Alternative agents and methods for chemical modification of wood

Fir wood (Abies alba Mill.) and beech wood (Fagus silvatica L.) were chemically modified with citric acid (CA) and sodium hypophosphite (SHP) as catalyst. The effect of chemical modification on dimensional stability of wood and the effect on colour changes of wood has been investigated. Wood modified with dimethyloldihydroxyethyl- eneurea (DMDHEU) and magnesium chloride as catalyst was used for comparison. For the purpose of thermal treatment after the impregnation step, a microwave treatment was performed and compared with classical method. Dimensional stability of modified wood was analysed by Anti Swelling Efficiency (ASE) using the water soaking method. The results revealed that wood treated with citric acid (CA) showed improved ASE by about 40 %, equally good on both wood species. Equally good ASE results have been obtained by using the microwave on wood modified with CA, but the ASE was lower in a case of DMD- HEU application. The influence of curing temperature and applied agent on colour stabil- ity have also been spectrophotometrically measured and expressed as ∆E.