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A contribution to the adsorption/desorption behaviour of zinc-hexa-fluoro-silicate in different soils
1995 - IRG/WP 95-50056
The estimation of a possible endangering of the groundwater through wood preservatives and thereof deriving measures for the avoidance of secondary damages require among others exact knowledge concerning the behaviour of wood preservative compounds in the soil matrix. Adsorption and desorption behaviour were determined at four soils of different characteristics, which were brought in contact with aqueous solutions of zinc-hexa-fluoro-silicate. For the respective experiments four concentrations were prepared containing 10, 50, 100 and 250 ppm zinc ions. Water of p.a. quality served as reference. As to be expected the soils in question behaved different: the adsorption of inserted ions increased with increasing clay content of the soil. On the other hand significant differences exist also with respect to the adsorption behaviour of the zinc cation in relation to the hexa-fluoro-silicate anion. Within the concentration interval investigated, the same soil adsorbed approximately the same proportional zinc quantity. However, when increasing the hexa-fluoro-silicate-ion concentration a proportional decrease concerning the degree of adsorption was observed. The results show that it is not possible to conclude from partial results achieved with individual preservative compounds to the overall system "wood preservative"-soil and that further investigations are necessary for an inclusive description of the problem.
E Melcher, R-D Peek

Preliminary modelling of methylisothiocyanate movement through Douglas fir transmission poles
1988 - IRG/WP 3466
Methylisothiocyanate is a volatile solid that is the active ingredient of several registered and experimental wood fumigants. Information on the sorption and diffusion of this chemical in Douglas-fir heartwood and sapwood was used to develop a two-dimensional model of fumigant movement within a single horizontal cross-section of a transmission pole. The model indicated that dry wood (14% MC) strongly sorbed MIT, which resulted in lower rates of MIT movement. Conversely, it was predicted that wetter wood (22 or 40% MC) held MIT less strongly and had a more rapid rate of chemical movement. In addition, predictions suggest that the presence of an oil-treated peripheral shell had a strong influence on loss of fumigant from the surface of the pole, but had little effect on concentration which developed in the heartwood zone. The results indicate that MIT movement can be effectively modeled. Further studies are underway to account for longitudinal movement of MIT in the model and to simulate extended time periods.
A R Zahora, P E Humphrey, J J Morrell

Determination of N-cyclohexyl-diazeniumdioxide (HDO) containing compounds in treated wood using GC-MS
2000 - IRG/WP 00-20201
Beside the biological effectiveness the approval of a chemical wood preservative requires also techniques for the analytical determination of active ingredients in different matrices. Fulfilling of the last requirement is particularly difficult in the case of impregnated timber treated with wood preservatives containing organic compounds. This paper describes a procedure for the determination of the organic ingredient N-cyclohexyl- diazeniumdioxide (HDO) in solid phases using gas chromatography coupled with mass spectrometry (GC-MS) in connection with a previous thermal desorption step. For this powdered samples are placed in a glass tube. Then the tube is reinserted into the thermal desorption unit which is placed in the GC-oven and directly connected with the capillary column. Afterwards the sample was quickly heated up to 200°C. The resulting gas mixture is pushed onto the column and the separation of the gas components took place. The single components could be identified by means of the retention time and the mass spectrum. A quantitative determination seems to be possible by means of the intensity of the signals. The suitability and reproducibility of this method of the determination of HDO were tested successfully by analysing a number of impregnated wood specimens treated with different formulations containing HDO.
P Jüngel, J Wittenzellner, E Melcher

The identification of organic compounds in wood using thermal desorption GC-MS - possibilities and limitations
2001 - IRG/WP 01-20224
There is a clear need for the analytical characterisation and identification of organic compounds and their derivatives in different phases especially in timber. In this context the paper describes a rapid and powerful gas chromatographic method for the determination of insecticides, biocides and "other" organic substances in treated and/or modified wood. The main advantage of this procedure is that wooden material can be analysed directly without any further sample preparation. In principle the technical equipment using a mass selective detector is suitable for identifying as well as quantifying thermal desorbable compounds in only one analytical run. The main emphasis of this contribution, however, is to show the possibilities and limitations of this technique.
P Jüngel, E Melcher

The quantitative determination of N-cyclohexyl-diazeniumdioxide (HDO) containing compounds in treated wood using TD-GC-MS
2001 - IRG/WP 01-20223
Last year we presented the paper (IRG/WP/00-20201) "Determination of N-cyclohexyl-diazeniumdioxide (HDO) containing compounds in treated wood using GC-MS". Based on the intensive discussion at the meeting, the first experiences made with the calibration of the system for this application will be reported. For the quantitative determination of N-cyclohexyl-diazeniumdioxide in treated wood, milled material containing a known concentration of the active ingredient were placed in special liners which were sealed with magnetic caps. The liners were then stored in a sample rack. Depending on the analytical program a certain liner was transported automatically into the thermal desorption unit. Afterwards the sample was quickly heated to 200°C. Only a part of the resulting gas mixture was pushed onto the column where the separation of the components took place. The component of interest could be identified by means of the retention time and the mass spectrum. The calibration of the system and the quantification are based on 5 different values (TIC, peak height/area with and without background subtraction, peak height/area of a selected mass fragment with and without background subtraction) received from the spectrum. For the quantification it is necessary to analyse at least 5 samples of identical concentration.
P Jüngel, J Wittenzellner, E Melcher

The use of thermal desorption and pyrolysis combined with a semiconductor VOC detector for the on-site detection of preservative-treated wood
2010 - IRG/WP 10-20456
The purpose of this study was twofold; to identify possible marker molecules released from preservative-treated wood upon heat treatment and then develop a prototype detector for this marker. Two methods for heating the samples were used: Pyrolysis combined with Gas-Chromatography with IR-detection and Thermal Desorption combined with Gas-Chromatography with mass detection. A first prototype detector was developed and tested for the detection of VOCs released from creosoted and organic type preservative treated wood.
I Svensson, A Gonzalez, L Irusta, Mª J Fernandez-Berridi, O Munné

Water absorption and desorption of non treated, pressure impregnated, and pine oil treated glulam made of small diameter Scots pine and Norway spruce
2012 - IRG/WP 12-40616
A growing proportion of harvested timber originates from the first or second commercial thinning stands in Finland, which means smaller average log volumes in comparison to final felling stands. Smaller log volume means challenging wood properties such as higher proportion of juvenile wood and sapwood. Due to these facts, products made of small diameter logs are prone to twist and check, and have reduced durability against weather. The objective of the study was to define the water absorption and desorption velocity of non treated, pressure impregnated and pine oil treated glulam. The 6 inner lamellae of the glulam beams originated from small-sized logs, whereas the surface lamellae were made of larger logs. Beams with 44 x 200 mm cross cut dimensions were glued using MUF resin and divided into three treatment groups. Treatment 1 was not impregnated, treatment 2 was impregnated into AB class with copper-based preservative in commercial pressure process, and treatment 3 was impregnated with pine oil using the process of Ekopine Ltd. After the treatments, 20 pieces of 200 mm-long specimens were sawn from each treatment group. The cross cut surfaces of the specimens were sealed using waterproof varnish to ensure that the water movement took place via the side surfaces of the specimens. The air-dry specimens (MC 7.7–12.6%) were immersed into water for 6 weeks. After that, they were brought to a standard climate (65% RH, 20 C temperature). Again, their mass was recorded until it did not change anymore. Pine oil impregnated glulam resisted the water absorption more than non treated and pressure impregnated glulam. Due to the low initial MC after the absorption period, pine oil impregnated glulam dried rapidly below 20% MC, while the drying of non treated and pressure impregnated glulam to the same level took 3-4 weeks. In conclusion, pine oil impregnation of timber from small-sized logs can be considered an effective and ecological preservation method for timber used in outdoor constructions. For load carrying structures, pine oil impregnation appears to be an efficient way to maintain the MC of wood below the level that enables mould growth.
H Heräjärvi, V Möttönen, R Stöd

Activities of moulds on wood as a function of relative humidity during desorption and absorption processes
2013 - IRG/WP 13-10794
Three different types of indoor moulds: Penicillium brevicompactum, primary colonizer; Alternaria tenuissima, secondary colonizer and Trichoderma harzianum, tertiary colonizer, grown on wood were measured for their activities under different relative humidity levels. The activities were measured by isothermal calorimetry. The activities of the moulds changed with the change of the relative humidity levels. The optimal relative humidity levels are different for these three moulds. The mould activities were also different from desorption to adsorption processes under the same relative humidity levels. This might be caused by the moisture hysteresis properties of wood. Therefore, besides of relative humidity, water availability also plays an important role for mould growth. Such information should be taken into account for modelling mould behaviour on building materials.
Yujing Li, L Wadsö