Wood discoloration

Shigo A L, Hillis W E 1973 Heart wood, discolored wood and microorganisms in living trees. Ann Rev Phytopathol 11 197 - 222... 

A promising way to reduce the rate of free radical formation and thereby minimize the occurrence of wood discoloration (photo-yeUowing) was recently presented [66] and involves the sUylation of the UV radiation sensitive groups at the wood surface (in air and at room temperature) in order to interfere with the photo-degradation process, the resulted photo-induced free radicals being determined using ESR spectroscopy. 

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

In detergent perfumes, the stabiUty of vanillin is not always certain. It depends on the association made with other raw materials, eg, with patchouli, frankincense, cloves, most of the animal notes, and such chemicals as amyl saUcylate, methyl ionones, heflotropin, gamma undecalactone, linalool, methyl anthrarulate, benzyl acetate, phenyl ethyl alcohol, cedar wood derivatives, oak mosses, coumarin, benzoin. Pern balsam, and cistus derivatives. In some cases, these mixtures can cause discoloration effects. 

Wood is an anisotropic material that undergoes uneven dimensional changes and, under extreme variations of environmental conditions, becomes distorted and warped (see Chapter 10). Exposed to the atmosphere, wood is also susceptible to the mechanical forces of wind and rain, and the effects of solar radiation the latter, in particular, causes discoloration initially, and then photochemical degradation, which often results in the wood s total decomposition. Wood is also prone to consumption by bacteria, fungi, insects, and rodent animals (Unger et al. 2001). 

K. Saito, T. Mitsutani, T. Imai, Y. Matsushita and K. Fukushima, Discriminating the indistinguishable sapwood from heartwood in discolored ancient wood by direct molecular mapping of specific extractives using time of flight secondary ion mass spectrometry, Analytical Chemistry, 80, 1552 1557 (2008). 

Sakuragawa, S. (1996). Dyeing of wood and protection of discoloration. Mokuzai Kogyo, 51(3), 102-106. 

Bacteria are also responsible for destruction of wood, for example in cooling towers,20 by breaking down the cellulose fibers. Certain bacteria derive their metabolic energy from the iron(II)-iron(III) redox cycle. These iron bacteria can proliferate to the extent that they block pipes. In any case, they will discolor water. In addition, objectionable growths of algae can occur in water tanks or circuits, given even minimal supplies of nutrients. Consequently, biocidal agents are widely used in the treatment of industrial, as well as municipal, water supplies. 

Castellan, A. Columbo, N., Nourmamode, A., Zhu, J.H., Lachenal, D., Davidson, R.S., Dunn, L., "Discoloration of ot-Caibonyl-Free Lignin Model Compounds Under UV Light Exposure", J. Wood Chem. Technol., 1990, 10(4), 461. 

The method used in the present work to obtain action spectra of wood pulps is analogous to that developed to construct the erythema action spectrum for human skin [7]. In order to evaluate the action spectra for the photochemical discoloration of the pulps, the spectral irradiance at the sample position must be measured and the response of the exposure, e.g. in terms of the reflectance at 457 nm, has to be analyzed. Thus, an action spectrum takes into account both the exposure dose and the character of the chromqphores that are photoactive in the pulp. The action spectrum for the yellowing is then obtained by plotting the reciprocal of the exposure dose necessary to produce a certain predetermined degree of yellowness versus wavelength. 

The central wood portion of the log depicted in Figure 1 is considerably darker in color than the part adjacent to the bark. The dark-colored wood is termed heartwood and the light-colored wood is termed sapwood. The discoloration is due to the production and secretion of substances which are a by-product of the death of food-storage cells. As new wood, that is sapwood, is formed to the outside of the tree stem, additional interior sap-wood adjacent to the heartwood zone is converted to heartwood. Some trees do not form discolored heartwood upon the death of... 

To prevent growth of wood-inhabiting fungi it is customary to treat wood with chemicals which are toxic to fungi. To pro-tect wood in service from deterioration by decay fungi, the chemicals, called wood preservatives, are applied in most cases by pressure treatment because deep penetration into the wood is essential. Wood products intended for use where the decay hazard is low are unlikely to require pressure treatment but in many instances may require superficial fungicidal treatment to prevent fungal discoloration. 

Planing air-dried lumber largely removes surface discoloration caused by moulds, but discoloration in the wood caused by staining fungi cannot be removed. 

Kiln-drying does not depend on the weather and, in addition, due to the high temperature used, the wood is essentially sterilized. However, if kiln drying is delayed mould and sapstain fungi may discolor the wood. 

This type of discoloration is less important in British Columbia than the discoloration caused By fungi. Surface dis coloration can be readily removed by surfacing of lumber, and usually objection is raised only when it s observed on an unfamiliar wood species as was the case with western hemlock. 

Yet, problems of erratic bonding, peeling, discoloration by wood extractives, and the rapid deterioration of transparent finishes remain. 

Ironically, modern papers, which were invented after the revolutionary changes of one hundred years ago, have serious problems—either in permanence or in durability. Most paper produced from wood fibers does not show the permanence of rag papers and discoloration is more critical than in rag papers. It has been noted that modern writing papers and books tend to have a much shorter life expectancy than those manufactured one hundred years ago. 

Five were clay filled and one had lime mud (calcium carbonate) as filler. The fiber furnish varied from all rag to mixtures of rag and sulfite wood pulp, to all wood fibers.. . . The sixth sample which had the lime mud was 75% sulfite and 25% soda wood fibers it had a pH of 8.9, while the other five samples had pH values varying from 3.6 to 4.3. When Edwin Sutermeister examined the samples in 1929 and retested them, his report said, all of the acid samples were badly discolored and were absolutely without strength, while the lime mud sample was much whiter and seemed as strong as ever. ... 

Modem papers, which were invented after the revolutionary changes of one hundred years ago, have serious problems—either in permanence or in durability. Most paper produced from wood fibers does not show the permanence of rag papers and discoloration is more critical than in rag papers. It has been noted that modern writing papers and books tend to have a much shorter life expectancy than those manufactured one hundred years ago (4-9). In essence, the increased use of wood fibers, the use of chemical additives (especially those promoting increased acidity), and environmental conditions have been given to account for these results. The literature dealing with these topics is now very large it would not be wise to attempt an extensive review here in addition to those that already exist (6,10-19). It is my intention in this chapter to consider the discoloration of modern papers, and the inhibition or the control of discoloration. 

Wood Preservation through Fumigation with Hydrogen Cyanide Blue Discoloration of Lime- and Cement-Based Interior Plaster... 

---