Dyeing of Eucalyptus globulus Veneers with Reactive Dye Using Sequential Vacuum and Varied Pressures

To investigate the potential application of vacuum-pressure methods for dyeing low-quality hardwood veneers produced from young, small-diameter logs, Eucalyptus globulus veneers were dyed with a 2% solution of the reactive dye Procion Brown PX-2R at a vacuum of -100 kPa for 15 min prior to pressure being applied. The effects of various pressures and pressure times on dye uptake, dye penetration, and colour change were evaluated. Veneers with varying moisture content (MC) were used and were labeled as green veneer (80% ± 5% MC) or dried veneer (12% MC). The dyeing method was based on the results of the preliminary experiments. The vacuum-pressure method had remarkable influence on the dye uptake, dye penetration, and colour change, particularly when the samples were dyed at a pressure of 1000 kPa and pressure time of 120 min. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy results indicated that the reactive dye was able to react with the wood compounds, and scanning electron microscopy (SEM) analysis showed that the ray parenchyma cells provided an effective radial path for dye penetration.