polyphenolic Content of Bark Extracts for Wood Adhesives
- Softwood Bark Pyrolysis Oil-PF Resols. Part 2. Thermal Analysis by DSC and TG
- Softwood Bark Pyrolysis Oil-PF Resols. Part 3. Use of Propylene Carbonate as Resin Cure Accelerator
- Steam Explosion of Aspen Wood. Characterisation of Reaction Products
- Characterization of Black Liquors from Soda-AQ Pulping of Reed Canary Grass (Phalaris arundinacea L.)
- Modification of the Nitrogen Content and C:N Ratio of Sitka Spruce Timber by Kiln and Air Drying
- High Resolution Measurement of the Surface Layer Moisture Content during Drying of Wood Using a Novel Magnetic Resonance Imaging Technique
- Longitudinal Permeability and Diffusivity of Steam in Beech Determined with a Wicke-Kallenbach-Cell
- UF/pMDI Wood Adhesives: Networks Blend versus Copolymerization
