Moisture content water-degraded woods

Moisture Content. Most water-degraded woods in archaeological collections have a moisture content of 100-500% on a dry-weight basis. It would therefore be counterproductive to simply replace the water with an equal volume of low-molecular-weight liquid PEG because this volume would be greatly in excess of the dry wood s sorption capacity and would produce a rather soggy product with poor dimensional stability. 

Experiments for fimgal degradation of pine flour were carried out by following an established procedure for fungal degradation of pulp (5). Pondarosa pine sapwood flour (30 mesh) was extracted with acetone/water (v/v, 9/1) and dried under vacuum. The moisture content was determined as 9.8 %. A mixture of wood flour (9.07 g oven-dried) and de-ionized water (10 mL) was autoclaved in 250 mL Erlenmeyer flask at 121 °C for 1 h. The autoclaved wood flour was inoculated with the P. cinnabarinus spore suspension (5 mL), and the moisture content of the wood flour adjusted to 80% with sterilized water. The culture was then incubated at 30 °C for pre-determined times. Twelve replicates were carried out for each cultivation time. 

Thermally and chemically modified wood is dimensionally more stable and has lower moisture content than untreated wood. The resistance to moisture or biological degradation can also be improved. The treatment may affect the wood s ability to absorb water, due to changes in the hydrophilic nature of the wood, and thus the setting time, the performance of the glueline, and the bond quality of the EPI adhesive may be influenced. 

Anaerobic microbes in the presence of water in the landfill will consume these natural products and produce methane, CO2 and humus. One study reported the average composition of 20 year old refuse to be 33 % paper, 22% ash and 12% wood [18]. Thirty core samples revealed a wide range of degradation and microbial activity that were directly attributed to sample moisture content. Recovered polyethylene degradation was evaluated and determined to be as high as 54 %. 

In wood pyrolysis, it is known that several parameters influence the yield of pyrolytic oil and its composition. Among these parameters, wood composition, heating rate, pressure, moisture content, presence of catalyst, particle size and combined effects of these variables are known to be important. The thermal degradation of wood starts with free water evaporation. This endothermic process takes place at 120 to 150 C, followed by several exothermic reactions at 200 to 250°C, 280 to 320 C, and around 400 C, corresponding to the thermal degradation of hemicelluloses, cellulose, and lignin respectively. In addition to the extractives, the biomass pyrolytic liquid product represents a proportional combination of pyrolysates from cellulose, hemicelluloses. 

Many of the properties of acetylated wood depend on the method of acetylation. The temperature of treatment, time of reaction, and type and amount of catalysts play a significant role in the extent that fibers degrade during treatment. The amount of moisture present in the wood also is important. Some moisture (2-5%) seems to be needed to obtain the best reaction, but above this level the water hydrolyzes the acetic anhydride to acetic acid. This loss by hydrolysis accounts for a 5.7% loss of anhydride with each 1% of water in the wood (36). The rate of acetylation decreases as moisture content increases (37). 

Moisture Content. In a specific circumstance (a treatment problem of a group of oak timbers), the moisture content and the amount of internal sound wood core were used instead of chemical analyses to assess degradation (6). The wood condition has been classified as follows Class I, the most deteriorated wood, contains over 400% water ([weight of water] / [oven-dry weight of wood] X 100) and virtually no core Class II is 185-400% water, with a core present and Class III is less than 185% water, with only the surface degraded. The analyses included moisture contents and the pin test to determine the extent of sound wood. 

All wood-degrading fungi and bacteria need water for their life processes and as a medium for the distribution of their degrading enzymes. Wood with a moisture content below fiber saturation will not be degraded by microorganisms. Insects that feed on or nest in wood are, however, fully capable of more or less complete destruction of the structure of dry wood. 

The distinction between fiber saturation point (the maximum water content of swollen cell walls) and the maximum possible moisture content has a diminishing value for degraded wood, which may eventually have no effective fiber saturation point at all. The ordered and disordered cellulose in sound wood are the main sites for water adsorption (ii). As they diminish over time, their relative role in determining fiber saturation also diminishes. Nevertheless, the measurement of relative water adsorption will have some value in determining the relative degradation in a wood sample. 

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