Impregnation of Norway spruce (Picea abies L. Karst.) wood by hydrophobic oil and dispersion patterns in different tissues

Summary Wood from Norway spruce ( Picea abies L. Karst.) is biologically degraded in exposed conditions. It also has anatomical features that make it diffi cult to impregnate with preservatives by currently available industrial processes. In the study reported here, we used the new Linotech process to impregnate Norway spruce wood with hydrophobic linseed oil and then quantifi ed its uptake and dispersal in anatomically distinct wood tissues. We also investigated the effects of the wood moisture content on the results of the impregnation. Samples (500 × 25 × 25 mm) were taken from 15 trees in a coniferous forest in northern Sweden (64° 10 ׳ N, 160 – 320 m a.s.l.). The parameters for the Linotech process were 2 – 3 h treatment time at 0.8 – 1.4 MPa and 60 – 140°C. To determine the level of uptake, the linseed oil was extracted from the impregnated wood using methyl-tertiarybutyl-ether. The uptake was quantitatively analysed by comparing X-ray microdensitometry values obtained following impregnation both before and after oil removal. In earlywood, initial moisture content had an obvious effect on the impregnation result. Six times more oil was taken up when the moisture content was greater than ~ 150 per cent than when it was less than 30 per cent. Theoretical calculations, based on density levels, suggest that the water-fi lled porosity of the wood (water volume divided by porosity volume) was positively correlated with the linseed oil uptake, and more strongly correlated in earlywood than in latewood. There were also signifi cant differences in uptake between different wood tissues; heartwood/mature wood and heartwood/juvenile wood showed 10 – 20 per cent weight increases due to linseed oil uptake, compared with 30 – 50 per cent in sapwood/mature wood. Examination by scanning electron microscopy confi rmed these uptake patterns. The moisture content after impregnation was about 5 per cent, irrespective of the Linotech process parameters, tissue type and initial moisture content. In conclusion, the impregnation process used here results in high levels of well-dispersed linseed oil uptake and should facilitate drying.