Volatile organic compounds (VOC) measured during drying of impregnated timber
N Terziev, V Djokic
Discussion about drying of impregnated timber has taken place in the Nordic countries under eighties and nineties and goes on nowadays. The drying increase the value of production and the customer gets fewer problems when handles the timber. This introduces a positive attitude to the impregnation as a process and its products. Beside the important information about the advantages of impregnated timber drying, a great help for the integrity of branch and customers will be the acquirement of drying schedules considering the timber quality and emissions of harmful VOC.
The objective of the present study was to measure the total content of possible emissions containing organic substances in the vented air during drying of Scots pine timber impregnated for above ground use (preservatives of class AB). A drying charge of 6 m3 consisting of 28120-mm boards was prepared for impregnation. The preservative, a copper-HDO (Wolmanit CX-8, 2 % conc.) was impregnated in the boards according to the full cell process carried out in an industrial autoclave. The impregnated charge was further dried in a laboratory batch kiln to final moisture content of 18.1 %. The duration of drying was 86 h.
The content of VOC emitted in the air from the aminoethanol in preservative was measured by gas chromatography technique. Samples from the air were taken directly in and beside the drying kiln. The measurements were carried out in the beginning, middle and at the end of drying. The gas chromatography technique showed to be appropriate for quantitative measuring of the VOC emitted during drying of timber impregnated with Wolmanit CX-8. The emissions measured in the kiln chimney were most intensive in the beginning of drying when the free water was evacuated (31.4 ppm) and decreased exponentially to 7.8 ppm at the end of the process. The study generated some ideas about the organisation of drying schedule for impregnated timber in order to decrease the content of VOC. The results are interpreted regarding the requirements approved by the environmental authorities in Sweden.